Transcript 7-1 The Special Senses

Somatic and Special Senses
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Senses
constantly provide us with information
about our surroundings
 Grouped into two major categories:
- general senses
- special senses
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Sensory Pathway

Includes:
- receptors
- sensory neurons
- sensory tracts
- sensory area
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Receptors
detect stimuli
 specific with respect to changes to which
they respond

Sensory Neurons
transmit impulses from receptors to
central nervous system
 found in both spinal and cranial nerves
(each carries only one type of receptor)
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Sensory Tracts
white matter in spinal cord or brain
 transmit impulses to a specific part of brain

Sensory Areas
most are in cerebral cortex
 feel and interpret sensations
 learning to interpret sensations begins in
infancy without awareness and continues
throughout life
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General Senses
Somatic:
- tactile - touch, pressure, vibration, itch, etc.
- thermal - hot and cold
- pain - acute and chronic
- proprioceptive - muscle, tendon, joint
 Visceral
- distension of viscera - internal organs
- chemical composition of extracellular fluid
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Special Senses
Somatic:
- visual - sight
- auditory - hearing
- equilibrium - static and dynamic
equilibrium
 Visceral:
- olfactory - smell
- gustatory - taste
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Skin Receptors
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Tactile Sensations

Touch receptors:
- root hair plexuses
- tactile discs
- type II cutaneous mechanoreceptors
- corpuscles of touch - (Meissner’s
corpuscles)
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Root Hair Plexuses
dendrites arranged around hair follicles
 receptors that rapidly adapt to detect
movements when hair is disturbed
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Tactile Discs
expanded (flattened) nerve endings
 slowly adapting touch receptors for
discriminative touch
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Type II Cutaneous
Mechanorecptors
also called end organ for Ruffini
 expanded nerve endings
 embedded in dermis
 receptors that adapt slowly to heavy
and continuous touch
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Corpuscles of Touch
(Meissner’s Corpuscles)
small, oval, encapsulated nerve endings
 rapidly adapting touch receptors
 recognize exactly what point to which
body is touched
 abundant in hairless portions of skin
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Corpuscles of Touch
(cont.)
rapidly adapting receptors that respond
to low frequency vibrations
 also respond to pressure and touch
stimuli
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Tactile Sensations

Pressure and vibration receptors:
- corpuscles of touch (Meissner’s)
- lamellated corpuscles (Pacinian)
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Lamellated Corpuscles
(Pacinian)
oval structures
 composed of connective tissue
 layered like an onion
 enclose a dendrite
 rapidly adaptive receptors that respond
to pressure and high frequency
vibrations
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Tactile Sensations
(itch and tickle receptors)

free nerve endings are receptors for
both tickle and itch sensations
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Thermal Sensations
(thermoreceptors)
heat receptors most sensitive to
temperatures above 25oC (77oF) and
become unresponsive at temperatures
above 45oC (113oF)
 cold receptors most sensitive to
temperatures between 10oC (50oF) and
20oC (68oF)
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Thermal Sensations
(cont.)
intermediate temperature sensory input
from combination of cold and heat
receptors
 both heat and cold receptors rapidly
adapt to continuous stimulation
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Pain Sensations
(Nociceptors)
free, naked nerve endings
 located between cells of epidermis
 respond to all types of stimuli
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Referred Pain
pain that feels as if it originated from a
part other than site being stimulated
 Example:
- pain from heart attack (myocardial
infarction) may be felt in left shoulder or
inside of left arm
- pain from gallstones may be felt in
right shoulder
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