The Auditory system

Question 1

What (briefly) makes up the outer, middle and inner ear?

Answer 1

• Outer - pinna + canal
• Middle - tympanic membrane, ossicles
• Inner - cochlea, oval window

Question 2

What are the differences between perilymph and endolymph?

Answer 2

• Perilymph - normal ECF conc (high Na, low K), surrounds the cochlear duct.
• Endolymph - Unusual ECF conc (high K, low Na), separated from perilymph by membranes and is within cochlear duct.

Question 3

What membranes surround the spiral organ?

Answer 3

• tectorial membrane (on top)
• basilar membrane (bottom) - separates from scala tympani

Question 4

What happens to the stereocilia to depolarise the hair cell?

Answer 4

• Sterocilia tilt in direction of longest one
• More potassium channels open
• K+ influx
• Depolarises (-40mv)

Question 5

What happens to the stereocilia to hyperpolarise the hair cell?

Answer 5

• Sterocilia move in direction of smallest one
• More K channels close
• Inner membrane remains negative
• Hyperpolarised

Question 6

What are (3) vulnerabilities in transduction and function of the auditory system?

Answer 6

• Conduction of sound wave can be blocked leading to conductive hearing loss
• Production and removal of endolymph must be balanced, can become imbalanced
• Destroyed hair cells can’t be replaced

Question 7

What is the physiology of loud sounds in the ear? How is this damaging?

Answer 7

• Large vibrations
• Bigger receptor potentials
• More transmitter released -> more APs
• Strong vibrations can damage sterocilia / kill hair cells

Question 8

How are we able to listen to different pitches?

Answer 8

Each pitch activates a characteristic set of receptors and labelled-lines.

Question 9

What is the primary auditory pathway?

Answer 9

• cochlear nerve
• cochlear nuclei
• inferior colliculus
• medial geniculate nucleus
• primary auditory cortex (temporal lobe)

Question 10

What is presbyacusis?

Answer 10

When old people lose high frequency hearing

Question 11

What is the difference in function between the lateral and medial superior olivary nuclei?

Answer 11

• Lateral - compares loudness of sounds in two ears (for high frequency)
• Medial - compares moment when sound reaches two ears (for low frequency)

Question 12

How many inner hair cells per ear do we have?

Answer 12

~3,500