Physiology of Hearing and Balance Flashcards
What is the general function of the external ear
Collect sound
What is the general function of the middle ear
Mechanical force amplifier
What is the general function of the inner ear
Sound transducer / analyser
What is sound
A pressure wave caused by oscillating molecules set in motion by a vibration
What does frequency dictate
Pitch
What does amplitude dictate
Intensity
What frequency can humans perceive
20-20000Hz
Why do mammals under water not need an external ear
Sound is different in water and does not need to be channeled like us
What is the overall pressure gain in the middle ear
x22
What is the function of the angular ligament
It suspends the stapes in the oval window
What happens if there is a very high frequency sound
There is rotation between the malleus and incus
How do we get a pressure gain in the middle ear
We need to transfer sound from air to liquid
To generate the power to do this, we require movement from the ossicles
What does the ossicular chain act as
Pistor or lever arm with varying efficiency depending on frequency of sound transmitted
What is the function of the Eustachian tube
Ventilation pathway for the middle ear mucosa
What is the eustachian tube made up of
Bony and cartilaginous portions
What is the resting state of the cartilaginous tube? Open or closed
Closed
What opens the Eustachian tube
Tensor veli palatini and levator palatine muscles
When might the Eustachian tube not open and close as it should?
Babies with cleft palates
Dysfunction of the Eustachian tube leads to what
Middle ear negative pressure
What do the oval and round windows in the cochlea allow
The transmission of pressure wave in enclosed canal and vibration of the basilar membrane
Where is the endolymph found
Scala media
Where is perilymph found
Scala vestibuli
Where is the scala media found
Suspended in between scala tympani and scala vestibuli
What are some of the important structures found on the organ of corgi
Basilar membrane
outer hair cells
inner hair cells
What can gentamicin cause damage to
The outer hair cells
What is the function of the outer hair cells
They are involved in modulating sounds
What is the function of the inner hair cells
Main ones involved in receiving information and sending it back towards the brain
In one word, what is the function of hair cells
Transduction: conversion of mechanical “bending force” into electrical impulse
When does depolarisation of the hair cells occur
When the hair cells are deflected towards the longest hair cells
When does hyper polarisation occur
When the hair cells are deflected away from the longest cilia (
What happens when hair cells bend
Generate Action potentials and generates a firing to the spiral ganglion
How is a frequency picked up?
Cells depolarise and fire an action potential to the cochlear nerve
How many electrodes are on a cochlear implant
20-24
What does ECOLI stand for
mneumonic for the central pathway Eight cranial nerve Cochlear nucleus Olivary complex Lateral lemniscus Inferior colliculus
Where is the location of the primary auditory cortex
Supeiror temporal gyrus (Brodman areas 41/42)
What systems are involves in balance
Ears Eyes Proprioception CNS Cardiac
What pathology can affect balance
Meningitis Migraines Diabetes Arthritis Stress SOL MS Arrythmias Postural Hypotension
What is the name of the structure involved with balance
Labyrinth
What is meant by the vestibular end organs
The posterior and superior semicircular canals
ampullae of lateral
maculae of the utricle and saccule
What is another name of the utricle and saccule
Otolith organs
Describe the appearance of the maculae of the otolith organs
Big gel membrane (gelatinous matrix) with crystals (otoconia) imbedded in it - the crystals give weight to the organ so you can perceive gravity
Crystals are pushed and pulled in the gel membrane
How can we tell that movement has stopped
The firing of action potentials will stop
What are otoconia made of
Calcium carbonate crystals
Describe the orientation of otolith organs
360 orientation so all planes of motion can be detected
You can sense angular or linear acceleration
What is the strola
a curvilinear landmark in the middle ear to which the hairs (hair cells) in the macula are oriented.
Describe the paring of the semi-circular canals
Orientated at 90 degrees to each other so paired, equal and opposite
In a semi-circular canal, where does the cupula and ampulla sit
The cupula sits inside the ampulla
What causes deflection in the semi-circular canals
Movement of perilymph
What does bending cause
Stereocilia to deflect
Describe the movement of liquid in the ear as you move your head
As you move your head to the right, the liquid moves and hits off of the left side
The side that you are turning to gets excited and the side you are turning away from has inhibition
What can cause a mismatch of the vestibulo-ocular reflex
Labyrinthitis
tumour
How can we test the vestibulo-coular reflex
Get the patient to put their thumb up out in front of them and focus their eyes on it. Ask them to shake their head from side to side. If the patient is very slow to do this, they may have a failure in the reflex
What is spontaneous nystagmus
Nystagmus is defined as involuntary movement of the eyes. Most frequently it is composed of a mixture of slow and fast movements of the eyes
Why does the abnormal eye movements occur
The eyes are being pushed the way that the brain thinks it is spinning and the eyes will flick back because they want to focus on one part.
What is a vestibular schwannoma and how does it cause imbalance
tumour of the VIII nerve sheath (schwann) cells
Causes imbalance due to slowly progressive loss of function
What does the central connections of the vestibular system have links to
Motor output to eyes
Motor output to the neck back and leg muscles
Vomiting centres
