1. The Peripheral Nervous System
Nervous structures outside the brain and spinal cord
Nerves allow the CNS to receive information and take action
Functional components of the PNS
Sensory inputs and motor outputs
Categorized as somatic or visceral
Sensory inputs also classified as general or special

2. The Peripheral Nervous System
Autonomic nervous system (ANS)
General visceral motor part of the PNS
ANS has two divisions
Parasympathetic
Sympathetic

3. Functional Organization of the PNS
Figure 14.1

4. Basic Structural Components of the PNS
Sensory receptors – pick up stimuli from inside or outside the body
Motor endings – axon terminals of motor neurons
Innervate effectors (muscle fibers and glands)
Nerves and ganglia
Nerves – bundles of peripheral axons
Ganglia – clusters of peripheral neuronal cell bodies

5. Basic Anatomical Scheme of the PNS in the Region of a Spinal Nerve
Figure 14.2

6. Peripheral Sensory Receptors
Structures that pick up sensory stimuli
Initiate signals in sensory axons
Two main categories of sensory receptors
Free nerve endings of sensory neurons
Monitor general sensory information
Complete receptor cells – specialized epithelial cells or small neurons
Monitor most types of special sensory information

7. Peripheral Sensory Receptors
Sensory receptors also classified according to:
Location
Type of stimulus detected
Structure

8. Classification by Location
Exteroceptors – sensitive to stimuli arising from outside the body
Located at or near body surfaces
Include receptors for touch, pressure, pain, and temperature
Interoceptors – (visceroceptors) receive stimuli from internal viscera
Monitor a variety of stimuli
Proprioceptors – monitor degree of stretch
Located in musculoskeletal organs

9. Classification by Stimulus Detected
Mechanoreceptors – respond to mechanical forces
Thermoreceptors – respond to temperature changes
Chemoreceptors – respond to chemicals in solution
Photoreceptors – respond to light – located in the eye
Nociceptors – respond to harmful stimuli that result in pain

10. Classification by Structure
General sensory receptors
Widely distributed
Nerve endings of sensory neurons monitor:
Touch, pressure, vibration, stretch
Pain, temperature, proprioception
Divided into two groups
Free nerve endings
Encapsulated nerve endings

11. Abundant in epithelia and underlying connective tissue
Free Nerve Endings
Abundant in epithelia and underlying connective tissue
Respond to pain and temperature
Monitor affective senses
Two specialized types of free nerve endings
Merkel discs – lie in the epidermis
Slowly adapting receptors for light touch
Hair follicle receptors – wrap around hair follicles
Rapidly adapting receptors

12. Unencapsulated Nerve Endings
Table 14.1

13. Encapsulated Nerve Endings
Consist of one or more end fibers of sensory neurons
Enclosed in connective tissue
Mechanoreceptors
Include four main types

14. Encapsulated Nerve Endings
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

15. Meissner’s Corpuscles
Table 14.1

16. Encapsulated Nerve Endings
Pacinian corpuscles
Single nerve ending surrounded by layers of flattened Schwann cells
Occur in the hypodermis
Sensitive to deep pressure – rapidly adapting receptors
Ruffini’s corpuscles
Located in the dermis and respond to pressure
Monitor continuous pressure on the skin – adapt slowly

17. Pacinian Corpuscles and Ruffini’s Corpuscles
Table 14.1

18. Encapsulated Nerve Endings
Proprioceptors
Monitor stretch in locomotory organs
Three types of proprioceptors

19. Three Types of Proprioceptors
Muscle spindles – measure the changing length of a muscle
Imbedded in the perimysium between muscle fascicles
Golgi tendon organs – located near the muscle-tendon junction
Monitor tension within tendons
Joint kinesthetic receptors
Sensory nerve endings within the joint capsules

20. Proprioceptors
Table 14.1

21. Structure of Proprioceptors
Figure 14.4