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