1. Human Anatomy & Physiology, Sixth Edition Elaine N. Marieb 13 The Peripheral Nervous System (PNS) Part A

2. Peripheral Nervous System (PNS)  Neural structures outside CNS, although soma may be w/in CNS  sensory receptors, peripheral nerves, ganglia, & motor endings  Divisions of PNS  Afferent division (sensory)  Efferent division (motor)  Somatic – innervate skeletal muscle  Autonomic – innervate smooth, cardiac, glands, visceral organs  Sympathetic – soma in spinal cord  Parasympathetic – soma in midbrain or sacrum

3. Efferent Division  Motor neurons of somatic division  Terminate at motor end plate  neuromuscular junction  Motor neurons of autonomic division  Varicosities in smooth & cardiac muscle & glands

4. Afferent Division - Sensory Neurons  Sensory neuron termini (dendritic processes) specialized to respond to stimuli  Activation triggers impulses to CNS  Perception in brain

5. Receptor Classification by Stimulus Type  Mechanoreceptors – change in neuron shape  Thermoreceptors - temperature  Photoreceptors - light  Chemoreceptors - chemicals  Nociceptors – pain-causing stimuli (chemicals)

6. Receptor Classification by Location:  Exteroceptors  Near body surface  Respond to stimuli arising outside body  Include special sense organs  Interoceptors  Respond to stimuli arising w/in body  Found in internal viscera & blood vessels  Proprioceptors  Respond to stretch  In skeletal muscles, tendons, joints, ligaments, & connective tissue

7.  Simple  Dendritic process triggered directly by stimulus  Encapsulated or unencapsulated  nociceptors  touch/pressure  Complex  Receptor cells w/in special sense organs  Sensory neuron stimulated by bipolar neuron  Photoreceptors  Mechanoreceptors  Olfactory receptors  Gustatory receptors Receptor Classification by Structure

8. Table 13.1.1

9. Table 13.1.2

10. Adaptation of Sensory Receptors  sensory receptors subjected to unchanging stimulus  Receptor membranes become less responsive  Receptor potentials decline in frequency or stop  Pressure, touch, & smell receptors adapt quickly  Merkel’s discs, Ruffini’s corpuscles, & interoceptors for blood chemicals adapt slowly  Pain receptors & proprioceptors do not adapt

11. Structure of a Nerve

12. Classification of Nerves by Directionality  Sensory (afferent) – signals TO CNS  Motor (efferent) – signals FROM CNS  Mixed –  both sensory & motor  most common  somatic & autonomic signals

13. Regeneration of Nerve Fibers Figure 13.4  Mature neurons are amitotic  If soma remains intact, neuron can regenerate

14. Cranial Nerves  12 pairs of nerves directly from brain  Sensory, motor, or mixed  I - XII according to anterior level of origin  Named by to innervated organs/function  Four cranial nerves carry parasympathetic fibers serving muscles & glands

15. Cranial Nerves

16. Summary of Cranial Nerves

17. Spinal Nerves Figure 13.6

18. Spinal Nerve Roots Figure 13.7a (ANS)

19. Nerve Plexuses  Interlacing nerve networks  cervical  brachial  lumbar  sacral  Branches of plexus contain fibers from several nerves  Every muscle innervated by multiple spinal nerves

20. Cervical Plexus Figure 13.8

21. Brachial Plexus Figure 13.9a

22. Figure 13.9c Brachial Plexus: Distribution of Nerves

23. Figure 13.7b Spinal Nerve Innervation: Back, Anterolateral Thorax, & Abdominal Wall

24. Lumbar Plexus Figure 13.10

25. Sacral Plexus Figure 13.11

26. Reflexes  Rapid, predictable motor response to a stimulus  Reflexes:  Intrinsic or acquired  Involve only PNS & spinal cord  Can relay to higher brain centers  Somatic reflexes – skeletal muscle  Autonomic reflexes – smooth muscle, glands

27. Reflex Arc Components  Receptor  Sensory neuron  Integration center  Motor neuron  Effector Receptor 1 2 3 4 Sensory neuron Integration center 5 Effector Motor neuron Stimulus Skin Spinal cord (in cross-section) Interneuron

28. Stretch & Deep Tendon Reflexes  Proprioceptors in tendons & muscle continually maintain postural contractions & muscle tone  These effects are via spinal reflex arcs

29. Muscle Spindles – Stretch Receptors  Intrafusal muscle fibers lacking myofilaments in central regions  Wrapped by type Ia & type II fibers afferent fibers  Innervated by  efferent fibers

30. Operation of Muscle Spindles Stimulates action potential in postsynaptic neuron Does not stimulates action potential in postsynaptic neuron

31. Stretch Reflex Figure 13.17

32. Flexor & Crossed Extensor Reflex Figure 13.19