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Special Senses
Hearing
Reading: Chapter 10
C. HEARING
1) Outer ear
a) auricle = pinna, why is this structure important?
b) external auditory meatus = ear canal
lined w/ wax glands & hairs
c) tympanic membrane = “ear drum”
vibrates when sound waves hit it
2) Middle ear
a) auditory ossicles
-malleus, incus, stapes
-stapes attached to oval window
b) tympanic cavity -cavity where ossicles are found
-Eustachian tube = pressure release,“pop” b/c
tympanic membrane moves
-bacteria & viruses move up tube to infect
middle ear (Otitis media)
3) Inner ear
a) Cochlea = a fluid filled tube (coiled  “snail shell”)
b) Semi-circular canals = 3 structures, monitor angular acceleration
c) Utricle & Saccule = within vestibule, monitor linear acceleration
NOTE: bony labyrinth &
membranous labyrinth
3) Inner ear
a) Cochlea = a fluid filled tube (snail shell)
2 windows:
3 tubes:
-oval window & round window
-scala vestibuli, filled with perilymph
-scala tympani, filled with perilymph
-cochlear duct, filled with endolymph
meet at
helicotrema
Cochlea “unwound”
3) Inner ear (cochlea con’t)
The 3 fluid filled tubes are separated by 2 membranes:
a) basilar membrane -separates cochlear duct from scala tympani
b) vestibular membrane -separates scala vestibuli from cochlear duct
Organ of Corti:
-a.k.a “spiral organ of corti”
-contains hearing transducers (hair cells)
-sits on basilar membrane
-hair cells stick into tectorial membrane
-movement of the hair cells creates AP’s
*
4) Physiology of hearing
a)
b)
c)
d)
e)
f)
Sound waves strike the tympanic membrane
Ossicles move, stapes moves pushes into oval window
Fluid wave moves the membranes of inner ear
Hair cells strike tectorial membrane
When hair cells bend, it creates an AP
Auditory cortex of
______ lobe interprets
sensory impulses
NOTE: Round window bulges to
relieve fluid pressure in
the bony labyrinth
Basilar membrane:
-high frequency waves vibrate near oval window
-lower pitch sound waves vibrate near helicotrema
Loud vs. Soft Noises
Volume increases as more hair cells are stimulated.
5) Deafness - 2 major types
a) conduction deafness:
Cause:
-lack of conduction to cochlea
-ear wax build up
-damaged tympanic membrane
-damaged ossicles
Solution: -stimulate cochlea directly
5) Deafness - 2 major types
b) nerve deafness:
Cause:
-damage to the organ of Corti
-damage to vestibulocochlear nerve
-tumors or bleeding in CNS
-some drugs
D. EQUILIBRIUM - inner ear, vision and proprioception
1) utricle & saccule -2 chambers within vestibule
-contain hair cells embedded in maculae
-otoliths = rocks in maculae
-linear or static movement detected
-Utricle detects horizontal acceleration
-Saccule detects vertical acceleration
2) Semicircular Canals - 3 fluid-filled canals
- At right angles to one another
- Hair cells embedded in a cupulae (sail)
- Detect angular acceleration
- Stimulation of the canals causes
nystagmus & sometimes vertigo
Post. = cartwheel
Lat. = long axis Sup. = somersault