Sound Physiology

Question 1

Components of the auditory pathway

Answer 1

1. Vestibulocochlear nerve (CNVIII)
2. Cochlear nucleus
3. Superior olivary nuclei
4. Lateral lemniscus
5. Inferior colliculus
6. Medial geniculate nuclei
7. Auditory cortex (Brodmann’s area 41, in temporal lobe)

Question 2

How are sensory nerve impulses from the cochlea relayed to the brain?

Answer 2

Travel via auditory nerve from cochlea to internal acoustic meatus to join vestibulocochlear nerve, where it travels to cochlear nucleus in brainstem (pons/medulla junction) and onto inferior colliculus, then thamalus and ultimately auditory cortex

Question 3

Transmission of sound in the ear

Answer 3

• Sound waves funnelled into ear by pinna & travels through EAM, and vibrate tympanic membrane
• Movement of ossicles & sound waves pass through oval window into inner ear
• Fluid within scala vestibuli of cochlea vibrates, ultimately causing vibration of basilar membrane
• Auditory receptor cells stimulated in Organ of Corti, which send impulses to brain via CNVIII

Question 4

Perilymph contains high concentrations of __ and low concentrations of __

Answer 4

• sodium
• potassium

Question 5

Endolymph contains high concentrations of __ and low concentrations of __

Answer 5

• potassium
• sodium

Question 6

Inner hair cells contain __ that connect channels from different stereocilia

Answer 6

tiplinks (cadherins)

Question 7

What happens when endolymph pushes stereocilia towards the kinocilium?

Answer 7

Tiplinks stretch & channels open. K+ and Ca2+ influx depolarises the cell. Ca2+ helps fuse synaptic vesicles with basilar membrane, leading to glutamate release. Glutamate acts on peripheral processes coming from spiral ganglion, resulting in more APs

Question 8

What happens when endolymph pushes stereocilia away from the kinocilium?

Answer 8

It hyperpolarises the cell (more negative), closing the channels and therefore less APs are generated

Question 9

Why is the endolymph so high in potassium?

Answer 9

The stria vascularis are specialised cells in the scala media that secrete potassium at a high rate

Question 10

Briefly describe the protective mechanism of outer hair cells

Answer 10

Increased noise increasing ACh release, causing hyperpolarisation of the cell. This relaxes prestin molecules, elongating the outer hair cell, causing downward bowing of basilar membrane. This results in decreased hair cell activation and therefore less APs.

Question 11

What happens when prestin molecules on outer hair cell contract?

Answer 11

Upward bowing of basilar membrane, leading to increased hair cell activation allowing for discrimination between different frequencies i.e. modulation of sound