AuD 6400 week 2 anatomy of the ear

anatomy

structure

physiology

function

anterior (ventral)

toward the front

posterior (dorsal)

toward the rear

superior (cranial)

higher

inferior (caudal)

lower

medial

toward the midline of the body

lateral

away from the midline of the body

proximal

closer to the point of attachment with the torso

distal

farther from the point of attachment with the torso

coronal (frontal) plane

divides the body into anterior (front) and posterior (back) portions

sagittal (lateral) plane

divides the body into right and left portions

midsagittal

divides the body into right and left portions at the midline of the body

parasagittal

parallel to the sagittal plane but not at the midline of the body

transverse (axial) plane

divides the body into superior (upper) and inferior (lower) portions

lateral

away from the midline/toward the side

ipsilateral

same side

contralateral

opposite side

unilateral

one side

bilateral

both sides

binaural

refers to both ears

ecto

external/outer

meso

middle

endo

internal/linear

supra

above

para

beside, near, abnormal

sub

below

anti

against/counteracting

central nervous system

the brain and spinal cord

peripheral nervous system

nerves outside the brain and spinal cord

two major divisions of the auditory system

peripheral mechanism & central mechanism

peripheral mechanism of the auditory system

outer ear, middle ear, inner ear, VIII cranial nerve (vestibulocochlear nerve)

central mechanism of the auditory system

brainstem & brain

efferent

exiting away from the brain - conduction of the descending nervous system tracts from central to peripheral

afferent

ascend toward the brain - conduction of the ascending nervous system tracts from peripheral to central

outer ear

auricle/pinna and external auditory meatus

crus (plural - crura)

an elongated portion of an anatomical structure

fossa

anatomical groove or depression

low air pressure

at the ear canal’s open end

high air pressure

at the end of the ear canal/at the eardrum

2.5 cm

average length of ear canal

temporal bone

houses the outer, middle, and inner ear; part of the skull base

external auditory meatus

ear canal

meatus

canal in a bone

skull base

bottom of the skull, contains intricate canals through which important structures course like the spinal cord, nerves, & blood vessels

4 main segments of the temporal bone

squamous, mastoid, petrous, tympanic

scutum

sharp bone formation where the external auditory canal and lateral wall of the tympanic cavity meet - where the tympanic membrane is attached

process

a projection from a larger anatomical body

mastoid process

projection of the temporal bone behind the ear; posterior and inferior to the external auditory canal

meatus

an anatomical channel/passage - external auditory canal opening

lumen

the space inside of a tubular anatomical structure

isthmus

a narrow cavity connecting two larger parts of a structure in the body - in the ear canal it’s in between the first and second bend

lateral 1/3 of the ear canal

cartilagnious portion

medial 2/3 of the ear canal

bony/osseous portion

first bend of the ear canal

between the lateral 1/3 and medial 2/3

second bend of the ear canal

about 5mm away from the tympanic membrane

about 0.6 cm

average ear canal diameter

why should you perform otoscopy before performing a hearing evaluation?

to ensure the canal is not blocked with wax or foreign bodies; to look for abnormalities in the ear canal/ear drum; and to look for possible infections

epithelium

skin tissue; covers cartilaginous and bony portions of the external auditory canal; hairs on surface; cerumen production

two types of cells that contribute to the production of cerumen

sebaceous cells & ceruminous glands

cerumen

ear wax; lubricating properties; slight antimicrobial/antifungal properties; insect repellent

epithelial migration

lateral self-cleaning/repair mechanism which moves dead skin cells, cerumen, and/or other debris away from the tympanic membrane and eventually out of the ear canal

Arnold’s nerve

associated with the cough reflex; inferior branch of cranial nerve X, joined by fibers from facial nerve

middle ear - tympanic cavity

consists of the tympanic membrane, ossicles, and the tensor tympani muscle & stapedius muscle

tympanic membrane (TM)

thin membranous tissue that separates the external auditory meatus from the middle ear space; forms the major portion of the lateral wall of the middle ear cavity; made up of 3 layers

lamina

plate or layer of tissue or bone

pars tensa

main larger portion of the TM; stiffer portion; organized radial and transverse fibers

pars flaccida/Shrapnel’s membrane

smaller, thicker portion of the TM; unorganized, loose connective tissues/fibers; located on the superior portion of the TM above the manubrium (handle) of the malleus

annulus tympanicus

fibrocartilaginous ring surrounding the tympanic membrane

umbo

projected end/center of the TM, tip of the manubrium of the malleus situated here

cone of light

cone-shaped reflection of light; anterior inferior quadrant of the tympanic membrane: 5 o’clock in the right ear & 7 o’clock in the left ear

three auditory ossicles

malleus (hammer), incus (anvil), stapes (stirrup)

admittance

the ease with which energy will flow through a vibrating system

impedance

the resistance of the system to the energy flowing through it

ossicular chain

links the tympanic membrane to the oval window; amplifies sound via impedance matching

ossicular ligaments

along with middle ear muscles, they support the positioning of the ossicles within the middle ear space

synovial joint

surfaces at the joint are covered with smooth cartilage that allows bones to move smoothly; most common type of joint in the human body; located in between all 3 ossicles

stapedius muscle

smallest striated muscle in the body; attached to the head of the stapes; innervated by the facial nerve (cranial nerve VII); when contracting it pulls on the stapes

tensor tympani

middle ear muscle that is attached to the manubrium of the malleus; extends between the malleus & the wall of the middle ear cavity; innervated by the trigeminal nerve (cranial nerve V); when contracting, it pulls the manubrium of the malleus inward and stretches the TM

acoustic/stapedial reflex

a reflexive contraction of the stapedial (dominant muscle) and tensor tympani muscles; theorized purpose is to protect the ear from loud sounds; tensor tympani pulls on the handle of the malleus, stapedial muscle pulls stapes outward, and these opposing actions stiffen the ossicular chain and attenuate the sound (increased impedance)

chorda tympani

branch of the facial nerve that arises from the mastoid segment of the facial nerve and passes through the middle ear cavity; conveys taste sensation from the anterior two-thirds of the tongue; carries fibers to the sublingual and submandibular salivary glands

canaliculus

a small duct or channel

eustachian tube

passageway leading from the nasopharynx to the anterior wall of the middle ear; usually closed but it opens to equalize pressure in the middle ear space and drain middle ear serous mucosal secretions during swallowing, yawning, & the Valsalva maneuver

middle ear serum (adjective: serous)

thin, clear mucosal fluid that moistens and protects the middle ear

cilia

microscopic hairlike structures in various parts of the body

tympanic membrane retraction

the eardrum does not maintain its neutral position and retracts into the middle ear space due to negative pressure, usually caused by eustachian tube dysfunction

Valsalva maneuver

done by keeping the mouth closed and gently blowing air through/toward the plugged nose

adenoids

lymphatic tissue located in the nasopharynx that helps protect the body from viruses/bacteria

promontory

the bony protrusion formed by the first (basal) turn of the cochlea; situated between the oval and round windows & serves as the wall of the basal turn of the cochlea

oval window

connection point of the middle ear to the inner ear; attached to the footplate of the stapes & leads to the scala vestibuli; sound vibrations transferred from stapes to perilymphatic fluid in the cochlea which result in the traveling wave on the basilar membrane

round window

on the wall of the labyrinth in the middle ear within the mesotympanum; leads to scala tympani; covered by membrane

mastoid air cells

air-filled spaces found within the mastoid process

theorized purposes of mastoid air cells

air flow to the middle ear; decrease weight of the skull; resonance during phonation

modiolus

center core (axis) of the cochlea; made of spongy bone around which the cochlear ducts are wrapped; houses nerve fibers & vascular structures

cochlea

composed of 3 fluid-filled membranous channels wrapped around the modiolus; contains neural components that respond to sound vibrations; approx. 2.3 turns, 31.-3.3 cm long uncoiled, completely enclosed in temporal bone

two labyrinths

bony & membranous; within the cochlea

bony/osseous labyrinth

aka otic capsule; channels within the petrous portion of the temporal bone

membranous labyrinth

made of soft tissue channels, filled with fluid, contain auditory and vestibular end organs

3 cochlear ducts

scala vestibuli, scala media (cochlear duct), scala tympani

scala vestibuli & scala tympani have this in common

filled with perilymph