9.4 Anatomy and Physiology of the Ear Flashcards
What is sound and what are the two aspects of sound?
A longitudinal wave of pressure variations in a medium made of pressure and displacement
What is the formula for sound power?
Pressure x particle velocity
What is the loudest possible sound?
194 dB
What is the outer ear composed of?
pinna to the tympanic membrane (ear drum)
What is the middle ear composed of?
3 ossicles: malleus, incus and stapes in air space
Vented by the eustachian tube
What is the inner composed of?
The cochlear and the semi circular canals
What does the eardrum and middle ear move in relation to?
The ear drum moves in relation to pressure of the soundwaves (much motion, little force) where as the middle ear has an increase in force (little motion, much force)
When the force increases the pressure is released on the oval window which lies at the foot of the stapes
What are the muscles in the ear, what is their innervation and what is their role?
Stapedius: VII
Tensor tympani: V3
These muscles act to protect the cochlear - the stapedius pulls on TT and this will contract the eardrum pushing the stapes into the fluid increasing the pressure in the ear
What is the organ of Corti and how does it work?
It is the sensory surface of the ear on the cochlear - composed of 3 layers of outer hair cells and one layer of inner hair cells
Which cells can amplify sound in the cochlear?
Outer hair cells
What is the general flow of sound into the ear?
Sound comes in - vibrate tympanic membrane - - vibrate ossicles - oval window moves - round window moves - displacement of cochlear fluid - hair cells sense this movement - release of glutamate - electrical signal through vestibulocochlear nerve
What part of the basilar membrane is tuned to what?
Base = high frequencies (near cochlear) Apex = low frequencies
What is the traveling wave theory?
Waves of a given frequency cause greatest movement of the basilar membrane at a particular spot
How do vibrations get converted into a neural signal?
Bending of the sterocilia depolarises - sound-vibration induced MET channel opening causes K entry - depolarisation - voltage depedent Ca channels open in inner hair membrane - calcium causes glutamate release - Activates AMPA receptors - depolarisation and AP of spiral ganglion cell - AP carried by vestibulocochlear nerve to brain
What are otoacoustic emissions?
A sound which is generated from the inner ear mostly below the threshold of hearing - sign of active process of the cochlear
OAEs are considered to be related to the amplification function of the cochlea. In the absence of external stimulation, the activity of the cochlear amplifier increases, leading to the production of sound
