Pharmacology PHL 211 Ninth Lecture By Abdelkader Ashour, Ph.D. Phone: 4677212 Email: aeashour@ksu.edu.sa

Regulation of Body Functions, NS & ES The nervous system has several properties in common with the endocrine system, which is the other major system for control of body function. These include: high-level integration in the brain the ability to influence processes in distant regions of the body extensive use of negative feedback both systems use chemicals for the transmission of information In the nervous system, chemical transmission occurs between nerve cells and between nerve cells and their effector cells Chemical transmission takes place through the release of small amounts of transmitter substances from the nerve terminals into the synaptic cleft The transmitter crosses the cleft by diffusion and activates or inhibits the postsynaptic cell by binding to a specialized receptor molecule

Organization of The Nervous System Central Nervous System “Brain and spinal cord” Peripheral Nervous System Autonomic Nervous System Somatic Nervous System Afferent Division Efferent Division Sympathetic “thoracolumbar” Parasympathetic “craniosacral”

Autonomic Nervous System

Efferent division of the peripheral nervous system

Some anatomic and neurotransmitter features of autonomic and somatic motor nerves

How do drugs influence the ANS? Drugs may mimic or block the effects of the two primary neurotransmitters, Acetylcholine and Norepinephrine/Epinephrine Drugs that mimic neurotransmitters are referred to as “receptor agonists” These drugs activate receptors Drugs that block neurotransmitters are referred to as “receptor antagonists” These drugs block the endogenous neurotransmitters from activating receptors

Classification of drugs affecting the ANS Parasympathetic nervous system. Drugs may: Mimic acetylcholine = cholinergic = muscarinic agonists = parasympathomimetic Block acetylcholine = anticholinergic = muscarinic antagonist = parasympatholytic Sympathetic nervous system. Drugs may: Mimic norepinephrine = adrenergic = adrenergic agonist = sympathomimetic Block norepinephrine = antiadrenergic = adrenergic antagonist = sympatholytic

Parasympathetic Nervous System

Drugs Acting on the Parasympathetic Nervous System, Responses to parasympathetic activation

Parasympathetic Neurons & Synapses Preganglionic neurons Long Synapse with postganglionic neurons at or near organ Release acetylcholine (ACh) to activate nicotinic receptors on postganglionic neurons Postganglionic neurons Short Synapse on the target organ Release ACh to activate muscarinic receptors on the target organ Cholinergic fibers: i.e., act by releasing acetylcholine. Include: all preganglionic efferent autonomic fibers the somatic (non-autonomic) motor fibers to skeletal muscle most parasympathetic postganglionic and a few sympathetic postganglionic fibers Parasympathetic Neurons & Synapses

Parasympathetic Ganglionic Synapse Acetylcholinesterase Ca2+ Na+ ACh a b Action Potential Nicotinic Receptor Na+ Preganglionic neuron Postganglionic neuron

Acetylcholinesterase Parasympathetic Organ Synapse Acetylcholinesterase Ca2+ Effector Organ Na+ K+ G Action Potential ACh Muscarinic Receptor Postganglionic neuron