Fig. 15.4

1. Autonomic Pathways Fig. 15.4 Fig. 15.7 Sympathetic Parasympathetic

2. Sympathetic thoracolumbar fight or flight mass activation possible e.g., vasoconstriction and  heart rate  blood pressure  blood flow to skin and viscera  blood flow to skeletal muscles e.g.,  [glucose]blood due to glycogenolysis Parasympathetic craniosacral “vegetative” functions no mass activation individual responses e.g.,  heart rate e.g.,  GI activity secretion motility Two Divisions of the ANS

3. Sympathetic and Parasympathetic • antagonistic effects • e.g., heart rate • no rule about which stimulates and which inhibits • separate effects • e.g., sympathetic:  myocardial contractility parasympathetic: no effect on contractility • cooperative effects • e.g., sexual function

4. Sympathetic Pathways • Preganglionic fibers • leave spinal cord via spinal nerves T1 – L2 • leave spinal nerve, travel to a ganglion of the sympathetic trunk (chain) and split into branches • various branches  synapse at that ganglion ascend or descend to another trunk ganglion and synapse there pass through the trunk to a prevertebral ganglion and synapse • celiac, superior mesenteric and inferior mesenteric ganglia • Different body segments can be simultaneously stimulated. • Mass activation is possible. Fig. 15.5

5. Sympathetic Pathways Fig. 15.4 • Postganglionic fibers • return to nerves • travel in nerves to target organs • Note: The adrenal medulla is like a sympathetic ganglion. Adrenal medullary cells are like postganglionic neurons. to blood: epinephrine norepinephrine

6. Parasympathetic Pathways Fig. 15.7 • Long preganglionic fibers travel in cranial nerves and in splanchnic nerves from the sacral region to parasympathetic ganglia in or near organs. • vagus nerve (X) • heart, lung, upper GI • pelvic splanchnic nerves • defecation, urination, sexual responses • Short postganglionic fibers spread out into organ.

7. Neurotransmitters • acetylcholine and norepinephrine • Rules: • Neurons are named by the main neurotransmitter they secrete. • adrenergic fibers • secrete norepinephrine (noradrenaline) • cholinergic fibers • secrete acetylcholine • Membrane receptors are named by the neurotransmitter they receive. • adrenergic receptors • receive norepinephrine and epinephrine (adrenaline) • cholinergic receptors • receive acetylcholine

8. Cholinergic and Adrenergic Fibers Sympathetic Usually NE ACh Target cell Preganglionic neuron ACh Occasionally: e.g., to sweat glands Postganglionic neuron Parasympathetic ACh Target cell ACh Postganglionic neuron Preganglionic neuron Fig. 15.8

9. Fiber Types • Simplistic associations • postganglionic neurons • sympathetic: adrenergic • parasympathetic: cholinergic • Detailed rules • adrenergic fibers • most sympathetic postganglionic neurons • norepinephrine • adrenal medullary cells • epinephrine (80%) • norepinephrine (20%)

10. Fiber Types • Detailed rules (cont’d) • cholinergic fibers • ALL preganglionic neurons • both sympathetic and parasympathetic • parasympathetic postganglionic neurons • a few postganglionic sympathetic neurons • to eccrine sweat glands • to blood vessels supplying skeletal muscle

11. Receptor Types Sympathetic Usually Adrenergic receptors: 1, 1, 2 Nicotinic cholinergic receptors NE ACh Target cell Preganglionic neuron ACh Muscarinic cholinergic receptors Postganglionic neuron Occasionally: e.g., to sweat glands Nicotinic cholinergic receptors Parasympathetic ACh Target cell ACh Muscarinic cholinergic receptors Postganglionic neuron Preganglionic neuron Fig. 15.8

12. Receptor Types • Cholinergic Receptors • nicotinic cholinergic receptors • channel-linked receptor / ligand-gated channel • location • cell bodies and dendrites of all postganglionic neurons • [neuromuscular junction of skeletal muscle fibers] • muscarinic cholinergic receptors • G-protein linked • work via intracellular (“second”) messengers • location • parasympathetic effector tissue

13. Receptor Types • Adrenergic Receptors • many  and  subtypes • for this course • 1, 1 and 2 adrenergic receptors • 2 is important for pharmacology, but will not be discussed in A&P. • All are G-protein linked. • location: • sympathetic effector tissue; examples: • 1: most vascular smooth muscle (vasoconstriction) • 1: heart ( heart rate,  myocardial contractility) • 2: bronchiolar smooth muscle, vascular smooth muscle of skeletal muscle blood vessels (bronchiolo- and vasodilation)

14. Autonomic Pharmacology • Various drugs can • act presynaptically to stimulate or inhibit the release of neurotransmitters • and/or • act postsynaptically to be agonists or antagonists to the different receptor types on the receiving cells. • For example, • propranolol: -blocker • phenylephrine: -agonist Fig. 15.8

15. Regulation of ANS Activity • The ANS always has some activity (“tone”). • There is always some release of neurotransmitter. • Regulation is not a matter of turning the neurons on or off, but of increasing or decreasing their secretion. •  sympathetic tone /  sympathetic tone • parasympathetic tone /  parasympathetic tone

16. Regulation of ANS Activity • Reflexes • via spinal cord and brainstem • e.g., cardiovascular, respiratory, micturition, defecation and sexual reflexes • Higher Brain Influences • via hypothalamus, limbic system, cerebral cortex • e.g., to activate “fight or flight”