Physiology of Hearing and Balance

Question 1

What is sound?

Answer 1

A pressure wave caused by oscillating molecules (set in motion by vibrations)

Question 2

What does frequency dictate?

Answer 2

Pitch

Question 3

What does amplitude dictate?

Answer 3

Intensity

Question 4

What range can human detect sounds in?

Answer 4

20-20000 Hz

Question 5

How does the external ear act as a receiver for sound?

Answer 5

Shaped to receive airborne sounds (huge variation in shape)

Question 6

What does the ossicular chain of the middle ear acts?

Answer 6

Piston/lever arm = varying efficiency depending on frequency of sound transmitted

Question 7

What is the tympanic to OW ratio in the middle ear?

Answer 7

18:1 (impedance matching air to liquid) = leads to pressure gain of 22x

Question 8

What is the ratio of the malleus handle to the incus long process in the middle ear?

Answer 8

1.3:1 = gain of 20-25dB (theoretical gain in 34dB)

Question 9

What is the Eustachian tube?

Answer 9

Ventilation pathway for middle ear mucosa = has bony and cartilaginous portions

Question 10

What is the resting state of the cartilaginous tube of the Eustachian tube?

Answer 10

Closed = opened by tensor veli palatini and levator palatine muscles

Question 11

What does dysfunction of the cartilaginous tube in the Eustachian tube cause?

Answer 11

Middle ear negative pressure

Question 12

What are the oval and round windows of the ear?

Answer 12

Two openings of the cochlea to the middle ear = have in-phase movement

Question 13

What do the oval and the round windows of the ear allow?

Answer 13

Transmission of pressure wave in enclosed canal and vibration of the basilar membrane

Question 14

Where is the pressure wave transmitted to from the oval and round windows of the ear?

Answer 14

Perilymph

Question 15

How is the inner ear structured?

Answer 15

Curved spiral lamina = two and a half turns around central modiolus (need to consider ultrastructure of cochlea)

Question 16

Where is the scala media (endolymph) of the cochlea located?

Answer 16

Suspended between scala tympani and scala vestibuli (perilymph)

Question 17

What is within the cochlea of the ear?

Answer 17

Coiled tube of liquid = actively maintained in specific concentration to power cells

Question 18

How does sound stimulate the 8th cranial nerve and then the central pathways?

Answer 18

Wave passes through cochlea, maximally stimulating a particular area of the basilar membrane, then the organ of Corti here depolarises and fires to stimulate nerve

Question 19

Where does sound activity culminate?

Answer 19

In the superior temporal gyrus

Question 20

What is the input and output displayed by the modified Romburg’s test for balance?

Answer 20

Input = vestibular
Output = vestibulospinal

Question 21

What is the structure of the inner ear like?

Answer 21

Complex structure termed the labyrinth = bony and membranous structures

Question 22

What are the five key vestibular end organs present in the inner ear?

Answer 22

SVN = lateral/anterior superior semi-circular canal, utricle
IVN = posterior semi-circular canal, saccule

Question 23

What are the hair cells of the inner ear?

Answer 23

Kinocilium and stereocilia = resting potential is 90 spikes/s, deflection towards increases

Question 24

What are the otolith organs of the ear?

Answer 24

Utricle and saccule

Question 25

What is present in the maculae of the otolith organs?

Answer 25

Stereocilia = project upwards into a gelatinous matrix with otoconia

Question 26

How are the stereocilia of the otolith organs orientated?

Answer 26

In all directions = all movements perceived by changes in resting firing rate

Question 27

How does the brain interact with the otolith organs?

Answer 27

Perceives position and movement when tilting head/linear motion (lend weight and due to gravity)

Question 28

How are the semi-circular canals of the inner ear orientated?

Answer 28

At 90 degrees to each other so paired, equal and opposite

Question 29

What sits within the ampulla of the semi-circular canals of the inner ear?

Answer 29

Cupula

Question 30

What does bending of the semi-circular canals of the inner ear cause?

Answer 30

Causes stereocilia to deflect

Question 31

What causes the semi-circular canals of the inner ear to deflect?

Answer 31

Movement of perilymph

Question 32

What does VOR stand for?

Answer 32

Vestibulo-ocular reflex

Question 33

What feeds into the cupula of the inner ear?

Answer 33

The christa ampullaris

Question 34

What occurs in the vestibulo-ocular reflex?

Answer 34

Movement of head to left causes inhibition | Movement of head to right causes excitation

Question 35

When may nystagmus occur during the vestibulo-ocular reflex?

Answer 35

When turning towards a particular side (ie on left side when turning left), on left side when there is neuritis

Question 36

What is the input and output to the vestibulo-ocular reflex?

Answer 36

``` Input = vestibular Output = vestiblo=ocular ```

Question 37

What is oscillopsia?

Answer 37

Objects appear to move or tremble when they are still = occurs when there is no vestibular input

Question 38

What is nystagmus?

Answer 38

Rhythmic abnormal eye movements

Question 39

What is the vestibulo-oculo reflex?

Answer 39

Activation of vestibular system of inner ear

Question 40

What does the modified Romburg's test assess?

Answer 40

Tests for presence of two out of three = neurological function for balance, assesses proprioception, vison and vestibular function

Question 41

What is the central pathway for balance?

Answer 41

Complex series of communications in vestibul nuclei

Question 42

Where do vestibul nuclei have output to?

Answer 42

Vestibulospinal, medial longitudinal fasciculus and ocular muscles, medial lemniscus and thalamus

Question 43

Where does the vestibulospinal tract have outputs to?

Answer 43

Motor output to neck, back and leg muscles

Question 44

Where do the medial longitudinal fasciculus and ocular muscles have output to?

Answer 44

Motor output to eyes

Question 45

Where do the medial lemniscus and thalamus send outputs to?

Answer 45

The cerebrum

Question 46

What is the function of the hair cells in the ear in terms of sound?

Answer 46

Transduction = conversion of mechanical bending force into electrical impulse

Question 47

How are stereocilia of the ear arranged?

Answer 47

In height order with tip links connecting them together

Question 48

When does hyperpolarisation and depolarisation of the ear hair cells occur?

Answer 48

Depolarisation occurs when deflected towards longest | Hyperpolarisation occurs when deflected away

Question 49

Where is the primary auditory complex of the brain?

Answer 49

Left posterior temporal gyrus = Brodman areas 41/42

Question 50

When does firing of the cilia in the otolith organs stops?

Answer 50

Stops with linear motion so you know movement has stopped (but continues with head tilt)

Question 51

How are the otolith organs orientated?

Answer 51

360 degree orientation so all planes of motion detected

Question 52

What type of hair cells are present in otolith organs?

Answer 52

Type 1 and 2

Question 53

What increase and decreases the resting potential of the otolith organs?

Answer 53

Direction of bend towards or away from the kinocilium