Anatomy 2019-2-19 chapter 17 special senses hearing and equilibrium PDF

Preview

Summary

Dr. Power's class...

Description

1 CHAPTER 16: The Special Senses – Hearing Hearing and equilibrium NEED TO KNOW        

Functions of ear Trace path of sound through auditory cortex Center for equilibrium What is the Organ of Corti? Why is the auditory nerve also called the vestibulocochlear nerve? Nervous pathway of hearing/equilibrium Types of receptors involved in hearing and equilibrium Ear disorders: o Deafness o Labyrinthitis o Vertigo o Middle ear infections o Conduction deafness o Central deafness o Nervous deafness

Internal ear 



Semicircular canal o Enlarged swelling end “ampulla”  Equilibrium receptors—Crista ampullaris  Angular (rotational) movement of head Cochlea—“snail like” bony chamber o 2.5 revolution in bony pillar “modiolus”

2



 

 

o Contains three chambers:  Cochlear duct—middle duct  Ends at apex  Contains spiral Organ of Corti o Hearing receptor  Scala vestibule—superior chamber  Continuous with vestibule  Contacts oval window  Scala timpani—inferior chamber  Contacts round window o Scala vestibule and timpani are composed of bony labyrinth filled with perilymph  Continuous at cochlear apex (“helicotrema”) Scala media (cochlear duct)—composed of membranous labyrinth filled with endolymph o Endolymph—secreted by cells in stria vascularis  Roof of cochlear duct Vestibular membrane (roof)—external wall is composed of Stria vascularis Basilar membrane (floor)—supports organ of Corti o Critical in sound reception o Narrow and thick by the oval window o Wide and thin at cochlear apex o Cochlear nerve of CN VIII—sound info to brain

Organ of Corti—turns sound into an action potential High frequency resonates at base of cochlea

3 

Low frequency sounds resonate at tip of cochlea

Conversion of a sound wave to an action potential 



Bending towards tall cilia—opens K+ and Ca2+ channels o Tension on tiplinks o Depolarization leads to action potential Bending away from tall cilia—closes K+ and Ca2+ channels o Relaxes tiplinks o Repolarization/hyperpolarization

4 Deafness  



Hearing loss Conduction deafness—blockade of sound conduction to inner ear fluids o I.e. thick earwax or perforated eardrum  Otosclerosis—aging, fusing of ossicles  Otitis media—middle ear inflammation Sensoryneural deafness—damage to neural circuitry o Gradual loss of hearing receptors o Loud music, cochlear nerve damage, cerebral infarction

Physiology of equilibrium   



Static (by the vestibule)—maintenance of body position relative to force of gravity Dynamic (by semicircular canals)—maintenance of body position (mainly head) in response to rotational acceleration and deceleration Receptors for equilibrium are hair cells in utricle, saccule and semicircular canals o Collectively called vestibular apparatus o Utricle—horizontal balance, side to side o Saccule—vertical balance, front to back Hair cells supplied by vestibular nerve of CN VIII

Semicircular ducts 

 

Dynamic equilibrium—Crista ampullaris o Ampulla of semicircular canals o Detects rotational movements Crista—small elevation in ampulla containing and supporting hair cells Cupula—mass of gelatinous material covering crista...