Week 2 - G - Pharmacology 5 - Sensory trandsuction (auditory and vestibular systems)

Question 1

When hearing a sound wave, what part of the wave determines the intensity/loudness of the sound? What is the intensity measured in? Which part of the wave determines the pitch?

Answer 1

The amplitude of the wave determines the intensity/loudness - measured in decibels - dB The frequency of the wave determines the pitch - high pitch = high frequency - low pitch = low frequency

Question 2

What does the timbre of the sound refer to? (this is pronounced tamber)

Answer 2

The timbre of the sound refers to the quality of the sound

Question 3

Give a brief overview from hearing sound to it being percieved in the auditory cortex Also where is the auiditory cortex located?

Answer 3

When sound is produced, this causes vibration of air into the eardrum where it hits the tympanic membrane - the vibration enters the middle ear and travels along the ossicles to the base of the stapes which is in contact with the oval window - the vibration of sound enters the inner ear where the vibration causes the movement of fluid (endolymph) which stimulates the inner ear hair cells to convert the physical vibration to neuronal neergy which travels to the auditory cortex - located in superior temporal gyrus of temporal lobe

Question 4

What are the three ossicles? Between which two ossicles is there a flexible connection? What are the two muscles in the inner ear that dampen the activity of the ossicles?

Answer 4

Malleus (hammer) Incus (anvil) Stapes (stirrup) Flexible connection exists between the incus and stapes Tensor tympani - attaches to handle of the malleus Stapedius - smallest skeletal muscle in body - attaches to the stapes

Question 5

What are the tensor tympani and the stapedius supplied by?

Answer 5

Stapedius- supplied by the facial nerve Tensor tympani - supplied by the mandibular nerve (CN V3)

Question 6

99.9% sound is reflected due to high impedance of fluid in the cochlea (0.1% sound is passed = - 30 dB sound loss from air - fluid impedance mismatch) What is the function of the ossicles therefore? how much is the increase in the decibels they cause = known as impedence matching

Answer 6

The ossicles increase sound pressure to make up for the sound loss due to impedance matching - increase the intensity of sound by 34dB This is known as impedence matching

Question 7

The impedance matching of the ossicles is basically the ossicles amplifying the sound. The ossicles do this via three ways: 1) Area ratio of the ear drum to the stapes footplate 2) Lever action of the ossicles 3) Buckling of ear drum What is the main way in which the ossicles gain the increase in the decibels?

Answer 7

This is due o the area ratio of the ear drum to the stapes footplate - provides 26 of the 34 dB

Question 8

What is the structure which carries out the physical sound to neuronal energy tansduction? Which membrane in the inner ear is it located on?

Answer 8

This would be the organ of corti located on the basilar membrane

Question 9

What type of neurons are sensory neurons usually? What is the gagnlion known as where the first order neurons are fired before travelling on the cochlear nerve to reach the brain?

Answer 9

Most sensory neurons are bipolar neurons - ie have 2 neurites - ie two axons (or dendrites) extend from the cell body of the neuron The spiral ganglion is the fibres that attach to the organ of corti to spread sound to the cochlear nerve The hair cells in the organ of corti are innervated by bipolar hair cells in the spiral ganglionn which is in contact with the audioty nerve – wiil reach the cochlear nucleus of the brain

Question 10

At the apex of the sterocilia are potassium channels These potassium channels can be blocked or can be opened - it is the lid at the top of the potassium channels that can do this – this cap like structure is linked by tip links The cap like structure of hair is known as the kinocilium If hair moves towards the kinocilium, what happens to the potassium channel and hence the afferent fibre firing? What happens if stereocilia move away from kinocilium?

Answer 10

If the hair moves towards the kinocilium, this opens potassium channels causing cell depolarization and increased afferent firing If the hair moves away from the kinocilium, this closes potassium channels causing cell hyperpolarization and decreased afferent firing

Question 11

The sterocilia bending resuting in afferent firing causing spiral ganglion to release neurons to cochlear nerve and sound to be heard in auditory cortex is one of the rare examples where potassium enters the cell instead of efflux Inner Hair cell is the MAIN SOURCE of afferent signal in auditory (VIII) nerve. Outer hair cells are the mian source of efferent inputs from the superior olivary complex, what is th emian fucntion of outer hair cells?

Answer 11

The main function of outer hair cells is to amplify membrane vibration

Question 12

Mutations in many of the genes resposbibble for the recylcing of patassium in the endolymph (potassium depolarizes the cell remember) can result in deafness. What is the most common genetic cause of deafness? (ie what gene is most commonly mutaion)

Answer 12

The GJB 2 gene (provide instructions to make gap junction beta 2)

Question 13

What do the sound waves hit in the middle ear which dampens the sound?

Answer 13

The sound waves are dampened by the round window

Question 14

Describe the auditory system pathway from cochlear nucleus to auditory cortex in the temporal lobe?

Answer 14

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Question 15

Locating sound in space is done by the auditory pathway Which nuclei in particular of the auditory pathway take part in sound localization?

Answer 15

It is the superior olivary nucleus which is located in the pons that localizes the sound

Question 16

What is the system in the ears that is used for balance?

Answer 16

This is the vestibular system

Question 17

The vestibular organ allows the answers to the questions Where am i going - head rotation and Which way is up - translational motion Is it the semicircular canals, utricle or saccules that correspond to head rotation? Which detect movement in a horizonatal or vertical plane?

Answer 17

Semicircular canals respond to head rotation The utricle detects movmeent in a horizontal plane The saccule detects movement in a vertical plane

Question 18

Semicircular canals (Rotational movement) What are the three semicircular canals? What connects the cochlea to the saccule part of the labyrinth?

Answer 18

Have the poster, anterior and horizontal semicircular canals Cochlea connected to the saccule by the ductus reuniens

Question 19

The basis for transduction in the labyrinth is similar to that in the cochlea….driven by hair cells In the cochlea vibration induced by sound deforms the hair cells. In the labyrinth acceleration/gravity deforms the hair cells. When stereocilia bend, the cell is either hyper or depolarized causing an AP to fire Which way to the sterocilia have to bend in order for this?

Answer 19

Stereocilia bend towards the kilicilium causing depolarization Stereocilia bend away from the kiliocilium causing hyperpolarization This is the same principle as what occurs in the cochlea with the sterocilia in the organ of corti

Question 20

In the semicircular, what angle are each canal in relation to one another?

Answer 20

The semicircular canals lie at right angles to one another

Question 21

What is the sheet where the hair cells are located in the canals? What is the bulge along the canal that contains this sheet?

Answer 21

The crista - this is the sheet where hair cells are clustered The ampulla is a bulge in the canal where the crista is located

Question 22

The otolith organs Sense linear acceleration and gravity Consist of the utricle and saccule saccule: movement in the vertical/sagittal plane utricle: movement in the horizontal plane What is the region in the utricle and saccule where the hair cells are located?

Answer 22

This is the maccula

Question 23

What are the three central vestibular pathways in the brain and what is there function?

Answer 23

Vestibular pathways Vestibulocoular pathway - keep the eyes still in space when the head moves. (eye movements) Vestibulocolic pathway - keeps the head still when you walk in space (orientation key) Vestibulospinal pathway - adusts posture for rapid changes in position (postural control)

Question 24

The vestibulocoular reflex is designed to maintain clear and stable vision in the presence of head movements. What does this VOR allow? ie spped of eye and head movement, direction of the movement, focus of object

Answer 24

The VOR allows: Eyes to travel at the same speed as the head is moving The eyes move in the opposite direction from the head And this allows the object to remain in focus during head movmement

Question 25

Vestibular system dysfunction can occur due to alcohol exposure resulting in dizziness when drunk

Alcohol is less dense than water. When you drink, alcohol enters the blood, and then into the cupula. The cupula becomes less dense. and floats more in the endolymph

What does this result in?

Answer 25

This results in the hair cells being moved slightly meaning you feel like your head is spinning (rotating - semicircular canals) but in actual fact you are still