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BIO 156
Chapter 11
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The Senses
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The General and Special Senses The body contains two types of senses:
general and special.
Receptors for the senses are grouped into
five functional categories:
Mechanoreceptors
Chemoreceptors Thermoreceptors
Photoreceptors
Nociceptors
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The General Senses Receptors for the general body senses generally fit into two
groups:
naked nerve endings encapsulated receptors.
Naked nerve endings in body tissues detect
Pain
Temperature
Light touchEncapsulated receptors consist of naked nerve endings
surrounded by one or more layers of cells.Encapsulated receptors detect pressure, light touch, and
muscle extension.
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Types of Pain
2.Somatic
3.Visceral
Referred Pain
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General Sense Receptors
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The special senses include
Taste
Smell
Vision
Hearing
Balance
The Special Senses
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Taste
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Taste buds respond to chemicals dissolved in food.
Located principally on the upper surface of the tongue.
Food molecules dissolve in the saliva and bind to the
membranes of the microvilli of the receptor cells. Taste buds respond to five flavors: salty, bitter, sweet,
sour, and umami.
Taste buds are preferentially responsive to one flavor.
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Smell
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The olfactory epithelium is a patch of receptor cells
that detects odors.
Located in the roof of the nasal cavities.
The receptor cells respond to thousands of differentmolecules.
The molecules bind to membrane receptors on the
olfactory hairs, stimulating nerve impulses that are
transmitted to the brain via the olfactory nerve.
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Vision
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The Visual Sense: The Eye
human eye consists of three distinct layers. The
The outermost layer consists of the sclera and the
cornea. The middle layer consists of the choroid, the ciliary
body, and the iris.
The innermost layer is the retina, the light-
sensitive layer,
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The retina contains two types of photoreceptors: rods and cones.
Rods function in dim light and provide black-and-white visionCones operate in bright light and provide color vision.
Cones are also responsible for visual acuity.
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The lens and cornea
focus light on theretina.
Alterations in the
shape of the lens andeyeball cause the
most common visual
problems.
Overlapping visualfields give us depth
perception.
Figure11-8
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Accommodation
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Extrinsic Eye Muscles
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Hearing and Balance: The Cochlea and Middle Ear
Th i t f th t i ll t ti th
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The ear consists of three anatomically separate portions: the
outer, middle, and inner ears.The outer earconsists of the auricle and external auditory
canal, both of which direct sound to the eardrum.
The middle earconsists of the eardrum and three smallbones, the ossicles, which transmit vibrations to the inner
ear.The inner earcontains the cochlea where the receptors
for sound are located
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The Structures of the Ear
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Hearing requires the participation of several structures.
The cochlea is a spiral-shaped, bony structure that contains three fluid-filled
canals. Separating the middle canal from the lower one is the flexible basilar
membrane that supports the organ of Corti.
Hair cells in the organ of Corti are embedded in the relatively rigid tectorialmembrane.
Sound waves create vibrations in the eardrum and ossicles, which are
transmitted to fluid in the cochlea.
Pressure waves in the
cochlea cause the basilar
membrane to vibrate, which
stimulates the hair cells.Pressure waves resulting
from a sound cause one part
of the membrane to vibrate
maximally.The hair cells stimulated in
that region send signals to
the brain, which it interprets
as a specific frequency.
Th tib l t h t th t
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The vestibular apparatus houses receptors that
detect body position and movement.
The semicircular canals, utricle, and saccule.
Fluid movement inside the semicircular canals deflectsthe cupula lying over the receptor cells, alerting the brain
to head movements.
The utricle and saccule contain receptors that respond to
linear acceleration and tilting of the head.
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End of Chapter 11