week 1 physiology of hearing and balance

Question 1

what are the values (dB) on audiogram denoting hearing range?

Answer 1

0-20= normal
20-40= mild hearing loss
40-60=moderate
60-90=severe
90+= profound

Question 2

what does the external ear act as? middle ear? inner

Answer 2

receiver
amplifier
RECEIVER / TRANSDUCER

Question 3

EUSTACHIAN TUBE is closed or open at rest?

Answer 3

closed

Question 4

how is the EUSTACHIAN TUBE opened? why?

Answer 4

by tensor veli palatini & levator palatine muscles

to ‘equalise ears’

Question 5

what does eUSTACHIAN TUBE dysfuction lead to?

Answer 5

middle ear negative pressure, (causing glue ear)

Question 6

what are the two openings of the cochlea to the middle ear.

Answer 6

Oval Window & Round Window

Question 7

how are sound waves transmitted fro middle to inner ear?

Answer 7

Wave transmitted to oval window and perilymph

Question 8

what does the inner ear consist of?

Answer 8

curved spiral lamina

2 1/2 turns around central modiolus

Question 9

where do the inner hairs sit?

Answer 9

organ of corgi

Question 10

how do we hear/ is hair moment made into sound?

Answer 10

Transduction: conversion of mechanical ‘bending force’ into electrical impulse

Question 11

when does Depolarisation occur? hyper polarisation?

Answer 11

Depolarisation occurs when deflected towards longest,
Hyperpolarisation occurs when deflected away.

Na+ channels

Question 12

summary of sound stimulation

Answer 12

External ear - sound collector
Middle ear - mechanical force amplifier
By the middle ear & (tympanic membrane & ossicles) and transmitted to the OW
Inner ear - sound transducer / analyser
Wave passes through the cochlea maximally stimulating a particular area of the basilar membrane. The organ of Corti here depolarises and fires – stimulating the VIIIth nerve and then the central pathways.
Culminating in activity in superior temporal gyrus

Question 13

the concentration of fluid varies in ear. how? disease related to dysfuction?

Answer 13

difference between endolymph and perilymph

Meniere’s disease

Question 14

what are the inputs to creating BALANCE?

Answer 14

vestibuar, proprioceptive, CVS, visual, vestibulospinal tract (legs), Vestibulo-ocular reflex (eyes)

Question 15

how can proprioception be damaged?

Answer 15

low vitamins, alcohol, peripheral neuropathy

Question 16

what is sensory conflict?

Answer 16

when visual input does not match proprioceptive input

EG: train moves off

Question 17

why does oscillopsia occur?

Answer 17

when we have no vestibular input

Question 18

what are the 5 key vestibular ‘end-organs’?

Answer 18

utricle & saccule, posterior canal, anterior canal and horizontal canal

Question 19

what are the OTOLITH ORGANS?

Answer 19

Utricle & saccule

Question 20

how do the OTOLITH ORGANS work?

Answer 20

Maculae of these organs have stereocilia projecting upwards into a gelatinous matrix with otoconia.

Stereocilia orientated in all directions so all movements perceived by depolarisation / hyper polarisation = detects back, forward, up, down + head tilt [note: Firing stops with linear motion so you know that movement has stopped, BUT it continues with head tilt - eg head to one side]

Question 21

what are the otoconia?

Answer 21

Calcium carbonate crystals in the saccule or utricle of the inner ear

Question 22

how do the SEMI-CIRCULAR CANALS help with balance?

Answer 22

Oriented at 90 degrees to each other so paired, equal and opposite- all range of movement

Deflection caused by movement of perilymph - ‘bending’ causes stereocilia to deflect

Question 23

what is the VESTIBULO-OCULAR REFLEX/ VOR?

Answer 23

the reflex by which the direction of the eyes remains constant when the head is moved

turn head to right, then right side is excited and left is inhibited - good table slide 36

Question 24

what occurs if VOR not working?

Answer 24

NYSTAGMUS - vision condition in which the eyes make repetitive, uncontrolled movements.(flickering)

Question 25

causes of defecting VOR

Answer 25

vascular, surgery, viral infection - stops signal

Question 26

what occurs if there is no VOR. what is a cause of this?

Answer 26

oscillopsia.

gentamicin injections side effect

Question 27

central pathways of the vestibular system

Answer 27

vestibular ganglion→ cerebellum
→CN3, 4, 6 (eye flickers)
→cerebral cortex (anxiety and nausea)
→Vestibulospinal tract (motor muscles to neck, back and legs)