Somatosensory Receptors

chemoreceptor

detects smell, taste, pH

photoreceptor

detects light (rods and cones or retina)

thermoreceptor

detects temperature

mechanoreceptor

detects touch, muscle length/force, auditory and vestibular stimuli

nociceptor

detects pain

encapsulated sensory receptors

surrounded by multiple layers of epithelial tissue

non-encapsulated sensory receptors

no connective tissue capsule (i.e. free nerve endings)

slow adapting cutaneous receptor

respond slowly to change; more active for static conditions

fast adapting cutaneous receptor

respond quickly to change; more active for changing conditions

free nerve ending

stimulus: crude touch, pain, temperature

innervation: A-delta and C fibers

encapsulation: no

adaptation: rapid or slow

skin type: glabrous and hairy

hair receptor

stimulus: movement of hairs

innervation: A-delta fibers

encapsulation: no

adaptation: rapid

skin type: hairy

Merkel’s receptor

stimulus: pressure, edges, and texture

innervation: A-beta fibers

encapsulation: no

adaptation: slow

skin type: glabrous and hairy

Meissner’s corpuscles

stimulus: light touch (static) and vibration; stereognosis, two-point discrimination

innervation: A-beta

encapsulation: yes

adaptation: rapid

skin type: glabrous

Pacinian corpuscles

stimulus: touch (not static) and vibration

innervation: A-beta

encapsulation: yes

adaptation: rapid

skin type: glabrous and hairy

Ruffini endings

stimulus: static pressure and stretch of skin

innervation: A-beta

encapsulation: yes

adaptation: slow

skin type: glabrous and hairy

receptor field

area of skin monitored by a receptor

lateral inhibition

process by which most intensely stimulated neuron of the most intensely activated receptor in overlapping receptor fields inhibits the less intensely stimulated neurons via the action of inhibitory interneurons in the spinal cord

joint receptors

• free nerve endings, Ruffini’s endings, Paciniform corpuscles, ligament receptors

• found in joints, joint capsules, and ligaments

• sensitive to joint movement, tension, and the extremes of joint position (full flexion or extension)