CH 11: The Auditory and Vestibular System

FNTB Exam 3

What is sound, what properties/variables does it have

Vibrational wave/pulse with frequency and amplitude

What are the broad sections of ear areas

Outer, middle, inner

What structures are in the outer ear, what are their functions

Pinna - external cartilage, convolutions can localize sound

Auditory canal - entrance to internal ear

What structures are in the middle ear, what are their functions

Tympanic membrane/eardrum - sound waves interact with it to move the associated ossicles

Ossicles - little bones - transfer tympanic movements to oval window. Malleus, Incus, Stapes

Tensor tympani muscle / stapedius muscle - stiffens the middle ear during onset of loud noise ( acoustic reflex)

Eustachian tube

What structures are in the inner ear, what are their functions

Oval window - hole in the skull

Cochlea - behind oval window - transforms oval window movement into neuronal response

What are the 3 scalae of the cochlea

scalae vestibuli, media, tympani

How does the membrane potential of the endolymph compare to the perilymph

Endolymph is more positive from active transport to have a much higher K+ interior and lower Na+ then perilymph

Where are the auditory receptors located? What are they called and what type of cell are they?

Organ of Corti, on basilar membrane - hair cells (specialized)endothelial cells

How does the structure of the basilar membrane impact function

In unrolled cochlea, it has a narrow, stiff base, wide, thin apex

What are the steps of sound propagation within the cochlea

Stapes hits oval window membrane, sending movement into perilymph, making a wave travel along basilar membrane form base to apex

How do hair cells transduce sound from basolateral membrane - cilia

Baso membrane moves up in response to sound, moving the reticular lamina and attached hair cells, that are linked together and attached to tectorial membrane. Inner hair cells respond to this movement by bending at base

How do cilia transduce bending to an electric potential

Base bending causes stereocilit tilt to/away from the tallest stereocilia, either stretching or closing the TCM channel. Open channel causes K+ influx and then voltage gated Ca2+ channels to open. Influc of Ca2+ causes excitatory (glutamate) release from synaptic vesicles

How does the endolymph voltage assist in transduction

Endolymph is high (+80mV) and doe not produce a change in K+ gradient end transduction channels open

What synapses with hair cells to connect to a nerve? What nerve is that>

Inner hair cells highly connected to spiral ganglion cells, connected to auditory nerve. outer hair cells less connected

How do outer hair cells amplify the signal

Motor proteins shrink in response to bending of stereocilia, causing K influx and depolarization. The shortening increase the basilar membrane movement

What is the auditory pathway from spiral ganglion to auditory cortex

Spiral ganglion through auditory nerve to ventral cochlear nucleus then superior olive in brain stem, then through lateral lemniscus to inferior colliculus (midbrain), to Medial geniculate nucleus (thalamus), then auditory cortex

How is the auditory cortex organized

A1, surrounded by Belt, then Parabelt

Within A1, increasing Hz ranges - tonopic organization via characteristic frequencies

How is sound intensity encoded

greater amplitude of basilar vibration, causing more extreme depolarization/hyperpolarization of hair cells, increasing/dec firing rates of nerves. Also more intense movement activates more nerves

How is frequency sensitivity enacted

Different parts of basilar membrane are sensitive to different frequencies (thicker = lower). Connected nerves also have characteristic frequencies, and carried onto cochlear nucleus

How is localization of sound divided? how does it occur in each division?

Horizontal plane - via interaural time differences - which ear receives sound first?, and interaural level differences - which ear receives louder sound?

Vertical plane - pinna curves assess elevation of sound source

Deafness occurs from; less optimal sound localization/pitch discrimination from (in relation to cerebral injury)

bilateral auditory cortex lesions; partial/unilateral lesion

Hearing loss (in relation to ear structure)

conductive loss from damage to external/middle ear

sensorineural loss from inner ear damage

Ear infection, treatment

characterized by undrained fluid in mid-ear, from swollen eustachian tube

can be treated with tympanostomy tube inserted to eardrum to drain fluid

How does a hearing aid work

Picks up sound waves, amplifies them, and sends them out with a speaker to the eardrum

Tinnitus - definition and causes

ringing in the ear, frequently involved with cochlea or auditory nerve disease/damage, or exposure to loud sounds, changes in central auditory structures, damage to cilia in inner ear, earwax blockage, or ear infections

What does the vestibular system do

Balance - head and body location, head and body movements

What structures are associated with the vestibular system

otolithic organs: utricle/saccule, and semicircular canals

Which vestibular component detects angular acceleration, which detects head tilt and linear acceleration?

semicircular canals, otolith organs

Otolith organ strucure → function

macula sensory epithelium is vertically oriented. Vestibular macula contains hair cells, on bed of supporting cells. Cilia project into gelatinous cap, encrusted with otoconia (calcium carbonate crystals). Key to the tilt sensitivity of macula, higher density than surrounding endolymph

How does tilting a head backwards affect the vestibular system

Gravity pulls the otoconia, deforming the gelatinous cap, bending the cilia. Bending towards the especially tall cilia (kinocilium) results in depolarizing, excitatory receptor potential. Away = hyperpolarization

How are the utricle/saccule hair cells oriented with respect to each other

90 degrees ( saccular maculae are vertical, utricular maculae are horizontal - giving more specifity to sensor

Vestibular innervation?

vestibular nerve (crainal nerve VIII) connected, synapse with hair cells. Nerves directly connect to medial and lateral vestibular nuclei on the same side of the brain stem

Semicircular canal structure -→ function

Senses rotations

hair cells clustered within a sheet of cells (crista)) in a bulge along the ampulla canal.

Describe push/pull activaiton of semicircular canals

Vestibular axons fire at high rates at rest. can easily be up or down regulated.

Long head rotation leads to adaptation. when stimuli ends, opposite fire occurs