audio ch. 3 textbook

rostral

toward the head

caudal

toward the tail

ventral

front side of the brain

dorsal

towards the backside of the cns or spinal cord

medial

middle or the inside

lateral

side or outside of the body or brain

peripheral auditory system

outer, middle, inner ear and the auditory nerve that leads from ear to the brainstem within the central auditory nervous system to process sound information and balance.

outer ear - auricle

consists of the pinna, lobe, trachus, helix, concha

function of the auricle

• shape of outer ear helps to collect and amplify sound and to funnel the sound into the external ear canal

• concha increases sound levels up to 10 to 15 db

• the outer ear enhances detection of sounds coming from the direction a listener is facing

localization

the process of determining where a sound is coming from

external ear canal

• made up of 2/3 cartilage and 1/3 bone

• auricle to tympanic membrane

• separates the middle ear area and the outer

cerumen

sebaceous and ceruminous glands

• protects from insects, fungal, and bacteria growth

• cerumen is basically earwax

• too much can block ear canal

middle ear

tympanic membrane

• separated middle ear space and external ear canal

• includes promontory, round and oval window

  • lying on the surface of the promontory is the tympanic nerve plexus, a branch up the eleventh or spinal accessory cranial nerve

• contains ossicles (malleus, incus, stapes) that amplify sound

• connects to the Eustachian tube to equalize pressure

two air filled spaces

aditus ad antrum and epitympanic recess

hypotympanum bone

forms the inferior floor of the middle ear space

pyramidal eminence

hollow structure containing the stapedius muscle that stabilizes the stapes and dampens sound transmission.

eustachian tube

connects the middle ear space to the back of the nose and mouth in the region called the nasopharynx

tympanic membrane

outermost structure of the middle ear system

• reflects a cone of light

• the diameter goes from 0.5 to 1cm

• slightly cone shape

annulus

the outer rim of the tympanic membrane where it connects with the bony wall of the external ear canal

pars flaccid

the most flexible region of tympanic membrane

near the edge in the anerior superior quad

pars tensa

largest and tightest - contributes mostly to hearing

ossicles

malleus incus and stapes - 3 little bones

• wiegh les than 35 mg or 0.001234 ounze

• stapes is lightest bone

function of the middle ear

matching the low impedance of the air in the external ear canal to high impedance of the fluid within the inner ear

inner ear

surrounded by skull bonesand contains the cochlea, semicircular canals, and vestibular system, playing a crucial role in hearing and balance

temporal bone