Thibodeau: Anatomy and Physiology, 5/e. Chapter 14: Peripheral Nervous System

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1 Thibodeau: Anatomy and Physiology, 5/e Chapter 14: Peripheral Nervous System To show the continuity between the peripheral nervous system (PNS) and the central nervous system (CNS), remind students that the discussion of the CNS ended with the somatic sensory and somatic motor pathways. This chapter on the PNS picks up that discussion with an exploration of the nerve pathways that lead to and from the CNS, together comprising the PNS. Discussion opens with the 31 pairs of spinal nerves that emerge from the spinal cord and the smaller nerves in turn emerging from them. Next, the 12 pairs of cranial nerves and their functions are discussed. The afferent and efferent divisions of the PNS are then introduced; the central discussion in this chapter focuses on the efferent division, which is further divided into the somatic motor nervous system and the autonomic efferent nervous system. Differentiations are made between the sympathetic and parasympathetic divisions of the autonomic nervous system. Objectives After students have completed this chapter, they should be able to: 1. Discuss the generalized structure or branching of a typical spinal nerve. 2. Identify the location of the four major pairs of plexuses. 3. Identify the cranial nerves by name and give the generalized function of each. 4. Identify the basic principles of somatic motor pathways. 5. List and discuss several of the somatic reflexes of clinical importance. 6. Identify the two major subdivisions of the autonomic nervous system. 7. Compare and contrast the structures of the parasympathetic and sympathetic pathways. 8. Identify the autonomic neurotransmitters and receptors and where they are found. 9. Explain the functional advantages of multiple types of autonomic neurotransmitters and receptors. 10. Discuss the function of the autonomic nervous system as a whole. 11. Compare and specify functions of the sympathetic and parasympathetic divisions of the autonomic nervous system. Lecture Outline I. Introduction (p. 413) II. Spinal Nerves (Fig. 14-1) A. Spinal nerve numbering system (Fig. 14-1) 1. Cervical nerves (8 pairs) 2. Thoracic nerves (12 pairs) 3. Lumbar nerves (5 pairs) 4. Sacral nerves (5 pairs) B. Structure of spinal nerves 5. Coccygeal nerves (1 pair) 1. Roots (Fig. 14-2) a. Ventral (anterior) root (includes motor fibers)

2 Chapter 14: Peripheral Nervous System 2 b. Dorsal (posterior) root (includes sensory fibers) 1) Dorsal root ganglion (spinal ganglion) 2. Spinal nerve rami (Fig. 14-2) a. Ventral ramus b. Dorsal ramus c. Sympathetic ramus C. Nerve plexuses (p. 415) 1. Definition of plexus 2. Four main pairs of plexuses (Fig. 14-1; Table 14.1) a. Cervical plexus (Fig. 14-3; Table 14-1) 1) C1 through C4, plus part of C5 and cranial nerves XI and XII 2) Major nerve: phrenic nerve b. Brachial plexus (Fig. 14-4; Table 14-1) 1) C5 through T1 2) Innervates lower shoulder and all of the arm c. Lumbar plexus (Fig. 14-5; Table 14-1) 1) L1 through L4 2) Innervates the thigh and leg d. Sacral plexus (Fig. 14-5; Table 14-1) 1) L5 through S4 2) Innervates the thigh and leg e. Coccygeal plexus (small plexus) (Fig. 14-5; Table 14-1) 1) S5 plus part of S4, along with the coccygeal nerve 2) Innervates the floor of the pelvic cavity D. Dermatomes and myotomes (p. 418) 1. Dermatome (Figs. 14-6, 14-7) 2. Myotome (Figs. 14-6, 14-8) III. Cranial Nerves (12 pairs) (Fig. 14-9) A. Types of axons in a cranial nerve (CN): sensory, motor, mixed (Table 14-2) B. Olfactory nerve CN I (Fig. 14-9; Table 14-3) C. Optic nerve CN II (Fig. 14-9; Table 14-3) D. Oculomotor nerve CN III (Fig. 14-9; Table 14-3) E. Trochlear nerve CN IV (Fig. 14-9; Table 14-3) F. Trigeminal nerve CN V (Figs. 14-9, 14-10; Table 14-3) G. Abducens nerve CN VI (Fig. 14-9; Table 14-3) H. Facial nerve CN VII (Figs. 14-9, 14-11; Table 14-3)

3 Chapter 14: Peripheral Nervous System 3 I. Vestibulocochlear nerve CN VIII (Fig. 14-9; Table 14-3) J. Glossopharyngeal nerve CN IX (Figs. 14-9, 14-12; Table 14-3) K. Vagus nerve CN X (Figs. 14-9, 14-13; Table 14-3) L. Accessory nerve CN XI (Figs. 14-9, 14-14; Table 14-3) M. Hypoglossal nerve CN XII (Fig. 14-9; Table 14-3) IV. Divisions of the Peripheral Nervous System (p. 429) glands) A. Divisions 1. Sensory (afferent) division (Chapter 15) 2. Motor (efferent) division B. Somatic motor nervous system C. Somatic reflexes (p. 429) a. Somatic motor nervous system b. Efferent autonomic nervous system 1. Basic principles of somatic motor pathways a. Anterior horn neuron stimulates skeletal muscles (somatic effectors) with acetylcholine b. Each skeletal muscle motor unit involves a single motor neuron from the anterior horn 1. Nature of a reflex V. Autonomic Nervous System (p. 431) a. Cranial reflex b. Spinal reflex c. Somatic reflex (involves skeletal muscle) d. Autonomic reflex (involves smooth muscle, cardiac muscle, or 2. Somatic reflexes of clinical importance a. Knee jerk reflex (Fig ) 1) Two-neuron reflex arc b. Ankle jerk reflex a) Sensory neurons b) Reflex center (synapses) c) Motor neurons 1) Two-neuron reflex arc c. Babinski reflex d. Corneal reflex e. Abdominal reflex A. Motor functions and sensory functions for motor feedback B. Two divisions

4 Chapter 14: Peripheral Nervous System 4 1. Sympathetic division 2. Parasympathetic division C. Structure of the autonomic nervous system pathways (Table 14-5) 6) 14-6) sympathetic axons beta-2 acetylcholinesterase 1. Basic plan of autonomic pathways a. Preganglionic neuron (Fig ) b. Autonomic ganglion (Fig ) c. Postganglionic neuron (Fig ) d. Effectors: cardiac muscle, smooth muscle, and glands e. Comparison of somatic motor and autonomic efferent 2. Structure of the sympathetic pathways (Figs , 14-17) a. Sympathetic preganglionic neurons (Figs , 14-17) b. Sympathetic postganglionic neurons (Figs , 14-17) 3. Structure of the parasympathetic pathways (p. 432) a. Parasympathetic preganglionic neurons (Fig ; Table 14- b. Parasympathetic postganglionic neurons (Fig ; Table 4. Autonomic neurotransmitters and receptors (Fig ) a. Norepinephrine and its receptors (Fig , A) 1) Norepinephrine released from postganglionic 2) Adrenergic receptors: alpha-1, alpha-2, beta-1, and 3) Norepinephrine and epinephrine action terminated slowly in two ways: a) Absorbed into postganglionic synapse by monoamine oxidase b) Broken down in synapse by catechol-omethyl transferase b. Acetylcholine and its receptors (Fig , B) 1) Acetylcholine released from: a) Autonomic preganglionic axons b) Parasympathetic postganglionic axons 2) Cholinergic receptors: nicotinic-1, nicotinic-2, muscarinic-1, muscarinic-2, and muscarinic-3 3) Acetylcholine action terminated swiftly by c. Dual innervation interaction (Fig , C) D. Functions of the autonomic nervous system (p. 439)

5 Chapter 14: Peripheral Nervous System 5 1. Overview of autonomic function a. Tonically active b. Parasympathetic and sympathetic antagonism (Table 14-7) c. Hierarchical control through autonomic centers (Fig ) a. Functions of the sympathetic division (Table 14-8) a. Fight or Flight reaction 3. Functions of the parasympathetic division (Table 14-7) VI. The Big Picture: Peripheral Nervous System and the Whole Body (p. 441) A. The PNS is made of all efferent and afferent pathways B. Peripheral pathways lead from the integrator CNS to the effectors C. Peripheral efferent pathways carry regulatory information to effectors D. The PNS influences all major organs directly or indirectly