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Ch 8 Hearing and Equilibrium

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Chapter 8
Special Senses:
Hearing & Equilibrium
The Ear
п‚· Houses two senses
п‚· Hearing
п‚· Equilibrium (balance)
п‚· Receptors are mechanoreceptors
п‚· Different organs house receptors for
each sense
Anatomy of the Ear
п‚· The ear is divided into three areas
п‚· Outer
(external)
ear
п‚· Middle
ear
п‚· Inner
ear
Figure 8.12
The External Ear
п‚· Involved in
hearing only
п‚· Structures of
the external
ear
п‚· Pinna
(auricle)
п‚· External
auditory canal
Figure 8.12
The External Auditory Canal
п‚· Narrow chamber in the temporal bone
п‚· Lined with skin
п‚· Ceruminous (wax) glands are present
п‚· Ends at the tympanic membrane
The Middle Ear or Tympanic Cavity
п‚· Air-filled cavity within the temporal bone
п‚· Only involved in the sense of hearing
The Middle Ear or Tympanic Cavity
п‚· Two tubes are associated with the inner
ear
п‚· The opening from the auditory canal is
covered by the tympanic membrane
п‚· The auditory tube connecting the middle ear
with the throat
п‚· Allows for equalizing pressure during yawning
or swallowing
п‚· This tube is otherwise collapsed
Bones of the Tympanic Cavity
п‚· Three bones
span the cavity
п‚· Malleus
(hammer)
п‚· Incus (anvil)
п‚· Stapes (stirrip)
Figure 8.12
Bones of the Tympanic Cavity
п‚· Vibrations from
eardrum move
the malleus
п‚· These bones
transfer sound
to the inner ear
Figure 8.12
Slide 8.25b
Inner Ear or Bony Labyrinth
п‚· Includes sense organs for hearing and
balance
п‚· Filled with
perilymph
Figure 8.12
Inner Ear or Bony Labrynth
п‚· A maze of bony chambers within the
temporal bone
п‚· Cochlea
п‚· Vestibule
п‚· Semicircular
canals
Organs of Hearing
п‚· Organ of Corti
п‚· Located within the cochlea
п‚· Receptors = hair cells on the basilar
membrane
п‚· Gel-like tectorial membrane is capable of
bending hair cells
п‚· Cochlear nerve attached to hair cells
transmits nerve impulses to auditory cortex
on temporal lobe
Organs of Hearing
Figure 8.13
Mechanisms of Hearing
п‚· Vibrations from sound waves move
tectorial membrane
п‚· Hair cells are bent by the membrane
п‚· An action potential starts in the cochlear
nerve
п‚· Continued stimulation can lead to
adaptation
Mechanisms of Hearing
Figure 8.14
Organs of Equilibrium
п‚· Receptor cells are in two structures
п‚· Vestibule
п‚· Semicircular canals
Figure 8.16a, b
Organs of Equilibrium
п‚· Equilibrium has two functional parts
п‚· Static equilibrium
п‚· Dynamic equilibrium
Figure 8.16a, b
Static Equilibrium
 Maculae – receptors in the vestibule
п‚· Report on the position of the head
п‚· Send information via the vestibular nerve
п‚· Anatomy of the maculae
п‚· Hair cells are embedded in the otolithic
membrane
п‚· Otoliths (tiny stones) float in a gel around
the hair cells
п‚· Movements cause otoliths to bend the hair
cells
Function of Maculae
Figure 8.15
Dynamic Equilibrium
 Crista ampullaris –
receptors in the
semicircular canals
п‚· Tuft of hair cells
п‚· Cupula (gelatinous cap)
covers the hair cells
Figure 8.16c
Dynamic Equilibrium
п‚· Action of angular head
movements
п‚· The cupula stimulates the
hair cells
п‚· An impulse is sent via the
vestibular nerve to the
cerebellum
Figure 8.16c
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