Chapter 12 Notes

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12 May 2011
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Chapter 12: Touch
Touch is mechanical sensation from mechanical movement of skin
oTactile is the movement
Kinethesis: perception of posn/movement of limbs
Proprioception: perception mediated by kinesthetic and vestibular receptors
oBroader system of kinethesis
Somatosensation: collective term for sensory sigs from body
touch requires more action for us to sense it
Touch Physiology
The Sense Organs and Receptors Units for Touch
skin is largest and heaviest sense organ
epidermis: outer layer of skin
dermis: inner of 2 layers of skin
ohas nutritive and connective tissue
skin has diff receptors called channels
oe.g. touch ice, different channels sends info about temp, shape and texture
attributes of receptors:
oType of stim. it responds to
E.g. pressure/vibration/temp
oSize of receptor field
oRate of adaptation (fast vs. slow)
fast-adapting(FA): burst of action potentials for onset/offset of stim,
doesnt respond when stim is static
slow-adapting(SA): active in steady state of stim.
TACTLE RECEPTORS
Mechanoreceptors: sensory receptor, responds to mechanical stim (pressure,
vibration and movement)
Has nerve fiber and expanding endings
Classed as A-beta fibers, allow fast neural conduction
Mechanoreceptors and afferent(going towards brain) fibers have properties similar to
hairless skin
Terminal endings:
oMeissner corpuscles: specialize nerve ending
FA I fibers, small RFendings at
junction of
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oMerkel cell neurite complex: specialized nerve ending
epidermis and dermis
SA I fibers, small RF
oRuffini endings: specialized nerve ending
SA II fibers, large RFDeeper in dermis
oPacninian corpuscles: specialized nerve ending
FA II fibers, large RF
Four types of mechanoreceptors: FA I, FA II, SA I, SA II
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Response characteristics of 4 mechanoreceptor populations:
Size of Receptive Field
Adaptation RateSmall Large
SlowSA I (Merkel)
-respond to steady
pressure, fine spatial,
freq vibe
-feel pressure
e.g. reading Braille
SA II (Ruffini)
-respond to sustained
pressure, fine lateral skin
stretch, more than one has to
be stimulated
e.g. picking up cup
FastFA I (Meissnner)
-respond best to freq vibe,
skin deformation
-feel wobble
- e.g. vibe on skin tells us to
tighten grip on rifle
FA II (Pacinian)
-respond best to freq vibe,
skin deformation
-feel buzz
e.g. tapping pencil on table
Mechanoreceptors work together to tell us about objects
KINESTHETIC RECEPTORS
Kinesthetic receptors: type of mechanoreceptors, help sense where limbs are and
movement
oIn muscles, tendons and joints
Muscle spindle: sensory receptor in muscles, senses tension
oHow we sense angle from limb and joint
oCommunicate how fast muscle fibers are changing in length
Without kinesthetic receptors we cant do movements without vision
THERMORECEPTORS
Thermoreceptors: tell about change in skin temp
oIn epi and dermal of skin
2 types of thermoreceptors:
oWarmth fibers: fire when skin temp
oCold fibers: fire when skin temp
More of these than warmth fibers
Skin 30 to 36 , fibers dont respond much at normal temps
NOCICEPTORS
Nociceptors: send info about painful stim. that can/does damage skin
oHave bare nerve endings
2 types of nociceptors:
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