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