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Cholinergics
Introduction to Autonomic Pharmacology II: Cholinergics
| Question | Answer |
|---|---|
| Atropine like drugs block all end organ actions of what system? | The cholinergic (parasympathetic) system |
| What two CNS functions should be considered cholinergic targets? | cognition and memory |
| Describe the innervation of the enteric nervous system | Innervated by CN X; vagal efferents carry serotogenic signals from gut to higher brain centers; it can function without vagal imput due to submucosal and myenteric plexuses |
| What is the general mode of action of most anesthetics? | They block conduction |
| In transmission, what would increasing the permeability of the membrane to cations do? | Increasing permeability to cations (Na+ or Ca++) would result in localized depolarization of membrane-->INCREASE EXCITATION |
| What would increasing the permeability a membrane to Cl anions result in? | Hyperpolarizes (or stabilizes) the membrane to cause an inhibitory postsynaptic potential |
| Increasing the permeability of K+ in a post-synaptic membrane would result in what? | Increase permeability to outward current-->hyperpolarizes the membrane-->stabilizes the membrane potential as Cl- enters (INHIBITORY EFFECT) |
| How can giving muscarinic agonists limit transmitter release? How can muscarinic antagonists enhance transmitter release? | Pre-synaptic auto and heteroreceptors source of feedback regulation and crossregulation between para and sympa thetic nervous systems; similary, antagonists can reverse the inhibitory effect |
| Heteroreceptor excitation of cholinergic transmission includes receptors for ___ | 5HT |
| Heteroreceptor inhibition of cholinergic transmission includes the receptors for...? | Opiods, dopamine, norepinephrine (alpha receptors), etc. |
| How is acetylcholine synthesized? | Made in presynaptic neuron cytoplasm from actyl-CoA and choline via choline acetyltransferase |
| Where does the presynaptic neuron get choline for synthesis? | From the extracellular fluid via a sodium dependent membrane choline transporter |
| What do hemicholiniums do? | They block the sodium dependent membrane choline transporter, preventing choline from being taken in to make ACh |
| What is the rate limiting step in actylcholine synthesis? | uptake into the presynaptic neuron via Na dependent membrane choline transporter |
| What happens to acetylcholine once it's synthesized? | Transported to vesicles via Vesicle associate transporter 9VAT) |
| What does vesamicol do? | blocks the action of the vesicle associate transporter (VAT), blocking the movement of acetylcholine from the cytoplasm into the secretory vesicles |
| How is acetylcholine released from the cell? | Action potential reaches terminal--> extracell. calcium enters through N-type calcium channels--> fusion of vesicle with membrane and release of ACh into synaptic space |
| What removes acetylcholine from the synaptic cleft? | Acetylcholinesterase (AChE) terminates action |
| Where is acetylcholinesterase found? | Mostly in synaptic cleft but alos in CSF and blood cells, many tissues |
| What is butyrylcholinesterase? | does same thing as AChE (degrade ACh into choline and acetate); has less specificity; found in blood plasma, liver, glia, many other tissues |
| Botulinum toxin: source, mechanism, effects | Clostridium botulinum; block fusion of vesicles to release ACh; blocks all transmission at ganglion and NMJ-->collapse of respiratory muscles |
| Latrotoxin: source, mechanism, effects | Black widow spider; activates presynaptic inward calcium channels-->prolonged vesicle release; tetany --> no time to repolarize; muscle cramps, abdominal pain, weakness, tremor, nausea, vomiting, fainting, dizziness, chest pain, resp. difficulties |
| Organophosphate and carbamate nerve gas (DFP, sarin, VG, VX, etc): mechanism, effects | inactivate acetylcholinesterase-->enhance ACh action by preventing degradation; block AChE at all ganglia (para and sympa) and end organs (including NMJ); death from loss of respiratory muscles |
| M1 receptors: location, postereactor mechanism | Nerves (no where else...?); IP3, DAG cascade |
| M2 receptors: location, postereactor mechanism | HEART, nerves, smooth muscle; inhibits cAMP production, activation of K+ channels |
| M3 receptors: location, postereactor 3echanism | Glands, smooth muscle, endothelium; IP3, DAG cascade |
| What structural feature do all muscarinic receptors share? | They all have seven transmembrane segments and are G-protein linked |
| What is the mechanism of action of nicotinic cholinergic receptors? | Na+/K+ depolarizing ion channel |
| What cholinergic receptors does the eye have? What structures respond? | M3, M2; sphincter muscle + iris (contraction), ciliary muscle (contraction for near vision), lacrimal glands (secretion); NOTE: radial muscle NOT innervated parasympathetically |
| What is the predominant cholinergic receptor subtype in the heart? | M2>>M3 |
| What type of innervation does the heart receive from the parasympathetic system? | Vagal innervation |
| What results in stimulation of the muscarinic receptors in heart? | SA node: Decrease in heart rate, Atria: decrease in contractility and shortened AP duration, AV node: decrease in conduction velocity, AV block, Ventricl3e: slight decrease in contractility, His-purkinje: not much :( |
| What is the parasympathetic innervation of the blood vessels (arteries and arterioles) | None in majority EXCEPT for salivary glands (M3, dilation) and endothelium (M3, increase NO synthesis) |
| Describe the parasympathetic innervation of the urinary bladder | M3>M2; detrusor (contracts-->expel urine), trigone and sphincter (relax-->allow it to empty) |
| What are the effects of muscarinic stimulation in the lung? | Tracheal and bronchial smooth muscle CONSTRICTS; bronchial glands SECRETE |
| What are the effects of muscarinic stimulation in the stomach and the intestine? | motility and tone INCREASE; sphincters RELAX; secretion INCREASES |
| What are the effects of muscarinic stimulation in the pancreas? | Acinar cells SECRETE |
| What are the effects of muscarinic stimulation in the salivary glands? | K+ and water SECRETION |
| What are the effects of muscarinic stimulation in the heteroreceptor? | Inhibition of NE release (acts on M2 and M4) |
| What are the effects of muscarinic stimulation in the parasympathetic terminal autoreceptor? | Inhibition of ACh release (acts on M2 and M4) |
| What class of AChE act reversibily? Irrerversibly? | Reversible: carbamate (neostigmine, physostigmine); irreversibly: organophosphate (saran, chlorpyrophos) |
Created by:
karkis77
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