Test 2: Auditory Pathway Flashcards
What CN is responsible for hearing and how does it happen?
Cochlear nerve CN VIII
-one of two nerves from CNVIII
Audition transduced by mechanoreceptors in cochlea
What are the two primary pathways roles?
Detect sound in space
Localize sound in space
What are the features of the inner ear vs. middle ear?
Middle ear:
- starts at tympanic membrane
- stapes, maleus, incus for amplification
- lesions=conductive hearing loss
Inner ear:
- starts at oval window (base of stapes)
- cochlea
- lesions=senorineural hearing loss
What are the initial receptors of auditory pathways
mechannoreceptors in cochlea
What are the 3 champers of the cochlea
- Scala media:
- fluid high in K; influx causes depolarization
- in organ of corti- sensory neuron 1CB - Scala vestibule:
- superior compartment
- perilymph - Scala tymponi:
- inferior compartment
- perilymph
What does perilymph in scala vestibule and tymponi do?
waves ossilate the basilar membrane
bends hair cells
starts transduction
What do the inner hair cells do?
On organ of corti- basilar membrane
- cilia imbedded in tectoral membrane that forms roof
- synapse on cochlear neurons
How do the sound waves go through the middle ear?
enter auditory canal of middle ear-> deflect tympanic membrane -> mobilzie small bones to amplify
MECHANICAL energy
How do sound waves transduce in the inner ear?
Sound waves into fluid wave in perilymph
deflects basilar membrain -> shear force bends tectoral hair cells
Bending hair cells-> midifies voltage -> depolarize BIPOLAR COCHLEAR NEURONS
What are the characteristics of 1 neurons?
Cochlear sensory neurons from CNVIII
CB in cochlear spinal ganglion
-transmit auditory signals to dorsal/ventral cochlear nerve
-pontemedullary junction in cerebellar peduncles
What is the difference in mechanical vs. electrical transduction?
Electrical: ossilation of basilar membrain and sterocillia in tectoral
Mechanical: fluid waves press stereocil into tectoral membrane- bends hair calls
What is the totonic map in the cochlea?
High frequency sounds hear close to oval window- more by middle ear
Low frequency sounds hear deeper by apex
How many neurons make up the most direct auditory pathway?
4
Where are the 2CB
Ventral or dorsal nuclei depending on sound frequency
What do the ventral cochlear nuclei neurons do
Contribute to horizontal path for LOCALIZATION
- relay bilaterally for redundancy
- ascend superior olives
- some decussate in basis pons in trapezoid body
What occurs at the level of the superior olives in the ventral pathway?
L/R comparison, timing, and amplitude
-project bilaterally
What do the dorsal cochlear nuclei neurons do
decussate in pons
PERCEPTION of sound
Both ventral and dorsal nuclei ascent in what tract?
Lateral leminiscus tract
-go to inferior colliculi to combine with other auditory input: reflexes, bilateral communication
Where are the 3CB
Inferior colliculous
-ascend in Brachium of inferiour colliculs to MGN
Where are 4CB
MGN thalamus
-form auditory radiations. go through posterior limb to A1
What is the difference between A1 and A2
1: concious detection of initial states of sound analysis
2: higher cortexes of receptive language/recognition in wernickes-BA22
What makes up the primary auditory cortex
transverse temporal gyrus
superior tempoeral gyrus
Where are different pitches heard
High hz/pitch deeper in cortex
Low hz/pitch more lateral in cortez
What is the BA number for A1
41
What neurons are traveling in the lateral lemniscal tract?
DGN to L/R superior olives
What neurons are traveling in the brachium of inferior colliculus
Inferior colliculous CB to MGN
What jobs do arcuate vs uncinate fasciulus do?
arcuate: where? spacial
uncinate: what? language
What blood supply feeds the cochlear nerve (caudal pons)
AICA
What supplys the medulla
vertebral- most
PICA- rostral
What supplies the caudal pons
Basilar- most
AICE- caudal
What supplies the rostral pons
basilar-most
-SCA dorsal
What supplies the caudal midbrain
basilar
-SCA and PCA
What supplies the rostral midbrain
PCA-most
Post comm, basilar, SCA
What supplies the MGM and auditory radiations?
Ant choiroidal: internal capsule
PCA: MGN and LGN
MCA: A1
