1.4: Physiology of Hearing and Balance Flashcards
Give an overview of function of the three parts of the ear?
External = Sound collection
Middle = Mechanical force amplifier
Inner = Sound transducer and analyser
Describe sound?
What dictates pitch?
What dictates intensity (loudness)?
Sound is pressure wave caused by ossicating molecules
The frequency dictates pitch (high or low sound)
Amplitdue dictates intensity (loudness)
What frequency can humas percieve?
20-20,000 HZ
Describe briefly how the middle ear works an amplifier?
Due to ossicles
Ossicles work as a chain
Tympanic membrane vibrates and these vibrations pass through the ossicles to the oval window
Describe impendance matching?
The ratio of pressure in the tympanic membrane:oval window is about 18:1
This ensures the vibrations from air are concentrated enough to travel through fluid
What is the function of the Eustachian tube?
A ventilated pathway for middle ear mucosa
Held open by the tensor veli palantini and the levator palatine muscles
It’s function is to equalise the ears and dysfunction leads to middle ear negative pressure
Describe the oval window and the round window?
These are two openings of the cochlea to the middle ear
They allow the transmission of the pressure wave in enclosed canal and vibration of the basilar membrane
Describe the inner ear?
This is a curved spiral lamina
There is 2 and 1/2 turns around the central modiolus
Describe the cochlear structure?
There is a scala tympanic and scala vestibuli both filled with perilymph
Suspended between these two is the scala media which contains endolymph
Describe the organ of corti?
Found in the cochlea in the scala media
This contains the sensory cells - innner and outer hair cells
The inner cells are involved in recieving sound
Describe how the hair cells recieve sound?
A wave of liquid rushes over the hair cells, causing them to bend - this is called transduction
The bending of the hair cells generates action potentials
How does the brain determine the frequency of sound?
The hair cells bend and cause an action potential when a wave of liquid passes over them
The brain detects the frequency of sound depending which areas of the cochlea the action potential came from
Apex = Low
Base = High
Describe what happens once the inner hair cells produce action potentials?
How do you remember the central pathway?
Which specific part of the brain does the impulses go to?
These action potentials stimulate the 8th cranial nerve (vestibulocochlear) and then initiates central pathways
Central Pathway = E.COLI (from ear to brain)
Primary Audiotory Cortex (Superotemporal)
Describe the structure of the inner ear?
The inner ear is complex structure called the labrinyth - there is the bony labrinyth and the membranous labrinyth
There is 3 semicircular canals and the cochlea
Describe the otolith organs?
Utricle and Saccule
They have cilia projecting into a jelly like matrix - when the head moves, these fibres bend and percieve movement
There are sterocilia projecting in all directions so all planes of movement can be detected