Auditory and Vestibular Receptors

Question 1

Define hearing

Answer 1

Analysis of very small pressure changes which are converted to neural signals by the auditory system

Question 2

What is the function of the middle ear?

Answer 2

Modify sound in a way which means the transfer of sound E from the middle to inner ear occurs with minimal E loss. Middle ear increases P and decreases amplitude of vibrations.

Question 3

Describe how sound is processed through the ear

Answer 3

1. Sound causes vibration of the tympanic membrane
2. Vibration is transmitted through the ossicles and causes the stirrup to push on the vestibular window
3. Vibration is also transmitted via the tympanic walls
4. Pressure is transmitted to the vestibular window and causes displacement of fluid in the upper canal of the cochlea which causes distension of the cochlea window
5. Basilar membrane is flexible so fluid displacement takes a short cut from upper to lower canal via bulging of the basilar membrane
6. Movement of the basilar membrane displaces the tectorial membrane relative to the hair cells
7. Movement of hair cells activates stretch sensitive ion channels causing an influx of K
8. This causes Ca channels to open
9. Influx of Ca causes vesicles of NT to bind to presynaptic membrane and release NT into the synaptic cleft
10. This causes depolarisation of the associated sensory neurone

Question 4

Describe the central projections of the hearing pathway

Answer 4

cochlea -> auditory nerve -> olivary nucleus -> cochlea nucleus -> lateral lemniscus -> caudal colliculi -> medial geniculate nucleus -> auditory complex

Question 5

How is sound localised?

Answer 5

Due to the time difference between low frequency sound waves reaching each ear.

Question 6

What is the function of the vestibular apparatus?

Answer 6

Give proprioceptive information about the head

Question 7

What is the function of the otolith organs?

Answer 7

Measure linear acceleration of the head. Cells sit on the macula with cilia projecting into a gelatinous layer. Otolith movement displaces the gel and causes cilia to bend. Bending of the cilia causes depolarisation of the macula.

Question 8

What is the function of the semicircular canals?

Answer 8

Sense rotational acceleration of the head.

1. Cilia of sensory cells are embedded in a gelatinous cupula
2. Rotation of the head causes endolymph to move in the opposite direction which bends the cupula and causes depolarisation of the sensory cells
3. Head rotation will stimulate one side and inhibit the other
4. Regulates eye movement