Chapter 13

General senses

-include tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sense No "one-receptor-one-function" relationship Receptors can respond to multiple stimuli Receptors have either: Nonencapsulated (free) nerve endings or Encapsulated nerve endings

Sensory receptors

-specialized to respond to changes in environment (stimuli) Activation results in graded potentials that trigger nerve impulses Awareness of stimulus (sensation) and interpretation of meaning of stimulus (perception) occur in brain Three ways to classify receptors: by type of stimulus, body location, and structural complexity

Nonencapsulated (free) nerve endings

Abundant in epithelia and connective tissues Most are nonmyelinated, small-diameter group C fibers; distal terminals have knoblike swellings Respond mostly to temperature, pain, or light touch Thermoreceptors Cold receptors are activated by temps from 10 to 40C Located in superficial dermis Heat receptors are activated from 32 to 48C located in in deeper dermis Outside those temperature ranges, nociceptors are activated and interpreted as pain Nociceptors: pain receptors triggered by extreme temperature changes, pinch, or release of chemicals from damaged tissue Vanilloid receptor: protein in nerve membrane is main player Acts as ion channel that is opened by heat, low pH, chemicals (example: capsaicin in red peppers) Itch receptors in dermis: can be triggered by chemicals such as histamine

Encapsulated dendritic endings

Almost all are mechanoreceptors whose terminal endings are encased in connective tissue capsule

Simple receptors of the general senses

Modified dendritic endings of sensory neurons Are found throughout body and monitor most types of general sensory information

PNS

Part 1 - Sensory Receptors Part 2 - Transmission Lines: Nerves and Their Structure and Repair Part 3 - Motor Endings and Motor Activity Part 4 - Reflex Activity

Interoceptors (visceroceptors)

Respond to stimuli arising in internal viscera and blood vessels Sensitive to chemical changes, tissue stretch, and temperature changes Sometimes cause discomfort but usually person is unaware of their workings

Exteroceptors

Respond to stimuli arising outside body Receptors in skin for touch, pressure, pain, and temperature Most special sense organs

Proprioceptors

Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles Inform brain of one's movements

Receptors for special senses

Vision, hearing, equilibrium, smell, and taste All are housed in complex sense organs Covered in Chapter 15

Hair follicle receptors

free nerve endings that wrap around hair follicles Act as light touch receptors that detect bending of hairs Example: Allows you to feel a mosquito landing on your skin

Tactile (Merkel) discs

function as light touch receptors Located in deeper layers of epidermis

Lamellar (Pacinian) corpuscles

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

Tendon organ

proprioceptors located in tendons that detect stretch

Joint kinesthetic receptors

proprioceptors that monitor joint position and motion

Chemoreceptors

respond to chemicals (examples: smell, taste, changes in blood chemistry)

Bulbous corpuscles (Ruffini endings):

respond to deep and continuous pressure Located in dermis

Photoreceptors

respond to light energy (example: retina)

Mechanoreceptors

respond to touch, pressure, vibration, and stretch

Thermoreceptors

sensitive to changes in temperature

Nociceptors

sensitive to pain-causing stimuli (examples: extreme heat or cold, excessive pressure, inflammatory chemicals)

Tactile (Meissner's) corpuscles:

small receptors involved in discriminative touch Found just below skin, mostly in sensitive and hairless areas (fingertips)

Muscle spindles:

spindle-shaped proprioceptors that respond to muscle stretch