Physiology of Auditory and Vestibular Systems Dr. Pierce

Question 1

Where in the basilar membrane are high frequency sounds heard the best? Characteristic of the membrane at that point?

Answer 1

At the base nearest the oval windows, the membrane is stiff and narrow

Question 2

Where in the basilar membrane are low frequency sounds heard the best and what are the characteristics of the membrane?

Answer 2

More apical near helicotrema Wider and more flexible near the helicotrema

Question 3

Describe hair cells.

Answer 3

Polarized epithelial cells that are stiff and full of actin. They have stereocilia on the apical surface and neural synapses on the basal side

Question 4

Describe the endolymph and what side of hair cells does it bathe?

Answer 4

Potassium rich sodium poor similar to ICF. Found in scala media made by stria vascularis Apical end of hair cells

Question 5

Perilymph and what side of hair cells does it bathe?

Answer 5

• Potassium Poor
  
  • Perilymph Potassium Poor
• Similar to ECF high sodium low K
• Found in scala vestibuli and scala tympani
• Basal end of hair cells

Question 6

What causes depolarization of hair cells?

Answer 6

• Deflection of stereocilia allows K ions to enter the cell and depolarize it
• Mechanically gated K channels open flowing in
• The change in charge allows Ca Voltage gated TRPA1 channels to open
• The influx of calcium can cause depol of the hair cells allowing release of glutamate

Question 7

What direction do stereocilia bend to depolarize and hyperpolarize?

Answer 7

• Deflection opposite of the tallest stereocilia causes hyperpolaraization
• Deflection toward tall stereocilia causes depolarization

Question 8

What is the action of the stria vascularis?

Answer 8

• Maintains electrochemical properties of endolymph
• Blood labrynth barrier, pumps k from blood across membrane into endolymph

Question 9

What is the primary function, arrangement, synspases and efferent activity of the Inner hair cells?

Answer 9

• Primary source of auditory info
• Arranged in a single layer
• Synapse with peripheral terminal of primary afferent sensory neuron
• Efferent neuron also modulates activity

Question 10

Outer hair cells function, arrangement, synapses and efferent activity

Answer 10

• Primary cells responsible for amplilfying sound waves. Contractile epithelilal cell which boosts the vibration of basilar membrane acting like an amplifyer
• Three rows
• Synapse with sensor yafferent peripheral terminnls from spiral ganaglion
• FOrm synpse with terminals from efferent neurons

Question 11

Where do motions of outer hair cells originate?

Answer 11

• Superior olivary complex called olivocochlear efferents

Question 12

What innervates inner and outer hari cells?

Answer 12

Medial olivary complex innervate outer hair

Lateral olivary complex innervate innher hair cells

Question 13

What are Otoacoustic Emissions

Answer 13

• Spontaneous or evoked
• evoked is the basis for newborn hearing test
• the outer hair cells generate a low intensity usually inaudible sound

Question 14

What specifically do the anterior and posterior cochlear nuclei do?

Answer 14

• Anterior processes temporal and spectral features of sound
• Posterior integrates acoustic with somatosensory information

Question 15

What isi the superior olivary complex and its divisions

Answer 15

First site where information from both ears meets. The binaural processesing is crucial for sound localization.

• Medial superior olivary nucleus generates a map of time differences to help localize the location and gets EAA input
• Lateral superior olivary nucleus looks at intensity differences to help localize where the sound is coming from

Question 16

Inferior colliculus function

Answer 16

• Suppresses information related to echoes
• Information about sound time and intensity converge here and this along with suppression of the echoes allows for sound localization

Question 17

Medial Geniculate Nucleus

Answer 17

• Precise info regarding intensity frequency and binaural properties are integrated and relayed on
• lots of converging from spectral and temporal paths occurs here allowing for processing of speech inflections

Question 18

Primary Auditory Cortex (A1)

Answer 18

• Essential for perception of sound
• higher order processing of sounds

Question 19

Secondary auditory complex

Answer 19

• Less specifically organized than primary AC
• Responds to more complex sounds, identifying a sound and speech

Question 20

What are the three general Efferent input to auditory system

Answer 20

• Olivocochelar efferents
• Middle ear mm motorneurons
• Autonomic innervation of inner ear

Question 21

What do the Olivocochlear efferents do

Answer 21

• Decrease basilar membrane motion reducing responses of inner hair cells and auditory nerve fibers, also reduces response to noise
• May protect hair cells from damage from intense sounds

Question 22

Middle ear efferents

Answer 22

• Includes motor innervation to tensor tympani and stapedius attenuating the sound
• Bilateral responsne to high sound levels contractions decrease transmission of sound
• Acts at low frequencies
• Implicated in tinnitus
• May prevent damage

Question 23

Autonomics to the inner ear

Answer 23

• Comes from CN 8 or superior cervical ganglion
  
  • Caroticotympanic nerve off of SCG to innervate mucous glands of tympanum and blood vessels of tympanic membrane
• Acoustic nerve supplies blood vessels sympathetic regulates vasuclar tone
• Sympathetic Adrenergics

Question 24

What causes sensorineural heraing loss and what cells are more succeptible to injury?

Answer 24

• Damage to hair cells nerve fibers or both
  
  • Noise, ototoxic drugs, age, or unknown etiology
• Outer hair cells more succeptible to injury, this will cause a decrease in sensitivityy and broader tuning
• Inner hair cells cuts off auditory inputs to CNS if they are injured

Question 25

What end of the cochlea is more succeptible to damage causing sensorineural hearing loss?

Answer 25

The base end which detects high frequencies

Cochlear implant can restore some hearing

Question 26

How does a cochlear implant work

Answer 26

Multiple electrodes threaded through cochlea to stimulate surviving nerve fibers

Question 27

What do the anterior semicircular canals do?

Answer 27

Detects rotation in the vertical plane forwards

Question 28

Horizontal semicircular canal detects ___.

Answer 28

Rotation in horizontal plane

Question 29

Utricle detects ____ and saccule detects ____

Answer 29

• linear acceleration forwards and backwards
• Linear acceleration up and down

Question 30

Rotation in the verticlal plane backwards maximallly activates ________.

Answer 30

Posterior semicircular canal