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The 3 parts of the ear

Inner, outer and middle

The parts of the ear involved with hearing

Outer and middle

Hearing and equillibrium


Receptors for hearing and balance

respond to separate stimuli, are activated independently

Components of the Outer Ear

Auricle (pinna)
External auditory canal
Tympanic Membrane (eardrum)

Auricle is composed of

The helix (rim)
Lobule (earlobe)

External auditory canal

short, curved tube filled with ceruminous glands

This is the thin connective tissue membrane that vibrates in response to sound

Tympanic membrane

Transfers sound energy to the middle ear ossicles

Tympanic membrane

Boundary between outer and middle ears

Tympanic membrane

Small, air filled, mucosa-line cavity

Middle ear

The tympanic cavity (middle ear) is flanked laterally by what?

By the tympanic membrane

The tympanic cavity (middle ear) is flanked medially by what?

Oval and round windows

Pharyngotympanic tube

Connects the middle ear to the nasopharynx

Function of the pharyngotympanic tube

Equalizes pressure in the middle ear cavity with the external air pressure

The 3 bones of the tympanic cavity, lateral to medial.

1) Malleus
2) Incus
3) Stapes

Tensor Tympani is suppled by which nerve


Stapedius supplied by which nerve


Function of the small bones in the tympanic cavity

Transmits vibratory motion of the tympanic membrane to the OVAL window dampened by the tensor tympani and stapedius muscles.

How to remember the 3 bones of the tympanic cavity

Lateral to Medial you never miss NIS

Bony labrynth

part of the inner ear. Tortuous channels worming their way through the temporal bone. Contains the vestibule, the cochlea and the semicircular canals.

What is the bony labrynth filled with?

Filled with PERILYMPH

What is Perilymph very low in

Very low in potassium

Membranous labrinyth

Par of inner ear. Series of membranous sacs within the bony labyrinth.

What is the membranous labyrinth filled with?

Filled with potassium rich fluid ENDOLYMPH


spiral, conical bony chamber

where does the cochlea extend from

extends from the anterior vestibule

What does the cochlea coil around

coils around a bony pillar called the MODIOLUS

Cochlea contains

the cochlear duct, which ends at the cochlear apex.

The Organ of Corti is in what

The cochlea

3 chambers of the cochlea

1) Scala Vestibuli
2) Scala Media (cochlear duct
3)Scala tympani

Which of the 3 chambers of the cochlea contain the hearing receptor?

scala media

Scala tympani terminates at

the round window

Scalas tympani and vestibuli are both filled with


The scala tympani and vestibuli are continuous with eachother via the

the helicotrema

Scala media is filled with


The "floor" of the cochlear duct is composed of

the bony spiral lamina and the basilar membrane which supports the organ of corti

Cochlear branch of which nerve runs from the organ of corti to the brain?


Sound vibrations beat against what membrane

the tympanic membrane

How the tympanic membrane works

Pushes the ossicles, which presses fluids in the inner ear against the oval and round windows

The movement of what sets up shearing forces that pull on mechanosensitive hair cells

tympanic membrane

The route of sound to the inner ear: Outer Ear

Pinnea, external auditory canal, tympanic membrane

The route of sound to the inner ear: Middle ear

Malleus, incus and stapes to the oval window

The route of sound to the inner ear: Inner Ear

Scalas vestibuli and tympani to the cochlear duct.

Mechanically gated ion channels are found where

found where the hair meets the cell

Transmission of sound to the inner ear needs

stimulation of the organ of corti and generation of impulses in the cochlear nerve

Audible sound waves

penetrate through the cochlear duct.
Vibrate the basilar membrane

The audible sound waves excites specific hair cells according to what

According to the FREQUENCY of sound

This is composed of supporting cells and outer and inner hair cells

The Organ of Corti

In the organ of corti, afferent fibers of the cochlear nerve attach

to the base of hair cells

In the organ of corti, the stereocilia (hairs) touch

the tectorial membrane


during the bending of stereocilia, when it opens MECHANICALLY GATED ion channels found where the stereocilia meet the hair cell.

Bending stereocilia causes

causes a graded potential and the release of a neurotransmitter: termed Mechanotransduction

The neurotransmitter released by mechanotransduction causes

cochlear fibers to transmit impulses to the brain, where sound is perceived

Impulses from the cochlea pass via the spiral ganglion to

the cochlear nuclei

Impulses from the cochlear nuclei are sent

to the superior olivary nucleus.
Inferior colliculus (auditory reflex center)

Pitch is perceived by

The primary auditory cortex
cochlear nuclei

Loudness is perceived by

Varying thresholds of cochlear cells
the number of cells stimulated

4 types of deafness

1) conduction deafness
2) Sensorineural deafness
3) Tinnitus
4) Meniere's syndrome

Conduction deafness

something hampers sound conduction to the fluids of the inner ear (e.g., impacted earwax, perforated eardrum, osteosclerosis of the ossicles)

Sensorineural Deafness

More common. Results from damage to the neural structures at any point from the cochlear hair cells to the auditory cortical cells


Ringing or clicking sound in the ears in the absence of auditory stimuli

Meniere's Syndrome

Labyrinth disorder that affects the cochlea and the semicircular canals, causing vertigo, nausea and vomiting. Also Progressive hearing loss.

2 parts of a balance vestibule

1) saccule
2) utricle

The saccule and the utricle each contain

each contain a macula (sensory receptor)

Vestibular receptors monitor

static equillibrium

Vestibular receptors respond to

gravity and changes in the position of the head

What is the maculae

The sensory receptors for static equillibrium

Maculae contain

contain supporting cells and hair cells

Each hair cell of the maculae has

has stereocilia and kinocilium embedded in the otolithic membrane

Otholithic Membrane

Jellylike mass studded with tinny CaCO3 stones called Otoliths

Utricular hairs respond to

horizontal movement

Saccular hairs respond to

vertical movement

Otolithic movement in the direction of kinocilia:

depolarizes vestibular nerve fibers
increases the number of action potentials generated

Otolithic movement in the opposite direction:

Hyperpolarizes vestibular nerve fibers
Reduces the rate of impulse propagation

DO the vestibular neurons have a constant signal?


Stereocilia move TOWARDS the kinocilium and what happens

and the signal increases in frequency (depolarization) compared to the normal tonic level

Stereocilia move AWAY from the kinocilium and what happens

and the signal decreases in frequency (hyperpolarization) compared to the normal tonic level.

Semiciruclar canals

cover three planes of space (x,y,z)


Single swollen end of each canal in the semicircular canals

Where is the crista ampullaris (equilibrium receptors)?

In the ampulla

Semicircular canal receptors respond to what

angular movements of the head (Dynamic Equillibrium)

Each crista contains what

Has support cells and hair cells that extend into a gel-like mass called the cupula

Vestibular nerve fibers innervate what

innervate hair cells

Cristae respond to changes in what

changes in velocity of rotatory movements of the head

Directional bending of hair cells in the cristae causes:

1) depolarizations, and rapid impulses reach the brain at a faster rate
2) Hyperpolarizations and fewer impulses reach the brain.

What is the result of the directional bending of hair cells in the cristae

result is that the brain is informed of rotational movements of the head

Horizontal control

Depolarization occurs in the SAME direction as the head movement. (Left head turn produces depolarization in the LEFT horizontal canal)

Anterior and Posterior Canals

Depolarization occurs in the OPPOSITE direction as the head movement (FORWARD head tilt produces depolarization of the POSTERIOR canals)

Components of the Vestibule

Saccule and Urticle

Receptor of the Vestibule


Dampening element of the Vestibule

Otolithic membrane

Modality of the Vestibule

Static equilibrium

Components of the Semicircular canals

Anterior canal
Horizontal (lateral) canal
Posterior canal

Receptor of the semicurcular canals

crista ampullaris

Dampening element of the semicurcular canals


Modality of the semicurcular canals

Dynamic equilibrium

Push-Pull system

When both Ampulla are working together


One side excited and the other inhibited

Visual-Vestibular Conflict

Ordinarily the head movement implied by the visual and vestibular signals are equal but there can be conflict resulting in a) motion sickness b) vertigo

Motion sickness

Nausea and vomiting. Occurs when the visual and vestibular signals are unequal


A perception of head motion when the head is still. Part of motion sickness

Benign Paroxysmal Positional Vertigo (BPPV)

One of the most common causes of vertigo. Otoliths from the utricle dislodge and float into the posterior canal, causing interference with cupula function.

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