Atlas of Human Anatomy by Netter

b. Contains membranous endolymphatic duct
Semicircular canals
Anterior, posterior, and lateral
Set at right angles to each other in three planes
Lie posterosuperior to vestibule
Each opens into vestibule
Swelling at one end of each canal: ampulla
Contain membranous semicircular ducts
Membranous labyrinth
Collection of ducts and sacs
Suspended within bony labyrinth
Filled with endolymph
Vestibular labyrinth
Utricle
a. Has specialized area of sensory epithelium: macula
b. Hair cells in macula innervated by vestibular division of vestibulocochlear nerve (CN VIII)
c. Hairs respond to tilting of head and linear acceleration and deceleration
Saccule
a. Communicates with utricle
b. Continuous with cochlear duct
c. Contains macula, identical in structure and function to that of utricle
Semicircular ducts
a. Within semicircular canals
b. Each has ampulla at one end
c. Ampullary crest in each ampulla senses movement of endolymph in plane of duct
d. Hair cells in crest innervated by vestibular division of vestibulocochlear nerve (CN VIII)
e. Detect rotational (tilting) movements of head
Cochlear labyrinth
Spiral ligament suspends cochlear duct from external wall of spiral canal
Cochlear duct
a. Triangular in shape
b. Filled with endolymph
c. Spans spiral canal, dividing it into two channels, each filled with perilymph
d. Two channels: scala tympani and scala vestibule, meet at apex of cochlea (helicotrema)
e. Third, middle channel = cochlear duct
f. Roof of duct = vestibular membrane
g. Floor of duct = basilar membrane
Spiral organ of Corti
a. Found on basilar membrane
b. Covered by gelatinous tectorial membrane
c. Contains hair cells-tips embedded in tectorial membrane
d. Hair cells innervated by cochlear division of vestibulocochlear nerve (CN VIII)
Propagation of sound
Initiated by sound waves
Transmitted as vibrations by ossicles
Stapes vibrates in oval window
Creates waves of pressure in perilymph of vestibule
Waves ascend in spiral canal in scala vestibule
Transfer to scala tympani at helicotrema
Pass down scala tympani to round window
Dissipated via secondary tympanic membrane in round window to air of middle ear cavity
Reception of sound
Deformation of cochlear duct by pressure waves in perilymph
Stimulates hair cells of spiral organ embedded in tectorial membrane
Base of spiral organ receives high frequency sounds and apex receives low-frequency sounds
Internal auditory (acoustic) meatus
1 cm long tiny canal in petrous ridge of temporal bone
Opening in posteromedial aspect of ridge in posterior cranial fossa
Transmits facial (CN VII) and vestibulocochlear (CN VIII) nerve