Sensory Receptors &

The PNS contains

all neural structures outside brain and spinal cord

The PNS is broken into 4 parts (NOT the different kind of systems)

1. Sensory receptors 2. Nerves: transmission lines 3. Motor endings and motor activity 4. Reflex activity

Five stimulus classifications of sensory receptors

mechanoreceptors, thermoreceptors, photoreceptors, chemoreceptors, nociceptors

Mechanoreceptors

respond to touch, pressure, vibration, and stretch

Thermoreceptors

sensitive to changes in temperature

Photoreceptors

respond to light energy

Example of a photoreceptor

retina

Chemoreceptors

respond to chemicals

Examples of Chemoreceptors

smell, taste, changes in blood chemistry

Nociceptors

sensitive to pain-causing stimuli

Examples of Nociceptors

extreme heat or cold, excessive pressure, inflammatory chemicals

Three location classifications of sensory receptors

Exteroceptors, Interceptors, Proprioceptors

Exteroceptors responds to

stimuli arising outside body

Exteroceptors located in

skin and most special sense organs

Interoceptors responds to

stimuli arising in internal viscera and blood vessels

Interoceptors sensitive to

chemical changes, tissue stretch, and temperature changes

Proprioceptors responds to

stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles

Simple receptors of the general senses are

Modified dendritic endings of sensory neurons

Simple receptors of the general senses are found

throughout body to monitor most types of general sensory information

General senses include

Tactile sensations, temperature, pain, touch, proprioception

Nonencapsulated (free) nerve endings

are mainly nonmyelinated with knoblike swellings found in epithelia and connective tissues

Examples of free nerve endings

Tactile discs, hair root plexus

Thermoreceptors, Chemoreceptors, Nociceptors

Encapsulated nerve endings

mechanoreceptors encased in connective tissue capsule

examples of encapsulated nerve endings

Lamellar corpuscles, tactile corpuscles, Bulbous corpuscles, Muscle spindles, Tendon organs

Adaptation

change in sensitivity in presence of constant stimulus

At the adaptation processing receptor levels, the receptor become

less responsive and receptor potentials decline in frequency or stop

Phasic receptors

(fast-adapting) send signals at beginning or end of stimulus

Examples of Phasic receptors

receptors for pressure, touch, and smell

Tonic receptors

adapt slowly or not at all

Examples of tonic receptors

nociceptors and most proprioceptors