Auditory & Vestibular System

audition

sense of hearing

vestibular system

regulates balance; personal, internalized; without conscious effort

sounds

audible variations in air pressure

frequency

number of compressed or rarefied patches of air that pass by ears each second; measured in Hertz

intensity

difference in pressure b/t compressed and rarefied patches of air; how loud a sound is

pinna

funnel of the ear

auditory canal/external acoustic meatus

entrance to internal ear

ossicles

smallest bones in the body; transfer movements of tympanic membrane into movements of oval window

cochlea

behind oval window, fluid filled, contains apparatus for neural transduction

outer ear

structures from pinna to tympanic membrane

middle ear

tympanic membrane and ossicles

inner ear

oval window to cochlea

malleus

ossicle attached to tympanic membrane, has a rigid connection with incus

incus

bridge between malleus and stapes

stapes

joins with oval window and moves in and out of the window

eustachian tube

joins air from middle ear with the nasal cavities

attenuation reflex

• neural response in onset of a loud sound causes middle ear muscles to contract

• protection function

• delayed

• makes high frequency sounds easier to discern in an environment with a lot of low frequency noise

• can understand speech more easily in noisy environments

tensor tympani

anchored to bone in middle ear and attaches to malleus

stapedius muscle

anchored to bone and attaches to stapes

cochlea

spiral shaped organ of hearing, size of a pea, has 2 membrane covered holes (oval & round window) and 3 fluid filled chambers (scala vestibuli, scala media, scala tympani)

organ of corti

contains auditory receptor neurons

tectorial membrane

hangs over the organ of corti

helicotrema

hole in membranes where scala tympani and scala vestibuli are

perilymph

fluid in scala vestibuli and scala tympani; ionic content is similar to CSF

endolymph

high ionic charged ECF in scala media

basilar membrane

• flexible and bends in response to sound

• wider at the apex than the base

• stiffness decreases from base to apex

• tonotopic map

inner hair cells

form a single row in the organ of corti, help transmit mechanical movements to electrical impulses to the brain

outer hair cells

form 3 rows in the organ of cotri, help transmit mechanical movements to electrical impulses to the brain; cochlear amplifiers

inner

most spiral ganglion neurons communicate with _______ hair cells

isofrequency bands

strips of neurons that have similar characteristic frequencies that run along the primary auditory cortex

bilateral

all auditory processing centers/nuclei (except for the cochlear nucleus) receive ______ input

otolith organs

detect the force of gravity, linear acceleration, and changes of the head angle

saccule and utricle

what are the 2 otolith organs?

macula

sensory epithelium, vertically oriented in the saccule, and horizontally oriented within the utricle when the head is upright; contains hair cells and cilia project into the gelatinous cap

vertically

how is the macula oriented in the saccule?

horizontally

how is the macula oriented in the utricle?

otoliths

crystals of calcium carbonate, encrust surface of macula’s gelatinous cap, near the tips of hair bundles, and are key to tilt sensitivity of macula

semicircular canals

sensitive to head rotation; 3 arcing structures of labyrinth and lie in orthogonal planes

angular acceleration

generated by sudden rotational movements and is the primary stimulus for the semicircular canals

ampulla

bulge along canal where hair cells are clustered

cupula

gelatinous area that cilia of hair cells project into

endolymph

fluid in the semicircular canals

vestibular/Scarpa’s ganglion

where cell bodies of the vestibular nerve axons live

vestibulo-ocular reflex

keeps eyes pointed in a particular direction even with head movement