Chapter 13 Peripheral Nervous System

Sensory receptors

Specialized cells unique to each sense organ that respond to changes (stimuli) in the external and internal environment.

Sensation

Awareness of stimulation.

Perception

Interpretation of the meaning of a stimulus.

Mechanoreceptors

Sensory receptors that respond to touch, pressure, vibration, and stretch.

Thermoreceptors

Sensory receptors that are sensitive to changes in temperature.

Photoreceptors

Sensory receptors that respond to light energy.

Chemoreceptors

Sensory receptors that respond to chemicals/solutes dissolved in fluid/water.

Nociceptors

Sensory receptors sensitive to pain-causing stimuli such as extreme heat/cold, excessive pressure, inflammatory chemicals.

Exteroceptors

Sensory receptors that respond to stimuli arising outside of the body.

Interoceptors

Sensory receptors that respond to stimuli arising in internal viscera and blood vessels.

Proprioceptors

Sensory receptors that respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles.

Simple receptors

Neurons with modified dendritic endings.

Sense organs

Organs that receive stimuli.

General senses

Tactile sensations such as temperature, pain, touch, pressure, vibration, proprioception.

Nonencapsulated nerve endings

Dendrites of nonmyelinated axons that respond mostly to temperature, pain, or light touch.

Encapsulated nerve endings

Dendrites enclosed in connective tissue capsule for pressure, vibration, and some touch sensations.

Tactile (Merkel) discs

Function as light touch receptors; located in deeper layers of epidermis

Hair follicle receptors

Free nerve endings that wrap around hair follicles that detect the bending of hairs.

Tactile (Meissner's) corpuscles

Small receptors involved in discriminative touch

Found just below skin, mostly in sensitive and hairless areas (fingertips)

Lamellar (Pacinian) corpuscles

Large receptors respond to deep pressure and vibration when first applied (then turn off)

Located in deep dermis

Bulbous corpuscles (Ruffini endings)

Respond to deep, continuous pressure, in dermis

Muscle spindles

Spindle-shaped proprioceptors that respond to muscle stretch

Tendon organ

Proprioceptors located in tendons that detect stretch.

Joint kinesthetic receptors

Proprioceptors that monitor joint position and motion.

Transduction

Energy of stimulus is converted into graded potential called generator potential or receptor potential.

Generator potential

A graded potential in a general sensory neuron.

Receptor potential

A grade potential in a special sensory neuron.

Perceptual detection

Ability to detect a stimulus (requires summation of impulses)

Magnitude estimation

Intensity coded in frequency of impulses.

Spatial discrimination

Identifying site or pattern of stimulus (studied by two-point discrimination test).

Feature abstraction

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.

Referred pain

Pain from one body region perceived as coming from a different body region.

Hyperalgesia

Increased sensitivity to pain.

Phantom limb pain

Pain in a limb (or extremity) that has been amputated.

Nerve

A cord-like bundle of neuronal axons and/or dendrites and associated connective tissue outside the central nervous system

Endoneurium

Loose connective tissue that encloses axons and their myelin sheaths.

Perineurium

Coarse connective tissue that bundles fibers into fascicles.

Epineurium

Dense connective tissue that surrounds entire nerve including fascicles and blood vessels.

Mixed nerve

Contains both sensory and motor fibers so impulses travel both to and from the CNS.

Sensory (afferent) nerve

A nerve containing only sensory fibers with impulses only toward the CNS.

Motor (efferent) nerve

A nerve containing only motor fibers with impulses only away from CNS.

Ganglia

Contain neuron cell bodies associated with nerves in PNS.