Auditory Pathway | Easy | Physiology | Primary (lemniscal) pathway
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- čas přidán 16. 08. 2020
- The auditory pathway conveys the special sense of hearing.
Information travels from the receptors in the organ of Corti of the inner ear (cochlear hair cells) to the central nervous system, carried by the vestibulocochlear nerve (CN VIII).
This pathway ultimately reaches the primary auditory cortex for conscious perception. In addition, unconscious processing of auditory information occurs in parallel.
Components of the Auditory Pathway
The auditory pathway is complex in that divergence and convergence of information happens at different stages.
There are two main components of the auditory pathway:
Primary (lemniscal) pathway - this is the main pathway through which auditory information reaches the primary auditory cortex (A1).
Non-lemniscal pathway - mediating unconscious perception such as attention, emotional response, and auditory reflexes.
Primary Pathway
Spiral Ganglion
The spiral ganglion houses the cell bodies of the first order neurons (ganglion refers to a collection of cell bodies outside the central nervous system). These neurones receive information from hair cells in the Organ of Corti and travel within the osseous spiral lamina. Their central axons form the main component of the cochlear nerve.
The vestibular nerve joins the cochlear nerve entering the internal acoustic meatus, and from this point onward they are collectively called vestibulocochlear nerve. This proximity is clinically relevant since lesions to this nerve will usually produce symptoms in both the auditory and vestibular components.
The nerve enters the cranium through the internal acoustic meatus and travels a short distance (around 1 cm) to enter the brainstem at the cerebellopontine angle. For more information on the vestibulocochlear nerve, its anatomical course and function please read this article.
The first order neurons synapse at the ipsilateral cochlear nuclei.
Cochlear Nuclei
Fibres from the cochlear nerve bifurcate and information is sent to the cochlear nuclei on each side of the brainstem:
Ventral (anterior) cochlear nucleus - located in the area where the nerve enters the brainstem.
Dorsal (posterior) cochlear nucleus - located posterior to the inferior cerebellar peduncle.
It forms a small bulge on the surface of the brainstem - known as the auditory tubercle.
From the dorsal cochlear nucleus, most fibers cross the midline and ascend in the contralateral lateral lemniscus. Other fibers ascend in the ipsilateral lateral lemniscus.
From the ventral cochlear nucleus, some fibers also ascend in the lateral lemniscus bilaterally. However, most fibers from the ventral cochlear nucleus decussate to the contralateral superior olivary nuclei in a region known as the trapezoid body. Although the ventral cochlear nuclei neurons decussate at the trapezoid body, some fibers synapse at the ipsilateral superior olivary nucleus. The superior olivary nucleus is located just next to the trapezoid body. It also projects upwards through the lateral lemniscus.
In summary, in both the dorsal and ventral nuclei, some fibers decussate while others don’t. For that reason, information from both ears travels bilaterally in each lateral lemniscus. This is important because supranuclear lesions (i.e. above the level of the cochlear nucleus) will not lead to serious hearing impairment. Therefore, hearing problems can be conductive or sensorineural but are rarely central.
Inferior Colliculus and Medial Geniculate Body
Fibers ascending through the lateral lemniscus from both cochlear nuclei and from the superior olivary nuclei arrive at the inferior colliculus, where all these fibers carrying auditory information converge.
These fibers project to the ipsilateral medial geniculate body (MGB) in the thalamus (recall that vision is relayed on the lateral geniculate body).
The MGB does not act as a simple relay centre: it has reciprocal connections with the auditory cortex and mediates refinement of the incoming information. Projections from the medial geniculate body proceed then to the primary auditory cortex.
Note: A good way to remember what information passes through each geniculate body is that music goes to medial and light goes to lateral.
Primary Auditory Cortex
The primary auditory cortex (A1) is located in the superior temporal gyrus, right under the lateral fissure. The primary auditory cortex is organized tonotopically, although its organisation is complex and the details are beyond the scope of this article.
Non-Lemniscal Pathways
These are pathways that do not lead to primary auditory cortex. They involve multisensory integration, reflexes, attention and emotional responses.
The best professor
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Do u also follow sembulingam because each nd every word is same.
But u make it so easy to understand 👌
Felt the same
i was about to comment the same thing
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Not from medial geniculate body the fibres go to inferior colliculus, some fibres bypass lateral lemniscus and go to the inferior colliculus. From there the pathway passes to medial geniculate body.
Yes ..
@@nishantvivek9973 🤭
I have read different books about this including ENT books, Audiology Books of Jack Katz and of other authors and I conclude that....
The connection from AVCN goes to
1. Contra MNTB -> Contra SOL-> Contra DNLL->Contra IC
2. Ipsi SOL->VNLL->Contra IC
From PVCN (Direct Bundle)goes to
1. Ipsi SOL-> IPSI DNLL->Ipsi IC
From DCN (Decussating Bundle) goes to
1. INLL->Contra IC
I sat glued to my screen as I was so impressed by this explanation and the fluidity of it.
Sembulingam 👍
This is a very great class to be honest but its too fast to catch up can't prepare notes in time. Please make your videos in a slow pace....its just a feedback overall this class was really helpful and I was able to understand each aspect
Noted,thank you soo much, keep watching😊
It's very simple and clear to understand.......... Your hardwork is truly appreciated.......but it would be better if the information given be a little bit deeper and we could solve our doubts........
Very simple and informative ,thank you
You're welcome 😊
Awesome 😎 clear cut explanation...... amazing 🤩
Thank you, keep watching ❤️
Just a advice ma’am the background sound is disturbing
Im sorry for the inconvenience, I'll improve in my upcoming videos.
Keep watching 💖
Trapzoid body in the pons not in medulla !!
Very nicely explained
Great job
Keep it up
Thank you,. Keep watching❤️😊
Comprehensive , Thank You 😊
Nice explanation.Except one mistake overall teaching is so cool and clear
Mam... pls xplain about visual pathway as soon as possible... becoz i feel comfortable on ur lectures only😁🌟
A lots of love mam♥️.....the way you make the concept is outstanding
Thank you 😊
This is very clear and helpful. I have been looking for a tutorial like this, thank you so much for posting!!
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You are great
Thank you 😊
Thank you mam..☺️☺️
You're welcome, keep watching ❤️
Jaypee ZINDABAD. Thanks for such precise explanation!
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Very easily explained thank you
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Thanks mam for best explanation 🙏🏻😊
Awesome ❤️
Nice mam..explain about visual pathway
Great...explanation .. ☺
Clear mam thank you mam😊
Very easy way for clear understanding
Mam sembulingam ko read to hum bhi kr skte hai aap easy language me bataiye plzzz
thanks mam
You're welcome 😊
Informative
Mam superior olivary nucleus is in lower pons and inferior olivary nucleus is in upper medulla na.... Please correct me if I am wrong
good explanation
Mam,vera level plz put more videos,if u have time cardiac cycle video
Thank you, sure 😊
Awesome explanation mam...tq mam
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Thanks
Very informative and well explained but you speak and write too fast. I was literally following keeping playback speed to 0.5x
Thank you 😊
Same here
Tqs mam
Do for us the visual pathway
From sembu
Sembu op
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Please send pdf
S.embulingam
Actually there are 5 order neuron not only 3
Mam can we just get the screenshot of this... It makes us easy to study or revise
Notes mil skate hi apke
Please don't add background music in next VEDIOs
It disturb in concentration
Best explanation
Sure, I'll not add.
Thank you.
And keep watching 💖
Mam PlzZz make visual pathway 😓😢😢😢😢😢😢
I had a hard time in focusing on this video because of that background music
not medulla but PONS !!!!!
Isnt the inferior olivary nucleus located in the medulla?
Sembulingam 👍