The Nervous System and Metabolism

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1 = P1: JZP 8 The Nervous System and Metabolism Dendrites Cell body Axon (may be sheathed in myelin) Nucleus Axonal terminals (synapses) Figure 8.1 Basic structure of a nerve cell (neuron). CH 3_ CH 3 CH 3 _ O _ N + --CH2--CH2--O--C--CH3 Acetylcholine HO-- HO-- OH -- --CH--CH 2--NH 2 Noradrenaline Figure 8.2 The structures of two important neurotransmitters, acetylcholine (neurotransmitter in the parasympathetic nervous system, parts of the sympathetic nervous system and in the somatic nervous system responsible for activating muscle contraction) and noradrenaline (neurotransmitter in the peripheral parts of the sympathetic nervous system). The route of synthesis of noradrenaline was given in Figure 6.10, p

2 Resting membrane potential -70 mv Extracellular [K + ] 5 mmol/l [Na + ] 150 mmol/l V K Intracellular K + channel [K + ] 150 mmol/l open [Na + ] 15 mmol/l Quiescent cell Na+ channel closed 3Na ATP 2K + ADP + P i Na + /K + ATPase Passage of an action potential K Na + channel open Depolarization Region of spreads K + channel opens; membrane potential restored - -depolarization Na + Figure AXON Electrical impulse (action potential) Axonal terminal Post-synaptic membrane Neurotransmitter molecules in vesicles Synaptic cleft TARGET CELL Signal transmission (e.g. via G-proteins to adenylate cyclase) Receptors Figure 8.2.1

3 Cerebrum Cerebellum Pons Medulla oblongata Figure 8.3 The human brain and its main components. Axonal terminal of a motor neuron Nucleus Sarcolemma of the muscle fibre Myofibrils Figure 8.4 The neuromuscular junction.

4 Muscle contraction SOMATIC NERVOUS SYSTEM Muscle blood vessels (dilatation) (not humans: see text) Blood vessels CENTRAL NERVOUS SYSTEM Heart (force and rate of contraction) Sweat glands Adrenal medulla (adrenaline secretion) Metabolic (lipolysis, glycogenolysis) Glucagon secretion increased Insulin secretion decreased SYMPATHETIC NERVOUS SYSTEM Salivary glands Insulin secretion increased PARASYMPATHETIC NERVOUS SYSTEM Figure 8.5 Types of neurotransmission in the central and peripheral nervous systems., cholinergic transmission; nic, nicotinic receptor; musc, muscarinic receptor;, noradrenaline. Based loosely on Rang and Dale (1991).

5 Plasma glucagon (pmol/l) Insulin Plasma adrenaline (nmol/l) Plasma noradrenaline (nmol/l) Time (min) Figure 8.6 Plasma glucagon, adrenaline and noradrenaline concentrations in response to rapid lowering of the blood glucose concentration (by injection of insulin). Based on Gerich et al. (1979). From American Journal of Physiology. Copyright 1979 by American Physiological Society. Reproduced with permission of American Physiological Society.

6 Change in glycerol (µmol/l) Exercise No propranolol Plus propranolol Time (min) Figure 8.7 Propranolol (a β-adrenergic blocker) inhibits lipolysis in response to exercise. The figure shows changes in the concentration of glycerol (released in fat mobilization) in the interstitial fluid in adipose tissue, measured with a small probe. During exercise (0 30 min) the glycerol concentration rises, indicating lipolysis. When propranolol is introduced (via the probe) the rise is inhibited. In separate experiments, when phentolamine (an α-adrenergic blocker) was introduced, glycerol release was not affected. Based on Arner et al. (1990). From Journal of Clinical Investigation. Copyright 1990 by American Society for Clinical Investigation. Reproduced with permission of American Society for Clinical Investigation.