The Peripheral nervous system

The PNS is functionally divided into two divisions

sensory, motor the those two are divided into

1-somatic and visceral,

2- general and special

General visceral motor part

Autonomic nervous system (ANS)

ANS has two divisions

Parasympathetic

Sympathetic

Sensory receptors

pick up stimuli from inside or outside the body

Nerves

bundles of peripheral axons

Ganglia

clusters of peripheral neuronal cell bodies

Motor endings

axon terminals of motor neurons

Innervate effectors

muscle fibers and glands

Peripheral Sensory Receptors

Structures that pick up sensory stimuli

Initiate signals in sensory axons

Two main categories of sensory receptors

1-Free nerve endings of sensory neurons

2-Complete receptor cells

Free nerve endings of sensory neurons

Monitor general sensory information

Complete receptor cells

Specialized epithelial cels or small neurons

Monitor most types of special sensory information

Classification by Location

Exteroceptors,

Interoceptors,

Proprioceptors,

Mechanoreceptors,

Baroreceptors,

Thermoreceptors,

Exteroceptors

sensitive to stimuli arising from outside the body

Located at or near body surfaces

Include receptors for touch, pressure, pain, and temperature

Interoceptors

receive stimuli from internal viscera

Located in digestive tube, bladder, and lungs

• Monitor: Changes in chemical concentration, Taste stimuli, Stretching of tissues, Temperature

Proprioceptors

Located in skeletal muscles, tendons, joints, and ligaments

Monitor degree of stretch

Mechanoreceptors

respond to mechanical forces: Touch, pressure, stretch, vibration, and itch

Baroreceptors

monitor blood pressure

Thermoreceptors

respond to temperature changes

Classification by Stimulus Detected

Chemoreceptors: Respond to chemicals in solution

Photoreceptors; respond to light Located in the eye

Nociceptors: Respond to harmful stimuli that result in pain

Classification by Structure

General sensory receptors are divided into two groups

1- Free nerve endings,

2- Encapsulated nerve endings

Free Nerve Endings

1- Abundant in epithelia and underlying connective tissue

2- Respond to pain and temperature

3- Monitor affective senses

Two specialized types of free nerve endings

1- Epithelial tactile complexes (Merkel discs)

2- Hair follicle receptors

Epithelial tactile complexes (Merkel discs)

• Consist of tactile epithelial cel innervated by sensory nerve ending

• Slowly adapting receptors for light touch

Hair follicle receptors

wrap around hair follicles

• Rapidly adapting receptors

Encapsulated Nerve Endings

Consist of one or more end fibers of sensory neurons

Enclosed in connective tissue

• Mechanoreceptors

• Mechanoreceptors

Tactile (Meissner’s) corpuscles

• Lamelar (Pacinian) corpuscles

• Bulbous corpuscles (Ruffini endings)

• Proprioceptors (not covered in detail

Tactile (Meissner’s) corpuscles

Spiraling nerve ending surrounded by Schwann cells

Occur in the dermal papillae

Rapidly adapting receptors for discriminative touch

Occur in sensitive, hairless areas of the skin

Lamellar corpuscles

Single nerve ending surrounded by layers of flattened Schwann cells

Occur in the hypodermis (and dermis)

Sensitive to deep pressure—rapidly adapting receptors

• Bulbous corpuscles

Located in the dermis and respond to pressure

Monitor continuous pressure on the skin and adapt slowly