Sensory (Ascending) Pathways | Touch vs. Pain and Temperature — Transcript

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1. 0:00hi everyone dr mike here in this video
2. 0:01we're taking a look at sensory pathways
3. 0:04also known as ascending pathways
4. 0:07pathways of the body that allow for
5. 0:08sensory information to make it up to the
6. 0:10brain for us to be consciously aware of
7. 0:13them
8. 0:14so to begin let's orientate ourselves
9. 0:16with what i've drawn up here we've got
10. 0:17our two cerebral hemispheres of our
11. 0:19brain
12. 0:20we've got the cortex
13. 0:23of our brain which is the outer two to
14. 0:24three millimeters of the brain and
15. 0:26remember if a sensory signal makes it to
16. 0:29the cortex
17. 0:30you will become consciously aware of it
18. 0:32there's actually a very specific part of
19. 0:34the cortex in the parietal lobe called
20. 0:36the
21. 0:37somatosensory cortex
22. 0:42somatosensory
23. 0:45cortex
24. 0:47now this cortex is important because it
25. 0:49actually contains a map of the body on
26. 0:52it so there's going to be an area map to
27. 0:54the hand an area map to the foot an area
28. 0:56map to the back for example
29. 0:59and think about like this areas of the
30. 1:01body that have a higher density of
31. 1:03neurons associated with them like the
32. 1:05hand for example it will have a larger
33. 1:08area of the somatosensory cortex
34. 1:10dedicated to it now
35. 1:13that's the cortex
36. 1:15when we go deeper into the brain you can
37. 1:16find a couple of structures here these
38. 1:18two things here they're called the
39. 1:20thalamus
40. 1:24the thalamus is the sorting center of
41. 1:26the brain it's the post office when a
42. 1:28signal gets there it takes it and
43. 1:30decides what it wants to do with it
44. 1:31where does it need to go
45. 1:33you've got the brain stem here
46. 1:36now with the brain stem you've got the
47. 1:39midbrain
48. 1:42you've got the pons
49. 1:45and you've got the
50. 1:46medulla
51. 1:48and so these are the three
52. 1:51parts
53. 1:52of the brain stem and you need to be
54. 1:54aware of these areas
55. 1:58and then you've got our spinal cord here
56. 2:01let's begin now there's actually a
57. 2:03couple different types of ascending
58. 2:06pieces of information or ascending
59. 2:07pathways or sensory pathways so we're
60. 2:10going to take a look at a pathway that's
61. 2:12called the
62. 2:13and it's got a terrible name i didn't
63. 2:15make it up so i apologize it's called
64. 2:17the
65. 2:18dorsal
66. 2:21column
67. 2:23medial
68. 2:26lemniscus
69. 2:30pathway isn't that an awesome name
70. 2:34your answer is no so what is the dorsal
71. 2:36column medial lemniscus pathway it
72. 2:38allows for us to have it basically sends
73. 2:42allows for us to send up to the brain
74. 2:44information about fine touch
75. 2:49two-point discrimination
76. 3:02and conscious proprioception
77. 3:05you might be looking at these going what
78. 3:06the hell are all these things
79. 3:10so fine touch not gross touch a very
80. 3:13specific touch to touch that if i were
81. 3:15to take a feather and tickle your hand
82. 3:17for example that sort of information
83. 3:20two-point discrimination is if you were
84. 3:22to take two pins
85. 3:24and i would close my eyes and you were
86. 3:26to put on my arm for example and put one
87. 3:28pin in one area and another pin a
88. 3:29certain distance apart and you ask me
89. 3:31can you feel those two pins as separate
90. 3:34things now in areas that have a high
91. 3:36density of neurons on my hands
92. 3:38well those pins are going to be only a
93. 3:41couple of millimeters apart before i go
94. 3:43yeah i can't distinguish
95. 3:45the difference between the two pins
96. 3:48but on my back where i've got a lower
97. 3:50density of neurons you can have those
98. 3:51two pins like five centimeters apart
99. 3:53from each other and i'll go oh it feels
100. 3:55as though it's one pin right that's two
101. 3:57point discrimination then you've got
102. 3:59conscious proprioception so that's
103. 4:01proprioception is knowing where you are
104. 4:03in your own space okay it's my ability
105. 4:06to close my eyes and you say touch your
106. 4:08nose and i can do it i can't actually
107. 4:10feel where my nose is but i know where i
108. 4:13know is where it is because of
109. 4:15proprioceptors okay
110. 4:18all right so that's conscious
111. 4:20proprioception so this is that pathway
112. 4:22we're going to focus on that and the
113. 4:23second pathway we're going to focus on
114. 4:25is that of
115. 4:27temperature and pain
116. 4:30which is an old pathway
117. 4:36that travels up to the brain together
118. 4:38and this is actually called the
119. 4:41spinothalamic pathway so i'm going to
120. 4:43write this as the spinothalamic pathway
121. 4:47let's
122. 4:48write it like this
123. 4:52because its actual name is the
124. 4:53spinothalamic pathway
125. 5:01and it is 4 just like i've done here
126. 5:04temperature and pain
127. 5:12so these are the two ascending pathways
128. 5:13we're going to take a look at first
129. 5:15let's take a look at the dorsal column
130. 5:16medial lemniscus pathway someone takes a
131. 5:19feather and tickles your finger it
132. 5:21triggers receptors in the neurons of
133. 5:23your hand and this begins to send an
134. 5:26action potential down the neuron of your
135. 5:28hand into your spinal cord
136. 5:31now what it does is as soon as it enters
137. 5:33your spinal cord it starts to ascend up
138. 5:36the same side of the spinal cord that it
139. 5:39enters it goes up up up up
140. 5:41up up until it hits the medulla
141. 5:44here at the medulla this neuron will
142. 5:47synapse or speak with a second neuron
143. 5:50and this neuron crosses to the other
144. 5:52side
145. 5:53when it crosses to the other side the
146. 5:54term we use is decussation it decasates
147. 5:59and then from here it continues to
148. 6:01ascend until it hits the thalamus so
149. 6:04again the sorting center here it's going
150. 6:06to sign up with another neuron this
151. 6:09third neuron
152. 6:11remember the thalamus being the sorting
153. 6:12center goes where does it need to go it
154. 6:14knows it's come from the hand
155. 6:16so i need to send it to the part of the
156. 6:18somatosensory cortex mapped to the hand
157. 6:20and that's exactly what it does through
158. 6:22the third neuron
159. 6:24and sends it to that somatosensory
160. 6:25cortex we have now just become
161. 6:27consciously aware of some sort of
162. 6:30whether it be fine touch two-point
163. 6:31discrimination or conscious
164. 6:33proprioception associated with the hand
165. 6:36what can you see it is a three neuron
166. 6:39chain
167. 6:40one
168. 6:42two
169. 6:43three
170. 6:45it a sends up the same side of the
171. 6:47spinal cord that it enters
172. 6:50so that's the dorsal column medial
173. 6:52lemniscus pathway let's compare it to
174. 6:54the spinothalamic pathway so now
175. 6:57somebody pricks your finger with a pin
176. 6:59it triggers nociceptors which will send
177. 7:02an action potential
178. 7:04down
179. 7:05a neuron into your spinal cord now when
180. 7:08it enters your spinal cord
181. 7:10it may ascend up a little bit it might
182. 7:12actually descend down a little bit but
183. 7:14at around about the level that it enters
184. 7:16it synapses with the second neuron and
185. 7:20it's here that it decasates or crosses
186. 7:23basically at the level that it enters
187. 7:26around about
188. 7:27it deca states once it synapses with the
189. 7:30second neuron now it ascends up
190. 7:33up up up the spinal cord
191. 7:35goes past the brain stem and goes
192. 7:37straight to the thalamus
193. 7:39hence why it's called the
194. 7:41spinothalamic pathway because it goes
195. 7:43from the spinal cord straight to the
196. 7:45thalamus here it synapses with the third
197. 7:48neuron again and throws it to a part of
198. 7:51the brain that deals with the hand but
199. 7:53now we know it's a painful stimulus
200. 7:56that's how we interpret that piece of
201. 7:58nociception so again still three neuron
202. 8:01chain first neurons synapses with the
203. 8:03second neuron which deca sates
204. 8:05immediately or at the level in which it
205. 8:07enters around about and then a sends up
206. 8:10sign synapses at the thalamus and then
207. 8:12goes to the area map to the head it also
208. 8:14throws it off to other areas like the
209. 8:16hypothalamus the amygdalin and so forth
210. 8:18so that you have those other
211. 8:22experiences associated with pain like
212. 8:24being wide awake
213. 8:25having a negative emotional experience
214. 8:27and so forth but let's just focus on
215. 8:29this conscious experience here
216. 8:31what is the major difference you can see
217. 8:33between these two pathways the major
218. 8:34difference is the side in which it
219. 8:36ascends
220. 8:38very important very important clinically
221. 8:40if somebody experiences a hemi lesion
222. 8:43some sort of damage to the spinal cord
223. 8:44on one side
224. 8:48as you can see
225. 8:49if a damage is on this side what does it
226. 8:52mean so remember you can see here that
227. 8:54obviously the opposing side of the brain
228. 8:56deals with the opposing side of the body
229. 8:58and vice versa but in this case if this
230. 9:01is me that's my right hand
231. 9:04but i've got damage to the right side of
232. 9:05my spinal cord
233. 9:07i'm going to have problems experiencing
234. 9:09fine touch two-point discrimination and
235. 9:11conscious proprioception but if you
236. 9:13pricked my right hand with a pin
237. 9:16what happens
238. 9:17i can still feel it because
239. 9:19it's not affected because it crossed the
240. 9:21other side
241. 9:22right and the same thing goes if you've
242. 9:25got some sort of hemi lesion on the
243. 9:26opposing side right this in part is
244. 9:29called brown cicada syndrome and i've
245. 9:30done a whole video on that as well so
246. 9:33this is a quick run through of the
247. 9:34differences between
248. 9:36the two types or two major types of
249. 9:39sensory or ascending
250. 9:41pathways
251. 9:42hi everyone dr mike here if you enjoyed
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