Chapter 11 Efferent Division: Autonomic and Somatic Motor Control

11.1 The Autonomic Division

1. The effecrent division of the peripheral nervous system consists of somatic motor neurons, which control skelctal muscles, and autonomic neurons, which control smooth musclc, cardiac muscle, many glands, lymphoid tissue, and some adipose tıssue. (p. 356)

2. The autonomic division is subdivided into a sympatheticbranch and a parasympathetic branch. (p. 356; Tbl. 11.4)

3. The maintenance of homeostasis within the body is a balance of autonomic control, endocrine control, and behavioral responses (p. 357; Fig 11.2)

4. The autonomic division is controlled by centers in the hypothalamus, pons, and medulla Some autonomic reflexes arc spinal reflexes. Many of these can be modulated by input from the brain. (p. 357; Fig 11.3)

5. The two autonomic branches demonstrate Cannon's properties of homeostasis: maintenance of the internal environment, tonic control, antagonistic control, and variable tissue responses. P. 358)

6. All autonomic pathways are composed of a preganglionic neuron from the CNS that synapses with a postganglionic neuron in an autonomic ganglion, Autonornic ganglia can modulate and integrate information passing through thern. (p. 358; Fig, 114

7. Most sympathetic pathways originate in the thoracic and lumbar regions of the spinal cord, Most sympathetic ganglia lie cither close to the spinal cord or along the descending aorta P. 359, Fig 115

8. Parasympathetic pathways originate in the brain stem or the sacral region of the spinal cord. Parasympathetic ganglia are located on or near their target organs. (p. 359; Fig. 11.5)

9. The primary autonomic neurotransmitters are acetylcholine and norepinephrine, All preganglionic neurons secrete ACh onto nicotinic cholinergic receptors. As a rule, postganglionic sympathetic neurons secrete norepinephrine onto adrenergic receptors, and postganglionic parasympathetic neurons secrete ACh onto muscarinic cholinergic receptors. p. 359; Fig, 11.6; Tbl. 1l.!

10. The synapse between an autonomic neuron and its larget cells is called the neuroeffector junction. p. 359

11. Postganglionic autonomic axons end with varicosities from which neurotransmitter is released. (. 361; Figs. 11.7, 11.8

12. The adrenal medulla secretes epinephrine and is controlled by sympathetic preganglionic neurons. (p. 364; Fig, 1 1.8

13. Adrenergic receptors are G protein-coupled receptors. Alpha receptors respond most strongly to norepinephrine. ß1-receptors respond equally to norepinephrine and epinephrine. ß2-receptors are not associated with sympathetic neurons and respond most strongly to epinephrine. B3-receptors respond most strongly to norepinephrine. (p. 364; Fig 11.9; Tbl. 11.2)

14. Cholinergic muscarinic receptors are also protein-coupled receptors.(p. 364)

11.2 The Somatic Motor Division

15. Somatic motor pathways, which control skelctal muscles, have a single neuron that originates in the CNS and terminates on a skeletal muscle. Somatic motor neurons are always excitatory and cause muscle contraction. (p. 368, Fig 11.9)

16. A single somatic motor neuron controls many muscle fibers at one time. (p. 368)

17. The synapse of a somatic motor neuron on a muscle fiber is called the neuromuscular junction. The muscle cell membrane is modified into a motor end plate that contains a high concentration of nicotinic ACh receptors. (p. 368; Fig 11.10)

18. ACh binding to nicotinic receptor opens cation channels.Net Na+ entry into the muscle fiber depolarizcs the fiber. Acetylcholine in the synapse S broken down by the enzyme acetylcholinesterase. (p. 368, Fig 11.10)