Chapter 8 – Special Senses Ear

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

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

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

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)

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

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.

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.

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.

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

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