Special Senses II Flashcards
the ear
- detects sound and movement of head
- signals transmitted via vestibulocochlear nerve (CN VIII)
- external, middle, and inner
external ear
- auricle
- external acoustics meatus
- tympanic membrane
auricle
- pinna
- funnel shapes visible part
- skin covered, elastic cartilage supported structure
- protects entry into ear and directs sounds waves in
external acoustic meatus
- bony tube extending through temporal bone
tympanic membrane
- eardrum
- delicate funnel shaped epithelial sheet
- separates external and middle
- termination of external acoustic meatus
- vibrates when sound waves hit it
- transmits sound wave energy into middle and inner ear
protection of ear canal
- cerumen, wax like secretion of ceremonious glands
- combines with dead sloughed cells to form earwax
- prevents larges objects from entering
- fine hairs guarding opening
- may helps impede growth of microorganisms
middle ear components
- auditory tube
- auditory ossicles
- auditory muscles
middle ear
- in petrous (hard) part of temporal bone
- has air filled tympanic cavity
- sound transmitted here via auditory ossicles
- bound medially by bony wall
- houses oval and round window
- separates middle form inner ear
oval and round window
- oval window= sound enters
- round window= sends sound back out
auditory tube
- eustachian tube
- passage from middle ear to nasopharynx
- normally closed at connection to nasopharynx
- allows pressure to equalize in middle ear
valsalva maneuver
- piping your ears
- pushes air in nasopharynx up tube to open it and equalize the pressure in middle ear
3 auditory ossicles
3 smallest bones of body
1) malleus
2) incus
3) stapes
malleus
- attached to medial surface of tympanic membrane
- resembles hammer
incus
- middle ossicle resembling and anvil
stapes
- resembles stirrup
- has disc-like footplate fitting into oval window
- beats on oval window where cochlea receives info
- marks lateral wall of inner ear
auditory ossicles
- amplify and transmit sound waves into inner ear
- vibrate when sound waves strike tympanic membrane
- causes stapes footplate to move in and out of oval window
- movement initiating pressure waves in inner ear fluid
- tympanic membrane 20 time greater that footplate so sound transmitted amplified 20-fold
pathway of sound in auditory ossicles
1) eardrum
2) malleus
3) incus
4) stapes
auditory muscles
- stapedius (stapes) and tensor tympani (malleus)
- tiny skeletal muscles within middle ear
- restrict ossicles movement when loud noises occur
- bone could be moved out of place
inner ear
- cochlea
- spiral organ
cochlea
- snail-shaped spiral chamber in bone of inner ear
- has spongy bone axis, modiolus
- houses spinal organ, responsible for hearing
- cochlear duct
cochlear duct
- membranous labyrinth that extends through cochlea
- roof formed by vestibular membranes
- floor formed by basilar membranes
- contains endolymph (like intracellular fluid)
membrane and chambers of cochlea
- filled with perilymph (like CSF)
- superior chamber: scala vestibuli
- inferior chamber: scala tympani
- merge through small channel (helicotrema) at apex of cochlea
spiral organ
- organ of Corti
- in cochlear duct
- thick sensory epithelium consisting of hair cells and supporting cells
- rests on basilar membrane
hair cells
- sensory receptors of inner ear of hearing
- release neurotransmitter molecules to sensory neurons
- covered on apical surface with long microvilli, stereo cilia
tectorial membrane
- In spiral organ
- gelatinous structure
- stereo cilia extend into here
pathway of hearing
- sound waves at tympanic membrane
- transmitted to oval window via ossicles
- initiate pressure waves in perilymph
- causes basilar membranes to flutter
- distorts stereo cilia, causing changes in neurotransmitter release
- sensory neurons stimulated (cell bodies housed within spiral ganglia in modiolus)
2 options of pathways for hearing
1) sound with frequencies below hearing travel through the heliocotrema and do not excite hair cells
2) sounds in the hearing rate go through cochlear duct, vibrating basilar membrane an deflecting hairs on inner hair cells
distinguishing different sounds
- sounds at different frequencies vibrate different portions of basilar membrane
- high pitched more stiff at basal portion of cochlea
- low pitches upper cochlea wider and more flexible
loud sounds
- cause greater vibration of basilar membrane
- stimulate more hair cells which our brain interprets as loud
vestibulocochlear nerve
- CN VIII
- cochlear branch of CN VIII carries sensory inputs for hearing into brain stem
- them projects to thalamus and primary auditory cortex
linear movement
- flexion and extension of neck
- receptors: maculae (sac of auricle and saccule)
rotational movement
- head spins and rotates
- receptors: crista ampullaris of semicircular ducts
physiology of equilibrium
both linear and rational receptors are housed in bony space called the vestibule
vestibule structure of linear motion
- utricle (large membranous sac, semicircular canals)
- macula of utricle
- scull (smaller membranous sac, cochlea)
- macula of saccule
macula
- raised area of sensory epithelium in utricle and saccule
- along internal wall of both sacs
- composed of layer of hair cells and supporting cells
- hair cells with stereociliaa and one lone cilium, kinocilium
- when both bent, changes in neurotransmitter released
otolithic membrane
- formed of gelatinous layer and otoliths
- otoliths, small masses of calcium carbonate crystals
- helps increase weight of otolithic membrane covering hair cells
- position influenced by head position
- stereocilia and kinocilia embedded in gelatinous layer
macula when head is upright
- otolithic membrane applying pressure directly onto hair cells
- minimal stimulation of hair cells
macula when head is tilted
- shift of otolithic membrane distorts the stereocilia
- de/hyperpolarization of hair cells
- increase or decrease neurotransmitter release
- increased or decreased nerve signal frequency along vestibular branch of CN VIII
head tilted backwards (up)
- hair cells go back
- excitation
- increase neurotransmitter release
- increase nerve signal frequency
head tilted forwards (down)
- hair cells go forward
- inhibition
- decrease neurotransmitter release
- decrease nerve signal frequency
semicircular cana
- 3 semicircular ducts connected to utricle
ampulla
- expanded region within base of each semicircular duct
crista ampullaris
- elevated region on ampulla
- covered by epithelium tissue of hair cells and supporting cells
capula
- overlying gelatinous dome
- kinocilia and stereocilic embedded here
- extends across semicircular duct to roof over ampulla
direction of rotational movement
- with head rotation, lagging of endolymph
- pushes against scapula, causing bending of stereocilia
- results in altered neurotransmitter release from hair cells
- stimulation of sensory neurons
- bending of stereo cilium in direction of kinocilium (increased frequency of nerve signals)
- response primarily to changes in velocity
alcohol- bed spins
- solvent density makes ampullarf scapula lighter than endolymph
motion sickness
- sensory conflict from eyes thinking car is stationary versus vestibular system body is in motion
tinnitus
- ear ringing
- after a loud concert stereocilia are damaged and send erroneous messages to brain
- tips break off but can grown back in ~24 hours
