Exam 3 Week 14 ppt 9 Auditory Pathways Flashcards
Where do cell bodies of the primary afferent bipolar neurons reside
in spiral ganglion
Where do axons of bipolar neurons enter brain stem?
lateral and slightly caudal to vestibular 1° afferents
Where do axons of bipolar neurons end?
on dorsal and ventral cochlear nuclei
How are cochlear relay nuclei tonotopically mapped?
high frequencies dorsal and low frequencies ventral
What are the Cochlear Nuclei in the ascending pathway?
the 2° or relay auditory neurons
What path do axons of cochlear nuclei take?
Axons take 1 of 3 paths:
- Ventral acoustic stria (trapezoid body) – running ventrally thru caudal pontine tegmentum
- Dorsal and intermediate acoustic stria (running more dorsally through caudal pons)
- Most ascend contralaterally as lateral lemniscus
- Some ascend in ipsilateral lateral lemniscus
- Some synapse on a variety of nuclei in pons – most prominent is superior olivary nucleus
- NOTICE BILATERAL PATH
True or false: Lateral lemniscus have only axons from 2° auditory neurons
False
Lateral lemniscus have both Axons from 2° auditory neurons and few 3° from superior olivary nucleus
How does lateral lemniscus ascend?
- Ascends lateral to spinothalamic tract
- A few synapse in nucleus of lateral lemniscus but most ascend to inferior colliculus
Inferior Colliculi in Ascending Pathway- 3 points to know
- Most 2° auditory neurons end on neurons in inferior colliculus (a few ascend to the thalamus)
- Axons from these 3° neurons ascend to thalamus as brachium of inf colliculus
- Tonotopic mapping with high frequencies more ventral and low more dorsal
Medial Geniculate Nucleus in Ascending Pathway- 3 points to know
- 3° axons end on 4° in medial geniculate nucleus of thalamus
- Axons give rise to auditory radiations to 1° auditory cortex
- Tonotopic mapping with high frequencies medial and low frequencies lateral
What makes up the Primary Auditory cortex?
Transverse temporal gyrus (1) and adjacent planum temporale (2)
Which side of brain has a larger representation of the primary auditory cortex
left
Tonotopic mapping of Primary Auditory cortex
low frequencies anterior and high frequencies more posterior
Where do 2° axons from cochlear nuclei decussate?
in 1 of 3 locations
1. Axons of superior olivary nucleus also decussate in the trapezoid body (inferior acoustic stria)
2, Commissural connections between the inferior colliculi
3. ? did not see anything clearly marked
Bilaterality of acoustic projections
means that loss of one central pathway or loss of auditory cortex does not produce deafness in one ear but issues related to sound localization and indentification
**Due to: axons that have already decussated may decussated again
What two peripheral mechanisms contribute to the ability to localize sounds?
- Difference in timing between sound arriving at one ear versus the other (interaural time difference - ITD)
- Difference in sound intensity between the two ears (interaural intensity difference - IID)
What is time difference best at?
determining the direction of low frequencies
What is intensity difference best at?
distinguishing the direction of high frequencies
What is head a great sound barrier for?
high frequencies
What does Pinnae of the ear do?
assists in sounds to the front, back and above which would not be distinguishable
What is Lateral superior olive specialized for?
high frequencies and cells measure IIDs by integrating ipsilateral excitatory and contralateral inhibitory inputs
What is Medial superior olive is specialized for?
low frequencies and measures ITDs using excitatory inputs from both sides
example of auditory reflexes
the tensor tympani/stapedius reflex
Afferent (sensory) limb of tympani/stapedius reflex
A few fibers from the auditory nuclei terminate in the nuclei of the facial and trigeminal motor nuclei
Efferent (motor) limb of tympani/stapedius reflex
Branch of facial nerve to stapedius
Branch of trigeminal nerve to tensor tympani
Function of tensor tympani/stapedius reflex
to limit amplitude of loud and high-frequency sounds and to filter out noise arising from the head itself
Name the major structures auditory pathways travel through, and indicate where decussation may occur. (7 structures, 2 levels of decussation)
- Cochlear Nuclei (Ventral and dorsal)
(decussation may occur in ventral, intermediate, or dorsal acoustic stria - ventral acoustic stria = trapezoid body) - Superior olivary nucleus (not all fibers go through this)
- Lateral lemniscus (tract and nucleus)
- Inferior Colliculi (nuclei)
(may deccusate here between the two inf. colliculi) - Brachium of inferior colliculus (tract)
- Medial Geniculate Nucleus (part of thalamus)
- Primary Auditory Cortex
Describe the tonotopic orientation of high frequency signals as they travel through the auditory pathway:
- Cochlear nuclei: dorsal
- Inferior colliculus: ventral
- Medial Geniculate Nucleus: medial
- Primary Auditory Cortex: posterior
Describe the tonotopic orientation of low frequency signals as they travel through the auditory pathway:
- Cochlear nuclei: ventral
- Inferior colliculus: dorsal
- Medial Geniculate Nucleus: lateral
- Primary Auditory Cortex: anterior
Name the options for decussation of the auditory pathway:
- After leaving the chochlear nuclei: Trapezoid body (ventral acoustic stria) OR dorsal or intermediate acoustic stria
- At the Inferior Colliculi
