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Neurology | Medulla Anatomy & Function — Transcript

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0:14Hi engineers. In this video today, we're
0:15going to talk about the medulla
0:17oblongata, or as Bobby Boucher from The
0:19Waterboy would say, "It's good the my my
0:21my my mama said it's alligator so ornery
0:24cuz they got all them teeth, no
0:25toothbrush."
0:27All right, guys. So, what we're going to
0:28do is we're going to talk about the
0:29medulla. We're going to have three cross
0:30sections, right? We're going to go over
0:31all the internal structures of the
0:32medulla just like we did with the
0:33midbrain and the pons.
0:36What I want to do though is we're going
0:37to have three sections. I want to
0:38explain at what cross section we're
0:41looking at, okay? So, first thing, let's
0:43go ahead and take and just do a frontal
0:45section. So, basically, I'm going to
0:47take and slice right here, okay? And
0:49we're going to look at this at three
0:50levels, right?
0:52So, here
0:54we have midbrain. Here's pons.
0:57Here's your medulla, and then
0:59continuation into the spinal cord,
1:00right? For you know, complicity, you
1:02know, completeness sake, we have the
1:03cerebellum.
1:05Now, what we're going to do is here's
1:08from this point here to this point here
1:09is our medulla, okay?
1:11The first one that we're going to look
1:13at, the first level, I'm going to slice
1:15it here with this red, is we're going to
1:17look
1:18at this level here. This transverse
1:21section or cross section is going to be
1:23at the pons medulla junction. This is
1:25going to be this section here, section
1:27one, is the most superior aspect or
1:30section of the medulla. Or another word
1:33that might come up is the most rostral
1:35portion of the medulla.
1:37Then what we'll do is we'll come at
1:38another level here,
1:40kind of within the middle.
1:42This middle portion is where we're going
1:44to call the sensory decussation. This is
1:47where you have that nucleus cuneatus,
1:49nucleus gracilis, the receiving the
1:51sensory information from the fasciculus
1:53gracilis, fasciculus cuneatus, and they
1:55cross and go up as the medial lemniscus.
1:58That's going to be the second part.
2:00Then we're going to come down here at
2:02the last part, the most inferior or
2:06caudal portion of the medulla.
2:08And this is going to be at the pyramidal
2:10decussation. So that's when you have
2:12those corticospinal fibers that are
2:14coming down and they're going to cross
2:16at that level. The lateral ones cross.
2:1885% cross into the lateral column and
2:2115% stay straight in the ventral column.
2:23Right? So three sections. First one's
2:26going to be here at the top. The middle
2:28one's going to be here in the bottom and
2:29the third one's going to be here at this
2:30right. Okay? So let's go ahead and start
2:32focusing on the most rostral portion.
2:37All right neuro nerds, so let's go ahead
2:38here and start with the rostral portion.
2:40Okay, this part here is the most
2:42superior, most rostral component of that
2:44medulla cross-section, right? And again,
2:46just to give you guys some orientation,
2:48this portion here is the ventral portion
2:50of the medulla. This portion back here
2:52is the dorsal portion of the medulla.
2:54All right? What we're going to do is, to
2:55help you guys out, is we're going to
2:57start here at this structure here and
2:59we're going to kind of work our way in a
3:00circle.
3:01And the nice thing is is that this video
3:03is going to be very repetitious because
3:05a lot of the things that you see at this
3:06level, you're going to see it pretty
3:07much all the other levels. So it's going
3:09to be very, very consistent,
3:10repetitious. By the end of this video,
3:12you guys will know this completely well.
3:14Okay? So let's go ahead and start here
3:15with this first structure that's paired
3:17on both sides.
3:19Do you guys look at this guy?
3:21This is called your hypoglossal nucleus.
3:24Hypoglossal nucleus is what cranial
3:26nerve? It's cranial nerve 12. So again,
3:29what is this guy? We're going to have a
3:30key. It's pretty long key, but it's the
3:32best thing that we could do here so we
3:33don't have arrows coming all over the
3:34place making this diagrams not very
3:36nice. So again, first one here, orange
3:38nucleus.
3:39That is going to be the hypo-
3:42glossal
3:43nucleus. Okay? This is for what cranial
3:47nerve? Cranial nerve 12. Okay?
3:50Next one. We got this structure. We're
3:52going to move a little bit. We're going
3:53to keep moving laterally and then
3:55forward, okay? So now we go here outside
3:57just a little bit lateral to the
3:58hypoglossal nucleus. What is this guy?
4:01This is the dorsal nucleus of vagus.
4:04Again, what is he?
4:06Dorsal
4:07nucleus
4:10of vagus. And again, what cranial nerve
4:14is the vagus nerve? This is cranial
4:16nerve 10. So again, hypoglossal nucleus
4:19and the dorsal nucleus of vagus.
4:21Move out a little bit more laterally and
4:23a little bit more anterior. What do we
4:24have here? We got this guy, the nucleus
4:27of tractus solitarius, right? So what is
4:30he called? The nucleus
4:33of
4:35tractus
4:36solitarius.
4:38Right? This guy is so cool.
4:41And again, we'll discuss more of their
4:42functions in a second. I just want to go
4:44ahead and start off by knowing the
4:45structures, then we'll get more to their
4:47function, okay? So hypoglossal nucleus,
4:50dorsal nucleus of vagus, what's a little
4:52bit more lateral and anterior?
4:54The nucleus of tractus solitarius. Okay,
4:56go out a little bit more. So a little
4:57bit more laterally.
4:59You have these two structures that are
5:01part of the whole nuclear complex.
5:04This is actually the vestibular complex,
5:07right? The vestibular nuclear complex.
5:08But if you guys remember in the pons
5:10video, we had four components of it, the
5:13superior, the lateral, the medial, and
5:16the inferior vestibular nuclear complex.
5:19If you guys remember in the pons video,
5:21you can really only see the superior,
5:23the lateral, and parts of the medial
5:25vestibular nucleus. You can't see the
5:27inferior at the pons, right? That lowest
5:29section of the pons.
5:30Now, in the medulla, you can see parts
5:33of the medial vestibular nucleus and
5:35primarily the inferior vestibular
5:37nucleus. So again, what are these two
5:39structures here?
5:41These are your medial and inferior
5:44So medial
5:46and inferior
5:49vestibular
5:53nucleus.
5:55Okay? Sweet.
5:58Next guy, these green guys. So, we're
5:59going to move a little bit more
6:00laterally. Hypoglossal nucleus, dorsal
6:02nucleus of vagus, nucleus of tractus
6:03solitarius, medial inferior vestibular
6:05nucleus. More laterally,
6:07you got your dorsal cochlear nuclei and
6:09your ventral cochlear nuclei. Again,
6:12dorsal more in the dorsal component of
6:13the medulla, ventral more in the ventral
6:15portion of the medulla. Pretty
6:17self-explanatory, right, guys? So,
6:19again, what do we got? Dorsal and
6:20ventral
6:23and ventral
6:25cochlear
6:28nuclei. Sweet deal.
6:32Okay, go a little bit more laterally.
6:34Over here, you got this big white matter
6:36tract. Okay, this is the white matter
6:38connection between primarily the medulla
6:42and the cerebellum. I know you guys know
6:43this.
6:44This is the inferior cerebellar
6:47peduncles. So, again, what are these?
6:49The inferior
6:52cerebellar
6:55peduncles.
6:58Sweet deal. Again, what is this? This is
6:59that white matter connection between
7:01primarily the medulla and the
7:03cerebellum. Okay.
7:05What do we got here again? Hypoglossal
7:07nucleus, dorsal nucleus of vagus,
7:08nucleus of tractus solitarius, medial
7:10inferior vestibular nucleus, dorsal
7:11cochlear nuclei, ventral cochlear
7:13nuclei, inferior cerebellar peduncles.
7:15Move out a little bit more laterally,
7:16what do you got here?
7:17This is the pontobulbar body. Okay? What
7:21is this little green here called? This
7:23is that pontobulbar
7:25pontobulbar
7:27body. Okay? And again, we'll talk about
7:30its relationship uh with this kind of
7:33blue
7:34fiber in a second. Okay?
7:36Okay, move a little bit more anterior
7:39now. What do we got? We got this pink
7:41tract here. What is this guy called?
7:44This is your ventral spinocerebellar
7:47tract. Okay, so what is he called? Your
7:49ventral
7:51spino
7:53cerebellar
7:56tract.
7:58Sweet deal. Okay.
8:01Move a little bit more anterior here.
8:03What do we got? We got our inferior
8:06olivary nuclear complex. Again, what is
8:09this guy here? This little weird-looking
8:11U-shape thing?
8:12That son of a gun right there is the
8:14inferior
8:17olivary
8:20nucleus. Okay?
8:23And we'll talk a lot about this guy a
8:25little bit later when we get to his
8:26function, okay?
8:28All right, move a little bit more.
8:29Again, and kind of medially and
8:31anteriorly here, we hit this blue
8:33structure. What is this guy called?
8:36This guy is the arcuate nucleus. So
8:39again, what is he called here? We have
8:41him as the arcuate
8:43nucleus.
8:46Okay, I want to take some time to
8:48explain what the heck all these like
8:49blue structures are moving all around
8:50the place.
8:51The arcuate nucleus is really cool
8:53because what it does is
8:55let's say again, this is our left
8:57medulla, right? The part of it, the left
9:00section of it. And this is the
9:02um right section of the medulla, right?
9:05So if I were to kind of slice this slice
9:07this in half, this is the left, this is
9:08the right.
9:09This left arcuate nucleus gives fibers
9:13that moves to the contralateral side as
9:15you see here. And it also gives
9:17ipsilateral fibers moving that you see
9:20here, okay?
9:22Now, these fibers, when they cross, they
9:25form these contralateral connections
9:28that move along these kind of like
9:30little divots on the anterior portion of
9:32the medulla and work their way towards
9:36this pontobulbar body.
9:38What are these fibers here called?
9:40These are called your anterior external
9:44arcuate fibers. Again, what are they
9:45called?
9:46anterior
9:50external
9:53arcuate
9:55fibers. And again, they are connecting
9:58between what? The arcuate nuclei and the
10:02pontobulbar body. Okay? But again, they
10:06have contralateral connection.
10:08Okay? Arcuate nuclei are actually
10:11interesting because they're believed to
10:12be the inferior kind of portion of the
10:16pontine nuclei. Remember those? We had
10:18the pontine nuclei in that pons. These
10:21are just believed to be an inferior
10:22extension of those pontine nuclei. And
10:25they're believed to play some type of
10:26role in maybe sleep. Okay? So again, you
10:29have these arcuate actually sleep in
10:31more of the breathing processes as well.
10:32But again, what I want you to know here,
10:35arcuate nucleus has the connections
10:37going to the pontobulbar bodies as the
10:39anterior external arcuate fibers.
10:42Now,
10:43these arcuate nuclei also give fibers
10:46that move
10:48on the same side so far. So this is
10:50ipsilateral. So from the left arcuate
10:52nucleus, this is the left. From the
10:53right arcuate nucleus, this is that
10:55right fiber.
10:56They're coming and working their way
10:57posteriorly through the midline of the
11:00medulla. As they work their way
11:02posteriorly through the midline of the
11:04medulla, they cross. So they come out
11:07the back and eventually they cross.
11:11And when they cross, they form another
11:13special structure. But look where
11:15they're moving towards. They're moving
11:17towards this
11:20ponto
11:21bulbar body.
11:23Okay? So again,
11:24arcuate nucleus gives its fibers that
11:26work posteriorly
11:28and cross to the contralateral side to
11:30that contralateral bulbar body. So
11:32again, right arcuate nucleus will give
11:34its fibers and this will cross over
11:35here.
11:37What is this blue structure here in the
11:39back of the medulla? This is an
11:41important one and we already talked
11:42about this in the pons. This is called
11:44the
11:45stria
11:49medullaris.
11:51This is called the stria medullaris. The
11:54stria medullaris is really important
11:56because you remember what we said about
11:57that structure?
11:59Remember we said that the fourth
12:00ventricle in the posterior part of the
12:03brainstem, at the pons and medulla area,
12:05you have the fourth ventricle.
12:07Forming the anterior wall of that fourth
12:10ventricle, right? Was the pons and the
12:12medulla. Above the stria medullaris,
12:15that fourth ventricle anterior wall was
12:17formed by the pons. Below the stria
12:20medullaris, right? The anterior wall of
12:22that fourth ventricle is formed by the
12:24medulla. And again, that is that stria
12:26medullaris. All right, so we hit this
12:28arcuate nucleus. Let's move a little bit
12:29more dorsally, right? So we've kind of
12:30gone from here and working our way
12:32around. Okay? This kind of red
12:35dicey-like structure here is called the
12:37corticospinal tracts, right? So this is
12:40going to be the corticospinal tracts. Do
12:42you guys remember those coming from the
12:43cortex, moving down to the spinal cord?
12:45Those are motor pathways. So again, what
12:47are those called?
12:49Those is called the corticospinal
12:51tract.
12:53tract.
12:55All right, sweet. Let's move a little
12:57bit more dorsally. So we're kind of just
12:59working our way around here. Now we're
13:00coming to this guy, this maroon son of a
13:02gun. What is this guy? This is our
13:04medial lemniscus.
13:07Medial lemniscus. Who comes up with
13:09these names, you know?
13:11So medial lemniscus. You guys remember
13:13this guy? You guys better remember him.
13:16We've talked about him so much. Again,
13:18this guy carries that proprioceptive
13:20information, that fine discriminative
13:22touch, that vibration sensations through
13:24that dorsal column. Again, we'll recap
13:26it a little bit later.
13:29Okay, we hit this one. Let's go here
13:30now. So, we're again working our way
13:31around here to this purple structure.
13:34What is this guy? This purple Where's my
13:36purple marker? Oh, I got him. This guy
13:38right here is called the
13:41spinal lemniscus. What is he called?
13:44The spinal
13:47lemna
13:48niscus.
13:51Okay, so good.
13:52We hit that one. So, we got went through
13:54here. We hit the medial lemniscus. We
13:56hit the spinal lemniscus. Now, what
13:58we're going to do is we're going to kind
14:00of work over here. And then we'll come
14:02back here to the middle, okay? So, we're
14:04going to go here and work our way here.
14:06So, now let's cover this structure.
14:09This guy right here is called we've seen
14:13him so many times. This is one of the
14:15trigeminal nuclei. Remember, at the
14:16medulla at the midbrain it's the
14:18mesencephalic nucleus. At the pons it's
14:20the the principal pontine or central
14:23pontine nuclei. And in the medulla it is
14:26the spinal nucleus of the trigeminal
14:28nerve. And associated with it is the
14:31trigeminal tract. Now,
14:35I'm going to write these down, but I
14:35want to explain something a little bit
14:37better than I did in the pons video with
14:38this one so that we completely
14:40understand this one. Okay, so again this
14:42is the spinal nucleus.
14:46And this is the
14:47tract.
14:49And this is for what of
14:52cranial nerve
14:54five, the trigeminal nerve. I want to
14:56take some time just really quickly to
14:58explain what this means.
15:00Okay.
15:01So, here I'm going to draw a
15:03a sagittal section here. So, okay,
15:05cerebrum, midbrain, pons, medulla,
15:07spinal cord, cerebellum, right?
15:11Since we're have this in that kind of
15:12navy blue color, I'm going to have here
15:14spinal nucleus
15:16of the trigeminal nerve.
15:18That central or principal pontine
15:20nuclei.
15:21And the mesencephalic nucleus. All of
15:24these are for the trigeminal nerve,
15:25right?
15:26If you guys remember from the trigeminal
15:28nerve video,
15:29we had that trigeminal ganglion, right?
15:31That gave off the V1, V2, V3 divisions,
15:34right? All those different things we
15:35talked about in that video. We're not
15:36going to go over that.
15:38But remember, they're picking up sensory
15:39information from in the entire face on
15:42the ipsilateral side.
15:43When they send this information in,
15:46and they go to these individual nuclei,
15:51this right here
15:55is the trigeminal tract, okay? Or that
15:57spinal tract, okay? So again, this part
16:00here, since we're talking about the
16:00spinal nucleus, this right here is that
16:03tract. That's the spinal tract of the
16:05trigeminal nerve. Then what we said is
16:08coming off of these nuclei,
16:12they give their fibers that move upwards
16:15towards the thalamus. What is that
16:17structure called? That is the trigeminal
16:19lemniscus, or the trigeminal thalamic
16:22tract. So again, I want to make sure we
16:23understand that this is the trigeminal
16:25lemniscus or the trigeminal thalamic
16:26tract coming from these nuclei, and this
16:29right here is the trigeminal tract,
16:32particularly at this portion here.
16:35This is the spinal tract, okay? All
16:38right.
16:40Let's go ahead and move on to the next
16:41structure here.
16:45All right. So the next one we got here.
16:48We went this way, medial lemniscus,
16:51spinal lemniscus, spinal nucleus and
16:54tract. Let's kind of come back over here
16:56to the middle, okay?
16:57So now we got this guy, this kind of
16:59blue tract here. What is this son of a
17:01gun?
17:02This guy is the tectospinal
17:06tract. There's so many things in the
17:07medulla, it's insane, right? So
17:09tectospinal tract.
17:11Again, this is that that tract we talked
17:13about already so many times. It's
17:15involved with what? The reflexive
17:17movements of the head and the eyes in
17:19response to superior colliculus is
17:21visual stimulus. Inferior colliculus is
17:23auditory stimulus. Done.
17:25Next one. Let's move out just a little
17:27bit back here. So, a little bit more
17:28posterior than a little bit laterally
17:30here. What have we got? We got this
17:31rubrospinal tract. We've talked about
17:33this one about a thousand times.
17:36What does this guy
17:38do?
17:39He carries descending motor pathways.
17:42Rubrospinal tract carries descending
17:43motor pathways from the red nucleus in
17:45the midbrain down to the spinal cord
17:49that can play a role with flexor
17:51movement. Okay? Done.
17:53Go a little bit backwards, a little bit
17:55more dorsally. So, we hit medial
17:56lemniscus, spinal lemniscus. Again, we
17:58hit the tectospinal, rubrospinal. We're
18:00at this green guy.
18:03This is one another one that we've hit
18:04like a thousand times. This is the
18:05medial longitudinal fasciculus. What is
18:08he called? The medial
18:10longitudinal
18:13fasciculus.
18:15Again, what does this guy do? He
18:17connects
18:20the medial vestibular nucleus, right? He
18:22sends the information to the sixth nerve
18:24nucleus. That sixth nerve nucleus sends
18:26contralateral fibers up that connects
18:28the third, fourth, and sixth cranial
18:30nerve nuclei. So, again, it's the
18:32connection between the three, four, six
18:34cranial nerve nuclei. Helps with
18:36conjugate movement of the eyes. Boom,
18:38done.
18:39Go a little bit more backwards here. So,
18:40a little bit more posteriorly. We hit We
18:42hit this black tract. Nucleus
18:46ambiguous.
18:52All right, weird name. All right,
18:54nucleus ambiguous, but it's actually a
18:55really cool um structure here.
18:57Responsible for the special visceral
18:59efferent fibers, which is going to be
19:00supplying muscles of your pharyngeal
19:02arches, and we'll talk about those
19:03later.
19:04All right, sweet.
19:06Move a little bit more laterally here.
19:08What have we got here?
19:09This brown one here is the inferior
19:13salivatory nucleus.
19:15All right, so this is the inferior
19:19salivatory
19:22nucleus. Again, so what is he? He's the
19:24inferior salivatory nucleus.
19:27This is actually specifically related to
19:30the glossopharyngeal nerve, right? So it
19:31connects the glossopharyngeal nerve has
19:33that general visceral efferent fibers
19:36and that basically connects to what's
19:38called the otic ganglion and has fibers
19:40that go from this nucleus out to the
19:43otic ganglion and then has
19:44parasympathetic fibers that go from that
19:46to the parotid gland, right? So plays a
19:48role in salivation.
19:50All right, sweet.
19:51So we hit the nucleus ambiguus, we hit
19:53the inferior salivatory nucleus. We got
19:54one more guy here and this one here as
19:57you move a little bit laterally here,
19:58what is this one?
19:59This one right here is actually super
20:01interesting. This is actually your
20:03descending
20:04sympathetic tract, okay, coming from the
20:07hypothalamus. We'll explain that later,
20:09okay? So again, what is this one? We
20:10have them a little bit down here.
20:13This one here, this blue one here with
20:15the dots, this is that sympathetic
20:20tract.
20:21And again, it's a descending tract. All
20:24right.
20:25Sweet. We hit a bunch of structures here
20:28within this most rostral portion, this
20:31cross-section of the medulla at the pons
20:33medulla junction. Now what we're going
20:35to go do is we're going to move
20:36caudally, right? So we're going to go a
20:38little bit we're going to take another
20:39slice kind of a little bit lower in the
20:41medulla, a little bit more caudally,
20:43inferiorly. All right, so now again, we
20:45have a cross-section at what level? The
20:47sensory decussation. Again, that's what
20:48I want you to remember. What we did up
20:50there was pons medulla junction. This
20:51section that's more caudal is at the
20:53sensory decussation. We'll explain what
20:55that means in a second.
20:57Again, let's start from the posterior
20:58aspect, work our way around here. A lot
21:01of this stuff is going to be things that
21:03we already covered. We'll pick up a
21:04couple structures along the way though.
21:06So it's going to be good repetition,
21:07okay?
21:08So, now, work here. What is this
21:10structure here in the most dorsal?
21:12Again, dorsal back here, ventral here.
21:14This is going to be What is this? This
21:17is the fasciculus gracilis. So, again,
21:20what is this guy here? This blue tract
21:22here. This is a tract. So, it's called
21:25the fasciculus
21:28fasciculus
21:29gracilis.
21:31The fasciculus gracilis is taking that
21:34sensory information, right? From the
21:36dorsal column carrying proprioception,
21:38fine discriminative touch, vibrations.
21:40But, where is those these this
21:42fasciculus, this tract coming from? I
21:45want you to remember that this is coming
21:46from the lower extremities, okay? So,
21:49lower extremity proprioception, fine
21:52discriminative touch, and vibrations.
21:54This thing, this fasciculus gracilis is
21:57eventually going to terminate
21:59on this nucleus a little bit more
22:02ventral. What is this guy? Well, this is
22:04the fasciculus gracilis. It terminates
22:06on the nucleus gracilis. So, what is
22:08this guy here?
22:09Nucleus
22:12gracilis.
22:15All right, sweet. Now,
22:17move a little bit more laterally, okay?
22:19As we move a little bit more laterally,
22:21so again, here's your nucleus, you got
22:22your fasciculus gracilis, and your
22:24nucleus gracilis. Move a little bit more
22:25laterally. You have your fasciculus
22:27cuneatus and your nucleus cuneatus.
22:31So, again, what is this son of a gun
22:32here? This is the
22:34fasciculus
22:37cuneatus.
22:40And this is the nucleus
22:44cuneatus.
22:46All right.
22:48Again, fasciculus cuneatus, it's
22:51carrying proprioceptive sensation, fine
22:53and discriminative touch, vibrations
22:56from the
22:57upper extremities, okay? And even a
23:00little bit from the trunk, Okay, so
23:02again, it's picking up sensations from
23:04the upper extremities. Gracilis is lower
23:07extremities. Simple as that.
23:10Okay, cool. We hit the sympathetic tract
23:12already. So if we were to move
23:13laterally, we know that what we would
23:14have here is the sympathetic tract.
23:16And again, we already covered this
23:18structure. What is this structure here
23:19called? This is the inferior cerebella
23:22peduncle. So again, we've hit fasciculus
23:24gracilis, fasciculus cuneatus, nucleus
23:26gracilis, nucleus cuneatus, inferior
23:29cerebella peduncle, and the sympathetic
23:31tract. All right, cool.
23:33You guys already know this one. What's
23:35this thing? We already covered it above.
23:37This is the spinal nucleus and the
23:40spinal tract of what cranial nerve?
23:42Cranial nerve five, the trigeminal
23:43nerve. Okay, move a little bit more
23:45anteriorly. This is a new one. We didn't
23:48cover this one before. This is the
23:49orange structure here. This is another
23:52tract. Okay?
23:54This one, if you guys remember, what was
23:55the pink one? This was the ventral
23:58spinocerebellar tract. This one's just a
24:00little bit more dorsal. What do you
24:02think it's called? The dorsal
24:03spinocerebellar tract, right? So this is
24:05the dorsal
24:07spino-
24:09cerebellar
24:12tract.
24:15Sweet deal.
24:16So again,
24:18we hit our sympathetic tract, we hit the
24:19spinal nucleus and tract, we hit our
24:21dorsal spinocerebellar tract. We already
24:23know what this one is, guys. This is
24:25your
24:26ventral spinocerebellar tract.
24:28Move a little bit more anteriorly here.
24:30What do we got here? This kind of bluish
24:32guy here
24:33actually is going to be a tract. It's a
24:35it's going to actually be a
24:37a descending tract. This is your
24:39olivospinal tract. So again, what is
24:41this guy here? This is the olivo-
24:45spinal tract. Again, we'll discuss this
24:48tract a little bit more in detail, but
24:50again, it's going from the inferior
24:52olivary nuclear complex down to your
24:54spinal cord, to this lower motor
24:56neurons, okay? Which will go out to your
24:58muscles. And again, we'll explain that
25:00later.
25:01Move a little bit more medially here.
25:03What do we got? We had olivospinal. What
25:04do we got here? This is actually spinal
25:07olivary tract, okay? So, this one is the
25:11spino-
25:14olivary
25:16tract. So, again, I want to make sure we
25:18understand here. Let's go over it again,
25:19right? What is this one? This is the
25:21olivospinal tract from inferior olives
25:23to the spinal cord. This is the spinal
25:26olivary tract coming from the spinal
25:28cord from sensations, proprioceptive
25:30sensations, okay? Bringing it up through
25:33this to the inferior olivary nuclear
25:36complex, okay? So, we understand that.
25:40Okay, cool. So, we covered the spinal
25:42Sorry, the olivospinal tract and the
25:44spinal olivary tract. Let's move a
25:45little bit more medially here. We
25:47already covered this one. What is he?
25:49This is your inferior olivary nucleus.
25:52Move a little bit more medially. We
25:53already covered this one. What is this
25:54guy? Your corticospinal tracts. Move
25:58posteriorly a little bit. You're
26:00starting to see some of the formation of
26:03What was that structure above? The
26:04medial lemniscus. We'll explain what I'm
26:07talking about in just a second, okay?
26:09But again, you're starting to see the
26:11beginnings of the medial lemniscus.
26:13Work here. What do we have? What was
26:15right behind the medial lemniscus?
26:17The tectospinal tract.
26:20What was just behind the tectospinal
26:21tract?
26:23The medial longitudinal fasciculus.
26:25Let's come out here for a second. Want
26:26to cover these last cuz we already know
26:27these.
26:28Let's cover this. Let's move over here.
26:30What do we got here? What is this green
26:32structure here?
26:33This green structure If you guys
26:34remember before it was one big clump
26:36called the spinal lemniscus, right? Do
26:38you guys remember what were the
26:39components of the spinal lemniscus? So,
26:41again, just more rostrally that the
26:43section above, this thing right here was
26:46the spinal lemniscus. Spinal lemniscus,
26:48I want you to remember three primary
26:49There's a lot of things, but three
26:50primary components of it.
26:52This one right here is the lateral
26:54spinothalamic tract. So, the green one
26:56is the
26:57lateral
26:58spinothalamic tract. Okay? So, lateral
27:03spinothalamic
27:06tract.
27:08What does this carry? This carries that
27:10pain and temperature sensations from the
27:13contralateral side.
27:14What is this one here? This purple one
27:16here. This guy is your
27:18spinotectal
27:21This is your spinotectal
27:23tract.
27:25So, this is picking up sensations
27:28from the body and taking it to the
27:30tectum. Okay? Which again is that
27:32superior colliculus and inferior
27:34colliculus.
27:36Move a little bit more anteriorly here.
27:37What do we got here? This blue one. This
27:39is your ventral spinothalamic tract.
27:42Okay? Or your anterior spinothalamic
27:45tract. We're just going to do ventral
27:47spinothalamic
27:52tract.
27:53Okay?
27:56And again, the ventral spinothalamic
27:58tract, you guys know what this carries.
28:00This bad boy
28:02is carrying that crude touch and
28:04pressure sensations from the
28:05contralateral
28:06aspect of the body.
28:08These three components will eventually,
28:10as they start moving and ascending
28:12rostrally or more superiorly, they'll
28:14fuse together and become the spinal
28:16lemniscus. Okay? But they haven't formed
28:18yet. So, that's what I want you to
28:19remember. That's the only kind of big
28:21thing that's really different at this
28:22point.
28:23We also have another structure. Do you
28:24guys remember we had the vestibular
28:26nuclei?
28:27The medial and the inferior vestibular
28:29nuclei?
28:30Well, what happens is the medial and
28:33primarily the lateral vestibular nuclei
28:35give off fibers that descend downwards
28:38as a particular tract.
28:40What is that called? The vestibulospinal
28:42tract.
28:43This is the vestibulospinal tract.
28:46So again, what is this black structure
28:47here? This is the vestibulo-
28:50vestibulospinal
28:53tract. What does this guy do? He's
28:55carrying descending motor pathways for
28:58your extensor muscles, anti-gravity
29:00muscles. Okay? Boom.
29:03Last portion here. Okay. And this dorsal
29:06gray matter component of the medulla,
29:09you have some nuclei. We already know
29:10these. What was the orange nuclei? And
29:12then it was dorsal aspect. That was the
29:14hypoglossal nucleus. That was cranial
29:16nerve 12 nuclei.
29:18More laterally, the purple ones was the
29:20dorsal nucleus of vagus. Dorsal nucleus
29:22of vagus, again, that is going to be for
29:23cranial nerve 10.
29:26And then more laterally to that was the
29:27nucleus of tractus solitarius, right?
29:30And again, we'll talk about its
29:32significance in just a second.
29:34But that is kind of the big structures
29:36that we talked about. The only other
29:37thing I want to make sure we understand
29:38here and explain
29:40is this sensory decussation.
29:42So, if you guys remember,
29:45very simple kind of concept here. Here,
29:48we are going to have two diagrams that I
29:50want to explain here.
29:52So, we'll have two diagrams.
29:55So, remember coming into the spinal
29:57cord, you had that sensory information,
29:59right? This is coming basically from
30:00your proprioceptors, right?
30:02Proprioceptors from muscle, tendons,
30:04joints, all that stuff.
30:05Let's say that this is coming from the
30:07legs.
30:09What they do is they move into the
30:10spinal cord more medially and then
30:12ascend upwards.
30:14And then, if you had again some more
30:17proprioceptive sensations coming from
30:19the arms,
30:21this will ascend inwards. This will move
30:24in and then ascend upwards a little bit
30:26more laterally. So, again, if we had the
30:28midline through the brainstem and the
30:30spinal cord, the most medial portion
30:32here is going to be
30:34through that dorsal column is going to
30:35be picking up sensations from the lower
30:36extremities. The more lateral is going
30:38to be picking up sensations from the
30:39arms.
30:40This bundle, this kind of arrow going up
30:43is the fasciculus
30:45gracilis. This one coming up here from
30:47the arms is the fasciculus cuneatus.
30:49Eventually, they terminate at nuclei in
30:52the medulla. The nuclei that's more
30:55medial is the nucleus gracilis. The
30:57nuclei that's more lateral is the
30:58nucleus cuneatus. So, again, here's our
31:01nucleus, lateral ones, nucleus cuneatus.
31:05Synapses
31:06on the nucleus cuneatus.
31:09Fasciculus gracilis
31:10is going to be the more medially ones.
31:12They are going to synapse on the nucleus
31:15gracilis. Okay?
31:17And then, what happens is the fibers
31:21of the nucleus, again, lateral one is
31:24cuneatus, medial one is the gracilis,
31:26they are going to
31:28cross and move to the contralateral
31:30side.
31:31So, they're going to cross this way. If
31:32it were coming from this side, they
31:34would also cross and move to the
31:36contralateral side. That crossing right
31:39here is the sensory decussation, and
31:42that's what we see at this point here.
31:44So, the fibers that are coming from the
31:45nucleus gracilis and the nucleus
31:47cuneatus are crossing and going into
31:50this component here. What the heck is
31:51this son of a gun? That's our medial
31:53lemniscus.
31:55We talked about it here. So, what is
31:56this fibers? After they cross and go up,
31:58what is this? Medial lemniscus on the
31:59left side. What is this one?
32:01Medial lemniscus on the right side.
32:03So, again, they cross and then ascend
32:06upwards as the medial lemniscus.
32:09Beautiful. So, that explains the rostral
32:11and the middle section of the medulla.
32:14Let's finish up, hit it home with the
32:16most caudal portion.
32:17All right. So, now we're at the last
32:19section of the medulla. We hit the first
32:20top section, okay? Pontomedullary
32:22junction. We hit the middle section at
32:24the level of the sensory decussation.
32:26Now, we're at the most caudal, inferior,
32:28lowest portion of the medulla, and this
32:30is at the pyramidal decussation. Okay? A
32:33lot of this stuff is going to already be
32:35very familiar. So, we're just going to
32:36abbreviate it. The only one that we'll
32:38kind of write out is the only thing
32:39that's really different here. All right,
32:41so let's start here dorsally and just
32:42kind of do what we've been doing, kind
32:43of working our way back around.
32:45So, again, at the most dorsal aspect,
32:46you guys better know this. What is this
32:48guy? This is your fasciculus gracilis.
32:51Again, they're paired, right? And then
32:53associated with it, where it will
32:54terminate, is the nucleus gracilis. More
32:57laterally is the fasciculus cuneatus.
33:00Again, they're paired. They'll terminate
33:02eventually on the nucleus cuneatus. This
33:05one's a little bit different. You saw
33:07this at a other area,
33:09but this is your spinal tract for that
33:13trigeminal nerve. And this is the spinal
33:16nucleus of the trigeminal nerve. So,
33:18again, they're paired. Spinal tract of
33:20the trigeminal nerve and spinal nucleus
33:23of the trigeminal nerve.
33:25This we already know this what this was
33:26your sympathetic
33:28tract, that descending sympathetic
33:31tract.
33:32And again, you don't see that
33:33hypoglossal nucleus. You don't see the
33:35dorsal nucleus of vagus. You don't see
33:37the nucleus of tractus solitarius here.
33:40What do we see? We see this guy. This
33:42was our dorsal spinocerebellar tract.
33:45This is our ventral spinocerebellar
33:47tract. Again, they're paired. Dorsal
33:49spinocerebellar, ventral spinocerebellar
33:51tract.
33:53Then we had this guy. This was the
33:54olivospinal tract going from the
33:57inferior olives down to the spinal cord.
33:59This is your spinal olivary tract coming
34:02from the spinal cord going up to the
34:03inferior olives.
34:05Then we already covered this, but this
34:07is going to be what?
34:09This is your corticospinal tracts. And
34:11again, we'll write here corticospinal
34:13tracts.
34:16We'll explain this in a little bit more
34:17detail in a second.
34:18Then, what do we have here? We already
34:20hit this one. This was your
34:21vestibulospinal tract. So, this is your
34:23vestibulo-
34:25spinal tract.
34:28This was carrying that descending motor
34:29pathways for the extensor muscles.
34:31This was the three components that
34:33eventually become the spinal lemniscus.
34:35This is your lateral spinothalamic
34:37tract. This is your spinal tectal tract.
34:40This is your What is this? This is your
34:43ventral spinothalamic tract.
34:46Okay? So, again, they're paired lateral
34:48spinothalamic tract,
34:50spinal tectal tract, and then ventral
34:53spinothalamic tract.
34:55The other thing we actually should add
34:56in here is again you What do you have
34:57What else do we have coming down? This
34:59was our tectospinal tract, right? And
35:02again, that was coming from the tectum.
35:03We should have had that one in there.
35:05And then again, you're also going to
35:06have your We'll put it right here.
35:09This is your rubrospinal tract, right?
35:11And that's going to be coming from the
35:12red nucleus coming down. So, again, what
35:14do you have here?
35:15Your tectospinal tract,
35:18paired,
35:19and then up here you're going to have
35:20your rubrospinal tracts. And again, this
35:23is going to be going to the distal
35:24muscles for
35:26the up upper extremities for flexion.
35:30And again, you'll notice here that we
35:31don't have the medial longitudinal
35:33fasciculus. We don't have the medial
35:34lemniscus because it hasn't been formed
35:36yet at this part. Okay?
35:38All right, the only thing that I really
35:39want to kind of end here
35:42is this pyramidal decussation. I'm going
35:44to explain this.
35:45So, again, you guys remember We had like
35:48a little mini diagram here.
35:50Here's our
35:51midbrain, pons, medulla, going down into
35:54the spinal cord, right? So, again, here
35:56we'll we'll kind of do this here.
36:00Here's our medulla,
36:02midbrain here, pons there, and again,
36:05spinal cord down at the bottom here.
36:07Do you guys remember
36:09the corticospinal fibers, right? Coming
36:11from the cortex. It'll come from an
36:12upper motor neuron, come down through
36:14the midbrain, come down through the
36:15pons, scatter through the pontine
36:17nuclei, come to the level of the
36:19pyramids, and when it gets to the bottom
36:21part of the pyramids,
36:23it crosses over,
36:25and then descends downwards, right?
36:27Then, same thing. If it was coming from
36:29the right side, comes down through the
36:30midbrain, through the crus cerebri,
36:31through the pons, through that scatters
36:33around the pontine nuclei, moves through
36:35the pyramids at the most lower part, it
36:37crosses over, and comes down as the
36:40corticospinal tracts. Right? The ones
36:42that cross,
36:44these are going to be crossing and
36:46forming the lateral corticospinal
36:50tracts. Again, we'll explain this in
36:52just a little bit in a second, but
36:54again, this portion here, you see how
36:56this is going to be the corticospinal
36:57fibers that are coming through the
36:59pyramids?
37:00Some of these fibers that cross
37:03and descend downwards, cross and descend
37:06downwards,
37:0785% of these corticospinal fibers do it.
37:12And they will form the lateral
37:16corticospinal
37:19tract.
37:21Okay? So again, what is this guy here?
37:23Some from these corticospinal fibers
37:25descending down through the pyramids,
37:27some will cross, 85% of them, and will
37:30descend downwards. And this is going to
37:32be your lateral
37:34corticospinal
37:37tract. Okay? Some of the fibers, 15% of
37:41them, will not cross. So they won't
37:43cross, and they'll just descend
37:45downwards,
37:46and eventually come down to the spinal
37:48cord, and at the level that they're
37:50going to be stimulating those motor
37:52neurons, they'll cross. And that's your
37:54ventral corticospinal tract. That
37:56accounts for about 15%.
37:58Okay? But this portion here,
38:02where the corticospinal fibers cross and
38:04move downwards as the lateral
38:06corticospinal tract, what is this
38:09called?
38:10This is called the
38:12pyramidal
38:15decussation.
38:20Okay? So the pyramidal decussation. All
38:22right.
38:24So, we've covered that. Now, that we
38:26have covered the most caudal portion,
38:29the most inferior, the bottom portion of
38:31the medulla, what I want to do is just
38:33really quickly cover some of the cranial
38:35nerves to recap what we've covered and
38:37to cover a little bit of the external
38:38anatomy of the medulla. Then, what we'll
38:41do is we'll start talking about a lot of
38:42the functions of a lot of these
38:43structures here, okay?
38:45All right. So, the last thing I want to
38:46do here, kind of covering the anatomy,
38:47so we kind of hit home this medulla
38:50neuroanatomy thing, is covering a little
38:51bit of this external anatomy. So, a lot
38:55of us will see, you know, whenever we're
38:57looking at the brainstem in this kind of
38:59a coronal view here, right? This is the
39:02anterior kind of portion of the
39:03brainstem, midbrain, pons, medulla,
39:05spinal cord, cerebellum, right?
39:08Some of the big things that we should
39:09understand is is when you look here at
39:11the medulla, right? So, again, medulla
39:12is going to be You see how this kind of
39:14have like this little jaggedy line here?
39:15From this portion here, that's all
39:17medulla. You have this line coming right
39:19down the middle. That's your anterior
39:21median fissure, okay? Then, you have
39:24these lines over here. And these are
39:26called your anterior lateral sulcus.
39:29There's a reason why I'm explaining
39:30this. Just give it a second. And then,
39:32the most outer ones here is your
39:34posterior
39:36lateral sulcus.
39:38And again, this kind of wavy line
39:41just above it is the pons. So, this is
39:43that pons-medulla junction. So, again,
39:46go a quick recap. Anterior median
39:47fissure,
39:48anterior lateral sulcus, posterior
39:50lateral sulcus. This is that
39:52pons-medulla junction, right? Okay.
39:56What I want us to know is all the
39:58cranial nerves that are coming off of
40:01the pons-medulla junction, the anterior
40:03lateral sulcus, and the posterior
40:04lateral sulcus. And then, what are the
40:06names of this and this? And then, some
40:09of these other structures that we'll
40:10cover just as an aside. All right. First
40:12thing, let's cover some of the nerves
40:13that are here on this ponto-medullary
40:14junction. Easiest thing to do is to kind
40:17of make
40:18a line to go right down the middle cuz
40:20this is all paired.
40:22All right, first one. Let's cover the
40:24blue ones here. Okay, right at this
40:25pontomedullary junction here. What are
40:27these two cranial nerves? I want you to
40:29remember that this is cranial nerve six
40:33or the abducens nerve. Okay?
40:36Go a little bit more laterally on this
40:38pons medulla junction here. What is this
40:39guy here? This is your facial nerve or
40:43cranial nerve seven. All right, cool.
40:47Let's go a little bit more laterally
40:50on this pons medulla junction. What is
40:51this called? The green component is for
40:55the cochlear nuclei, the ventral dorsal
40:57cochlear nuclei. Right, so that's the
40:58cochlear branch. The red one is going to
41:02the superior medial medial inferior and
41:04lateral vestibular nuclei. That's the
41:06vestibular branch. This is the
41:08vestibulocochlear
41:09nerve or cranial nerve
41:12eight.
41:13Okay, and it's paired here. Okay, sweet.
41:17Let's move down. So, we got eight. We're
41:19going to come here on this
41:20posterolateral sulcus, so anterior
41:22median fissure, anterior lateral sulcus,
41:23posterior lateral sulcus. On the most
41:25top portion of this,
41:27this guy here is going to be cranial
41:30nerve nine or the glossopharyngeal
41:34nerve. So, again, this is the glosso-
41:36pharyngeal nerve.
41:38A little bit more caudal or inferiorly,
41:42we have this guy. This is cranial nerve
41:4510 or the vagus nerve. Sweet.
41:50And at the most inferior portion, a tiny
41:53little portion of this outer
41:55uh posterolateral sulcus around the
41:57inferior portion of the medulla, you
41:58have this kind of bluish one. This is
42:00the accessory nerve and it's the cranial
42:03part of the accessory nerve. Okay, cuz
42:06there's two parts of the accessory
42:08nerve. One part of the accessory nerve
42:09is is off of the medulla And another
42:12part is coming from
42:14the cervical segments of the spinal
42:17cord, like C1 all the way down to like
42:19C4. Okay?
42:21So again, this is the spinal component,
42:24which is coming from C1 to C4.
42:26And then this is the
42:28cranial component.
42:30All right, sweet. Now, come more
42:33medially onto this anterolateral sulcus.
42:36On the anterolateral sulcus, we have
42:39these guys. What are these? This is
42:41cranial nerve 12.
42:44And cranial nerve 12 is the
42:47hypoglossal nerve. Okay?
42:50Okay, we covered that. Next thing,
42:54we give a specific name to these little
42:56fat bulges coming out the anterior
42:58portion of the medulla. What is this
43:00guy? This is your pyramids, and they're
43:03paired. Okay?
43:05Then you got two other fat bulges, okay,
43:07on the lateral sides of the pyramids.
43:10This is your olives. Okay, so the
43:14anterior median fissure separates the
43:15the two pyramids, and the anterolateral
43:18sulcus separates the olives. Sweet.
43:21All right, from all the olives from the
43:23pyramids. Okay. Then, we got these
43:25little tubes that are connecting the
43:27three parts of the brain stem to the
43:29cerebellum. In order, at this level, is
43:32the inferior cerebellar peduncle. So,
43:34what is this guy here? This is your
43:36inferior cerebellar peduncle. This one
43:39here is your medial cerebella middle
43:42cerebellar peduncle. And at the most
43:44superior portion between the midbrain
43:45and the cerebellum, is the superior
43:48cerebellar peduncle. So again, superior
43:50cerebellar peduncle,
43:51middle cerebellar peduncle,
43:54inferior cerebellar peduncle. Okay?
43:58Now, while we're here, might as well hit
43:59some other structures. What is this
44:01cranial nerve nuclei? It's always good
44:03to do repetition. It's the best way to
44:04learn, right? What is this cranial nerve
44:07nuclei here? This is cranial nerve five,
44:09the trigeminal nerve. That's kind of at
44:11the pons, right? So, we hit that section
44:13in the pons video. Then you come over
44:15here, and we got two cranial nerves
44:17coming out of the midbrain. One's coming
44:20through that interpeduncular fossa. What
44:21is this son of a gun? This is cranial
44:24nerve three, oculomotor nerve.
44:27And then this last one that kind of
44:29comes around the back, crosses, and
44:31comes around the sides of the midbrain.
44:33This is cranial nerve four,
44:36or the trochlear nerve. Okay?
44:39So, this covers that nice little
44:41external anatomy questions that kind of
44:42come up that you might see on certain
44:44exams for the medulla. All right. Now,
44:47let's hit it home with the general
44:48functions of a lot of these structures.
44:51The structure is complementing the
44:53function. So, we It's It's not just
44:55important for us to know what is the
44:57name of this structure. Okay, what is
44:58the name of this fiber? What is the name
45:00of this nucleus? We need to know kind of
45:01an idea of what these things do.
45:04So, we're going to kind of have a
45:05general overview on some of these things
45:06cuz we have more detailed videos that
45:08cover these topics exclusively. Okay,
45:10this would be a 3-hour video if we go
45:12through everything. Okay? So, so we're
45:14going to cover it generally.
45:15First thing we're going to cover is
45:17these corticospinal tracts, these
45:18descending motor pathways. We've already
45:20talked about this so many times. You
45:21guys know this, you know, like the back
45:24of your hand. So, again, we have these
45:25upper motor neurons, right? Coming from
45:28the
45:30primary motor cortex, the premotor
45:32cortex, the primary somatosensory area,
45:35all sending these corticospinal fibers
45:38down.
45:39They move their way down. They go
45:41through the, you know, you guys remember
45:42the internal capsule.
45:44They'll move through the crus cerebri.
45:46They'll move through the pons and kind
45:48of scatter. You know, they scatter
45:49around some of those pontine nuclei, but
45:51then some of them reform.
45:53And eventually they come to the medulla.
45:56And they move through that pyramid, that
45:57big fat chunky thing here in the
45:59anterior portion.
46:00And when they do that, they move down
46:02through this portion of the pyramids.
46:05And what happens is these corticospinal
46:07fibers, remember I told you, as we get
46:09to the lowest portion of the pyramids,
46:11some of the fibers will cross, and they
46:14move a little bit posteriorly, and then
46:16descend downwards. Do you guys remember
46:19what those fibers were? Whenever they
46:21cross,
46:23they move a little bit posteriorly,
46:25and then descend downwards.
46:27And they descend downwards into the
46:29lateral
46:30white column, okay?
46:33What was that that decussation called?
46:34That was called the Here, we'll
46:36abbreviate it. Pyramidal decussation,
46:38right? And the fibers that move
46:41laterally and descend downwards, this is
46:43your lateral corticospinal tract.
46:46Now, this was 85% of the fibers that are
46:48crossing. We said that some of the
46:51fibers will not cross,
46:55and will just descend downwards into the
46:58ventral column, okay? Some of the fibers
47:01will not cross, and will descend down
47:03into the ventral column, and eventually
47:06at the level
47:09will cross, okay? Stimulating those
47:12lower motor neurons. Here, we'll
47:13represent this to really differentiate
47:15the color, we'll do blue. So, here,
47:17we'll have some blue motor neurons here
47:19that are coming out.
47:21Right? So, ventral cross at that level,
47:23dorsal crosses at the and the lateral
47:26crosses at the pyramids, and they'll
47:28synapse on these lower motor neurons.
47:32So, again, lateral corticospinal tracts
47:34are 85% of the fibers that decussate at
47:36the level of the pyramids. The ones here
47:38that are ventral that don't cross at the
47:40level of the pyramids is the ventral
47:42corticospinal tract. They account for
47:44about 15%. Lateral corticospinal tract
47:47accounts for about 85%.
47:49Okay? And again, this will stimulate the
47:51lower motor neurons that will go out to
47:54your skeletal muscles
47:56to allow for contraction
47:58of those skeletal muscles. Simple
48:00concept there. Okay?
48:02So, again, that's covering the
48:04corticospinal fibers with the pyramidal
48:07decussation covering the ventral
48:09corticospinal and the lateral
48:10corticospinal tract.
48:11Let's move over. Okay, now we're going
48:13to cover the sensory pathways that I I
48:15think we've hit like a million times,
48:16but it's Yeah, it's worth going over and
48:18hitting it home one more time.
48:20So,
48:22you guys remember we had the medial
48:24lemniscus and the spinal lemniscus. We
48:26already talked about the trigeminal
48:27lemniscus, so we can kind of knock that
48:29one out for
48:30for right now. But, you guys remember
48:32dorsal column, right?
48:34Picks up medial lemniscus. This is
48:36picking up sensations, proprioception,
48:39vibration,
48:40fine discriminative touch.
48:42Taking this in to the
48:45posterior gray horn, right? You guys
48:47know it moves into the posterior gray
48:48horn.
48:49And then as it moves into the posterior
48:51gray horn, it moves into the dorsal
48:53white column. When it moves into that
48:55dorsal white column, it then ascends
48:57upwards. If it's picking the sensory
49:00information from the legs, it's going to
49:02be coming up as the fasciculus gracilis.
49:05If it's coming from the upper
49:06extremities, which is more laterally,
49:07that's the fasciculus cuneatus. We know
49:09this, okay?
49:11Let's repeat it though. Again, coming
49:13here is the
49:15fasciculus gracilis. Coming here is the
49:17fasciculus cuneatus. They'll eventually
49:19come up and they'll synapse on the
49:22medial is the nucleus gracilis, lateral
49:24is is the nucleus cuneatus, and these
49:27fibers will cross.
49:29And whenever these fibers cross, what is
49:31that cross called? That's called the
49:33sensory decussation. But then, whenever
49:36they're kind of moving towards that
49:38decussation, before the decussation,
49:40that's called the internal arcuate
49:42fibers. So, just before they cross over
49:44is the internal arcuate fibers, but the
49:46decussation is called the sensory
49:48decussation.
49:49Then they ascend upwards as the
49:52medial lemniscus. We've
49:55We've knocked that cold, right? We know
49:57that now.
49:58Okay.
49:59Hit another one. Let's say here we have
50:02pain,
50:03temperature,
50:04crude touch, pressure.
50:06All of those sensations are coming in
50:10dorsal root ganglion, coming into the
50:12dorsal gray horn, synapsing on the
50:15neurons in the dorsal gray horn,
50:17and then crossing over. If it's the pain
50:19and temperature, it's going laterally
50:21and then ascending upwards. If it's
50:23crude touch and pressure, it's going
50:25ventral and ascending laterally.
50:28Again, there's also the spinotectal
50:30pathway that will eventually fuse. But
50:32if again, the one that's going
50:34ventrally, that's your ventral
50:35spinothalamic tract. The one going
50:37laterally for pain and temperature is
50:38the lateral spinothalamic tract. And
50:40again, another tract that will come in
50:42here,
50:43I'll just add him in blue here,
50:46is your spinotectal tract. What happens
50:49when the lateral spinothalamic tract,
50:51ventral spinothalamic tract, and the
50:53spinotectal tract come together and
50:55fuse? They make the spinal lemniscus.
50:59So, what is this called? Spinal
51:01lemniscus.
51:02And some of these will go to the
51:03thalamus, some of it will give
51:04collaterals off to the reticular
51:06formation, a lot of different
51:08components of that pathway. Okay?
51:11We already covered the trigeminal
51:12lemniscus. So again, we know the medial
51:14lemniscus, we know the spinal lemniscus.
51:16That's good. And again, we know the
51:18trigeminal lemniscus, so we can move on.
51:21Next thing that I got to talk about
51:22that's a little bit different is the
51:24inferior olives. Now, you guys remember
51:27the inferior olives are very important.
51:29We've talked about this in a couple
51:30different videos, some in the
51:32uh descending tract video, some in the
51:34cerebellar video. So, this kind of might
51:37be a recap, but again, it's important
51:39for us to just kind of quickly go over
51:40this, give a general concept.
51:42Remember I told you that there was two
51:44tracts that we talked about in the
51:45medulla.
51:46Okay, we had the spinal olivary tracts
51:50and the olivo spinal tracts. And this is
51:53important. It's pretty simple though,
51:54right? Spinal olivary is sensations
51:57coming from the spine going to the
51:58olives. Olivo spinal is going from the
52:01olives down to the spinal cord not to
52:02the muscles.
52:03So, let's kind of talk about that.
52:06Okay, olivo spinal pathway.
52:08It's relatively simple. You have again
52:11dorsal root ganglion here. Sensations
52:14and then again, what kind of sensations
52:15is this?
52:16This is proprioceptive sensations. Okay,
52:19this is
52:20uh a little bit of uh pressure and touch
52:23that is going to be sending information
52:25to these inferior olives. Okay, so
52:27again, these are going to be coming from
52:29proprioceptors from muscles, uh
52:32spindles, uh joint capsules, ligaments,
52:34tendons, all of that stuff.
52:36Sending that information into the dorsal
52:39gray horn.
52:40And then what happens is it crosses over
52:42into this kind of like ventral portion
52:44of the white column and then ascends
52:46upwards here
52:48to the inferior olives. Okay? So, again,
52:51here's an inferior olive, here's an
52:52inferior olive.
52:54Now, when these fibers cross over to
52:56this ventral white column, ascend
52:58upwards, go to the inferior olives, the
52:59inferior olives will then take the
53:01sensory information
53:02and they do something really cool here.
53:04They cross it over to the contralateral
53:07cerebellum, right? So, in the same way
53:10here, if it was coming from this side,
53:13right? So, here you're going to have
53:14proprioceptors
53:15and you know, from and and vibration,
53:17all of that stuff uh coming in here,
53:19synapsing on the dorsal root ganglion,
53:22crossing over into the ventral white
53:23column, coming upwards, synapsing on the
53:25inferior olives.
53:26The inferior olives will then do what?
53:28Uh then cross that information over into
53:32the contralateral cerebellum. There's an
53:34important reason to mention this.
53:37One of the reasons why is that these
53:38fibers that are going into the
53:41cerebellum here, right? Going into the
53:43cerebellum is very important. Coming
53:46from the inferior olives. These are
53:47called climbing fibers. I want you guys
53:49to burn this into your memories. These
53:52are called climbing
53:55fibers.
53:57So, the climbing fibers are going to be
53:58the fibers coming from the inferior
54:00olivary nucleus going into the
54:02cerebellum via the inferior cerebellar
54:03peduncles.
54:04All the other sensory fibers going into
54:07the cerebellum are called mossy fibers.
54:09Okay, good.
54:11So, we covered here, which one was this
54:13one? Spinal cord to olives. That's
54:15spinal olivary tract. What about the
54:18olivospinal tract? There's a lot of
54:20controversy. Some of the books I read um
54:22in an article
54:24said that there's a little bit of
54:25controversy and doubt on whether this
54:27tract actually exists. Um I'm going to
54:29just briefly cover it, okay? Cuz there
54:31is some newer things that they're
54:32saying.
54:34The inferior olives
54:36are believed to receive information
54:39from the red nucleus, right? So, you
54:41know the cerebellum has a bunch of
54:43different cerebellar nuclei, right? The
54:45dentate, the emboliform, the globose,
54:48all of those things.
54:50They believe that some of the
54:51information
54:52will go into
54:54the contralateral red nucleus from these
54:57deep cerebellar nuclei, right?
54:59And that these red nuclei
55:02can then send some of this information
55:04down to
55:06these inferior olives, okay?
55:09So, what does that mean? Remember the
55:11cerebellum is is aware of all of your
55:13proprioceptive sensations. It knows
55:15where your muscles, your tendons, your
55:16ligaments, your joint capsules are in
55:18space.
55:19It sends it to the red nucleus. Red
55:21nucleus sends this to the inferior
55:22olives. It receives that sensation. The
55:24cortex
55:26also has the ability Let's do this in a
55:29different color here. Let's do pink.
55:32The cortex also has the ability to send
55:34down the motor plan
55:38to the inferior olives, letting them
55:40know what the motor plan is. So, the
55:42cerebellum tells them tells the inferior
55:44olives all the position of your muscles,
55:45your tendons, your joint capsules, all
55:47that stuff.
55:48Cortex tells them the motor plan. Then,
55:50here's the interesting newer information
55:52that I read about.
55:54You know where you have the putamen and
55:55the globus pallidus externus and
55:57internus, all of that comportion of like
55:59the striatum, they are believed to send
56:02information down to the inferior olives.
56:05This is the newest thing and this is
56:06what they believe it might be involved
56:08in. So, they believe
56:10that there might be some type of
56:12connection or association between the
56:14basal ganglia and the inferior olives.
56:17But, here's the final concept. What they
56:19think is that the inferior olives
56:22will send down descending motor fibers.
56:26They'll send down descending motor
56:28fibers.
56:30And these descending motor fibers will
56:32go to muscles
56:35that are believed to control reflexive
56:37movements. Okay, that's all that we
56:39really know. It's again, it's kind of
56:40unknown about this tract, but again, I
56:42wanted to make sure that you guys
56:43understand there is some
56:45belief that the inferior olives receive
56:47information from the
56:49cerebello-rubro-olivary
56:51fibers
56:53and they also receive information from
56:55the cortex and they receive information
56:57from the striatum. The newest
56:59information is that they believe there's
57:00an association between the striatum, the
57:02basal gang- part of the basal ganglia
57:04and the inferior olives. And they
57:06believe that it's involved with
57:07reflexive movements. Okay?
57:10That covers these inferior olives. Now,
57:13let's move on.
57:15Okay, we've already covered this one
57:17like a million times, too, but the
57:18vestibular system.
57:20You guys remember the vestibular nuclei,
57:22superior, middle, medial, inferior,
57:24lateral. They're all receiving
57:25information from what?
57:28They're receiving information from two
57:29things. One is from the inner ear,
57:31right? From the, uh, cristae
57:34ampullaris, right? And then the macula,
57:37right? You guys remember these
57:38structures? Crista ampullaris is for the
57:40rotational acceleration. Macula is going
57:43to be for more of the linear
57:44acceleration. They send information to
57:47these vestibular nuclei.
57:48Then you have the fastigial nucleus, and
57:50he sends information to the vestibular
57:53nuclei about all the different
57:55proprioceptive sensations in the body.
57:58Now,
57:59this vestibular nucleus then has a
58:00choice. It decides, "I'm going to send
58:03descending information down to
58:07motor fibers to cause contraction of
58:10specific muscles, extensor muscles,
58:12anti-gravity muscles." What is this
58:14tract?
58:16This is going down to the spinal cord
58:18from the vestibular nucleus. This is
58:19your vestibulospinal tract. We talked
58:21about that one.
58:23Then, it also can connect from the
58:25vestibular nucleus, it can connect to
58:28the fastigial nucleus, right? We know
58:31that there's a connection between those
58:33via the inferior cerebellar peduncles,
58:35via the juxtarestiform body.
58:38So, it can go into the cerebellum, it
58:40can go down to the spinal cord, or it
58:42can send information up to the thalamus,
58:44and it can do one more thing.
58:47It can send information to your abducens
58:50nerve.
58:51And then the abducens nerve
58:54will do what?
58:55It'll send information to the
58:57contralateral third and fourth nerve
59:00nucleus. What is that blue tract?
59:03The medial longitudinal fasciculus,
59:04right? So, it The medial longitudinal
59:06fasciculus technically can extend from
59:09the medulla all the way up to the
59:11midbrain.
59:12Okay?
59:13So,
59:14we know now vestibulospinal tract,
59:17we know
59:18the connection to the fastigial nucleus
59:20via the inferior cerebellar peduncles,
59:22we know the connection between the
59:24vestibular nucleus and the medial
59:26longitudinal fasciculus.
59:27That covers it. Boom, we move on.
59:30All right, so let's cover this next
59:31point. We already talked about the
59:32tectospinal tract and the rubrospinal
59:33tract like a thousand times. It's worth
59:35repeating though, right? So,
59:36tectospinal, superior colliculus,
59:38inferior colliculus, we already know.
59:40That's a part of the tectum, posterior
59:41portion of that midbrain, right? Sends
59:43information downwards. That can go to
59:45two points. One, to the spinal cord.
59:47What is that called?
59:49The tectospinal tract, right? But it can
59:52also give off
59:54fibers to go to the cranial nerve nuclei
59:57that go and supply different muscles of
59:59the eye. What is the importance of this
1:00:02tectospinal tract? It's to supply
1:00:04muscles of the head and neck via the
1:00:06spinal cord and muscles of the eye for
1:00:09move reflexive movements. If someone
1:00:10calls your name, that stimulates the
1:00:12inferior colliculus. Move your head and
1:00:14your eyes that way. If you're watching
1:00:16somebody move, that's the superior
1:00:18colliculus and it's going to be causing
1:00:20you to move your head and your eyes in
1:00:21that direction. If you step on
1:00:23something,
1:00:24when you step on something, it sends
1:00:26information upwards
1:00:28to your tectum. Let's your tectum know
1:00:31that you're receiving this sensory
1:00:33information. What is that called? Let's
1:00:35do this in a different color just to
1:00:36recap this. You receive sensory
1:00:38information, you step on something.
1:00:41That comes here into your uh your actual
1:00:43spinal cord. Ascends upwards, stimulates
1:00:46the tectum. What is that tract called?
1:00:47You better tell me. The spinal tectal
1:00:50tract. The one going down is the
1:00:52tectospinal tract.
1:00:54Okay, last one here. Red nucleus. We
1:00:57know this one, right? We know that this
1:00:59guy is going to it forms that ventral
1:01:00tegmental decussation and then descends
1:01:02downwards, goes to
1:01:05lower motor neurons that go to the
1:01:07flexor muscles primarily of the upper
1:01:09extremity.
1:01:10Done.
1:01:11Okay.
1:01:12Let's move on.
1:01:14All right, so the next one we got to
1:01:15cover is that sympathetic tract. You
1:01:17guys remember the sympathetic tract,
1:01:18right?
1:01:19Sympathetic tract, remember you have the
1:01:21hypothalamus, right? The hypothalamus
1:01:22has two portions. One portion that's a
1:01:24parasympathetic portion here. We'll
1:01:25We'll draw the parasympathetic portion.
1:01:27We'll do it in here like a red.
1:01:30And then there's a portion of the
1:01:31hypothalamus that has a sympathetic
1:01:33portion. That's going to be in this baby
1:01:34bluish teal color, right?
1:01:37This hypothalamus will have fibers that
1:01:39will then come backwards, you know,
1:01:42posteriorly, and then descend downwards
1:01:45through the midbrain, through the pons,
1:01:48through the medulla,
1:01:50and go into the spinal cord,
1:01:53where it'll synapse
1:01:56on preganglionic motor neurons within
1:01:58the thoracolumbar portion of the spinal
1:02:00cord.
1:02:02And then from this, do you guys remember
1:02:04what we said here from that T1 all the
1:02:06way to like L2? That thoracolumbar
1:02:09outflow?
1:02:11That's all going to be for sympathetic
1:02:13outflow.
1:02:14So, I just wanted to make sure we
1:02:15understand what the heck the sympathetic
1:02:17tract is. The sympathetic tract is that
1:02:19descending sympathetic pathway coming
1:02:21from the hypothalamus that'll then
1:02:23synapse on some of these
1:02:26uh the preganglionic motor neurons
1:02:28located within the intermediolateral
1:02:31portion of the spinal cord at T1 to L2
1:02:33that'll control the thoracolumbar
1:02:34outflow.
1:02:36Boom.
1:02:37Let's move on.
1:02:39All right. So, next thing we got to
1:02:40cover that we talked about in those
1:02:41medulla structures was um the
1:02:43spinocerebellar tracts. And again, we're
1:02:45not going to go into total detail on
1:02:46this. If you guys want, we have another
1:02:48video on this.
1:02:49But, to give you an idea of what they're
1:02:52doing. Remember, you have that uh the
1:02:54dorsal spinocerebellar tract. Do you
1:02:56guys remember We We talked about it
1:02:57really quickly in the in in that video.
1:03:00If you have here uh midline portion of
1:03:02the spinal cord, right? And let's say
1:03:04that we go here at the top, we have C1.
1:03:07Then we'll go about right here. We'll
1:03:08say that's about C8. Then we'll go about
1:03:10right here. Let's say that's at like L2
1:03:12L3. Then we'll go down a little bit
1:03:14more, and let's say that this is going
1:03:15to be like coccygeal one. Okay?
1:03:18If you guys remember from C8, well,
1:03:20actually, let's do this in order. From
1:03:22C1
1:03:23to C8,
1:03:25this was picked up by that
1:03:27cuneocerebellar tract. I'm just going to
1:03:29put CT.
1:03:31Okay? And then from C8 to L2 L3, this
1:03:35was picked up by that dorsal
1:03:37spinocerebellar
1:03:39tract. We'll put DCT.
1:03:41And then from L2 L3 down to the
1:03:43coccygeal one was picked up by the
1:03:46ventral
1:03:47spinocerebellar
1:03:49tract. We'll put VCT.
1:03:51Okay?
1:03:53This is basically picking up
1:03:55proprioceptive sensations,
1:03:57uh you know, some uh pressure and even a
1:04:01little bit of touch and taking it to the
1:04:03cerebellum, which has a kind of an
1:04:06unconscious
1:04:07uh basically a awareness of all of these
1:04:10proprioceptive and touch sensations.
1:04:12Okay? And they're carrying it to the
1:04:14cerebellum.
1:04:16Again, really quickly to cover this.
1:04:19Cuneocerebellar, that's taking it kind
1:04:22of like mainly from C1 to C8. Okay? So,
1:04:26you're getting more of like the neck, uh
1:04:28a little bit a teensy bit of like the
1:04:30upper extremities. Okay?
1:04:32So, you're going to have that
1:04:33cuneocerebellar tract picking up
1:04:35proprioceptive sensations, moving into
1:04:37the dorsal gray horn, moving into that
1:04:40little funiculus, ascending upwards, and
1:04:42going to that Remember this guy?
1:04:45The accessory cuneate nucleus.
1:04:47So,
1:04:48here, let's remind us. What color do we
1:04:51have? Okay. Here was the nucleus
1:04:53cuneatus, nucleus cuneatus. What did we
1:04:55have medially, guys? You guys better
1:04:58tell me. Nucleus gracilis, nucleus
1:05:00gracilis.
1:05:01So, there's another nucleus just lateral
1:05:04to that called the accessory cuneate
1:05:05nucleus. It's receiving information
1:05:08from the cuneocerebellar tract, will go
1:05:11to this nucleus, and then send it in via
1:05:14the inferior cerebellar peduncle into
1:05:16the cerebellum. Okay? Boom, done.
1:05:20Dorsal spinocerebellar tract receive
1:05:22proprioceptive sensations from the
1:05:26structures from C8 to L2 L3.
1:05:29Takes that into the dorsal gray horn.
1:05:32When it synapses in the dorsal gray
1:05:33horn, it moves ipsilateral into the
1:05:35lateral white column, right? And then
1:05:37does what?
1:05:39It ascends.
1:05:41And then as it ascends, what does it do?
1:05:42Eventually, it will go into the inferior
1:05:45cerebellar peduncles.
1:05:47And it'll synapse there, right? Again,
1:05:50this is your
1:05:51dorsal
1:05:52cere- uh spinocerebellar tract.
1:05:55The light blue one here
1:05:57is your cuneo-
1:05:59cerebellar tract and let's hit the last
1:06:01one.
1:06:02Which I think we had in pink in the over
1:06:04there. So, where that was going to be
1:06:05the ventral spinocerebellar tract. So,
1:06:08this is picking up proprioceptive
1:06:10sensations, touch sensations from L2 L3
1:06:12down to coccygeal one, comes into that
1:06:14dorsal
1:06:16gray horn, synapses, and then what does
1:06:18it do? It crosses over and it moves into
1:06:21the lateral white column, but more
1:06:22ventrally to the dorsal
1:06:25spinocerebellar tract. And then does
1:06:27what? Ascends upwards, ascends upwards,
1:06:30and then it goes all the way up to the
1:06:32midbrain at the
1:06:34superior cerebellar peduncles.
1:06:36And then what does it do? It does that
1:06:38really weird thing where it moves into
1:06:40the cerebellum via superior cerebellar
1:06:42peduncles
1:06:43and then runs behind the midbrain
1:06:46into the contralateral
1:06:48cerebellum. Okay? Because everything
1:06:51from these proprioceptive to the
1:06:53cerebellum, these pathways all have to
1:06:55be ipsilateral. So again, that covers
1:06:57those tracts giving you an idea of what
1:06:59they're doing, putting a function to the
1:07:01name.
1:07:03Sweet. And again, do you guys remember
1:07:05what these nuclei are called
1:07:08from C1 as we go down here?
1:07:10Remember that? That was called Clark's
1:07:12column.
1:07:13So again, those are those first order
1:07:15neurons that are within the dorsal gray
1:07:17horn that they're synapsing on and then
1:07:18either crossing over or moving into the
1:07:21same lateral white column. All right.
1:07:25Sweet deal. All right, let's move on to
1:07:26the last thing here
1:07:28um and then we'll cover the the cranial
1:07:29nerves a little bit. But this was that
1:07:31cochlear pathway. You guys remember what
1:07:33the cochlear nerve pathway does? I think
1:07:35we've done this like three times. But
1:07:37this is it's always worth repeating, I
1:07:38guess, right? So let's hit this one.
1:07:40Again, you got the inner ear coming from
1:07:41what portion of the inner ear?
1:07:43The cochlea. What part of the cochlea?
1:07:46The spiral organ of Corti, which is
1:07:48taking auditory sensations.
1:07:50Remember, vestibulocochlear nerve,
1:07:53it has the two portions, cochlear
1:07:55branch, vestibular branch.
1:07:56This is going to be the vestibular
1:07:57branch. I'm sorry, the cochlear branch.
1:07:59And that synapses
1:08:02on what two structures in that pons
1:08:04medulla junction?
1:08:07The cochlear nuclei. The ventral
1:08:09cochlear nuclei and the dorsal cochlear
1:08:11nuclei. Then, what did we say? Some of
1:08:13the dorsal cochlear nuclei will cross
1:08:16over
1:08:17and ascend up. Some of these ventral
1:08:19cochlear nuclei, what do they do?
1:08:21They'll cross over
1:08:24and they'll ascend up, but some of them
1:08:26will synapse on what structure?
1:08:29Remember, some of them will synapse on a
1:08:31structure called the
1:08:33superior olives. All right, some of them
1:08:36will synapse on the superior olives
1:08:39and then those will ascend upwards.
1:08:42But do you guys remember what this is
1:08:44called whenever there's this crossing
1:08:47of the cochlear nuclei?
1:08:49That's called the trapezoid body. We
1:08:51talked about that before in the pons.
1:08:53But you got the cochlear nuclei, they're
1:08:55receiving information via the
1:08:56vestibulocochlear nerve, synapse on
1:08:58these cochlear nuclei. Some of the
1:09:00cochlear nuclei will cross. Some of them
1:09:02will synapse on the superior olives and
1:09:05then ascend upwards.
1:09:07When they ascend upwards, they go to a
1:09:09portion
1:09:11of the midbrain that you guys know
1:09:14called the inferior colliculus.
1:09:16What is this structure though called
1:09:18that's ascending upwards?
1:09:21Do you guys remember? This was called
1:09:23the lateral lemniscus.
1:09:26And eventually it'll synapse on the
1:09:28inferior colliculus
1:09:30in the midbrain.
1:09:32And the inferior colliculus will have a
1:09:34connection called the brachium of the
1:09:36inferior colliculus.
1:09:38And that brachium of the inferior
1:09:40colliculus will connect to the thalamus.
1:09:46And the thalamus will then relay that
1:09:48information to the temporal lobe.
1:09:51Okay? So again, what I want you to
1:09:53remember is that the cochlear nuclei
1:09:54that are in that area are responsible
1:09:55for sensory information, primarily
1:09:58hearing. Okay?
1:10:00Covered that.
1:10:02Let's finish up briefly talking about
1:10:05these cranial nerves that we've seen
1:10:07within the medulla.
1:10:09Again,
1:10:10we have videos that discuss these
1:10:12cranial nerves in way more detail on
1:10:14their anatomy. We're just going to cover
1:10:16the general functions of them here. All
1:10:18right, so now what I want to do is is
1:10:20just really kind of just basic overview.
1:10:22I just want you guys to be able to know
1:10:24what the functions of these things are
1:10:25because whenever there's lesions, cuz
1:10:27that's what we're going to cover,
1:10:28medullary lesions,
1:10:30what can happen if there's damage to the
1:10:32hypoglossal nerve? You just have to know
1:10:33the general functions, okay?
1:10:35So, hypoglossal nerve is responsible for
1:10:38movement of the tongue, right? So, it's
1:10:40primarily a motor nerve. And the types
1:10:42of motor fibers that it has is those
1:10:45general somatic efferent fibers. What I
1:10:47want you to know is that it controls the
1:10:49muscles
1:10:52of the tongue.
1:10:53Okay?
1:10:55And again, what kind of fibers are they?
1:10:57Just to kind of write it down here? This
1:10:59is G
1:11:01S E fibers, general somatic efferent
1:11:04fibers.
1:11:05I want you guys to tell me though, just
1:11:07so we know because one of them is very
1:11:09important, the muscles of the tongue.
1:11:12What are the muscles? The styloglossus,
1:11:17the hyoglossus,
1:11:21the what else do we got? We got the
1:11:23genioglossus. This is the really
1:11:25important one that I want us to really
1:11:27know.
1:11:28And then the last one is your intrinsic
1:11:32intrinsic
1:11:33muscles of the tongue.
1:11:36If you guys really want to know
1:11:37styloglossus really quickly, elevates
1:11:39the back of the tongue, kind of retracts
1:11:40it. Hyoglossus depresses, retracts.
1:11:43Genioglossus primarily protrusion of the
1:11:46tongue, if you guys remember. It does
1:11:48play a little bit with retraction, but
1:11:49primarily protrusion of the tongue. And
1:11:52then intrinsic muscles of the tongue,
1:11:53they help you to change the shape of the
1:11:54tongue, right? Like
1:11:55you know, doing something like that.
1:11:57So, it's really important that you guys
1:11:58understand the the function of the
1:12:01hypoglossal nerve, but the real big one
1:12:03that I want you guys to know is it's
1:12:04going to come up when we talk about
1:12:05lesions, is the genioglossus. Again,
1:12:07primarily for that protrusion of the
1:12:10tongue.
1:12:11Okay.
1:12:12Glossopharyngeal nerve, this is a
1:12:14mammoth, you know, not as compared to
1:12:15the vagus, but it's a pretty beast, you
1:12:17know, kind of guy.
1:12:18We're going to cover some of the nuclei
1:12:20that we talked about, okay?
1:12:23What was one of the nuclei that we had?
1:12:25We went kind of as we went medially, we
1:12:26had hypoglossal nucleus, dorsal nucleus
1:12:28of vagus. What was that next one? The
1:12:30nucleus of tractus solitarius, right? If
1:12:33you guys remember, the nucleus of
1:12:34tractus solitarius is important because
1:12:36it picks up sensory information from
1:12:38what kind of structures. So, let me draw
1:12:40here a tiny diagram here for you.
1:12:43So, again, here we're going to have the
1:12:44kind of a sagittal section here, and
1:12:46then what we'll do is we'll draw a kind
1:12:47of a little small section here for this
1:12:50guy's face.
1:12:52Okay?
1:12:57Okay.
1:12:58So, what I want you guys to know here
1:13:01is the tongue, right? The tongue, you
1:13:04have different taste that comes from the
1:13:06tongue.
1:13:07And these taste fibers, right? That is
1:13:09going to be serving what portion of the
1:13:10tongue? The posterior 1/3 of the tongue.
1:13:13The taste sensations from the posterior
1:13:151/3 of the tongue is going to be taking
1:13:17this into the medulla and going to what
1:13:20nucleus?
1:13:22The nucleus of tractus solitarius. So,
1:13:24what is one of the functions of the
1:13:25glossopharyngeal nerve? Because it
1:13:27connects with that nucleus of tractus
1:13:29solitarius. It plays a role within taste
1:13:32of what portion
1:13:34of the posterior
1:13:371/3 of the tongue.
1:13:41Okay, cool. What was another structure
1:13:43that we talked about there?
1:13:45Another one
1:13:47is that it's also associated with that
1:13:50nucleus ambiguus. Do you guys remember
1:13:53the nucleus ambiguus when we talked
1:13:54about that? The nucleus ambiguus
1:13:56controls a lot of different muscles, but
1:13:58one of the muscles that it goes to is
1:14:00called the stylopharyngeus.
1:14:02Do you guys remember that guy? The
1:14:04stylopharyngeus helps to kind of elevate
1:14:06the soft palate. That was another one.
1:14:08But, what was the nucleus that was
1:14:09associated with it? The nucleus
1:14:12ambiguus. That was one of the nuclei
1:14:14that we talked about over there. So, it
1:14:15also plays a role within
1:14:18uh the deglutition process, right? So,
1:14:21uh so, it also plays a role within the
1:14:23deglutition
1:14:25deglutition
1:14:27process, okay? Because the
1:14:28stylopharyngeus does help to play a role
1:14:30with kind of elevating that soft palate.
1:14:33Going back here, taste. What kind of
1:14:35fibers is it that's actually carrying
1:14:37there? That is your Do you guys
1:14:39remember? SVA fibers, sensory visceral
1:14:42efferent fibers.
1:14:43The fibers for deglutition, these are
1:14:45motor fibers. This is your SVE fibers.
1:14:49That's your special visceral efferent
1:14:51fibers. You guys remember special
1:14:52visceral efferent is for pharyngeal
1:14:53arches. Which pharyngeal arch does the
1:14:56glossopharyngeal nerve serve? The third
1:14:59pharyngeal arch. First is trigeminal,
1:15:01second is facial, third is
1:15:02glossopharyngeal.
1:15:04Okay, cool.
1:15:05We had another nucleus. The other
1:15:07nucleus that we had there was the
1:15:09inferior salivatory nucleus. And the
1:15:11inferior salivatory nucleus we said
1:15:13would go to the otic ganglion and then
1:15:16go to a gland. What was that gland
1:15:18called? The parotid gland. What does the
1:15:20parotid gland do? Plays a role with
1:15:22salivation. You guys are so awesome. I
1:15:24know you guys knew that, right? So, it
1:15:26also plays a role with salivation.
1:15:29And again, via what nucleus?
1:15:32The inferior salivatory nucleus. What
1:15:34kind of fibers is that?
1:15:37General visceral efferent fibers. And I
1:15:38knew you guys knew that, right? So,
1:15:39general visceral efferent fibers. Cool.
1:15:42Okay.
1:15:44The other thing it does is it picks up
1:15:47uh sensory information from the soft
1:15:51palate from the pharynx, from the
1:15:54posterior 1/3 of the tongue.
1:15:57Okay, we already said the soft palate
1:15:58uvula. So, again, what does it also pick
1:16:00up? It picks up sensory
1:16:04sensations, okay? So, visceral
1:16:06sensations coming from the posterior 1/3
1:16:09of the tongue
1:16:10coming from the soft palate, coming from
1:16:12the uvula, coming from the pharynx, and
1:16:14carries it back. And they believe that
1:16:17most of these fibers synapses on the
1:16:20nucleus of tractus solitarius.
1:16:22What are these fibers, the sensory
1:16:24fibers that are picking up sensations
1:16:25from the soft palate, the uvula, the
1:16:27posterior 1/3 of the tongue, the
1:16:29pharynx? These are GVA fibers.
1:16:32If you guys want to be rock stars, which
1:16:34I know you guys are, it also picks up
1:16:37some sensations
1:16:39from the
1:16:41areas called the carotid bodies
1:16:44and the carotid
1:16:46sinus, right? You guys know your GVA
1:16:47aortic arch.
1:16:51And then you have your
1:16:54sinus there. And again, the sinus is
1:16:56going to be having the
1:16:57baroreceptors.
1:16:59The baroreceptors are going to be
1:17:00picking up uh they're going to have
1:17:01these GVA fibers that will also be
1:17:03carried on the glossopharyngeal nerve.
1:17:05And then you're also going to have the
1:17:07carotid bodies, which are going to be
1:17:08carrying the chemoreceptor information.
1:17:10That's also going to be carried on the
1:17:12glossopharyngeal nerve. But again,
1:17:14all of these fibers,
1:17:16sensations from the soft palate, from
1:17:18the posterior 1/3 of tongue, all that
1:17:19stuff.
1:17:20And then from these chemoreceptors and
1:17:23uh baroreceptors is all carried on GVA
1:17:25fibers. So it plays a role with
1:17:27sensations.
1:17:31Uh we're just going to put of oral
1:17:33cavity.
1:17:34Okay? Of the oral
1:17:37cavity.
1:17:38And again, those sensations that we're
1:17:41picking up from the chemoreceptors and
1:17:44the baroreceptors.
1:17:46The last one, that's really kind of an
1:17:48easy one, thank goodness, um is that
1:17:50it's also picking up sensations, pain
1:17:52sensations, from the external ear, pain,
1:17:54temperature, touch sensations from the
1:17:55external ear, tympanic membrane, middle
1:17:57ear, pharyngotympanic tube. So it's also
1:18:00picking up
1:18:01kind of uh ear
1:18:04sensations.
1:18:06Okay? And those types of sensations go
1:18:08to your spinal
1:18:11nucleus of the trigeminal nerve.
1:18:13Okay? So again, that's all the kind of
1:18:15the functions of the the
1:18:16glossopharyngeal nerve.
1:18:17Let's move on to this
1:18:19beast,
1:18:21the vagus nerve.
1:18:22Again, this one's it will never cover
1:18:24everything here, you know, so again,
1:18:25it's just general. Vagus nerve, what I
1:18:28want you to remember,
1:18:29here that dorsal nucleus of vagus, the
1:18:31dorsal nucleus of vagus carries
1:18:33primarily
1:18:35general visceral afferent fibers, which
1:18:36are all the sensations
1:18:38of your larynx, of parts of the soft
1:18:41palate, of all your thorax and abdominal
1:18:45parts of your abdominal viscera. All of
1:18:47that information, secretion,
1:18:50contraction, and sensations are all kind
1:18:54of carried to and out of the dorsal
1:18:57nucleus of vagus that we talked about
1:18:59over there. So, again, if we were to
1:19:01cover some for the GVA fibers, it picks
1:19:03up sensations.
1:19:06Okay?
1:19:07Okay, and we can say here from what
1:19:09structures? From the larynx,
1:19:14the trachea, I'm I mean, we we're going
1:19:16to go on forever here. We'll put thorax,
1:19:21abdomen, all of that stuff, right?
1:19:24And then also plays a role within
1:19:26secretion
1:19:28and motor function. So, peristalsis and
1:19:30things like that, right? So, secretion
1:19:32from glands and peristaltic activity.
1:19:34So, plays a role within secretion
1:19:40and motor functions. All for the same
1:19:42thing. For structures of the larynx, for
1:19:45the trachea, for the thorax, for the
1:19:46abdomen. All of these different things.
1:19:49And again, if you guys want more detail
1:19:50on that, go watch that video.
1:19:52The other thing,
1:19:53so again, what kind of the sensations
1:19:55are carried on what things? GVA.
1:19:59The secretomotor fibers are GVE, and
1:20:02these are primarily coming from the
1:20:03dorsal nucleus of vagus.
1:20:05The nucleus of tractus solitarius also
1:20:08is going to be receiving information
1:20:09from the vagus nerve. That's picking up
1:20:11taste from primarily the oral pharynx,
1:20:15the posterior wall, right? Of the
1:20:16pharynx, the oral pharynx, and even it
1:20:19also will pick up some sensations from
1:20:21like the valleculae on the epiglottis,
1:20:23so taste sensations. So, those are
1:20:25special visceral afferent fibers. So,
1:20:27plays a tiny role within taste. Okay?
1:20:30And again, the two portions that it
1:20:32picks it up on is the oropharynx.
1:20:36And there's also some a tiny bit of
1:20:38taste receptors on the epiglottis.
1:20:42Okay, the vallecula of the epiglottis.
1:20:44And what kind of fibers are those? SVA
1:20:46fibers. What are they going to? The
1:20:48nucleus of tractus solitarius.
1:20:51Okay, it also plays a role and has
1:20:55connections to the nucleus ambiguus. The
1:20:58nucleus ambiguus is going to have what
1:21:00kind of fibers? SVE fibers that we
1:21:03talked about for the glossopharyngeal
1:21:05nerve. It's also going to have SVE
1:21:07fibers for the vagus nerve. That's going
1:21:09to be going to muscles of the pharynx,
1:21:11the pharyngeal constrictors, muscles of
1:21:13the larynx, okay? And that's really,
1:21:17really important for the deglutition
1:21:19process and for phonation. Right? So,
1:21:22the the laryngeal muscles, right? So, if
1:21:24you're cricopharyngeus, you have your
1:21:26cricothyroid, you have the all those
1:21:27cricoarytenoid muscles. All of those
1:21:29things are important for phonation, for
1:21:31speech. And then the superior, middle,
1:21:33inferior pharyngeal constrictors for
1:21:35that kind of deglutition process. So
1:21:37again, those
1:21:39are going to be coming from the nucleus
1:21:42ambiguus via the SVE. SVE fibers, that's
1:21:46going to be uh basically ca- uh
1:21:48supplying the pharyngeal arches. The
1:21:50vagus nerve supplies what two pharyngeal
1:21:52arches? Four and six. One is trigeminal,
1:21:55two is facial, three is
1:21:56glossopharyngeal, four and six is vagus.
1:21:58Good. So, it's going to supply muscles
1:22:03of larynx
1:22:05for speech and the muscles of the
1:22:08pharynx.
1:22:09Primarily those constrictors for
1:22:12deglutition.
1:22:14And thankfully, the last thing is it
1:22:16also picks up the pain, temperature,
1:22:18touch sensations from the external ear,
1:22:20the uh tympanic membrane, and even a
1:22:22little bit of the uh middle ear cavity.
1:22:25So again, it picks up sensations from
1:22:28the ear. And again, what kind of fibers
1:22:30are those going to be?
1:22:32Those are going to be your GSA fibers.
1:22:34What kind of structure is it going to go
1:22:35to? The spinal nucleus of the trigeminal
1:22:37nerve.
1:22:38Boom. Okay.
1:22:40Finally, oh, thank goodness, the last
1:22:42one, the accessory nerve, cranial nerve
1:22:4511. So, we hit cranial nerve 12, we hit
1:22:47cranial nerve nine, we hit cranial nerve
1:22:4810, we hit cranial nerve 11 now.
1:22:51Accessory nerve. This guy, thank
1:22:54goodness,
1:22:55it's really important to know that this
1:22:57guy
1:22:58is primarily supplying two muscles,
1:23:00okay? So, primarily has general somatic
1:23:03efferent fibers that supply two muscles.
1:23:05One is the sterno-
1:23:09cleido-
1:23:10mastoid muscle, okay? So, the
1:23:13sternocleidomastoid muscle, which it has
1:23:15a lot of different functions that we've
1:23:17talked about in other videos.
1:23:18The other one is it supplies the
1:23:20trapezius.
1:23:23Okay? This is going to be really
1:23:26important to know these, okay? But,
1:23:27here's the other thing. This is
1:23:29primarily supplied by the spinal
1:23:31component, that C1 2 3 4 that moves up
1:23:34through the lateral funiculus and
1:23:36combines with that cranial portion of
1:23:38the accessory nerve we talked about on
1:23:39the external anatomy.
1:23:42They supply primarily the
1:23:44sternocleidomastoid and trapezius. Some
1:23:46of the kind of parts coming off of the
1:23:48brain stem, a little bit of that goes
1:23:50into this internal
1:23:51uh kind of parts that supply the
1:23:54pharyngeal plexus, okay? So, there's
1:23:56three parts of the pharyngeal plexus.
1:23:59Okay? What are the three parts of the
1:24:01pharyngeal plexus? One part of the
1:24:02pharyngeal plexus is the vagus nerve.
1:24:05Second part is the glossopharyngeal
1:24:07nerve. And the third part is the
1:24:09accessory nerve.
1:24:11Okay? These three structures here make
1:24:15up your pharyngeal plexus.
1:24:18All of these three components are recei-
1:24:21are their pharyngeal plexus is formed by
1:24:24the fibers coming off of the nucleus
1:24:26ambiguus.
1:24:27So again, accessory nerve, a thing that
1:24:29you have to remember is that it is a
1:24:31part of the pharyngeal plexus. So it's a
1:24:34component
1:24:37of the pharyngeal plexus
1:24:40which is going to be
1:24:41ca- uh carrying fibers, SVE fibers from
1:24:44the nucleus ambiguus.
1:24:47And it's a one of the three components
1:24:49of the pharyngeal plexus which is made
1:24:50up of the vagus nerve, the
1:24:51glossopharyngeal nerve, and the
1:24:52accessory nerve. All of the fibers of
1:24:55the nucleus ambiguus that are coming
1:24:56from vagus, glossopharyngeal, and even a
1:24:58little bit from the accessory nerve.
1:25:00Okay?
1:25:02That covers all of the functions of all
1:25:06of these things within the medulla. All
1:25:07right, Niche Nerds. This was a monster
1:25:10of a video, and we covered so much. It
1:25:13was so so in-depth, and I really hope
1:25:16that a lot of this stuff made sense. I
1:25:17hope that you guys did enjoy it. And at
1:25:19the end of this video, I hope that you
1:25:20can literally name every single thing
1:25:22within the medulla and what they do.
1:25:24If you guys did learn a lot from this
1:25:26video, if you loved this video, please
1:25:28hit that like button, comment down in
1:25:29the comment section, and please
1:25:31subscribe. Also, if you guys get a
1:25:33chance down in the description box,
1:25:34we'll have links to everything that you
1:25:35guys need to communicate with us,
1:25:36Facebook, uh Instagram, uh even our
1:25:39Patreon, all of those things. If you
1:25:40guys want to go there, check that out.
1:25:42We appreciate it. Niche Nerds, we love
1:25:44you. We thank you for everything that
1:25:45you do, all the support and kind
1:25:47comments that you give. We do look at
1:25:49them, and we do appreciate them. All
1:25:50right, Niche Nerds, as always, until
1:25:51next time.

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