the ear I

auditory system

sense of hearing, audition, by the cochlear division

detect sound, perceive and interpret nuances

the vestibular system

sense of balance, head and body location, head and body movements

frequency

rate of air pressure change

external ear

pinna and associated structures

auditory in nature

middle ear

tympanic membrane, ossicular chain, round window and oval window

auditory in nature

inner ear

cochlea

includes vestibular and auditory functions

conductive hearing loss

blockage of external ear canal, perforation or rupture of tympanic membrane, middle ear infection

attenuation reflex

response where onset of loud sound causes tensor tympani and stapedius muscle contraction

adapt ear to loud sounds, understand speech better

bony labyrinth

structure in inner ear

system of bony tubes

membranous labyrinth

structure in the inner ear

membranous tube suspended within the bony labyrinth

perilymph

fluid inside bony labyrinth

similar to the cerebrospinal fluid (high sodium and low potassium)

endolymph

fluid located within the membranous labyrinth

similar to the intracellular fluid (high potassium)

basilar membrane

runs the length of the coiled tube of the cochlea

organ of corti

sensory receptor organ lying on the basilar membrane that is composed of hair cells and support structures

semicircular ducts

endolymph flows from here into utricle

utricle

endolymph flows from the semicircular ducts into here

cochlear duct

endolymph flows from here into the saccule

saccule

endolymph flows from the cochlear duct into here

meniere’s disease

defective circulation or absorption of endolymph

swelling of membranous labyrinth

transient attacks of vertigo, nausea, hearing loss, ringing in the ears

inner hair cells

a single row near the edge of the osseous spiral lamina

total about 3500 cells / per ear

outer hair cells

3-5 cells wide, directly above the basilar membrane

total about 15000 cells / per ear

hair cells

specialized microvilli in one end and the other end form synapses onto cranial nerve VIII

hair cell microvilli

multiple stereocilia + 1 single kinocilium

intensity

is coded by the action potential firing rate of VIII nerve fibers and the numbers of the nerve fibers

frequency

indicated by the particular part of the organ of Corti that is most active

location

depends on a comparison of sounds reaching the 2 ears and the CNS

prestin

required for outer hair cell movement

hyperacusia

increased activity in the tensor tympani muscle that is part of the “startle response” to some sounds

lowered reflex threshold is is activated by the perception / anticipation of loud sound

also called tonic tensor tympani syndrome

otoacoustic emissions

vibrating tympanic membrane would behave like a tiny loud speaker producing sound

after a brief sound stimulus, a sensitive microphone in the external auditory canal can detect faint sounds emitted by the ear itself

useful for testing the hearing of infants

air conduction

requires normal function of the outer, middle, and inner ears

tested by using an earphone

bone conduction

involves direct transmission of vibrations from the skull to the fluids of the inner ear, by passing the outer and middle ears

tested by using a vibrator applied to the mastoid process

conductive hearing loss

someone who hears normally by bone conduction but not by air conduction

neural part of the auditory system is intact

sensorineural hearing loss

someone who has hearing loss in both air and bone conduction

peripheral mechanism

interaural time delay and interaural intensity difference

central mechanism

each superior olivary nucleus receives inputs from both cochlear nuclei

sensitivity of binaural neurons in the superior olivary nucleus to sound location

time differences of the neuronal signals reach to the superior olivary nucleus

primary auditory cortex

axons leaving the MGN project to here

structure is similar to corresponding visual cortex areas