unit 4 special senses: the...
TRANSCRIPT
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ESSENTIALS
OF HUMAN
ANATOMY
& PHYSIOLOGY
Unit
4 Special Senses: The Ear
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The Ear
�Two senses� Hearing� Equilibrium (balance)
�Mechanoreceptors
�Different organs house receptors for each
sense
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Anatomy of the Ear
�Divided into three areas� Outer (external) ear� Middle ear� Inner ear
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External Ear
�Hearing only
�Structures� Pinna (auricle)� External auditory canal
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External Auditory Canal
�Narrow chamber in the temporal bone
�Lined with skin
�Ceruminous (wax) glands
�Ends at the tympanic membrane
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Middle Ear (Tympanic Cavity)
�Air-filled cavity within the temporal bone
�Only involved in hearing
�Two tubes are associated with the inner
ear� The opening from the auditory canal is
covered by the tympanic membrane� The auditory tube connecting the middle ear
with the throat� Equalizing pressure during yawning or swallowing
� Otherwise it is collapsed
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Bones of the Tympanic Cavity
�Three bones� Malleus (hammer)� Incus (anvil)� Stapes (stirrup)
�Vibrations from eardrum move the malleus
�Bones transfer sound to the inner ear
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Inner Ear (Bony Labyrinth)
�Sense organs for hearing and balance
�Filled with perilymph
�Maze of bony chambers within the
temporal bone� Cochlea� Vestibule� Semicircular canals
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Inner Ear or Bony Labrynth
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Organs of Hearing
�Organ of Corti� Located within the cochlea� Receptors = hair cells on the basilar
membrane� Gel-like tectorial membrane is capable of
bending hair cells� Cochlear nerve attached to hair cells
transmits nerve impulses to the brain
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Organs of Hearing
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Mechanisms of Hearing
�Vibrations from sound waves move
tectorial membrane
�Hair cells are bent by the membrane
�Action potential starts in the cochlear
nerve
�Continued stimulation can lead to
adaptation
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Mechanisms of Hearing
Figure 8.16a–b
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Organs of Equilibrium
�Receptor cells are in two structures� Vestibule� Semicircular canals
�Two functional parts of equilibrium � Static equilibrium� Dynamic equilibrium
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Organs of Equilibrium
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Static Equilibrium
�Maculae- receptors in the vestibule� Report on the position of the head
�Anatomy of the maculae� Hair cells embedded in the otolithic
membrane� Otoliths (tiny stones) float in a gel around the
hair cells� Movements cause otoliths to bend the hair
cells
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Function of Maculae
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Dynamic Equilibrium
�Crista ampullaris- receptors in the
semicircular canals� Tuft of hair cells� Cupula (gelatinous
cap) covers the haircells
�Action of angular
head movements� Cupula stimulates
the hair cells