Auditory and Vestibular Processing

Question 1

Hearing

Answer 1

Brain’s perception of sound energy (sound energy is mechanical energy; pressure waves in air)

Question 2

Pitch

Answer 2

Our interpretation of frequency (of sound waves)

Question 3

Loudness

Answer 3

Our perception of intensity or amplitude of sound waves

Question 4

What can processing of sound tell us?

Answer 4

Distance, direction and movement

Question 5

External ear structure

Answer 5

Pinna (=auricle; elastic cartilage covered with skin); external auditory canal (meatus); tympanic membrane (eardrum)

Question 6

Middle ear structure

Answer 6

Eustachian tube; ossicles (malleus -> against tympanic membrane; incus; stapes -> against oval window - inner ear)

Question 7

Inner ear structure

Answer 7

Bony labyrinth (tunnels in temporal bone) which surrounds and protects membranous labyrinth

Question 8

Membranous labyrinth

Answer 8

Auditory organ; fluid filled; cochlear duct with organ of corti (inside cochlea); 3 semicircular ducts (inside canals) with 1 crista amupullaris in each (sensitive to rotational acceleration); utricle/saccule (inside vestibular apparatus) with 1 macula in each (can detect linear acceleration and head position; otoliths are crystals that move in response to gravitational force or acceleration)

Question 9

Explain the steps of hearing

Answer 9

1) Sound waves strike the tympanic membrane and become vibrations
2) Sound wave energy is transferred to the three bones of the middle ear, which vibrate
3) Stapes is attached to the membrane of the oval window; vibrations of the oval window create fluid waves within the cochlea
4) Fluid waves push on the flexible membranes of the cochlear duct; hair cells bend and ion channels open, creating an electrical signal that alters neurotransmitter release
5) Neurotransmitter release onto. sensory neurons creates APs that travel through the cochlear nerve to the brain
6) Energy from the waves transfers across the cochlear duct into the tympanic duct and is dissipated back into the middle ear at the round window

Question 10

What is the pathway of pressure waves through the cochlea

Answer 10

Oval window, vestibular duct, helicotrema, tympanic duct, round window (old vegetables help tame rabbits)

Question 11

Cochlea

Answer 11

Each coli has 3 ducts (sometimes called channels); vestibular duct and tympanic duct contain perilymph (essentially ECF or plasma); cochlear duct contains endolymph (secreted by epithelial cells, very high concentration of K+); vestibular membrane separates cochlear duct from vestibular duct, and basilar membrane (has variable sensitivity to sound wave frequency along its length; low frequency in flexible region near helicotrema, high frequency in stiff region near round window) separates cochlear duct from tympanic duct; tectorial membrane is a flap which covers hair cells of organ of corti

Question 12

Stereocilia

Answer 12

Villi on the hair cells; tallest is the kinocilium; connected by tip links; have special K+ channel proteins that are mechanically gated; excitation: when the hair cells bend in towards kinocilium, the cell depolarizes, which increases AP frequency in the associated sensory neuron; inhibition: if the hair cells bend away from kinocilium, ion channels close, the cell hyper polarizes and sensory neuron signalling decreases

Question 13

What are the synapses of the auditory pathways?

Answer 13

Medulla (cross over); medulla; midbrain; thalamus; auditory cortex

Question 14

Conductive hearing loss

Answer 14

Damage (or defect) to tympanic membrane, ossicles, or round window; ear canal or Eustachian tube blocked

Question 15

Sensorineural hearing loss

Answer 15

Damage (or defect) to inner ear

Question 16

Central hearing loss

Answer 16

Damage (or defect) to pathways between middle ear and cortex

Question 17

Vestibulocochlear nerve

Answer 17

Some hair cells synapse with it; some axons will synapse with neurons in medulla, medulla thalamus, cortex; some axons will synapse with cerebellum directly (no thalamus)