Transcript The Somatic Senses

The Somatic Senses
Sensory reception of the five
senses
Receptors
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Five types of receptors
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Chemoreceptor – changes in chemical
concentrations
Pain – tissue damage
Temperature (thermoreceptors)- changes in
temp
Mechanoreceptors – changes in pressure and
movement
Photoreceptors – changes in light energy
Sensation – what is it?
When you touch an objects actually, are
they really hot or cold?
What is happening when you touch hot
water or step outside when it is very
“cold” out?
Sensation is..
The feeling when the brain interprets
sensory impulses.
 What you feel when you touch something
“hot” or “cold” is the energy transfer into
or out of your body.
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Projection is …
When the cerebral cortex causes the
feeling to seem to come from the
stimulated receptors. This is at the same
time the sensation forms.
 Basically the brain projects the sensation
back to its apparent source.
 This allows to pinpoint the region of
stimulation.
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The eyes seem to see; the ears seem to hear.
Sensory adaptation…
When sensory receptors are continuously
stimulated
 As receptors adapt, the impulses
decrease, and continue to decrease, and
the reception may even stop
 Change in strength of the stimulus will
trigger impulses again
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Touch and Pressure Mechanoreceptors:
Three kinds of receptors: sensory
nerve fibers (free end), Meissener’s
Corpuscles, Pacinian corpuscles
 These receptors perceive sensations
such as pressure, vibrations, and
texture.
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Touch and Pressure Mechanoreceptors:
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Those found in the very top layers of the
dermis and epidermis and are generally
found in non-hairy skin such as the
palms, lips, tongue, soles of feet,
fingertips, eyelids, and the face.
Those located deeper in the dermis and
along joints, tendons, and muscles
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feel sensations such as vibrations
traveling down bones and tendons,
rotational movement of limbs, and the
stretching of skin. This greatly aids your
ability to do physical activities such as
walking and playing ball.
Temperature Senses
Two types of free nerve
endings: warm and cold
 Warm Receptors
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Most sensitive at temps above
77oF
Unresponsive at temps above
113oF
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This will stimulate pain receptors,
produces burning sensation
Cold receptors
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Most sensitive between 50-68oF
Temps below 50oF stimulate pain
receptors, produces freezing
sensation
Temperature Senses
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Cold receptors are found in greater density
than heat receptors. The highest concentration
of thermoreceptors can be found in the face
and ears (hence why your nose and ears
always get colder faster than the rest of your
body on a chilly winter day).
Pain receptors
Free nerve endings
 Widely distributed throughout the body,
except in the nervous tissue and brain
 Adapt poorly, if at all
 Once stimulated, may continue to send
impulses to the CNS = persistent pain
 Pain is poorly understood
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Pain
Pain elicited during a muscle cramp stems
from sustained contraction that squeezes
capillaries and interrupts blood flow.
 Deficiency in oxygen-rich blood may
trigger pain sensations
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Referred pain
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Pain that is coming from some part of the
body other than the part being stimulated
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Pain from the heart may be felt from the left
shoulder or upper left limb.
Generally comes from visceral pain = deep
within the body/ visceral tissue
Special Senses = smell, taste, sight,
hearing /equilibrium,
Sense
Organ
Smell
Olfactory organs
Taste
Taste buds
Hearing/ equilbrium
Ears
Sight
eyes
Smell
Olfactory receptor cells =
bipolar
 Stimulated fibers synapse
with neurons in olfactory
bulb
 Impulses from the olfactory
bulb travel along olfactory
tracts to the limbic system
 Major interpretation sites are
found in the temporal lobes
and parts of the frontal lobe.
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Olfactory Stimulation
Uncertain how this stimulation begins
 Smells are interpreted as a code
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For example, if there are 10 receptors, parsley may
stimulate receptors 3, 4, & 8 and chocolate might
stimulate 1,5, & 10
Olfactory organs are located high in the
nasal cavity
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May need to force air in during inhale to get a
faint smell
Undergo sensory adaptation rapidly
Taste
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Each taste bud has a group of taste cells
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Each bud has 50-150 cells replaced every three days
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Entire structure is within the taste pore
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Tiny projections are called taste hairs
Taste
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Salivary glands dissolve chemicals in order for
the tongue to taste
4-7 taste sensations
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Sweet
Sour
Salty
Bitter
Metallic
Alkaline
Umami – detects MSG
Taste
Each taste cell can detect two sensations,
although one sensation may dominate
over the other
 Taste cells undergo sensory adaptation
rapidly
 Impulses move from taste cells through
facial, glossopharyngeal and vagus nerves
to medulla oblongata
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They then move to the thalamus to the
parietal lobe
Hearing
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The ear has an external, middle and inner
part
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External ear has two parts – auricle and the
external auditory meatus
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Both direct sound waves toward the middle ear
Middle ear – includes tympanic cavity, eardrum,
and auditory ossicles (three small bones)
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Eardrum moves back and forth in response to vibrations
of the sound wave
These vibrations are transferred to the auditory ossicles,
which then stimulate the hearing receptors
Hearing
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The ear has an external, middle and inner
part
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Inner Ear – comprised of two labyrinths which
include semicircular canals and the cochlea
Sound waves move through this area exciting
hair cells (nerve cells)
Sound frequency stimulates only certain cells
Cells do not have dendrites or axons, but act
very much like a neuron
Impulses are interpreted in the temporal lobe
of the brain
Sight