ANP 1106 Lecture Notes - Lecture 25: Ear Canal, Cochlear Duct, Stria Vascularis Of Cochlear Duct
29 Apr 2018
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ANP1106 – Hearing and Balance
Hearing and Balance
- 3 parts of the ear:
o 1) Outer ear – starts at pinna, goes external auditory canal (secretes
cerumen), to tympanic membrane
▪ Helix is thicker cartilage edge
▪ Lobule softer non-cartilage part
▪ Tympanic membrane is thin, translucent, fibrous conjuctive
▪ Cerumen is brown-yellow wax, repels insects
o 2) Middle ear – forms tympanic cavity (opens into pharyngotympanic
tube leads to nasopharynx), contains ossicles (malleus, incus, stapes),
transmits movement from tympanic membrane to oval window
o 3) Inner ear or labyrinth – has sensory receptors, in temporal bone,
formed of bony labyrinth covered with endostium, 3 parts
▪ Cochlea – cochlear duct transduces sound
▪ Vestibule – utricule and saccule tranduces head posture
▪ Semicircular canals – semicircular ducts transduces head
movements
- Fluids
o Membranous labyrinth contains a liquid called endolymph
(intracellular) formed by stria vascularis
o Between bony and membranous labyrinth is perilymph (extracellular
or CSF) formed by perilymphatic duct leading to subarachnoid space
- Sound is caused by changes in air pressure
o Waves enter the external auditory canal & apply pressure to tympanic
membrane, transmitted to malleus, incus, stapes, strikes oval window,
causes waves in perilymph
o These waves go to scala vestibule, helicotrema, scala tympani ending
on round window which absorbs the energy and buldges
o These waves cause oscillations of cochlear duct and spiral organ of
Corti
▪ Spiral organ of Corti rests on basilar membrane
▪ Composed of supporting and sensory hair cells (stereocilia)
attached to tectoral membrane
• Outer hair cells – boost or dampen sounds
• Inner hair cells – detect sounds
o Basilar membrane extends from base of cochlear membrane to
apex/helicotrema
▪ High frequency sound vibrates the base of basilar membrane
▪ Low frequency sound vibrates the apex
▪ Stronger sound causes greater amplitude of basilar membrane
vibrations so more cochlear fibers/hair cells are stimulated
which leads to perception of higher intensity of sound
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