Special Senses - Hearing

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Special Senses
Hearing
Hearing
• Ear is a very sensitive structure.
– The sensory receptors convert vibrations 1,000
times faster than the photoreceptors of the eye
can respond to light
Structure
• Three main regions
– Outer Ear
• Collects sounds waves and channels them inward
– Middle Ear
• Conveys the sound vibrations to the oval window
– Inner Ear
• Which houses the receptors for hearing and
equillibrium
Structure of the Ear
Outer Ear
• Consists of:
– Auricle
– External Auditory canal
– Eardrum
Auricle
• Part of the ear you see
• Structure:
– Skin covered flap of elastic cartilage
• Function:
– Collect sound waves and direct them toward
external auditory canl
External Auditory Canal
• Structure:
– Two structures help keep out invaders
• Few Hairs
• Ceruminous gland
– Secret cerumen (earwax)
• Function:
– Curved tube directs sound waves toward the
eardrum
Eardrum
• A.k.a. Tympanic membrane
• Structure:
– Thin, semitransparent partition between external
auditory canal and the middle ear
• Function:
– Changes sounds waves into vibrations
Middle/Inner Ear
Middle Ear
• Small, air-filled cavity between eardrum and
inner ear
• Consists of
– Auditory tube
– Auditory ossicles
Auditory Tube
• Opening in the anterior wall of the middle ear
leads to auditory tube (Eustachian tube)
– Connects the middle ear to upper portion of
throat
– When it is open, air pressure equalizes on both
sides of the eardrum
• When closed – if air pressure builds the eardrum can
rupture
– Swallowing or yawing opens up the auditory tube
Auditory Ossicles
• 3 tiny bones span across the middle ear by
means of ligaments
– Malleus
– Incus
– Stapes
• Forms a small opening, oval window, where the inner
ear begins
• Function
– To pass the vibration from the outer ear to the
inner ear
Ossicles
Inner Ear
• Divisions
– Bony Labyrinth
• Series of cavities in the temporal bone, including the
cochlea, vestibule, and semicircular canals
• Contains a fluid called perilymph
– Inner membranous labyrinth
• Series of sacs and tubes with the general shape as the
bony labyrinth
• Contains a fluid called endolymph
Bony Labyrinth
• Cochlea
– Sense organ for hearing
• Semicircular canals and vestibule
– Sense organs for balance and equilibrium
Inner Ear
Process of Hearing
• Auricle directs sound waves to
external auditory canal
• External auditory canals
continues to direct sounds
waves to the eardrum
• Eardrum converts sound
waves into vibrations
• Eardrum vibrates the malleus
• Malleus vibrates the incus
then to the stapes
• Stapes move back and forth
and pushing oval window in
and out
• Movement of oval window
sets up the fluid pressure
waves in the perilymph of the
cochlea
• Fluid pressure waves build and
eventually cause the
endolymph to transmit waves
to the hairs inside the cochlea
• Hairs are stimulated they
release neurotransmitter
molecules, change waves into
electrical impulses
• Electrical impulses to the brain
through the auditory nerve

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