Chapter 13- The Peripheral Nervous System

sensation

awareness of stimulus

perception

interpretation of the meaning of stimulus occurring in brain

interceptors (visceroceptors)

respond to stimuli arising in internal viscera and blood vessels, sensitive to chemical changes, tissue stretch, and temperature changes, sometimes causes discomfort but usually a person is unaware of their workings

propioceptors

respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bone and muscles, inform brain of one’s movements

nonencapsulated (free) nerve endings

abundant in epithelia and connective tissues, most are nonmyelinated, respond mostly to temperature, pain, or light touch

Cold receptors (nonencapsulated)

activated by temps from 10-40 C, located in superficial dermis

Heat receptors (nonencapsulated)

activated from 32-48C located in deeper dermis 

Nociceptors (nonencapsulated)

triggered by extreme changes, pinch, or release of chemicals from damaged tissue 

Vanilloid receptor

protein in nerve membrane is main player, actts as an ion channel opened by heat, low pH, chemicals and also acts as a itch receptors triggered by chemcals such as histamine

Tactile (Merkel) cells (nonencapsulated)

function as light touch receptors and located in deeper layers of epidermis

Hair follicle receptors (nonencapsulated)

free nerve endings that wrap around hair follicles and act as light touch receptors that detect bending of hairs 

tactile (Messner’s) corpuscles (encapsulated)

small receptors involved in discriminitive touch, found just below skin, mostly in sensitive and hairless areas

Lamellar (Pacinian) corpuscles (encapsulated)

large receptors respond to deep pressure and vibration when first applied (then turn off) located in deep dermis

Bulbous copscules (Ruffini endings) (encapsulated)

respond to deep and continuous pressure, located in dermis 

Processing at the receptor level

AP much reach CNS, stimulus must be applied within receptive field and specificity, transduction, and graded potentials much reach threshold 

Transduction

energy of stimulus is converted into graded potential (generator potential in general receptors or receptor potential in special sense receptors)

Adaptation

change in sensitivity in presence of constant stimulus, receptor membranes become less responsive and potentials decline in frequency or stop

Phasic receptors

fast acting, send signals at the beginning or end of stimulus 

Ex. pressure, touch, smell

Tonic receptors

adapt slowly or not at all

Ex. nociceptors and most proprioceptors

Feature abstractication

identification of more complex aspects and several stimulus properties

Quality discrimination

ability to identify submodalities of a sensation

Pattern recognition

recognition of familiar or significant patterns in stimuli

Processing at the circuit level

3 order neurons conduct and transmit to the CNS, third order, then somatosensory cortex (perceptual)

Processing at the perceptual level

interpretation of sensor input depends on specific location of target neurons in sensory cortex

Visceral pain

results from stimulation of visceral organ receptors, felt as vague aching, gnawing, burning, activated by tissue stretching, ischemia, chemicals, muscle spasm

Referred oain

pain from one body region perceived as coming from a different region due to visceral and smatic pain fibers travel along same nerves, so brain assumes stimulus comes from common somatic region 

Ex. left arm pain during heart attack 

ganglia

contian neuron cell bodies associated with nerves in PNS,

ganglia associated with afferent nerve fibers

contain cell bodies of sensory neurons, dorsal root ganglia (sensory, somatic)

ganglia associated with efferent nerve fibers 

contain autonomic motor neurons, autonomic ganglia (motor, visceral)