Mechanisms Of The Auditory System

Question 1

Define the following; sound, pitch, loudness, intensity

Answer 1

Sound is a transverse wave that consists of compressed and rarefied air.

Loudness depends on the amplitude of the wave (measured in decibels, log scale). Humans can hear from 20Hz to 20,000Hz - 0dB to 120dB.

Pitch is the perception of frequency and timbre is what distinguished two sounds of same frequency.

Sound intensity: amount of energy delivered per second.

Question 2

Summarise how war detects sound waves

Answer 2

The ear detects sound waves in the air and via series of mechanical couplings, project the stimuli onto the hair cells, the sensory receptor of the internal ear. Hair bundle is a cluster of modified microvilli called stereocillia.

Question 3

Describe the anatomy of the middle ear and how it relates to sound conduction.

Answer 3

In the middle ear there are 3 ossicles, melacus, incus, stapes (smallest bones of the body), they transmit the vibration of the tympanic membrane (the tympanic cavity is filled with air) onto the cochlea (which is a snail shaped organ filled with fluid, and has a role to match the impedance and reduce the loss in energy as the vibration goes from air to the cochlea).

The impedance measure the reluctance of a system in receiving the energy from a source, the frequency at which the impedance of the system in minimal is called resonant frequency.

Mellasus and Incus,s position can be adjusted be the tensor tympanic muscle and steepidus muscles to control the tension of the tympanic membrane

Question 4

Describe the effect of conductive hear loss

Answer 4

The ear is not capable of transmitting the vibrations of sound waves onto the cochlea. This could be due to cerumen (earwax), infections such as otitis and tumours.

Question 5

Describe the role of the cochlea

Answer 5

The motion of stapes generates a difference in pressure between the two liquid filled chambers of the cochlea which in turn causes the vibration of the basilar membrane

Question 6

Describe the structure and role of the basilar membrane

Answer 6

The basilar membrane is an elastic structure of heterogenous mechanical properties that vibrate at different positions along its length in response to different frequencies. The impedance of the basilar membrane varies along its length, so does the resonant frequency. The basilar membrane breaks complex sounds down by distributing the energy of each component along its length. Therefore need sensory receptors (hair cells) along the whole length of the basilar membrane in order to detect all frequencies.

Hair cells: sensory receptors, bending of stereocilia towards the tallest, changes the voltage of the cell, eventually producing electrical signals to the brain - mechano transduction (MT)

The stereocillia are connected by filamentous linkage called tip links (work as small springs) = tip links share their location with ion channels, this disruption abolishes mechano-transduction

The opening of the MT channels in response to external stimulus relaxes the tip link and whole hair bundle - active process.

Question 7

Explain the type of hair cell and their role

Answer 7

1. Inner hair cells (95% of afferent from cochlea to brain as they provide sensory transduction)
2. Outer hair cells (most of the efferent transduction).

Role: form synapses with sensory neurones in the cochlear region (spiral ganglion). Each ganglion cell responds best to stimulations at a particular frequency. The tonotopic sound-location map.

Question 8

Explain sensorineural hearing loss and possible treatment

Answer 8

Problem is rooted in sensory apparatus of the inner ear or vestibulocchlear nerve - the most wide spread hearing loss, causes loud noises, genetics and antibiotics, ageing etc.

Put cochlear implants: hearing loss is primarily due to loss of hair cells they do not regenerate,. So could bypass the hair cells and stimulate nerve fibres directo,y, an elongated coil in to the cochlea with pairs of electrodes

Question 9

Describe the superior olivary complex:

Answer 9

1. Medical superior olive: sounds are first detected by the closest ear before the reach the other (intraaural delay)
2. Lateral superior olive: different intensity between the two ears (intraaural level different) r3ad lecture slice

Question 10

Describe the auditory cortex

Answer 10

Inferior colliculus: all ascending auditory fibres converge here, the more toward the cortex the more able to hear complex sounds

Superior colliculus : neurones are tuned to respond to stimuli with specific sound direction - fundamental for reflex

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