Exam #3 Ch 8 Auditory System; Inner Ear

MIDDLE EAR FUNCTION #1; TRANSFORMER

overcomes impedance mismatch by increasing sound pressure so that more will be admitted into the liquid of the cochlea

Middle ear Transformer level 1

30 dB increase; in the middle ear

Middle ear Transformer level 2

25 dB increase; area difference (eardrum vs. oval window)

Middle ear Transformer level 3

5 dB increase; lever principle of the ossicles

MIDDLE EAR FUNCTION #2; ATTENUATE LOUD SOUND

Acoustic reflex happens when a loud sound hits the middle ear/Stapedious muscle contracts in response to high sound pressure

MIDDLE EAR FUNCTION #3; EQUALIZE AIR PRESSURE

Maintain relatively equal air pressure on either eardrum side despite atmospheric pressure changes by Eustachian tube action/ Pressure difference leads to discomfort; ex) Swallowing, Yawning, Chewing

What are the inner ear anatomy

perilymph, cochlear duct, endolymph, vestibular system, cochlea

Inner ear

the vibrations are again transformed from mechanical vibrations to hydraulic vibrations in the fluid-filled organ of the cochlea

Perilymph

Fluid between the bony and membranous canals, snail shape

Perilymph function

transmits vibrations for both hearing and balance

cochlear duct

Located inside the bony canal/membranous canal often referred to as the cochlear partition. base of duct is basilar membrane (BM)

Cochlear duct function

contains the sensory receptor for hearing

Endolymph

Fluid within the membranous canal

Endolymph function

rich in potassium and low in sodium, which is crucial for transmitting sensory information for hearing and balance

vestibular system function

maintain balance, spatial orientation, stable visual gaze; sensing head movements/position relative to gravity/ done by detecting changes in fluid + motion in inner ear/sending signals to brain( crucial for coordinating eye movements/controlling posture)

COCHLEA

oval window, connective tissue membrane located at end of middle ear/inner ear beginning

INNER EAR anatomy

COCHLEA & VESTIBULAR ORGAN

TONOTOPIC ORGANIZATION

arrangement of frequency sensitivity according to place(Low frequency, High frequency), maintained throughout the auditory system.

Low frequency tonotopic organization

apex

High frequency tonotopic organization

base

The peak displacement of the traveling wave will also depend on

the intensity of the signal.

Signals of greater amplitude produce

larger basilar membrane displacement.

A low-frequency signal of high intensity significantly affects

high-frequency (basal) end; accounts for upward spread of masking phenomenon

Upward spread of masking

low frequencies are able to mask, or interfere with, the perception of higher frequencies.

INNER EAR

COCHLEA; Perilymph, Endolymph

FROM THE EAR TO THE BRAIN

Primary auditory cortex/Medial geniculate/Inferior colliculus/Superior olive/Cochlear nucleus

Primary auditory cortex: region in temporal lobe responsible for initial processing of auditory information; pitch, volume, sound locations

Medial geniculate

part of the thalamus that relays auditory information from the inferior colliculus to the primary auditory cortex

Inferior colliculus

sound localization, auditory reflexes, and processing complex auditory information like pitch and rhythm

Superior olive

group of nuclei in brainstem, collectively calledthe superior olivary complex (SOC); crucial for auditory system

Cochlear nucleus

first central auditory structure in brainstem that receives all auditory information from cochlea via auditory nerve