Physiology Of Hearing

Question 1

What are the sub structures of the cochlea?

Answer 1

Scala vestibuli

• filled w/ perilymph and connects to the oval window
• is 0 mV charge

Scala media

• filled with endolymph and has high potassium content
• is +80mV charge

Scala tympani

• filled w/ perilymph and connects to the round window
• is 0 mV charge

the charge difference between media and tympani/ vestibuli is called the endochoclear potential

Question 2

What structure in the inner ear is responsible for keeping potassium concentration high in the scala media?

Answer 2

The stria vascularis

Question 3

What is the organ or corti?

Answer 3

A structure in the inner ear composed of the following structures:

• inner hair cells
• outer hair cells
• tectorial membrane

Are responsible for perceiving sound waves and processing them into electrical signals

Question 4

Auditory transduction steps for outward movement of the tympanic membrane

Answer 4

In outward movement of the tympanic membrane
- 1) the incus pulls outward, the scala vestibuli pulls outward and the scala tympani and round window pull inwards

• 2) basilar membrane of the organ corti moves upward, with the tectorial membrane being shift right
• 3) the sterovilli of the outer hair cells are pulled right as well, which causes the channels in these hair cells to allow potassium to influx into the outer hair cells
• 4) this causes depolarization of the outer ear cells and causes activation of Prestin proteins (job is to amplify the signal by further pullin the basilar membrane upwards)
• 5) ultimately exocytosis occurs of glutamate molecules which leaves via afferent dendrites to the spiral ganglion -> CNS
• allows for you to hear sounds*

Question 5

Auditory transduction steps for inward movement of the tympanic membrane

Answer 5

In outward movement of the tympanic membrane
- 1) the incus pulls inward, the scala vestibuli pulls inward and the scala tympani and round window pull outward

• 2) basilar membrane of the organ corti moves downwards, with the tectorial membrane being shift left
• 3) the sterovilli of the outer hair cells are pulled left as well, which causes the channels in these hair cells to inhibt potassium influx into the outer hair cells (the channels are blocked with movement to the left)
• 4) this causes hyperpolarization of the outer ear cells and causes deactivation of Prestin proteins (job is to amplify the signal by further pullin the basilar membrane upwards)
• 5) ultimately exocytosis occurs of GABA molecules which leaves via efferent dendrites to the spiral ganglion -> CNS
• used to tune out sounds of allow for you to decide what you want to hear*

Question 6

Where in the basement membrane are different sounds heard?

Answer 6

Low-frequency sounds (near 20-50 Hz)

• at the apex of the basilar membrane
• possesses far more long fibers than short

Medium-frequency sounds (near 200-500 Hz)

• in the middle of the basilar membrane
• possesses equal amounts of long and short fibers

High-frequency sounds (2000+ Hz)

• at the base of the basilar membrane
• possesses far more short fibers than long
• base is far more narrow and stiff than the apex*

Question 7

What is the general CNS pathway for hearing

Answer 7

Spiral organ of corti -> spinal ganglion of cochlear nerve -> modular in the auditory nuclei -> superior olivary nuclei -> nucleus of the lateral lemniscus in the pons -> inferior colliculus -> medial geniculate nucleus -> primary auditory cortex

Question 8

Nerve deafness (sensory nerual deafness)

Answer 8

Loss of hearing

Shows a decrease in both air and bone conduction

More common in older people

More commonly caused by increased low-frequency loud sounds
- this is caused because the hair cells are super active at this time, releasing mass amounts of ROS (which causes damage in excess)

Also can be caused by drug sensitivity to antibiotics (destroy/weaken hair sounds)

Question 9

Audiogram

Answer 9

A graph that measures for hearing and conduction loss

Measures loss of hearing (y) vs frequency (x)

Also measures loss of hearing with respect to air and bone conduction mechanisms

Question 10

Conduction deafness

Answer 10

Loss of inability to precisely hear sounds

Caused by

• repeated infections
• otosclerosis
• akaylosed stapes

does not cause a decrease in bone conduction, but a mass decrease in air conduction (especially at low frequency sounds)