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Which cells do afferent fibers of the spiral ganglion cells synapse?

How do these afferent fibers synapse?

95% Inner hair cells (multiple fibers per inner hair cell)
5% outer hair cells (one fiber synapses on multiple outer hair cells)


What is the fluid in the scala tympani called? What is it made of?

Name: perilymph

Made of: low K+, 0 mV


What is the fluid in the Scala media called? What is it made of?

Name: endolymph

made of: High K+, 80 mV


What is the fluid in the inner hair cells made of?

Low K+ and -45 mV


How is fluid seperated between the inner hair cells and scala media?

reticular lamina


How does a downward wave defection effect the stereocilia? (3)

1) Deflects stereocilia towards the modiolus (away from taller stereocilia)

2) Tip links closes pores

3) K+ can't get in and hair cells are hyperpolorized


How does an upward wave effect the stereocilia?

1) stereocilia deflected away from mediolos (towards taller stereocilia)

2) Tiplinks open pores and positive K+ ions from endolymph flow into hair cells

3) hair cells depolarize and release neurotransmitter


What is an audiogram?

Hearing level in patients is plotted to determine what they can hear.

Softest sound that can be detected at each frequency is plotted. Anything below line (and thus louder at each frequency) can be heard


What are the types of hearing loss?

Conductive loss


What is conducive hearing loss?


Something blocking the external or middle ear

Treatments: surgery, medication, sometiems can't be treated


What is sensorineural hearing loss?

Causes? (4)

Involves structures of inner ear and cochlea.

Causes: Congenital, Noise exposure/trauma, Medication, age
Treatment: permanent, not much can be done to cure, can't restore structures


Where do auditory nerves synapse?

Cochlear nucleus


What are the functions of the two pathways that originate in the cochlear nucleus?

1) Recognition of sound patterns

2) Localizing sounds


What is the pathway for recognition of sound patterns starting from the cochlear nucleus?

Dorsal + Ventral coclear nucleus (DCN and VCN) --> Contralateral Inferior colliculus --> medial geniculate nucleus (MGN) --> primary auditory cortex


What is the pathway for localizing sounds starting from the cochlear nucleus?

Ventral cochlear nucleus (VCN) --> Superior olivary complex (SOC on both sides) --> Inferior colliculus (IC) --> Medial geniculate nucleus (MGN) --> primary auditory cortex


What is the lateral lemniscus?

carries sound pattern information from Dorsal and Ventral cochlear nuclei to contra-lateral inferior colliculus


Where is the first place for binaural convergence?

Superior olivary complex


Where is the superior olivary complex (SOC)?

In the pons


Where is the medial geniculate nucleus?

In the thalamus


Where is the auditory cortex?

Broadman's area?
Area of brain?

Broadmans area: 41

Area of brain: superior temporal lobe - Heschel's gyrus


Why is topography and laterality of limited use for diagnosis of pathology? (2)

1) Because the only place in the brain NOT binaural is cochlear nucleus

2) duplication of pathways makes it difficult to selectively cut afferents from one ear alone (unless at periphery or from cochlear nucleus)


Where is Wernicke's area and what does it do?

Where: left hemisphere in superior gyrus of temporal lobe

Purpose: speech interpretation


What is the characteristic frequency of a cell?

It is the frequency in which a cell maximally responds


What is a frequency tuning curve?

A graph that describes how well a cell responds to higher and lower frequencies


What is the result of an INCREASE in sound intensity in regards to a tuning curve?

the curve broadens


What is the result of an DECREASE in sound intensity in regards to a tuning curve?

the curve narrows


What is the purpose of broca's region?

Important for speech production (the motor aspect of speech)


Where is area 41/A1 (auditory cortex)?

buried in the lateral sulcus


What is unique about cells in the auditory cortex relative to cells in other parts of the auditory pathways?

Cells in auditory cortex can be selectively responsive to complex features of sounds

Example: some cells are selective for speech components (dynamic beginning followed by sustained tone)


What are the two factors that allow the brain to localize sound?

1) Extra distance between the sounds going to each ear

2) "shadowing" produced by the head makes sound going into one ear more intense than the other