ANAT2511 Lecture Notes - Lecture 16: Hair Cell, Vestibular Nerve, Auditory Cortex
4 Jun 2018
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• Function: hear and maintain sense of balance
• Located in temporal bone
• External opening: external acoustic meatus
• Internal opening (in cranial cavity): internal acoustic meatus
Three regions
• External ear
o Cartilaginous
o Includes canal leading in - first part of sound transduction
• Middle ear
o Air filled cavity in petrous part of temporal bone
o Acts as auditory ossicles
• Internal ear (labyrinth)
o Vestibular cochlear organs
o Bounded laterally by middle ear, bounded medially by internal acoustic meatus
EXTERNAL EAR
• Pinna (or auricle) - visible external portion of ear
o Helical shape acts as funnel: collects, localises, resonates sound into ear canal
• External acoustic meatus - S-shaped tube in temporal bone
o Protects ear drums (while transducing sound)
o extends from pinna to tympanic membrane
o Lateral 1/3 is cartilage, medial 2/3 is bony.
TYMPANIC MEMBRANE - separates external/middle ear
• Thin, transparent oval membrane
• Lateral - epidermis, medial - mucous membrane
• Receives incoming sound waves, transmits to auditory ossicles in middle ear
o Vibrates in response to sound waves
MIDDLE EAR/TYMPANIC CAVITY
• Air filled cavity lined by mucous membrane
• Divided in 2 regions:
o epitympanic recess (superior)
o tympanic cavity (inferior), next to tympanic membrane
• Transduces vibrations from tympanic membrane to internal ear via auditory ossicles
o Malleus, incus, stapes
▪ Malleus: attached to tympanic membrane
▪ Stapes: in contact with oval window
• 2 windows in middle ear
o Oval window
o Round window
• Ossicular chain
o Amplifies sound waves up to 20x
o Due to flexibility of round window, movement of stapes against oval window causes
displacement of perilymph within internal ear, thus allow vibrations to enter the
labyrinth.
EUSTACHAIN TUBE (Auditory tube)
• Connects middle ear with nasopharynx
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