1. Chapter 8 – Special Senses
Ear

2. Outer Ear Pinna – aka auricle – ear lobe
External acoustic meatus (external auditory canal)
About 1inch long and ¼ inch wide
Goes through temporal bone
Lined with ceruminous glands – secrete cerumen (earwax)
Ends at tympanic membrane (eardrum) – which soundwaves cause to vibrate

3. Middle Ear – aka tympanic cavity
Ends at oval window and round window – openings in bone
Pharyngotympanic (auditory) tube – connects ear to throat
Normally closed – yawning and swallowing can open it to equalize pressure
Unequal pressure causes eardrum to bulge – causes hearing difficulties

4. Middle ear cont. Otitis media – inflammation – occurs with sore throat
May have to lance eardrum and insert tubes to allow pus to drain – myringotomy
Contains 3 small bones (smallest in body) referred to as the ossicles
Transmit vibrations from eardrum to fluid of inner ear
Hammer (malleus), anvil (incus), and stirrup (stapes) – presses of oval window

5. Inner ear Made of osseous labyrinth – bony chambers 3 divisions
Cochlea – snail shape
Vestibule – chamber between cochlea and canals
Semicircular canals
Contains perilymph (plasma like fluid) in which are membranous sacs that contain endolymph (a thicker fluid)

6. Mechanisms of Equilibrium
Vestibular apparatus – equilibrium receptors of inner ear
Static equilibrium (up/down)
Maculae – membranous sacs in vestibule
Each cell contains a receptor hair that extends into the otolithic membrane (gel-like material)
Within the otolithic membrane are otoliths – calcium salt stone

7. Equilibrium cont.
When the head moves gravity causes the otoliths to roll and pull on the otolithic membrane.
The movement of the membrane causes the hairs to move which then send the message along the vestibular nerve to the brain.

8. Equilibrium cont. Dynamic equilibrium (angular/rotatory)
Crista ampullaris – receptor region within the semicircular canals
Made up of tufts of hair called cupula
Head moves – endolymph lags behind – causing cupula to bend – stimulates impulses to vestibular nerve
Your body will adjust to constant speed.

9. Mechanisms of Hearing 3 chambers in cochlear duct
2 chambers (scalae) w/ perilymph
Organ of Corti
Contains hair cells – hearing receptors
Rest on basilar membrane
Above hairs rests the tectorial membrane
Endolymph
Sound waves are transmitted by ossicles to oval window
Waves cause vibrations in the basilar membrane
Vibrations cause hairs to press into tectorial membrane
Bending of hair sends impulses down cochlear nerve to brain
Receptors adapt to constant tones – we are no longer aware of them
Hearing is the last sense to leave awareness.

10. Hearing & Equilibrium Deficits
Deafness – hearing loss of any degree
Conduction deafness – interference with sound waves – earwax, fusion of ossicles (ostosclerosis), ruptured eardrum
Hearing aids are able to help
Sensorineural deafness – degeneration or damage to receptor cells in organ of Corti, cochlear nerve, or auditory cortex
Continuous loud sounds
Equilibrium
Nausea, dizziness, balance
Meniere’s disease – deafness, nausea, vertigo

11. Development Newborn responds reflexively 3/4 months – localize sounds
Toddler – critical listening
60 – presbycusis – degeneration of organ of Corti
Is becoming more common in younger – noise pollution