| 00:02 | This is uh Neuroscience M Three We started with hearing the properties of |
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| 00:07 | compressed air molecules traveling at the sound speed 343 m per second. Our |
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| 00:16 | perception falls within 20 to 20,000 Hertz that animals can perceive in different |
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| 00:23 | So frequencies are uh pitch and high are high pitch and intensity is really |
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| 00:30 | volume of these sound waves. And the sound waves reach our air, |
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| 00:35 | outer air, the pinna, it through the auditory canal or external auditory |
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| 00:42 | it uh moves the sym membrane or airdrome, which now moves the oss |
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| 00:49 | the middle air which subsequently move, the oval window that goes into the |
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| 00:54 | , which is a part of the cochlea para and out of the |
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| 00:58 | you'll have uh auditory portion of the cochlea nerve, a cochlear portion of |
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| 01:06 | nerve, a vestibular cochlear nerve going the brain stem. Now, uh |
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| 01:12 | is again the review of the same except we added information here about the |
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| 01:18 | tube going into the pharynx. And of that tube is to equalize the |
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| 01:23 | in the air inner ear in middle , as well as the pharynx and |
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| 01:29 | cavity. Uh obstacles are the bones allow to increase the torque and thereby |
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| 01:37 | movement translate the movement of the air into amplified movement of the oval |
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| 01:44 | And once these obstacles are being they're being controlled by these little |
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| 01:49 | We talk about attenuation reflex by controlling stiffening of these muscles to prevent the |
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| 01:55 | uh to obstacle on the oval And if you take uh unroll cochlea |
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| 02:02 | the snail like structure to life structure it cross section, we reveal three |
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| 02:09 | . These three chambers are scali, and scala. They have different |
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| 02:16 | And the which is rich in potassium in the scala media which also contains |
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| 02:21 | organ of corti. There's a opic map arrangement that means that the cells |
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| 02:28 | are located at the closest to the window and the hair cells will be |
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| 02:33 | responsive to the sounds that have the possible frequencies from our perception, 20 |
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| 02:40 | Hertz, 18 16 kg Hertz. the middle of this unrolled cochlea |
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| 02:46 | you have hair cells that are most to middle range frequencies. And at |
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| 02:52 | apex also called the helicotrema. The cells will be most responsive to the |
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| 02:57 | frequencies of sound all the way down the 20 Hertz low range. This |
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| 03:03 | of air molecules and subsequently movement of fluid causes the mechanical displacement of the |
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| 03:11 | membrane and as the basilar membrane gets , it contains the organ of |
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| 03:18 | you have the hair cells that are receptor cells and they contain the |
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| 03:24 | And once they're displaced mechanically, the gets displaced in one direction, it |
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| 03:31 | cause depolarization. Uh And if the membrane is displaced in the opposite |
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| 03:36 | the CIA with respect to the tector will lead to the left causing hyper |
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| 03:42 | . Therefore, this faciliatory sound wave oscillation or movement of the fluid gets |
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| 03:49 | into an electrical receptor potentials that are by the hair cells. There's one |
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| 03:57 | of inner hair cells and three rows outer hair cells from her being contacted |
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| 04:02 | spiral gang cells which comprise the auditory of the vestibular coat in the |
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| 04:10 | When the hair cell is banned, CIA is banned, it contains mechanically |
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| 04:16 | T R P A. One channels are permeable to potassium and under for |
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| 04:23 | will allow for influx of potassium. channels are mechanically gated and they are |
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| 04:29 | by these tip links. Opening of channel will encourage the opening of another |
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| 04:34 | channel. On the adjacent tip an influx of potassium will cause depolarization |
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| 04:40 | this hair cells that will open voltage calcium channels. So the depolarization here |
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| 04:47 | through potassium which is a different mechanism opening of the voltage gated calcium channels |
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| 04:52 | calcium influx will contribute to the excitatory release onto the spiral gangling neurites generating |
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| 05:02 | the receptor auditory potential sound amplification is in part by the auditory cells as |
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| 05:13 | in the sensory neural circuit because they these motor proteins. And these motor |
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| 05:18 | are spring like proteins and they can compressed and they can extend. So |
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| 05:24 | there is a movement of basilar membrane respect to the dial membrane here and |
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| 05:28 | organ of corti, the outer hair will be amplifying that information. And |
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| 05:35 | you'll see, most of the output from the inner a cell. So |
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| 05:39 | amplifying the movement to having these motor hands, the outer aerosols are also |
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| 05:47 | uh the encoding that is taking place the inner aerosols. Once again, |
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| 05:53 | can see most of the information is processed from the inner aerosols and a |
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| 05:59 | bit from the outer hair cells despite fact that there are three rows of |
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| 06:03 | outer hair cells. So it's really the pathway for auditory processing. |
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| 06:10 | you can look at the cut one and let's cut this uh through the |
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| 06:15 | stem region. This is the spiral gang axons that project onto the |
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| 06:22 | uh cochlea and dorsal cochlea nucleus from cochlea nucleus is projecting into the superior |
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| 06:31 | . And some of the projections are sil lateral and other projections are crossing |
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| 06:38 | at the level of the superior olive laterally. Therefore, at the level |
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| 06:43 | this lower brain stem, uh you by oral information processing from superior olive |
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| 06:52 | travels into the inferior colliculus right tattoo through the midbrain and from inferior |
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| 07:00 | , it travels into the medial geniculate of the thalamus and into the primary |
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| 07:06 | cortex. A one uh this tonotopic or encoding of high frequencies by the |
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| 07:14 | that are located close to the oval or the base of the cochlea versus |
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| 07:19 | low frequency encoding by the hair cells are located at the apex or helicotrema |
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| 07:26 | the cochlea. This tonotopic map is present in spiral ganglion cells. It's |
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| 07:31 | with spiral gang cells and it's encoded the cochlea nucleus as well as all |
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| 07:38 | way through the primary auditory cortex where will have the columns within the auditory |
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| 07:44 | of cells that are mostly responsive to the high frequencies mid-range frequencies or low |
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| 07:50 | of sound. We talk about sound and how sound gets essentially channeled through |
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| 07:57 | interesting structure of our auto air their a into the external auditory in |
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| 08:04 | And we also talked about how other like owls and we watched the video |
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| 08:09 | much better sound localization and space and mapping. And animals can hunt in |
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| 08:16 | or into the snow, finding their . That's something we're not really capable |
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| 08:21 | . But we do still have pretty sound localization and which way uh there's |
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| 08:27 | cellular mechanism in which we accomplish the of localization. So signals coming from |
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| 08:33 | or right ear would reach different neurons they're still in the topic map. |
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| 08:38 | then in this left right map in locations of the superior, all of |
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| 08:44 | where the signal is coming from left . For example, here versus right |
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| 08:50 | or the front or the back as may be. And then we talk |
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| 08:54 | hearing impairments. We said a lot , most of the hearing impairments are |
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| 08:58 | impairments or damage to Airdrome. For , that means the airdrome cannot vibrate |
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| 09:04 | . So it's a conduction impairment damage oops, calcification of the os |
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| 09:10 | The more serious problem is sensory neural impairments. That means that you have |
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| 09:17 | loss of hearing or partial loss of . And there's partial loss or full |
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| 09:23 | in many in in some instances of is due to the loss of hair |
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| 09:28 | that do not regenerate. And if is sensory neural impairment and hearing loss |
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| 09:34 | is often accompanied by by tinnitus or . Uh And if there is a |
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| 09:40 | hearing loss, that means there's a loss of the hair cells, it |
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| 09:44 | be cochlear implants that used. In case they are receivers that process different |
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| 09:49 | of sound, send it to the electrode. It is wound inside the |
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| 09:54 | , this electrode in the absence of hair cells will stimulate spiral gang leon |
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| 10:01 | and this processor will allow different electrodes different extent to stimulate high frequencies, |
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| 10:08 | gangle cells close to the open middle frequencies in the middle here, |
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| 10:12 | well as uh low frequencies here at apex of the cochlea accordingly as the |
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| 10:19 | is being received processed. And then stimulation is sent to the appropriate sides |
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| 10:26 | the spiral gang cells and trying to a regimented representation of the sound in |
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| 10:33 | absence of hair cells. And in cases of hair loss, not just |
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| 10:40 | hearing, which is typically remedy with aids, but hear loss in those |
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| 10:48 | . OK. So this concludes our system. I'm gonna uh see if |
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| 10:53 | are any questions in the chat. see any questions in the chat. |
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| 10:58 | welcome to put questions in the chat I move through the material and I'll |
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| 11:03 | them. We next move into the of sensory system where we talked about |
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| 11:09 | some matter of sensory receptors are quite and they're distributed throughout the whole body |
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| 11:16 | they process. Touch temperature, uh body position of proprioception, how |
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| 11:23 | lot of these nerve endings and soma sensory receptors are distributed throughout the skin |
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| 11:29 | has blabs and hair, skin You'll find a lot of them in |
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| 11:34 | darkest region of the skin meles uh free nerve endings, sma co |
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| 11:39 | hair particle, Petri and corpuscles, endings and they come in different sizes |
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| 11:44 | they have certain other not just different properties, smaller or larger but also |
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| 11:50 | properties accordingly. We also understood that is this two point discrimination test with |
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| 11:56 | help of which we can determine which of the body are most somatic sensory |
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| 12:03 | or have the highest resolution discrimination. such as the case with the |
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| 12:08 | index fingers and thumb and hands. we also saw that certain regions like |
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| 12:14 | back of the torso or the forearm or the calf region of our bodies |
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| 12:19 | not have a very good spatial discrimination different stimuli. And so it's not |
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| 12:27 | the sizes like, for example, corpo that are very small and along |
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| 12:32 | discrimination corpo that are important. There's uh that these s corros corpus are |
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| 12:40 | rapidly adapting um um sensory neurons and merkel discs and rouen are slowly adapting |
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| 12:50 | well. So it's not just anatomy also physiology. The information from the |
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| 12:56 | is being carried by four types of . The largest number one type of |
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| 13:00 | processes, prop acceptor information. It also the fastest uh group two |
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| 13:07 | mechanoreceptor, uh group three processes, and temperature. And within this uh |
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| 13:14 | sensor in our fiber bundle, we'll have group four fibers that are my |
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| 13:19 | and they are responsible for processing temperature and itch. So all of the |
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| 13:25 | comes into the dorsal root gang into dorsal column nuclei which is descending |
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| 13:32 | And we saw that each spinal nerve a dermato associated with it. So |
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| 13:38 | dose or with and has a associated it on the left and right side |
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| 13:43 | each spinal nerve has a left and component to it. And we saw |
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| 13:49 | in the cases of shingles, it's herpes osto virus that initially appears as |
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| 13:56 | . And this virus can stay dormant it's capable of both an entire grade |
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| 14:00 | retrograde migration. And this virus can decades later. And when it does |
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| 14:07 | and after dormancy typically be in 50 years of age, which can be |
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| 14:11 | painful condition and people get hospitalized. having shingles and shingles here is shown |
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| 14:19 | represent and reappear in only single one on one side of the body. |
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| 14:25 | it would be probably like number number five dermato that we're looking at |
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| 14:31 | . So all of the information as mentioned from dorsal Regan comes into the |
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| 14:36 | column nuclei, a dorsal column, says the dorsal column nuclei at the |
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| 14:42 | of mela and there from dorsal column . That information which is up to |
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| 14:49 | is if the lateral now crosses over laterally. So from the upwards, |
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| 14:56 | of the information is contralateral processed by , ventral posterior thalamus, posterior nucleus |
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| 15:05 | the thalamus projecting into the body areas the primary somatosensory cortex. Uh So |
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| 15:14 | how this information from the face and head is being processed and that is |
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| 15:20 | being processed by a spinal nerves that's processed by, for example, trigeminal |
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| 15:25 | cranial nerve five, where the inputs large me counter receptor axons go into |
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| 15:31 | principal sensor trigeminal nucleus. And from principle sensor trigeminal nucleus, it sounds |
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| 15:40 | it crosses over contralateral at the level the ponds into the ventral posterior |
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| 15:50 | Where if a mental bacteria nucleus of thalamus is projected into the head and |
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| 15:56 | areas of the primary somatosensory cortex. one. So primary somatosensory cortex receives |
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| 16:05 | dense input from V P but also regions of thalamus. It has projections |
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| 16:11 | into the thalamus. Neurons. In cortical regions are responsive to somatosensory |
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| 16:18 | Um Somatic sensations, if you stimulate uh neurons, electrical stimulation will evoke |
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| 16:26 | experiences. And if there are lesions the primary somatosensory cortex, it will |
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| 16:32 | somatic sensation. So a person may be able to process somatic sensations. |
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| 16:37 | for very sensitive, as you can , there is S one and S |
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| 16:43 | , a three B 57. multiple areas in the somatosensory cortex and |
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| 16:48 | in the postal cortex that are processing that is related to somatosensory information. |
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| 16:56 | like we saw in the visual there were many different areas eventually going |
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| 17:01 | the areas that are we call association that we process information for a single |
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| 17:07 | . And before that information gets associated merged with information from other sensors. |
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| 17:14 | in the somatosensory cortex, we also this digit region. And obviously, |
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| 17:20 | have a lot of brain space dedicated digit region. And this digit region |
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| 17:24 | have its own interesting column will structure have a most of the uh innervation |
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| 17:30 | rapidly adapting neurons into the cortex. it will also have each digit will |
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| 17:36 | a rapidly adapting neuron column. And will have a slowly adapting neuron column |
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| 17:41 | the primary somatosensory cortex. So in , if we look at the soma |
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| 17:47 | or somatotopic map, this map is continuous in relation to the body. |
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| 17:53 | is also not scaled to human And there's more brain space dedicated to |
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| 18:00 | uh organs of uh in our bodies as hands and face for somatosensory sensations |
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| 18:08 | uh and, and genitals, for , that will help us survive and |
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| 18:14 | and, and rodents. Uh a of the map and some of sensory |
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| 18:18 | will be occupied by a whisker pad the exact number of rows that you |
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| 18:24 | in the whisker, 12345 will have own exact anatomical representation at the level |
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| 18:33 | the primary somatosensory cortex, which is referred to this barrel cortex is referred |
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| 18:39 | as barrel cortex. Because each one these anatomical units called the cortical barrel |
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| 18:45 | be responsible for processing information from a whisker on the whisker pad. So |
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| 18:52 | you wiggle this whisker, that information activate a contralateral s uh uh |
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| 19:00 | some primary somatosensory cortex barrel here. if you stimulate whisker in row C |
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| 19:07 | two, it should activate and uh activity in the barrel uh in the |
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| 19:14 | row, second barrel. And such the case, we discussed imaging |
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| 19:20 | And in this case, you can Whisker two C two and wiggle Whisker |
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| 19:25 | two. And with some delay, uh 2030 millisecond delay, this original |
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| 19:30 | cortex map then eventually will spread. we can image this kind of |
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| 19:36 | brain map activity in brain wave traveling . Using calcium imaging, using a |
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| 19:42 | of sensitive dye imaging. We discuss experimental neuroscience techniques for tracking neuronal activity |
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| 19:50 | in this case, neural network And in this experiment here, the |
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| 19:57 | two whisker activity in the cortex but blocked by applying C N Q X |
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| 20:04 | A PV C N Q X aina receptor channels and A PV blocks |
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| 20:11 | MD A receptor channels. And we that with a blockade uh specifically C |
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| 20:17 | area, there's a complete blockade off this map here. Uh But if |
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| 20:25 | wiggle whisker E two, you can see a clear propagation and clear activation |
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| 20:31 | whisker E two maps. So this really interesting system great for manipulation. |
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| 20:38 | But uh that example that we used structural and functional rearrangement uh plasticity in |
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| 20:47 | brain was this example of the digit that we have in the primary somatosensory |
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| 20:53 | . And in the monkey, once digit D three was lost the area |
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| 20:58 | primary somatosensory cortex is no longer processing from digit three. But instead the |
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| 21:05 | that are processing a adjacent digital information four and D two are now anatomical |
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| 21:11 | functionally enlarged and uh uh enhanced ex the expense of the lost digit. |
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| 21:21 | we also talked about how a frequent of uh repeated use of one or |
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| 21:26 | digits. In this case is just of the um animals, two digits |
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| 21:33 | an increase and a change in the . And obviously in the function, |
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| 21:38 | is synonymous um uh structuring the function these Samadi cortical lines. And then |
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| 21:47 | ended by watching a talk by uh Ramachandra and Doctor Ramachandra and talked about |
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| 21:56 | conditions and I asked you to remember three conditions, remember the reasons the |
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| 22:03 | for these three conditions. So, areas that are involved and the treatments |
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| 22:08 | the applied. So the three conditions cob grass delusion and the cause for |
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| 22:14 | was traumatic brain injury or cut connectivity certain regions of the brain that are |
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| 22:21 | such as fusiform gyrus, facial recognition , angular gyrus amygdala activation of the |
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| 22:31 | nervous system for emotional response. And the technique that he used uh was |
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| 22:38 | galvanic skin response measurements to determine their response. The second condition that he |
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| 22:46 | was phantom limb. In that it is caused by the loss of |
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| 22:50 | arm or a structural and functional rearrangement the somatosensory cortical area still imagining that |
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| 22:59 | still an arm, still imagining or leg or a limb that there's still |
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| 23:05 | only that uh arm or limb, there's also pain associated with it. |
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| 23:10 | he talked about learned paralysis. He talked about plasticity and he talked about |
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| 23:17 | a critical input, uh critical importance visual input and to rearranging uh this |
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| 23:26 | plasticity and getting rid of phantom And the technique that he used was |
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| 23:32 | box. And the third condition that discussed, the synaesthesia, which has |
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| 23:38 | genetic component involves a AAA trimming gene we talked about. And uh uh |
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| 23:48 | of the number and the digit and the sound or tone area are located |
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| 23:56 | closely to each other. And this gyrus area, the tuning may not |
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| 24:03 | properly. Therefore, there will be of census and cross modal uh interpretation |
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| 24:14 | color could be interpreted in a sound numbers could be interpreted as color. |
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| 24:21 | , and we are all in some uh in the teeth because we all |
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| 24:27 | an association and a common denominator for associating different sensors together. So please |
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| 24:35 | that information for your exam. And gonna check in the chat if there's |
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| 24:39 | questions on the somatosensory system. Do know we need to know the causes |
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| 24:45 | the impairments in the air? Um we talked about in the auditory |
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| 24:52 | we talked about mechanical impairments or rupture Airdrome. It's pretty easy to know |
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| 24:59 | then sensory neural, well, I , a loss of hearing, we |
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| 25:05 | talk about um what leads to loss hearing. But if you have loss |
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| 25:10 | hearing and you have tinnitus, which very common in the air is associated |
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| 25:15 | loss of hearing. Yeah, it's you need to know and the distinction |
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| 25:20 | what is a hearing aid versus what a um cochlear implant. Uh So |
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| 25:28 | hope that answers your question. OK. So the matter of sensor |
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| 25:38 | , any questions in the chat, some amount of sensor and Audi neurons |
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| 25:51 | over in the same. Oh, , somebody has enabled the closed caption |
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| 26:03 | you have to stop |
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