Anatomy of Ear and additional information

outer/external ear

consists of a pinna/auricle and the external auditory canal (EAC) and ends with the tympanic membrane (TM).

middle ear

"chamber" that hosts the ossicles (malleus, incus, and stapes)

tiny, air-filled cavity inside the temporal bone

inner ear

consists of the cochlea and the semicircular canals

outer ear functions

collects mechanical sound waves and directs them to the TM. It also protects the ear by using wax and hair to trap debris and microorganisms from entering deeper structures

middle ear function

amplifies sound waves via the ossicles and transmits them to the inner ear. It regulates pressure via the Eustachian tube, ensuring equal air pressure on both sides of the TM for optimal sound transmission

inner ear function

converts mechanical sound energy into electrical signals in the cochlea, sends them to the brain for interpretation (hearing), and manages balance (semicircular canals)

pinna

movable cartilage covered by the skin, giving the ears a unique shape and size

helix

prominent curved outer ridge

antihelix

Parallel to it is another curved prominence

tragus

On the opposite side, a small, cartilaginous projection, partially covers the ear canal

earlobe (lobule)

Inferiorly is the fleshy projection

external auditory canal (EAC) is

short (~2.5 cm)

slightly curved tunnel that connects the visible ear opening (external acoustic meatus) to the tympanic membrane (eardrum) and serves as the passageway for sound waves

outer (lateral) 1/3 of EAC

encased with cartilage and covered with skin, hair, sebaceous, and ceruminous glands that produce cerumen (earwax)

how does cerumen migrate out of the EAC?

jaw movement (chewing, talking)

cerumen protects the EAC

Its sticky quality helps trap debris.

Its acidic pH inhibits bacterial and fungal growth.

Its hydrophobic quality helps repel water.

inner (medial) 2/3 of EAC

surrounded by the temporal bone and lined by thin, hairless skin (more sensitive and prone to injury and infection)

isthmus

narrowest part of the canal where the cartilaginous (outer) and bony (inner) portions of the EAC join

normal flora of EAC is dominated by ___ (bacteria present but less common)

S. auricularis, S. Epidermis

tympanic membrane (TM)

eardrum, separates the outer ear from the middle ear

how does the Tympanic Membrane (TM) appear?

translucent, pearly gray membrane that normally appears slightly concave.

cone of light

On otoscopic examination, a healthy TM reflects light in the anteroinferior quadrant

pars flaccida

small, superior section of the TM

pars tensa

larger, inferior section

annulus

outer fibrous rim anchoring the TM to the surrounding bone

umbo

malleus is partly visible through the TM, pulling the center inward at a depression

middle ear contains

auditory ossicles or ossicular chain (malleus, incus, stapes)

middle ear connects to external ear via ___, inner ear via ____, and nasopharynx via ___

TM, oval and round windows, Eustachian tube

inner ear is located w/in temporal bone in a structure known as

bony labyrinth

bony labyrinth is rigid, protective casing made of bone, filled with

perilymph

Suspended within the perilymph is the __, filled with endolymph, which contains the sensory organs:

1. __

2. __

3. __

membranous labyrinth

1. cochlea

2. vestibule

3. semicircular canals

cochlea

snail-shaped, fluid-filled structure that is responsible for hearing. It converts sound vibrations into electrical signals that are sent to the brain via the cochlear nerve

vestibule

located in the center of the bony labyrinth and contains two small chambers, the utricle and saccule, which are involved in sensing linear acceleration and head position

semicircular canals

are 3 fluid-filled canals arranged at right angles to each other and are responsible for detecting rotational movements of the head

inner ear is filled with

fluid

perilymph

fills the space between the bony labyrinth and the membranous labyrinth and provides cushion and support for the delicate membranous labyrinth. It is rich in Na (low in K)

endolymph

fills the membranous labyrinth. It is rich in K (low in Na), which is critical for hair cell depolarization and signal transmission

are the perilymph and endolymph part of the lymphatic system?

no

mechanism of hearing involves 3 main levels

1. peripheral (ear)

2. brainstem

3. cerebral cortex

what happens when sound (mechanical waves) enter the EAC?

vibrate the TM

TM vibrations are amplified by ___ and transmitted to the __ of the cochlea

ossicles (malleus, incus, and stapes), oval window

TM vibrations transmitted to the oval window of the cochlea generates ___ w/in the cochlea, stimulating ___ in the ___

fluid waves, hair cells, organ of Corti

hair cells in the organ of Corti convert mechanical vibrations into __ (action potentials) and send them via the __ to the cochlear nuclei in the brainstem

electrical signals, cochlear nerve (branch of vestibulocochlear CN VIII)

specialized brainstem nuclei compare input from

both ears, assess intensity and timing differences, and determine sound localization

from the brainstem, signals reach the thalamus and then the

primary auditory cortex

auditory cortex assigns ___ to sound (e.g., speech, music, alerts) and integrates it into context for an appropriate __ or __ response

meaning, motor, emotional

air conduction (AC)

primary and most efficient pathway

mechanism of air conduction (AC)

normal mechanism ,

external ear → brainstem → auditory cortex

bone conduction (BC)

pathway bypasses the external and middle ear

mechanism of bone conduction (BC)

vibrations of the skull bones stimulate the cochlea directly.

some types of hearing aids uses ___ pathway

bone conduction

1 multiple choice option

sound frequency

pitch (high or low)

sound amplitude

how loud it is

vestibular system

provides the brain with information about motion, balance, and spatial orientation of the body

2 parts of the vestibular system

1. peripheral vestibular system

2. central vestibular system

peripheral vestibular system

located in the inner ear

central vestibular system

located in brainstem and cerebellum

together peripheral and central vestibular systems allow us to maintain

equilibrium and coordinate movement

the peripheral vestibular system is houses within the ___ of the temporal bone and contains___

bony labyrinth, 5 sensory end organs (2 otolith organs and 3 semicircular canals)

otolith organs detect

linear acceleration and gravity

otolith organ: utricle

horizontal movement (e.g., forward/backward)

1 multiple choice option

otolith organ: saccule

vertical movement (e.g., up/down)

1 multiple choice option

otoconia (otoliths)

otolith organs contain contain specialized hair cells embedded in a gelatinous matrix topped with tiny calcium carbonate crystals

what happens when the head tilts or accelerates?

heavy otoconia shift, bending the matrix and hair cells and generating nerve impulses that travel via the vestibular branch of cranial nerve VIII to the brain.

each semicircular canal contains an ___(swelling at its base), which houses the ___, a ridge of hair cells embedded in a gelatinous structure called

ampulla, crista ampullaris, cupula

what happens in the semicircular canals when he head rotates?

endolymph within the canal lags behind, displacing the cupula and bending the hair cells

also generates signals transmitted by CN VIII to the brain..

in the central vestibular system, signals from the vestibular organs travel to the __ and then the ___

vestibular nuclei of the brainstem, cerebellum

dysfunction of the vestibular system can lead to

conflicting sensory signals, producing dizziness, disorientation, and imbalance

can you train vestibular system?

yes, excercises may help retrain the system, improve input accuracy, and restore stability

the peripheral system ____, while the central system ___

detects motion and position, integrates this input with vision proprioception

2 main division of Vestibulocochlear N (CN VIII)

cochlear: sends information about sound (hearing)

vestibular: sends information about balance, motion, and spatial orientation

together vestibulocochlear nerve provides the brain with a

bilateral picture of auditory and vestibular input

otalgia

ear pain

otorrhea

ear discharge (may be serous, purulent, or bloody)

pruritus

itching sensation in the ear canal

aural fullness/pressure

sensation of blockage or increased pressure in ear

tinnitus

perception of ringing, buzzing, or other phantom noises

autophony

abnormally loud hearing of one's own voice or internal sounds

vertigo

sensation of spinning or movement

disequilibrium

general imbalance without spinning sensation

nystagmus

involuntary rhythmic eye movement, often associated with vestibular dysfunction

otorrhagia

bleeding from ear

photophobia

fear or intolerance of sound

presbycusis

age -releated sensorineural hearing loss

hyperacusis

increased sensitivity to sound

pneumatic otoscope

special otoscope that assesses TM mobility

has special attachment (rubber bulb w a tube) connected to head of otoscope

when pneumatic bulb is squeezed, a small puff of air is delivered to EAC, if the TM moves away then

healthy TM

when pneumatic bulb is squeezed, a small puff of air is delivered to EAC, if the TM movement is reduced or absent

middle ear pathology (e.g., effusion, scarring, perforation)

whispered voice test results

Have the patient occlude one ear. Stand 1-2 feet behind the patient on the side of the unoccluded ear.

Whisper 3 random numbers and letters (e.g., "4-K-2") and ask the patient to repeat what was heard (repeat on the other side).

pt repeats all 3 words correctly = normal hearing

pt repeats only 1 or 2 words correctly =possible hearing impairment

weber test

helps determine sound lateralization (which ear hears better) and differentiate between sensorineural and conductive hearing loss

weber test interpretation

sound is louder in affected ear = conductive hearing loss

sound is louder in unaffected ear - sensorineural hearing loss

Rinne test

does not assess lateralization but helps differentiate sensorineural vs conductive hearing loss

Rinne Test interpretation

normal = AC>BC

conductive = BC > AC (negative)

sensorineural = AC > BC (positive)

audiometry

noninvasive test for assessing hearing thresholds

pure-tone audiometry

gold standard test that helps to determine the type and degree of hearing loss

tympanometry

evaluates middle ear function by measuring TM movement in response to pressure changes and helps detect conductive pathology (e.g., effusion, TM perforation)

Otoacoustic Emissions (OAE)

assesses hair cell function in the cochlea. Commonly used in newborn hearing screening

Auditory Brainstem Response (ABR)

measures the electrical activity of the auditory nerve and brainstem in response to sound. Used in infants, non-verbal patients, or to assess for retrocochlear pathology (e.g., acoustic neuroma).

cerumen (earwax)

mixture of desquamated epithelial cells, hair, and secretions from sebaceous and ceruminous glands of the EAC

functions of cerumen (earwax)

1. Protective barrier (traps dust, debris, and microorganisms).

2. Lubricates the ear canal.

3. Acidic and antimicrobial properties help prevent infection

wet cerumen (honey-brown and sticky)

more common in Caucasian and African populations