Transcript Hearing and Balance

Sense of Hearing: Three Parts of Ear
1. External to
tympanic
membrane
2. Middle from
tympanic
membrane to oval
window
3. Inner behind oval
window
1
Three Parts of Ear: Contents
• External
– Auricle, external auditory canal
• Middle
– Malleus, incus, stapes
– Eustachian tube
• Inner
– Cochlea, vestibule, semicircular canals, origin of
CN VIII
2
3
Middle ear
Starts at the tympanic membrane
Tiny, epithelium-lined cavity hollowed out of
the temporal bone
Contains three auditory ossicles (bones)
• Malleus (hammer)—attached to the inner
surface of the tympanic membrane
• Incus (anvil)—attached to the malleus and
stapes
• Stapes (stirrup)—attached to the incus
4
Eustachian Tube
• Connects throat with
middle ear
• Equalizes pressure
across tympanic
membrane
• In young child, short
and horizontal
• In adults, longer and
more vertical
5
Inner ear
Structure of the inner
ear
Bony labyrinth
• Vestibule
• Cochlea
• Semicircular
canals
6
Structure of the inner ear (cont)
 Vestibule and semicircular canal organs are
involved with balance
 Cochlea—involved with hearing
 Endolymph—clear, potassium-rich fluid filling
the membranous labyrinth
 Perilymph—similar to cerebrospinal fluid,
surrounds the membranous labyrinth, filling
the space between the membranous tunnel
and its contents and the bony walls that
surround it
7
Receptors : Organ of Corti
• Mechanoreceptors
(hairs) in cochlea of
inner ear
• Organ of Corti in
endolymph
• Cochlear branch of
CN VIII
8
How Hearing Occurs
• Pathway of vibrations
 Sound waves
tympanic membrane
oval window
organ of Corti
ossicles
• Pathway of nerve impulses
 Organ of Corti
temporal lobe
CN VIII (cochlear branch)
9
Recap: How Hearing Occurs
Copyright © 2011, 2007 by Saunders,
an imprint of Elsevier Inc. All rights
reserved.
10
Receptors for Balance
• Mechanoreceptors
(hairs) in vestibule
and semicircular
canals of inner ear
• Hairs in endolymph
• Vestibular branch of
CN VIII
Copyright © 2011, 2007 by Saunders,
an imprint of Elsevier Inc. All rights
reserved.
11
12