Special Senses: the Ear

function of the outer ear

funnels vibrations to the tympanic membrane (eardrum)

components of the outer ear

• auricle (pinna)

• external auditory canal

auricle (pinna)

shell-shaped structure formed by elastic cartilage that funnels vibrations to the external auditory canal

external auditory canal

passage leading from the auricle, through the temporal bone, to the tympanic membrane

location of the middle ear

tympanic cavity

components of the middle ear

• tympanic membrane

• pharyngotympanic (auditory) tube

• auditory ossicles

• muscles: tympanic reflex (stapedius and tensor tympani)

tympanic membrane

“ear drum” that separates the external auditory canal from the tympanic cavity; transfers vibrations to the auditory ossicle

pharyngotympanic (auditory) tube

passageway to the nasopharynx and functions to equalize pressure between the middle and outer ear

auditory ossicles

• smallest bones in the human body

• function: transfer vibrations from the tympanic membrane to the inner ear

• components: malleus, incus, stapes

malleus

part of the auditory ossicles; “hammer” that is found between tympanic membrane and incus; connected to tensor tympani muscle

incus

part of the auditory ossicles; “anvil” found between malleus and stapes

stapes

part of the auditory ossicles; “stirrup” that is found between incus and oval window; connected to the stapedius muscle

tympanic reflex in the middle ear

muscle group (stapedius and tensor tympani) that muffles the transfer of vibrations during loud sounds by altering tension on malleus and stapes

stapedius

part of the tympanic reflex; reduces motion of stapes to lessen effect on the inner ear

tensor tympani

part of the tympanic reflex muscle group; pulls malleus away from eardrum

location of the inner ear

in the temporal bone passageways called the bony labyrinth (the bony labyrinth houses the membranous labyrinth)

perilymph

part of the inner ear; cushioning fluid found between the bony and membranous labyrinth

endolymph

part of the inner ear; fluid found within the membranous labyrinth

cochlea

part of the inner ear; coiled, snail-shell-shaped organ for hearing that arises from the vestibule

• oval window: connected to the stapes; transfers vibrations to cochlea

• round window: found at the end of the cochlea acting as a pressure relief

scala vestibuli

part of cochlea that is filled with perilymph; begins near the oval window

scala media (cochlear duct)

part of cochlea that is filled with endolymph; contains Spiral Organ of Corti

scala tympani

part of cochlea that is filled with perilymph; ends at the round window

vestibular membrane of the cochlea

separates the scala vestibuli from the cochlear duct

tectorial membrane of the cochlea

feather-shaped gelatinous substance that acts to open channels for depolarization; part of the Spiral Organ of Corti

basilar membrane of the cochlea

separates the cochlear duct from the scala tympani

spiral organ of corti

structure of the cochlea that converts vibrations to neural impulses; stereocilia (hairs) vibrate, pressing up against the tectorial membrane in order to open channels allowing for depolarization

physiological workflow of hearing

vibrations are captured by the auricle and funneled by the external auditory canal to the tympanic membrane. the tympanic membrane transfers vibrations through the auditory ossicles to the oval window. vibrations travel through perilymph (fluid), ascending up the scala vestibuli (which vibrates the vestibular membrane). the vibration of the scala vestibuli vibrates the endolymph (fluid), causing movement of the stereocilia (hairs) against the tectorial membrane (depolarizing the neural cells). vibrations travel through the basilar membrane to the scala tympani, out through the round window.

Vestibule

chamber that contains the organs of equilibrium

oval window

the beginning of the inner ear that is attached to the stapes

saccule

portion of the Vestibule that leads to the cochlea; contains maculae and is responsible for linear acceleration

utricle

portion of the Vestibule that leads to the Semicircular Canals; contains Maculae and is responsible for linear acceleration

maculae

equilibrium receptors found in the Vestibule that respond to gravitational pull and changes in head position

static equilibrium

the body is stationary but the head is tilted; perceived by Macula found in the Saccule and Utricle

Semicircular Canals

• responsible for sense of equilibrium

• made up of anterior, posterior, and lateral ducts, which respond to angular movement of the head

dynamic equilibrium

perception of motion or angular acceleration; perceived by the semicircular canals

vestibulocochlear nerve (CN VIII)

• formed from the Vestibular Nerve and Cochlear Nerve

• composition: mixed

• function: hearing and balance

• damage: deafness and impaired balance