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Introduction to ans, cholinergics system
This document provides an introduction to autonomic pharmacology and discusses cholinergic and anticholinergic drugs. It describes the autonomic nervous system, including its sympathetic and parasympathetic divisions. Cholinergic transmission is mediated by acetylcholine and hydrolyzed by cholinesterase. Cholinergic drugs such as acetylcholine act on muscarinic and nicotinic receptors to affect various organs. Anticholinesterases inhibit cholinesterase and amplify the effects of endogenous acetylcholine. They are used to treat conditions like glaucoma, myasthenia gravis, and postoperative ileus. Their overdose requires supportive care and antidotes like atropine.
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Introduction to ans, cholinergics system
- 1. Introduction to autonomic pharmacology,Cholinergics and anticholinergics Dr. S. Parasuraman Associate Professor, Faculty of Pharmacy, AIMST University, Malaysia. Introduction to Pharmacology - for allied health sciences
- 2. Nervous System Central nervous system Peripheral nervoussystem Afferent division Efferent division Somatic system Autonomic nervous systemSympathetic (thorcolumbar outflow) Come from the thoracic and lumbar regions (T1 to L2/3) of the spinal cord Parasympathetic (craniosacral outflow) Come from brainstem (Cranial Nerves III, VII, IX, X) or the sacral spinal cord (S2, S3, S4) Enteric nervous system
- 3. Spinal nerves • Thereare 31 pairs of spinal nerves – 8 cervical – 12 thoracic – 5 lumbar – 5 sacral – 1 coccygeal The human spinal column is made up of 33 bones. • 7 - cervical region • 12 - thoracic region • 5 - lumbar region • 5 - sacral region • 4 - coccygeal region
- 4. Autonomic Nervous System •The autonomic nervous system (ANS) is a complex set of neurons that mediate internal homeostasis without conscious intervention or voluntary control. • The ANS maintains blood pressure, regulates the rate of breathing, influences digestion, urination, and modulates sexual arousal. • There are two main branches to the ANS – the sympathetic nervous system and the parasympathetic nervous system. The effects of autonomic control are rapid and essential for homeostasis
- 5. Motor neuron pathwaysin the (a) somatic nervous system and (b) autonomic nervous system
- 6. Structure of thesympathetic division of the autonomic nervous system Trachea and bronchi: Bronchodilation Liver: Glycogen glucose conversion increased Iris muscle: Pupil dilated Blood vessels in heart : Vasoconstriction Heart: Rate and force of contraction increased Salivary glands: Secretion inhibited Stomach: Peristalsis reduced Sphincters closed Intestines: Peristalsis and tone decreased Vasoconstriction Kidney: Urine secretion decreased Bladder: Smooth muscle wall relaxed Sphincter closed Sex organs: Generally Vasoconstriction
- 7. Structure of theparasympathetic division of the autonomic nervous system Trachea and bronchi: Bronchoconstriction Liver: Blood vessels dilated Secretion of bile increased Iris muscle: Pupil constricted Heart: Rate and force of contraction decreased Salivary glands: Secretion increased Stomach: Secretion of gastric juice and peristalsis increased Intestines: Digestion and absorption increased Kidney: Urine secretion increased Bladder: Muscle of wall contracted Sphincters relaxed Sex organs: Male: erection; Female: variable
- 8. Summary of theneurotransmitters released
- 9. Autonomic Motor Pathways PreganglionicNeurons • Autonomic Ganglia – There are two major groups of autonomic ganglia • sympathetic ganglia • parasympathetic ganglia • Sympathetic Ganglia: – The sympathetic ganglia are the sites of synapses between sympathetic preganglionic and postganglionic neurons. – There are two major types of sympathetic ganglia: • sympathetic trunk ganglia • prevertebral ganglia
- 10. Autonomic Motor Pathways PreganglionicNeurons • Autonomic Ganglia – There are two major groups of autonomic ganglia • sympathetic ganglia • parasympathetic ganglia • parasympathetic ganglia: – Preganglionic axons of the parasympathetic division synapse with postganglionic neurons in terminal (intramural) ganglia. They are the ciliary ganglion, pterygopalatine ganglion, submandibular ganglion, and otic ganglion
- 11. Autonomic Motor Pathways PostganglionicNeurons • A single sympathetic preganglionic fiber has many axon collaterals (branches) and may synapse with 20 or more postganglionic neurons.
- 12. Autonomic Motor Pathways Relativelengths of neurons
- 13. ANS Neurotransmitters andReceptors ANS Receptor Receptor Sub-type Parasympathetic nervous system Nicotinic cholinergic receptors Nn, Nm Muscarinic cholinergic receptors M1, M2, M3 Sympathetic nervous system α adrenergic receptor α1, α2 β adrenergic receptor β1, β2, β3 Sympathetic nervous system Parasympathetic nervous system
- 14. Functions of theautonomic nervous system • Sympathetic stimulation prepares the body to deal with exciting and stressful situations, e.g. strengthening its defences in danger. sympathetic stimulation mobilises the body for 'fight or flight'. • Parasympathetic stimulation has a tendency to slow down body processes except digestion and absorption of food and the functions of the genitourinary systems. Its general effect is that of a 'peace maker' allowing restoration processes to occur quietly and peacefully.
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- 16. Cholinergic System • Cholinergictransmission – Acetylcholine (ACh) is a major neurohumoral transmitter at autonomic, somatic as well as central sites. • Synthesis, storage and destruction of Ach Ach is synthesized locally in the cholinergic nerve endings by the following pathway
- 17. Cholinergic System • Cholinesterase Immediatelyafter release, Ach is hydrolyzed by the enzyme cholinesterase and choline is recycled.
- 18. Cholinergic System • Sitesof cholinergic transmission and type of receptor involved
- 19. Cholinergic Drugs (Cholinomimetic, Parasympathomimetic) •These are drugs which produce actions similar to that of ACh, either by directly interacting with cholinergic receptors (cholinergic agonists) or by increasing availability of ACh at these sites (anticholinesterases).
- 20. Cholinergic Drugs (Cholinomimetic, Parasympathomimetic) Cholinergic drugs Cholinergic agonists Cholineesters E.g.: Acetylcholine, Methacholine, Carbachol, Bethanechol Alkaloids E.g.: Muscarine, Pilocarpine, Arecoline Anticholinest erases Reversible Carbamates E.g.: Physostigmine, Neostigmine Acridine E.g.: Tacrine Irreversible Organophosphates E.g.: Dyflos (DFP), Malathion Carbamates E.g.: Carbaryl, Propoxur
- 21. Pharmacological actions ofCholinergic Drugs • ACh as prototype Organ/ System Muscarinic actions Heart • Cardiac muscarinic receptors are of the M2 subtype • ACh hyperpolarizes the SA nodal Cells - decreases heart rate -bradycardia Blood vessels • Muscarinic (M3) receptors are present on vascular endothelial cells • All blood vessels are dilated, Fall in BP and flushing Smooth muscle • Smooth muscle in most organs is contracted (mainly through M3 receptors) • Bronchial muscles constrict Glands • Secretion from all parasympathetically innervated glands is increased via M3 and some M2 receptors Eye • Contraction of circular muscle of iris - miosis
- 22. Pharmacological actions ofCholinergic Drugs • ACh as prototype Organ/ System Nicotinic actions Autonomic ganglia • Both sympathetic and parasympathetic ganglia are stimulated Skeletal muscles • i.v. injection – no effect • Intra-arterial injection - can cause twitching and fasciculations • Iontophoretic application causes contraction of the fibre CNS actions • ACh injected i.v. does not penetrate blood- brain barrier and no central effects • direct injection into the brain produces arousal response followed by depression
- 23. Pharmacological actions ofCholinergic Drugs • ACh as prototype
- 24. Uses Cholinergic Drugs •ACh is not used because of evanescent and nonselective action. • Methacholine was occasionally used to terminate paroxysmal supraventricular tachycardia but is obsolete now. • Bethanechol has been used in postoperative/ postpartum nonobstructive urinary retention, neurogenic bladder to promote urination. • Pilocarpine: a third-line drug in open angle glaucoma. • Muscarine, Arecoline: Not used therapeutically
- 25. Pharmacological actions ofanticholinesterases • P’cological actions of anticholinesterases • The actions of anti-ChEs are due to amplification of endogenous ACh. • Lipid-soluble agents (physostigmine) have more marked muscarinic and CNS effects. • Lipid-insoluble agents (neostigmine) produce more marked effect on the skeletal muscles.
- 26. Pharmacological actions ofanticholinesterases • P’cological actions of anticholinesterases Organ/ System Pharmacological actions Ganglia • Anti-ChEs stimulate ganglia primarily through muscarinic receptors present there. • High dose: depolarization of the ganglionic nicotinic receptors and blockade of transmission CVS • Cardiovascular effects are complex. Whereas muscarinic action would produce bradycardia and hypotension, ganglionic stimulation would tend to increase heart rate and BP. • overall effects are often unpredictable and depend on the agent and its dose.
- 27. Pharmacological actions ofanticholinesterases • P’cological actions of anticholinesterases Organ/ System Pharmacological actions Skeletal muscles • Force of contraction in partially curarized and myasthenic muscles is increased. • Higher doses cause persistent depolarization of endplates resulting in blockade of neuromuscular transmission weakness and paralysis. CNS actions • Cognitive function may be improved in Alzheimer’s disease. • higher doses produce excitement, mental confusion, disorientation, tremors and convulsions followed by coma. Other effects • Stimulation of smooth muscles and glands of the gastrointestinal, respiratory & urinary tracts
- 28. Uses Cholinergic Drugs(anticholinesterases) • As miotic: In glaucoma, anticholinesterases (pilocarpine) reduce the intro ocular tension (i.o.t.) by increase the tone of ciliary muscle and sphincter pupillae. • Myasthenia gravis: Neostigmine and its congeners improve muscle contraction by allowing Ach released from prejunctional endings to accumulate and act on the receptors. • Postoperative paralytic ileus/urinary retention: This may be relieved by 0.5–1 mg s.c. neostigmine.
- 29. Uses Cholinergic Drugs(anticholinesterases) • Postoperative decurarization: Neostigmine 0.5–2.0 mg (30–50 µg/kg) i.v., preceded by atropine or glycopyrrolate 10µg/kg to block muscarinic effects. • Cobra bite: Neostigmine + atropine prevent respiratory paralysis induced by cobra venom. • Belladonna poisoning: Physostigmine 0.5–2 mg i.v. repeated as required is the specific antidote for poisoning with belladonna or other anticholinergics. • Alzheimer’s disease: The relatively cerebroselective anti-ChEs, rivastigmine, donepezil and galantamine are now commonly used.
- 30. Treatment for anticholinesterasepoisoning • Anticholinesterases are easily available and extensively used as agricultural and household insecticides; accidental as well as suicidal and homicidal poisoning is common. • Treatment – Maintain patent airway – Supportive measures—maintain BP, hydration, control of convulsions – Specific antidotes: Atropine, Cholinesterase reactivators (Pralidoxime)
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Editor's Notes
- #4 Cervical spine: 7 vertebrae (C1–C7) Thoracic spine: 12 vertebrae (T1–T12) Lumbar spine: 5 vertebrae (L1–L5) Sacrum: 5 (fused) vertebrae (S1–S5) Coccyx: 4 (3–5) (fused) vertebrae (Tailbone)