1、Chapter 5Pharmacology on theEfferent Nervous System傳出神經(jīng)藥理1Nervous Systemnervous systemcentral nervous systemperipheral nervous systemafferent divisionefferent divisionsomatic systemautonomic systemorthosympatheticparasympatheticafferent = towards the CNSefferent = from the CNS2Neurons 神經(jīng)元 and Synaps

2、es 突觸Stimuli are transmitted along the axon by the propagation of a depolarization caused by the opening of a voltage-dependent sodium channelInformation is exchanged in chemical form at the level of the synaptic junction, through the release of neurotransmitters detected by corresponding receptors

3、on the post-synaptic side3Somatic SystemThe somatic system is mediated by a single cholinergic neuron emanating from the CNS, and leading to nicotinic synapses on skeletal musclesacetylcholinenicotinicreceptorsomaticsystem4Neuromuscular JunctionStriated muscles are under the command of somatic fiber

4、s, at the neuromuscular junction5Neuromuscular-Blocking AgentsBoth agonists and antagonists of acetylcholine at the neuromuscular junction are used to induce neuromuscular blockThe antagonist atracurium 阿曲可寧 prevents depolarization, and therefore muscle contractionThe agonist succinylcholine causes

5、a depolarization. After some initial muscle contraction, the sustained depolarization inactivates that sodium channel around the junction. The advantage is a rapid onset and short duration of action because of fast hydrolysis7Kinetics of Neuromuscular-Blocking AgentsAtracurium and succinylcholine we

6、re designed to be rapidly inactivated. Their half-lives are less than 30 minutesTubocurarine and other suchlike non-depolarizing agents have longer actionsThose drugs are all quaternary ammonia, and cannot diffuse across membranes wellOnset and duration of action determine the clinical use8Role of C

7、NS, and Reflex ArcsActivity of the autonomic system is regulated by reflex controls, and impulses from the CNSEmotions play a significant roleThe autonomic system is not entirely efferent, and possesses afferent fibers as well, which are important in reflex regulation. The receptors sensitive to art

8、erial pressure in the carotid sinuses and aortic arch are an example10Anatomy of the Autonomic SystemThe autonomic system carries impulses from the CNS to organs by means of a line of two neuronsThe sympathetic action is more diffuse, as many postganglionic fibers can be connected to a single pregan

9、glionic fiber. Release of adrenaline is also a factorParasympathetic action is more punctual, with less postsynaptic fibersganglionic transmitterneuroeffector transmitterCNSpreganglionic neuronpostganglionic neuron11Sympathetic GangliaThe bodies of sympathetic postganglionic fibers are located in pe

10、ripheral ganglia serving as relay stations12Other TransmitterssympatheticparasympatheticrapidresponseintermediateresponseslowresponseATPNAneuropeptide YAChNOvasoactive intestinal peptideNoradrenaline and acetylcholine are the main postsynaptic transmitters. Other molecules occur as primary transmitt

11、ers in enteric or sensory neurons, and as cotransmitters with NA and ACh14(Ortho)sympathetic FunctionThe sympathetic function mediated by noradrenaline is mainly to:increase heart beatincrease blood pressuredivert blood flow from skin and internal organs toward musclesdilate pupils and airwaysdecrea

12、se intestinal motility, and contract sphincters15Parasympathetic SystemParasympathetic nerves control vital functions. Its actions is not global, as with the sympathetic system, but more discrete, organ by organMain actions are:slowing of heart beatsaliva secretionintestinal motilityconstriction of

13、airwayscontraction of pupil(Ex, secretion of tears)17Enteric Nervous SystemThe movements of the intestine is controlled by neurons with cell bodies in the plexuses in the intestinal wallThose neurons are capable to function independently, and are modulated by autonomic fibers18Anticholinergic Effect

14、Many drugs cause an adverse effect called anticholinergic, by repression of cholinergic stimuli on muscarinic receptorsThey may be drugs used in the management of depression, Parkinsons disease, asthma, or urinary incontinenceThey have the inconvenience of:decreasing intestinal motility, causing constipationreducing salivation, causing a dry mouthbluring the visioncausing confusioncausing urinary retention19Indirect RegulationDrugs may be used to regulate autonomic functions, without being either an agonist nor an antagoni