Sympathetic Nervous System: Animated Scheme (Ganglia, Neurons, Plexuses) — Transcript

Full transcript

1. 0:06What’s up, Taim talks med here. In this video  we’re gonna talk about the sympathetic nervous
2. 0:11system. As you see from this brief diagram, the  sympathetic and the parasympathetic parts of our
3. 0:16nervous system controls more or less all our  internal organs. Sympathetic being the fight
4. 0:22or flight response, and parasympathetic  being the rest and digest response. And
5. 0:27they’re both as you see here a part of the  autonomic nervous system, which again is
6. 0:31the motor division of our peripheral nervous  system. So, in this video again, we’re going
7. 0:37detailed into the sympathetic nervous system. And we’re gonna do that by first going through
8. 0:43the general structures of the sympathetic, or  the autonomic nervous system in general. Just
9. 0:47some basic concept that you need to know in order  to understand the sympathetic nervous system,
10. 0:53like the different paravertebral and prevertebral  ganglia, pre and post synaptic neurons,
11. 0:59which neurotransmitters are released, etc. Then we’re gonna cover the main highway for
12. 1:04the sympathetic nervous system which is the  sympathetic trunk, or the sympathetic chain
13. 1:08ganglia. And we’re gonna do that in two segments  by first covering the innervation of the head,
14. 1:14neck and thorax, then the innervation of the  abdominal and the pelvic viscera. I’ll show
15. 1:20you the relation between the different plexuses  in our abdominal and thoracic cavity. This is to
16. 1:26understand the relation between ganglia, organs  and the plexuses. So, after you’ve watched this
17. 1:32video, and understood everything regarding the  sympathetic nervous system, I’m gonna test you
18. 1:37with a little quiz. You’re not escaping that one,  it’s a simple quiz to check if you paid attention.
19. 1:42Let’s go ahead and begin with some terms. Now the  autonomic nervous system - so both the sympathetic
20. 1:48and parasympathetic nervous system is made up of a  relay that includes two neurons. And when there’s
21. 1:55a group of nerve cell bodies that are next to each  other within the actual central nervous system,
22. 2:00the whole thing is called a nucleus, while a  group of nerve cell bodies that are located
23. 2:06outside of the central nervous system is called  a ganglion. Alrgiht? That is the first thing I
24. 2:12want you to understand. The second thing I want  you to understand is that this is pons, alright?
25. 2:19Below it is the Medulla, then we got the spinal  cord. When we talk about the sympathetic ganglia
26. 2:25in general, we divide those into two groups  based on their location. They can either be
27. 2:31paravertebral ganglia located laterally to  the spinal cord. And we got some midline
28. 2:37ganglia located in front of the vertebra  and the aorta, called prevertebral ganglia.
29. 2:43The paravertebral ganglia run alongside  the spinal cord, and they’re interconnected
30. 2:48forming a sympathetic chain of ganglia as you see  here. And this chain receives nerve fibers from
31. 2:55the thoracolumbar area of the spinal cord. Some  sources write C8-L2, some sources say T1 to L2.
32. 3:03Take it with a grain of salt, but you’re never  wrong when you say thoracolumbar region. Fibers
33. 3:09may go up, down, synapse with nuclei at the same  level, or they may leave as splanchnic nerves and
34. 3:18go synapse with the prevertebral ganglia. Alright,  this is the second thing I want you to understand.
35. 3:24The third thing. The third thing I want you to  know about the autonomic nervous system is that,
36. 3:30you know they can innervate the eye, the salivary  glands, cardiovascular, respiratory system,
37. 3:36gastrointestinal system, urinary system and so on,  right? If we group them all together, and add the
38. 3:42brain and the spinal cord here. The third thing  I want you to know is actually something I said
39. 3:48earlier but the sympathetic nervous system  originate from the thoracolumbar region,
40. 3:54giving off pre-ganglionic fibers to either  the paravertebral or prevertebral ganglia,
41. 4:00to then give off postganglionic  fibers towards the target organ.
42. 4:05Parasympathetic nervous system has two components.  A cranial part that consists fo cranial nerves,
43. 4:11primarily the oculomotor, facial, glossopharyngeal  and the vagus nerve. And it has a sacral part.
44. 4:18Notice what’s common for both the sympathetic  and the parasympathetic nervous system?
45. 4:23They both have pre and post-ganglionic neurons. The preganglionic and postganglionic neurons
46. 4:30release different neurotransmitters  and this is really important.
47. 4:34The preganglionic neurons release  acetylcholine, and that’s why the preganglionic
48. 4:39neurons are called cholinergic neurons. Acetylcholine binds to nicotinic receptors
49. 4:47on the cell membrane of postganglionic neuron. Nicotinic receptors are ion channels that open
50. 4:55when acetylcholine binds to them; and they allow  positive ions like sodium and calcium to cross the
51. 5:01cell membrane, activating the postganglionic  neurons and initiating an action potential.
52. 5:08Most postganglionic neurons in the sympathetic  nervous system are called adrenergic neurons
53. 5:14because they release adrenaline and noradrenaline,  or catecholamines. There are postganglionic
54. 5:22neurons that release acetylcholine as well in the  sympathetic nervous system to sweat glands for
55. 5:27example, but postganglionic cholinergic neurons  are primarily related to the parasympathetic
56. 5:33nervous system, while postganglionic adrenergic  neurons are primarily for the sympathetic
57. 5:39nervous system, releasing catecholamines. Catecholamines activate the adrenergic
58. 5:45receptors on the cells of the target organs. And there are two main groups of adrenergic
59. 5:50receptors, alpha and beta receptors. So, we have alpha1 and alpha2, and beta1,
60. 5:57beta2 and beta3, which are all g-coupled  receptors. G-proteins gets activated when
61. 6:04catecolamines bind, which ultimately enable cells  to change, and that’s how the sympathetic nervous
62. 6:11system creates change at the cellular level. I’ll  try to cover their function as we go through the
63. 6:16scheme for the sympathetic nervous system. So that was the third thing that I wanted you
64. 6:21to know. The fourth and last thing I want you to  understand before we dive into the actual scheme,
65. 6:28is that if we take out a segment of the  spinal cord within the thoracolumbar area,
66. 6:33you’ll see that the preganglionic fibers come  from the lateral horns of the thoracolumbar
67. 6:39spinal cord segment. Preganglionic  fibers here are denoted in a dotted line.
68. 6:45These axons leave the spinal cord through  the anterior nerve roots to reach the
69. 6:50spinal nerve. Then they enter the white rami  communicantes to reach the sympathetic trunk
70. 6:57When the preganglionic fibers are within  the sympatheic trunk, 4 things can happen.
71. 7:03They can descend and synapse in  a lower paravertebral ganglion.
72. 7:07They can ascend and synapse in  a higher paravertebral ganglion,
73. 7:11which are usually the cervical parts. They can skip the sympathetic chain completely,
74. 7:16and go all the way towards the prevertebral  ganglia. Once they pass through the sympathetic
75. 7:21trunk, they may combine with fibers from other  levels to form something called a splanchnic
76. 7:26nerve. So it’s the splanchnic nerves that  synapse on a prevertebral ganglia. So they
77. 7:32can either go to pre-vertebral ganglia,  or directly towards the suprarenal gland.
78. 7:38The fourth way is that they may synapse directly  in a paravertebral ganglion at the same level.
79. 7:44Now what happens is, after synapsing inside  the ganglion, postganglionic fibers leave
80. 7:50through the gray ramus communicans and  they re-enters the same anterior ramus,
81. 7:56which it initially travelled through, to continue  with the spinal nerve, innervating all structures
82. 8:02related to the branches of the anterior and  posterior rami of the same spinal nerve.
83. 8:07These fibers can also combine with fibers  from other levels to form splanchnic nerves,
84. 8:13which then pass onto the thoracic viscera. Same goes to the pre-vertebral ganglia. The
85. 8:18postsynaptic fibers pass onto the abdomen and  pelvic viscera via a visceral motor nerve plexus.
86. 8:26Alright, so that was the 4 major things that  I wanted you to keep in mind. The first thing
87. 8:31being the difference between the word nuclei  and ganglion. The second thing being where the
88. 8:36parasympathetic and sympathetic outflow  is located, and the difference between
89. 8:41a pre-ganglionic and post-ganglionic fiber is.  Third thing being the anatomical relation between
90. 8:47the sympathetic ganglia. They can either be  paravertebral as in the sympathetic chain,
91. 8:52or prevertebral ganglia as in the celiac  ganglia, superior mesenteric ganglia,
92. 8:57and so on. The fourth thing I want you to know  is that prevertebral fibers can do 4 things once
93. 9:04they enter the sympathetic chain. They can go  down, up, leave towards the prevertebral ganglia,
94. 9:12or they can synapse with cell bodies within the  ganglia at the same level. Alright. Finally,
95. 9:18let us now make a scheme for the sympathetic  nervous system. Just remember that this is
96. 9:23just a scheme, nothing that is topographically  correct. This is just to make it easier for you
97. 9:28to remember. And keep in mind there are a lot  of variations to these things, two different
98. 9:33sources may show you to different schemes.  I’ll just try to show you the general one.
99. 9:39Alright. Now. Let’s cover the sympathetic trunk.  Here again we see Pons, Medulla and the spinal
100. 9:45cord. Laterally to the spinal cord we see the  paravertebral ganglia, also called the sympathetic
101. 9:51chain, or the sympathetic trunk. It receives it’s  sympathetic fibers from the thoracolumbar area,
102. 9:58that’s T1-L2 but again take it with a grain of  salt. Sources also say C8 to L2, L3 region. When
103. 10:06fibers reach the sympathetic trunk, they may  ascend and synapse with a nuclei located some
104. 10:12segments above. They may decend. They may synapse  with nuclei at the same level, or they may leave
105. 10:19the sympathetic trunk as preganglionic fibers. The sympathetic trunk is divided into cervical
106. 10:26ganglia, which are three pairs usually. Thoracic  gangli, which are 10-11-12 pairs approximately,
107. 10:34Lumbar ganglia, which are 4-5 pairs,  sacral ganglia, usually 4 pairs,
108. 10:40and last ones are the coccygeal ganglia, they’re  often fused together to form gnalgion impar,
109. 10:46which is the unpaired ganglion at the bottom. Now, let’s talk about the sympathetic innervation
110. 10:52of the head, neck and thorax. Most of which  are innervated by the cervical ganglion.
111. 10:57Now the cervical ganglion received fibers  from approximately T1-T4, and since it’s
112. 11:03not adjacent to the thoracolumbar outflow, they  don’t have white rami communicans, only gray rami
113. 11:10communicans. Kinda makes sense doesn’t it? Now, the cervical ganglia are divided into
114. 11:15the superior cervical, which is the largest  one of them. Middle cervical ganglion, which
115. 11:21is extremely small. It may be divided into 2-3  smaller parts, or sometimes it may be even absent.
116. 11:28And we got the inferior cervical ganglia, which  is often fused with the 1st thoracic ganglion,
117. 11:34to which then it’s called cervicothoracic  ganglion, or stellate ganglion. It’s a headache
118. 11:39sometimes studying the sympathetic nervous  system, there are a whole lot of variations.
119. 11:44But let’s start with the superior cervical first. The gray rami communicans of the superior cervical
120. 11:51ganglion is going to continue into the rami of the  first 4 cervical nerves, innervating structures
121. 11:57associated with those nerves, but what’s special  here is that the superior ganglion is going to
122. 12:03give off the postganglionic internal carotid  nerve, which forms the internal carotid plexus
123. 12:10around the internal carotid artery. From  here, these postganglionic fibers will go
124. 12:16through the otic ganglion without synapsing with  it, then further on towards the eye and release
125. 12:23norepinephrine. Now think about it logically,  in a fight or flight response, what is the eye
126. 12:28gonna do in order to help in this situation?  Well you wanna be able to see all options that
127. 12:34you have in a fight or flight situation right? So the pupils are gonna dilate. So norepinephrine
128. 12:40si gonna act on the dilator pupillae muscle,  causing pupillary dilation, allowed more light
129. 12:45to come in and give you possibility to see far. The norepinephrine is also gonna act on the
130. 12:51ciliaris muscle, to flatten the lens,  allowing to focus on far vision aswell,
131. 12:57this is called accommodation, so norepinephrine  here also helps with accommodation.
132. 13:03Alright what else do we have from the internal  carotid plexus? We got a deep petrosal nerve,
133. 13:09which carries sympathetic fibers into the  pterygopalatine ganglion and remember those
134. 13:14are postganglionic fibers, they’re not  gonna synapse in these ganglia. These
135. 13:19postganglionic fibers come from the superior  cervical ganglia. The deep petrosal nerve is
136. 13:25gonna act on two places. It’s gonna act on the  blood vessels supplying the lacrimal glands,
137. 13:30releasing norepinephrine, decreasing the blood  flow to decrease the lacrimation. Or it can act
138. 13:36directly on the lacrimal gland decreasing the  lacrimation, decreasing the tear production
139. 13:41basically. Other places is it can act also on  glands located in the oral cavity, nasal cavity,
140. 13:47and the sinuses, specifically the maxillary  and sphenoid sinus. It’s gonna do the same
141. 13:52here. Norepinephrine cause vasoconstriction,  decrease blood flow to these areas. It’s also
142. 13:58gonna act on the salivary glands within the  oral cavity, to make a thick mucus production.
143. 14:05So that is the branches associated with the  internal carotid plexus. Since we have an
144. 14:10internal carotid nerve, we gotta have an external  carotid nerve as well, right? This one is gonna
145. 14:17form a plexus around the external carotid artery. From here, we gonna have the sympathetic root
146. 14:23going towards the submandibular ganglion, and  a Sympathetic root towards the otic ganglion,
147. 14:29both providing sympathetic innervation to  primarily the major salivary glands, which
148. 14:34are the parotid, submandibular and the sublingual  glands. Decreasing the mucus production there too.
149. 14:41The superior cervical nerve aso give off  a laryngopharyngeal nerve which join the
150. 14:47pharyngeal branches from the glossopharyngeal  and vagus nerves and form the pharyngeal
151. 14:53plexus to basically provide motor, sensory and  sympathetic innervation to the pharyngeal area.
152. 14:59Alright let’s do the middle cervical one. Remember  the middle cervical ganglion is extremely small
153. 15:05and varies between the population. After receiving  its preganglionic fibers from the upper thoracic
154. 15:11segments, it’ll give off gray rami communicans  towards 5th and 6th cervical nerves and supply
155. 15:18structures associated with them. There are  gonna be fibers from the middle cervical,
156. 15:23as well as from the inferior cervical  ganglion that’s going towards the thyroid
157. 15:28and the parathyroid glands. Remember these glands  are under hormonal control from the pituitary
158. 15:36gland. So sympathetic nerves act as vasomotor  nerves, not secretomotor, basically increasing
159. 15:43blood flow to help produce more thyroid hormones  for energy during the fight or flight response.
160. 15:50From the inferior cervical ganglion, we  got gray rami communcans that join the 7th
161. 15:56cervical nerve and the 1st thoracic  nerve. Again there are variations,
162. 16:01but the inferior cervical ganglion also give  off a vertebral nerve that travels towards the
163. 16:07vertebral artery and forms a plexus around it. Other nerves we got here is a Superior cervical
164. 16:14cardiac nerve, a middle cervical cardiac  nerve, and an inferior cervical cardiac nerve,
165. 16:21which all go together towards the heart,  to help form the a cardiac plexus. So that
166. 16:27was everything for the cervical ganglia. Now the thoracic ganglia all have gray rami
167. 16:32communicans that join the intercostal nerves. But  what they also have are fibers that contribute
168. 16:38to the sympathetic innervation of the thoracic  viscera. From approximately T2, T3, T4 and T5,
169. 16:46we got thoracic cardiac nerves, which join in with  the cardiac plexus to help with the sympathetic
170. 16:52innervation. Now, if you remember from the  anatomy of the heart, the heart has mainly
171. 16:57two systems. It has a myocardial system, and a  conducting system. The sympathetic nerves are
172. 17:04gonna act on both of them, what do you think is  gonna happen now? In a fight or flight response?
173. 17:11The conducting system is composed of nodule  cells, right? The SA node primarily is the
174. 17:16functional one. They function to regulate the  heart rate, so what’s gonna happen is that the
175. 17:21sympathetic nervous system is gonna try to  increase the heartrate, so it has a positive
176. 17:26chronotropic action. And we said the heart has two  main systems, the other one being the myocardium.
177. 17:34You’re in a fight or flight response, you need  more blood to the body, and so you need the
178. 17:40cardiac muscles to contract harder to increase  its cardiac output and again increase the blood
179. 17:45pressure. So that’s the other thing that’s gonna  happen, it’s gonna increase the contractility,
180. 17:51we call that positive inotropic effect. Alright. Now let’s add some more organs
181. 17:56here. From around the same region, there’re  gonna be postganglionic fibers that’s’ gonna
182. 18:03give sympathetic supply to the esophagus  and the bronchi, basically to help form
183. 18:08the oesophageal plexus and the pulmonary plexus.  You don’t eat while you’re fighting or running,
184. 18:15usually. So you’d wanna decrease the  peristalsis in the esophagus. That’s
185. 18:20basically what the sympathetic innervation  here does. The respioratory system is opposite,
186. 18:28you need oxygen during a fight or flight response,  so it causes bronchodilation, and vasoconstriction
187. 18:34of the bronchial arteries to decrease the blood  flow and decrease the secretion of glands to help
188. 18:40open up the airways as much as possible. So that was mainly what I wanted to talk
189. 18:45about when it comes to the innervation of the  head neck and thorax. Let’s do the sympathetic
190. 18:49innervation of the abdominal and pelvic viscera. There are two main things here that you need to
191. 18:56remember. The first thing is that all nerves that  exit and supply the organs are called splanchnic
192. 19:02nerves. Remember those are pre-ganglionic fibers.  They don’t synapse with the paravertebral ganglia
193. 19:09at all. What they do, is that they exit and travel  towards the pre-vertebral ganglia. This is so
194. 19:16important that you understand this concept. Here  you see a section of the abdominal aorta along
195. 19:21with some plexuses aswell. The pre-vertebral  ganglions we have are the celiac ganglia,
196. 19:28superior mesenteric ganglia, aorticorenal ganglia,  and the inferior mesenteric ganglia. These ganglia
197. 19:36have postganglionic fibers that travel through  their plexuses to innervate specific organs.
198. 19:42Again before we continue, there are  a whole lot of variations when it
199. 19:47comes to the sympathetic outflow. Different  sources may give you different information,
200. 19:52and to be fair they are all true. The reason  is many of these ganglia are interconnected,
201. 19:58but let’s go through a very basic scheme. From approximately T5 to T9, we got preganglionic
202. 20:06fibers called the greater splanchnic nerves,  that carry their fibers to the celiac ganglia.
203. 20:12After synapsing, the celiac ganglia give off  postganglionic fibres that travel along the plexus
204. 20:18on the arterial branches from the celiac trunk,  and they mainly provide sympathetic innervation
205. 20:24to the upper organs here. So it goes to the liver  to promote glycogenolysis, we’re in a flight or
206. 20:30flight situation so we need sugar. We’re breaking  down glycogen into glucose. Fibers will also go
207. 20:36to the stomach and upper part of the duodenum  to inhibit peristalsis, and also increase the
208. 20:42contraction of the pyloric sphincter. We really  don’t need our GI tract to be active at this
209. 20:46moment, so the bile pathway is also inhibited.  The pancreas is also innervated here to basically
210. 20:52help keep our blood sugar high, it’s going to  increase the glucagon and decrease the insulin
211. 20:58production. Fibers can also go to the spleen. Now the spleen is ideally positioned within
212. 21:05the circulatory system as a blood filter  to detect, respond to, and protect against
213. 21:10blood-borne antigens. So it’s packed with  blood and lympocytes. In the spleen we got
214. 21:16a non-lymphoid red pulp and a lymphoid white  pulp, and between them is a marginal zone,
215. 21:23a transitional site from circulation to peripheral  lymphoid tissues. One important function of the
216. 21:29marginal zone is to trap particulates and  initiate innate responses against them,
217. 21:35or to initiate immune tolerance. The sympathetic  nerves here theoretically help regulate the
218. 21:41immune activities within this system through  norepinephrine. I’m not sure to what extent it’s
219. 21:46completely relevant to the overall sympathetic  response, but I’ll put my sources down in the
220. 21:51description if you wanna read a bit more about it. Now. The greater splanchnic nerve can have a
221. 21:57branch that comes off here and goes to the adrenal  medulla. What does that mean? That means that the
222. 22:03adrenal medulla receives pre-ganglionic fibers  directly, and so these fibers go directly towards
223. 22:11the chromaffin cells in the adrenal medulla, we  call these an ‘’intramural ganglia’’. And when
224. 22:17the chromaffin cells are stimulated, it’s gonna  release norepinephrine and epinephrine directly
225. 22:22into the bloodstream to have a widespread  strong effect on the whole body. Alright.
226. 22:28From T10 and T11, we got the lesser splanchnic  nerve that primarily go to the superior mesenteric
227. 22:35ganglion, which supplies things like the  ascending colon, cecum, the proximal 2/3
228. 22:41of the transverse colon. The small intestine  and the distal duodenum. All to inhibit the GI
229. 22:47system, again. Decrease peristalsis, decrease  absorption by constricting the blood vessels,
230. 22:52and decreasing the secretion process. Then from T11, we got the least splanchnic
231. 22:58nerve which may go to the aorticorenal ganglion.  Again there are lots of variations. Fibers from
232. 23:05the lesser splanchnic nerve may go to the  aorticorenal ganglion. The least splanchnic
233. 23:10nerve may go directly to the renal plexus.  Different sources might tell to different things,
234. 23:15just keep those things in mind. But essentially  what’s important is that postganglionic fibers
235. 23:20are gonna innervate the kidneys. Now what do  you want the kidneys to do in a fight or flight
236. 23:25response? You don’t really wanna pee. So you cause  vasoconstriction of the blood flow to decrease
237. 23:32the urine production within the kidneys. And,  remember we got a RAAS system, a renin angiotensin
238. 23:38aldosterone system. So sympathetic response  help produce more renin from the kidneys to help
239. 23:44increase the blood pressure. Fibers also go to the  ureter to decrease the peristalsis of the ureters.
240. 23:52From the lumbar region, we got the lubar  splanchnic nerves going towards the
241. 23:57inferior mesenteric ganglion. The inferior  mesenteric ganglion is the most inferior
242. 24:03of the prevertebral sympathetic ganglia in the  abdomen. It’s a small ganglion and sometimes it
243. 24:10may just be a loose collection of cells rather  than a defined ganglion. So some sources don’t
244. 24:16even consider it as a ganglion, you might  find some sources write that preganglionic
245. 24:21fibers synapse with cells within the plexuses  of this region, wether that may be the inferior
246. 24:26mesenteric plexus or the intermesenteric  plexus. But the overall postganglionic
247. 24:32supply is the same. And that is highlighted  here. Basically supplying the rest of the GI
248. 24:37tract which is the descending colon, sigmoid,  the distal transverse colon and the rectum.
249. 24:44Postganglionic fibers also go towards the smooth  muscles within the walls of the urinary bladder.
250. 24:50Do you wanna urinate when you’re in a flight  or fight response? No. So it’s gonna decrease
251. 24:56the contraction of the urinary bladder. And it’s  going to increase the constriction of the internal
252. 25:01urethral sphincter to help keep the urine in. Then we got the genitals. So ovaries, uterus,
253. 25:08and so on for the female. For male it’s  the penis, scrotum and so on. In male,
254. 25:14the sympathetic response is gonna primarily  help with ejaculation. For female it will
255. 25:19act on the uterus to primarily cause uterine  contractions. Not to go in too much detail.
256. 25:25Lastly we have the sacral splanchnic nerve,  which may contribute to the innervation of
257. 25:31organs around the inferior hypogastric plexus,  mainly the gonads. Remember I keep telling you
258. 25:37this that there are a lot of variations when it  comes to this system, and different ganglia and
259. 25:42fibers are interconnected between each other. The  last thing I wanna mention here is, something I
260. 25:48haven’t mention here. But you see all of those  nerves in between the ganglia? Those are all
261. 25:54the plexuses in the abdominal region that contain  autonomic nerves in general, so both sympathetic
262. 26:01nerves and also parasympathetic fibers through the  vagus nerve. So for example, the celiac ganglia,
263. 26:09how does it reach its target organs? Through  the celiac plexus. Which may be connected to
264. 26:15the superior mesenteric ganglia as well. There is the superior mesenteric plexus,
265. 26:21the inferior mesenteric plexus. In the pelvis  we have the superior hypogastric plexus and
266. 26:26the inferior hypogastric plexus. We got the  intermesenteric plexus aswell. They contain
267. 26:33cell bodies that act as postganglionic fibers.  And when these cell bodies are clustered,
268. 26:39that is when we get those prevertebral ganglia.  And remember I told you the inferior mesenteric
269. 26:45ganglion is sometimes scattered so much it’s  not even considered a ganglion. So some sources
270. 26:51might write that fibers synapse with cells within  the inferior mesenteric plexus for example. But
271. 26:57overall this is how the plexuses are arranged in  the abdominal and pelvic cavity. In the thorax you
272. 27:04know you may have the pulmonary plexus, cardiac  plexuses, and also the esophageal plexuses. There
273. 27:09are some other plexuses here aswell. But overall  that was mainly all I had for the sympathetic
274. 27:15nervous system. I hope it made sense! Now, comes the fun part. Remember I
275. 27:20told you that we got some important preganglionic  nerves coming from the thoracic lumbar and sacral
276. 27:25region going towards the prevertebral ganglia?  What’s the name of those preganglionic fibers?
277. 27:3310 points if you got that one correct. What about  here? What’s the 4 main branches that is given
278. 27:38off from the superior cervical ganglion? And I’ll  reveal the answer now. Got those correct aswell?
279. 27:47In that case you’ve grasped the most important  things that you need to know when it comes to
280. 27:51the anatomy of the sympathetic outflow The next video is going to be about
281. 27:55the parasympathetic nervous system. Thank you so much for watching another
282. 27:59one of my videos. If you enjoyed, learned  something from it, please remember to like,
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