The Ear Hearing and Balance Ear Structure Ear

The Ear Hearing and Balance

Ear Structure

Ear Structure Divided into 3 Regions 1. 2. 3. Outer Ear Middle Ear Inner Ear

Outer Ear

Outer Ear • external • auricle (pinna) § made of cartilage and skin § directs sound into auditory canal

Auditory Canal or External Auditory Meatus § to tympanic membrane (eardrum)

Auditory Canal or External Auditory Meatus lined with: § hairs § sebaceous glands § ceruminous glands § produce cerumen or ear wax § sticky trap foreign bodies

Tympanic Membrane • eardrum • boundary between outer and middle ear • function - transmit vibrations to bones in middle ear

Middle Ear

Middle Ear • tympanic cavity • air filled • mucosa lined

Eustachian Tube • connects middle ear to throat to equalize pressure

Ossicles • span middle ear (bones) • malleus (attached to eardrum), incus, stapes (attached to oval window) • amplify vibrations acting as levers

1. 2. 3. 5. 4. • when vibrations passes from large to smaller surface area membranes, the strength increases from eardrum to oval window 8. 7. 6.

1. 2. 8. 3. 5. 4. 7. 6. 1. 2. 3. 4. 5. 6. Ossicles Malleus Incus Stapes Oval window Eustachian tube 7. Tympanic membrane 8. External auditory canal

• attaches wall and malleus • contracts as a reflex during loud noises to pull ossicles more tightly and lessen the chances of the eardrum vibrating so hard it tears • stapedius is the antagonist Tensor Tympani Muscle

Inner Ear Labyrinth

Inner Ear • deep in temporal bone • 2 major divisions 1. bony labyrinth twisting tubes 2. membranous labyrinth lining of bony

Membranous Labyrinth • lining of bony • sacs and membranes • fluids conduct sound vibrations from oval window to nerves in cochlea

perilymph § between bony and membranous bone endolymph membrane endolymph § fills membranous labyrinth

Divided into 3 Regions Bony Labyrinth 1. cochlea (hearing) 2. vestibule (balance) 3. semicircular canals (balance)

Cochlea Hearing

• spiral chambers • coils around a bony pillar - modiolus • running through center of coils like a wedge shaped worm is cochlea duct (scala media) • it plus a shelf like extension of modiolus divides the cavity into 3 regions Cochlea

cochlear duct scala vestibuli • scala vestibuli superior • continuous with vestibule and abuts the oval window and the scala media or cochlear duct • scala tympani – inferior § which ends in round window scala tympani

cochlear duct • both the scala vestibuli and scala tympani have perilymph • vestibular membrane - “roof” of cochlear duct • thought to secrete endolymph scala vestibuli endolymph vestibular membrane perilymph scala tympani perilymph

• the “floor” is cochlear duct and basilar membrane, membrane which supports the organ of Corti

• A branch of the cochlear nerve (joins vestibular nerve to form vestibulocochlear nerve) nerve runs from the organ of Corti, Corti through the modiolus → brain

• Vibrations from oval window → perilymph → basilar membrane

• Vibrations from oval window → perilymph → basilar membrane scala vestibuli scala tympani Organ of Corti

• When maximum vibrations occur, the organ of Corti hair cells are pulled by attached “awning” – tectorial membrane.

• When maximum vibrations occur, the organ of Corti hair cells are pulled by attached “awning” – tectoral membrane.

Their movement causes ion channels in hair cell membranes to open. Neurotransmitters are released and nerve endings below hair cells are stimulated.

Cerebral cortex “processes” sounds.

• hair cells nearest oval window = high pitch • near cochlear apex = low pitch • amplitude = more hair cells in the area are vibrated

Sound Pathway

What is the scientific name for ear wax? cerumen Pinna Collects sound Auditory Canal Tympanic Membrane Transmits vibrations

What is its function? Trap foreign objects Pinna Collects sound Auditory Canal Tympanic Membrane Transmits vibrations

Ossicles What prevents the eardrum from rupturing? Tensor tympani muscle tightens ossicles Malleus Incus Amplifies vibrations Stapes

Ossicles What is the function of the Eustachian tube? Equalizes pressure between middle ear and throat Malleus Incus Amplifies vibrations Stapes

What is behind the stapes? Oval Window

What is behind the oval window? window Oval Window Perilymph

Vestibular membrane Basilar membrane

Vestibular membrane Endolymph Organ of Corti Basilar membrane Endolymph

Tectorial membrane Hair cells

Hair cells scrape against the tectorial membrane.

Action Potential Cochlear Nerve

Vestibulocochlear Nerve Cerebral (Auditory) Cortex Of Brain