Sensory Transduction: Auditory System

Question 1

Define sound

Answer 1

Repetative vibrations in a medium such as air

Question 2

What are the 3 physiology dimensions which affect the sound we hear

Answer 2

1. Loudness/ intensity = determined by the amplitude of the sound wave. Measured in decibels. Greate amplitude = louder sound
2. Pitch - can be high or low tone. Determined by the frequency of sound. High freq = high tone
3. Timbre = quality of sound

Question 3

Give a brief overview of hearing

Answer 3

1. Sound causes vibration of air
2. Vibrate the tympanic membrane, the malleus, the incus, and the stapes
3. The vibration spreads to the cochlea.
4. Vibration of air is converted to movement/vibration of fluids in the cochlea
5. The vibration in the cochlea is captured by hair cells
6. Transduction (physical vibration is transduced to neural energy)
7. Perceived in the auditory cortex

Question 4

What are the 3 bones of the middle ear and what is their function ?

Answer 4

1. Malleus - attached to the tympanic membrane
2. Incus
3. Stapes - attached to the oval window

Think MSI (this isn’t in the right order tho)

There function is to amplify and transmit vibrations of the tympanic membrane to the chochlea

Question 5

What are the 2 main structures which make up the inner ear ?

Answer 5

• Choclea - part of the auditory system
• Labyrinth - part of the vestibular system

Note that the pic shows the oval and round windows

Question 6

Describe the anatomy of the cochlea

Answer 6

There is 3 fluid filled cavities:

1. Scala vestibuli
2. Scala media
3. Scala tympani

Scala vestibuli is separated from the scala media by reissners membrane

Scala media is separated from scala tympani by the basilar membrane

Note you can see the organ of corti which is composed of hair cells - its function is to transduce mechanical sound vibrations into nerve impulses

Question 7

Describe how sound is converted from mechanical vibrations into electrical impulses

Answer 7

1. Tramission of vibrations from stapes to the oval window causes vibrations in perilymph (fluid in the cochlea) this in turn causes vibrations in the basilar membrane
2. It causes membranes in the Organ of Corti (tectorial membrane) to shear against the hair cells
3. The hair cells (organ of corti) on the basiliar membrane convert the sound waves into electrical impulses by releasing neurotransmitter and ==> stimulating nerve fibres to the spiral ganglion

Question 8

Describe how signal are transmitted from the organ of corti

Answer 8

1. Essentially the hair cells (auditory receptors with sterocilia) synapse onto bipolar neurons with their cell bodies in the spiral ganglion
2. From the spiral ganglion signals are transmitted to the auditory nerve

Question 9

where is the organ of corti located ?

Answer 9

Between the basilar membrane and the tectorial membrane

Question 10

Where is perilymph and endolymph located in the cochlea ?

Answer 10

Question 11

Describe what is meant by tonotopy

Answer 11

Is the spatial arrangement of where sounds of different frequency are processed in the brain. Tones close to each other in terms of frequency are represented in topologically neighbouring regions in the brain.

Question 12

Describe the pathway of the auditory/ cochlear nerve (1 of 2 components of the vestibulocochlear nerve) to the primary auditory cortex and state the location of the primary auditory cortex

Answer 12

1. Cochlear nerve from either R or L ear synapses onto ventral cochlear nucleus on the same side as it originates, then axons to the dorsal cochlear nucleus
2. After the cochlear nuclei some fibres decussate ==> inout above the level of the cochlear nuclei is bilateral
3. Axons the synapse onto the superior olivary nucleus.
4. Axons then referred to as part of the lateral leminiscus then travel to the inferior colliculus
5. Then to the medial genticulate body which then sends axons to the primary auditory cortex - superior temporal gyri