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PowerPoint Presentation
to accompany
Hole’s Human Anatomy
and Physiology, 9/e
by
Shier, Butler, and Lewis
Chapter 12
Somatic and Special Senses
Receptors
• Chemoreceptors: sense change in chemicals
• Nociceptors: stimulated by tissue damage
• Thermoreceptors: sense temperature
changes
• Mechanoreceptors: sense mechanical forces
including proprioceptors, baroreceptors, and
stretch receptors
• Photoreceptors: respond to light
Sensory Impulses
• Stimulation of sensory receptors cause local
changes in membrane potentials (receptor
potentials)
• Sensory impulses are generated directly or
indirectly to the CNS
• Sensation: a feeling that occurs when the
brain interprets sensory impulses
• Projection pinpoints region of stimulation
Sensory Adaptation
• Continuous stimulation leads to the receptor
becoming less responsive to the stimulus
• Eventually receptors stop sending signal
• Increasing the strength of stimulus will
trigger impulses
Touch and Pressure Senses
• Sensory nerve fibers:
free nerve endings in
epithelium respond to
touch and pressure
• Meissner’s corpuscles:
found in lips, palms,
soles, nipples, fingertips,
genitalia, respond to
sensation of light touch
Figure 12.1
Touch and Pressure Senses
• Pacinian corpuscles:
deep subcutaneous
tissues, respond to
heavy pressure and
vibrations
Figure 12.1
Temperature Senses
• Two groups of free nerve endings located in
the skin
• Heat receptors respond to temperatures
between 25 and 45 degrees C
• Cold receptors respond between 10 and 20
degrees C
• Outside of these ranges, pain receptors are
stimulated
Sense of Pain
• Free nerve endings sense pain.
• Pain receptors may respond to more than
one stimulus or be sensitive to only one
type of change.
• Pain receptors adapt very little if at all.
Visceral Pain
• Internal organs have
only pain receptors.
• Referred pain is pain
that feels like it
comes from a
different location
than the site
stimulated.
• Referred pain may
come from common
nerve pathways.
Figure 12.3
Figure 12.4
Pain Nerve Pathways
• Acute pain fibers, A-delta fibers: thin,
myelinated fibers that conduct impulses
rapidly. These cause sharp pain
• Chronic pain fibers, C-fibers, are thin,
unmyelinated nerve fibers that conduct
impulses more slowly. These cause dull,
aching pain
• Awareness of pain occurs at the thalamus
Postsynaptic Potentials
• Neuropeptides can block pain signals by
inhibiting presynaptic nerve fibers.
• Enkephalins suppress acute and chronic
pain.
• Serotonin stimulates enkephalin release.
• Endorphins are morphine like substances
released in response to extreme pain.
Stretch Receptors
• Muscle spindles
are found in
skeletal muscles
where they join
tendons.
• The stretch reflex
opposes muscle
lengthening.
Figure 12.5
Stretch Receptors
• Golgi tendon
organs are found
in tendons where
they attach to
muscles.
• They stimulate a
reflex that opposes
the stretch reflex.
Figure 12.5
Sense of Smell
• Olfactory receptors:
chemoreceptors that work
closely with sense of taste
• Olfactory receptor cells
are bipolar neurons
surrounded by columnar
epithelium
• Odorant molecules enter
as gases and dissolve. The
molecules bind to
receptors and depolarized Figure 12.6
them
Figure 12.6
Olfactory Nerve Pathways
• Olfactory receptor fibers synapse with
neurons in the olfactory bulbs.
• Impulses travel along the olfactory tracts to
the limbic system.
• Impulses are interpreted in olfactory cortex.
• Olfactory receptor neurons are in direct
contact with the environment and can be
replaced if damaged.
Sense of Taste
• Taste buds are found on tongue papillae.
• Taste buds contain taste cells, modified
epithelial cells that act as receptors.
• Taste buds are spherical with a taste pore.
• Taste hairs, the sensitive parts of the cell,
are microvilli that protrude from taste cells.
• Dissolved chemicals bind to taste hairs.
Figure 12.8