Sensory Systems - Ear Flashcards
what is the auricle?
irregularly shaped internal plate of elastic cartilage
-thin skin w/ hair and sebaceous glands
describe lining of external auditory meatus
thin skin - also lines outer surface of ear drum
- has large sebaceous glands
- has coiled tubuloalveolar ceruminous glands
what is ear wax?
mixture of ceruminous and sebaceous secretions + desquamated meatal cells
tympanic cavity: what is in it and what does it connect?
- houses ossicles
- connected to pharynx by eustachian tube
lining of tympanic cavity
simple squamous epithelium that changes to pseudostratified ciliated columnar near the opening to the auditory tube
what are the oval and round windows?
small, membrane-covered regions devoid of bone that separate the middle ear from the bony labyrinth of the inner ear
what are the three ossicles?
malleus, incus, stapes
function of the ossicles
transmits tympanic membrane movements to oval window
describe the inner ear
a fluid-filled membranous labyrinth within a bony labyrinth
endolymph vs. perilymph
endolymph = fluid inside membranous labyrinth (like intracellular fluid, w/ low Na+, protein and high K+) perilymph = fluid outside membranous labyrinth (like ECF, but low protein)
what do the semicircular canals contain?
semicircular ducts of membranous labyrinth
what is contained by the vestibule?
contains perilymph and houses saccule and utricle (which have endolymph)
describe the cochlea
winds 2.5x around modiolus and subdivided into 3 spaces:
- scala vestibuli (filled w/ perilymph)
- scala tympani (filled w/ perilymph)
- scala media (cochlear duct)
what is the modiolus?
bony core of cochlea that has blood vessels and spiral ganglion
what do the lateral extensions of the modiolus form?
osseous spiral lamina
what is the thickened periosteum around the cochlea?
spiral ligament
where are the saccule and utricle found?
inside the vestibule
what are the saccule and utricle and what is their lining?
sac-like bodies of CT lined by simple squamous epithelium that each give off a duct
where do the ducts of the saccule and utricle end up?
they join to form the endolymphatic sac
what do the saccule and utricle contain?
maculae - specialized regions that have 2 types of neuroepithelial hair cells
in general, what are vestibular hair cells?
neuroepithelial cells that have 50-100 rigid stereocilia arranged in rows + a single cilium (kinocilium)
-round, basal nucleus
function of the stereocilia on vestibular hair cells
sensory microvilli
describe location of vestibular hair cell cilia
extend from apical surface of hair cells to an overlying gelatinous layer (otolithic membrane)
describe type I hair cells
- bulbar shape w/ round nucleus
- surrounded by cup-shaped afferent nerve ending
describe type II hair cells
- columnar w/ a round, basal nucleus
- contact small afferent nerve terminals w/ synaptic vesicles
describe support cells
- columnar w/ round, basal nucleus
- have prominent terminal web
what is the otolithic membrane?
thick, gelatinous (glycoprotein) layer that contains small calcified particles (otoliths/otoconia)
what is the function of the otolithic membrane?
detection of linear acceleration
where do the semicircular ducts arise from?
the utricle
what are the ampullae ?
dilated area of semicircular ducts near junction w/ utricle
what are the cristae ampullares?
specialized sensory areas in ampullae that are similar to maculae but w/ thicker, cone-shaped glycoprotein layer (cupula) and NO OTOLITHS
function of cristae ampullares
detect angular acceleration of the head along any of the three axes
where does the endolymphatic duct lead?
to the endolymphatic sac
lining of endolymphatic sac
- columnar cells w/ irregular shaped nucleus
- columnar cells w/ long microvilli
what might you find in the lumen of the endolymphatic duct and what is their function?
phagocytic cells (macrophages, neutrophils) - endolymph reabsorption
what is the cochlear duct?
- specialized area of saccule that has the spiral organ of Corti
- surrounded above by scala vestibuli
- surrounded below by scala tympani
how do the scala vestibuli and scala tympani communicate with each other?
by a small hole near the cochlear apex called the helicotrema
describe the basilar membrane of the cochlea
thick layer of amorphous material w/ keratin-like fibers
describe tectorial membrane of cochlea
-makes contact w/ the processes of the hair cells
what cells secrete tectorial membrane?
interdental cells of spiral sulcus
describe the spiral organ of Corti
- has hair cells and supporting cells
- lies on basilar membrane
- has inner tunnel of Corti and outer tunnel that communicate via intercellular spaces
describe inner hair cells
- organized in a single row along length of cochlear duct
- receive afferent synaptic terminals on basal surface
describe outer hair cells
- organized in 3-5 rows w/i a cup-shaped afferent nerve ending
- stereocilia embedded in gelatinous tectorial membrane
function of outer hair cells
sound reception and response to different sound frequencies
describe inner and outer pillar cells
- closely associated w/ each other
- rest on basilar membrane
- enclose and support inner tunnel of Corti
describe inner and outer phalangeal cells
- closely associated w/ inner and outer hair cells, respectively
- support nerve fibers that form synapses w/ hair cells
describe cells of Hensen and border cells
mark the inner and outer borders of the spiral organ of Corti
describe how the ear functions for auditory purposes
sound strikes tympanic membrane -> vibration via ossicles, movement of stapes at oval window -> disturbs perilymph -> deflects basilar membrane in organ of Corti -> pillar cells on basilar membrane move laterally -> lateral shearing of stereocilia on sensory hair cells against tectorial membrane -> movement of stereocilia transduced into electrical impulses -> travels via cochlear nerve to brain
describe how the ear functions for vestibular purposes
change in head position -> flow of endolymph in semicircular ducts (circular) or in saccules/utricles (linear):
- movement in semicircular canals -> displaces cupula overlying cristae ampullares -> bending of stereocilia on sensory hair cells
- movement in saccules/utricles -> displaces otoliths -> transmitted to the maculae via overlying gelatinous layer -> bending of stereocilia on sensory hair cells
movement of stereocilia transduced into electrical impulses -> transmitted to brain via vestibular nerve fibers
what is nerve deafness?
lesion in nerves transmitting impulses from organ of Corti
what can cause nerve deafness?
- disease
- drugs
- prolonged loud noise
what is conductive hearing loss?
hearing loss that occurs prior to oval window - defect in sound wave conduction
what can cause conductive hearing loss?
- inflammation (otitis media)
- otosclerosis in middle ear
how can you test for conductive hearing loss?
using bone conduction: when a tuning fork is touched to head, vibrations conduct directly to the cochlea through bone
a person w/ only conductive hearing loss can detect tuning form sounds as well as someone w/ normal hearing
