a&p ch 12

special senses

smell
taste
vision
hearing
balance

general senses

somatic senses
visceral senses

somatic senses

tactile sensations
thermal sensations
pain sensations
proprioceptive sensations

tactile sensations

touch
pressure
vibration
itch
tickle

thermal sensations

warm
cold

proprioceptive sensations

joint & muscle position sense

movements of limbs & head

visceral senses

provide information about conditions within internal organs

sensation

conscious or subconscious awareness of changes in external or internal environments

for sensation to occur, must have:

stimulus (light, heat, pressure, mechanical energy, chemical energy)

sensory receptor

conduction of nerve impulses

integration of nerve impulses

perception

conscious awareness/interpretation of sensations

primarily a function of cerebral cortex

adaptation

decrease in strength of sensation during prolonged stimulus

sensory receptors grouped by:

structure

function

STRUCTURAL classification of sensory receptors:

free nerve endings

encapsulated nerve endings

separate cells

FUNCTIONAL classification of sensory receptors:

MECHANORECEPTORS
---pressure
THERMORECEPTORS
---temperature
NOCICEPTORS
---pain
PHOTORECEPTORS
---light
CHEMORECEPTORS
---chemicals in mouth (taste),
nose (smell), and body fluids
OSMORECEPTORS
---osmotic pressure of body fluid

free nerve endings

bare dendrites

associated with:
pain, thermal, tickle, itch, and some touch

encapsulated nerve endings

dendrites enclosed in connective tissue capsule

ex: corpuscle of touch

separate cells

receptor cell synapses with sensory neuron

located in:
retina (photoreceptors)
inner ear (hair cells)
taste buds (gustatory receptors)

tactile receptors of the skin or subcutaneous layer

*FREE NERVE ENDINGS
---itch and tickle

*CORPUSCLES OF TOUCH
*HAIR ROOT PLEXUSES
*TYPE I AND II CUTANEOUS MECHANORECEPTORS
*LAMELLATED CORPUSCLES
---touch, pressure, vibration

TOUCH
corpuscles of touch

aka: meissner corpuscles

located in hairless skin

egg-shaped

encapsulated nerve endings

TOUCH
hair root plexuses

free nerve ending wrapped around hair follicles of hairy skin

detect movement on skin surface that disturbs hairs

TOUCH
type I cutaneous mechanoreceptors

aka: merkel discs

saucer shaped, free nerve endings

make contact w/ merkel cells in stratum basale

fingertips, hands, lips, external genitalia

TOUCH
type II cutaneous mechanoreptors

aka: ruffini corpuscles

elongated, ecapsulated receptors

located deep in dermis, in ligaments and tendons

hands, soles of feet

*most sensitive to stretching of digits or limbs

pressure

sustained sensation, felt over larger area than touch

involved receptors:
-corpuscles of touch
-type I mechanoreceptors
-lamellated corpuscles

lamellated corpuscles

large, oval, multilayered

adapt rapidly

widely distributed in body: dermis, subcutaneous layer, joints, tendons, muscles, periosteum, mammary glands, external genitalia, pancreas, urinary bladder

vibration

rapidly repetive sensory signals from tactile receptors

-corpuscles of touch: lower frequency vibration

-lamellated corpuscles: higher frequency vibration

itch

stimulation of free nerve endings

often result of local inflammatory response

tickle

stimulation of free nerve endings and lamellated corpuscles

can only occur when someone else touches you, not when you touch yourself