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18 Cards in this Set
- Front
- Back
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What receptors are found in the Parasympathetic Nervous System?
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Nicotinic
Muscarinic |
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What are the sub-types of muscarinic receptor and what are their functions?
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M1 - "Secretory"
M2 - "Cardiac" M3 - "Glandular" M4 - CNS M5 - Eyes, Salivary Glands and CNS |
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Mechanism of M1 and M3 Receptors. Examples of their function.
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- Activates Phospholipase C
- Produces IP3, DAG - IP3 increases calcium - DAG activates Protein Kinase C M1 - Parietal Stomach cells (gastric acid secretion) M3 - Salivary glands M3 - Smooth Muscle contraction, but not in vasculature. |
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Mechanism of M2 receptor.
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ALPHA SUBUNIT
- Inhibition of Adenylate Cyclase - Reduction in cAMP - Reduction in PK-A - Reduced phosphorylation of calcium channels, so fewer are activated. BETA-GAMMA - Directly inhibits Calcium channels - Directly activates Potassium channels The overall effect is a hyperpolarisation, making it less likely that action potentials will occur. |
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What is meant by indirect and direct modulation of heart rate?
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Direct - Beta/Gamma action
Indirect - reduce phosphorylation of Calcium Channels |
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Role of M3 receptors in vasculature.
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Cause vasodilatation.
ACh ---> M3 Production of NO NO activates Guanylyl cyclase cGMP levels increase cGMP activates PK-G PK-G activates myosin light chain phosphatase Stops cross-bridges forming Causes relaxation |
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Effect of stimulating Muscarinic receptors on:
Secretions, Heart Rate, G.I Tract and Eye |
Secretions:
- All increase: Salivary, bronchial, gastric etc. Heart Rate: - Reduces conduction velocity - Reduces contractility - Together with vasodilatation produces a drop in B.P G.I Tract -stimulates secretions -stimulates motility Eye: - Miosis (pupillary constriction) - Accomodation for near vision (squashing of lens by contraction of cillary muscles) |
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Effect of blocking Muscarinic receptors on:
Secretions, Heart Rate, Male Genetalia and Eye |
Secretions:
All reduced: Dry nasopharynx, dry mouth, bronchial dryness, dry eyes etc. Heart Rate: - Conduction velocity increases - Contractility increases - Loss of vagal reflexes Male Genitalia - causes impotence, vasoconstricton Eye: - Dryness - Mydriasis - Cyclopegia (loss of accomodation) |
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What is the common feature of muscarinic antagonists?
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Contain an aromatic group which replaces the acetyl group. Competetive.
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Why is it important to be aware of ganglion activating nAChr drugs?
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- They might be expected to produce parasympathetic effects in areas with parasympathetic tone (i.e. urinary bladder, G.I Tract etc)
- Autonomic reflexes mean this may not happen. |
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How is Acetylcholine synthesised in pre-synaptic varicosities?
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- Co-transport of choline with sodium
- Choline acetyltransferase moves acetyl group from Acetyl-CoA to Choline = ACh. - ACh gradient coupled to proton gradient between vesicles and cytoplasm. Counter-transport - Ca2+/ACh autoreceptor stimulate exocytosis. - ACh binds to receptors (relevant to region: nAChr, M) - AChE hydrolyses |
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Therapeutic application of the botulinium toxin
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Excess salivation prevention
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Anticholinesterases
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Inhibit AChE
Increase ACh concentration slow down breakdown |
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AChE has two sites. What are they?
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Esteric (Serine) - binds Acetate
Anionic (glutamate) - binds choline |
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Acetylcholinesterase
Butrylcholinesterase Choline-acetyltransferase Explain their functions. |
1 - breakdown
2 - is 1 in the cytoplasm 3 - transfer of Acetyl to choline |
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What are the effects of anticholinesterases on the PSNS?
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- Bradycardia, hypotension
- Accomodation for near vision - Lowered intraocular pressure - Bronchoconstriction - Miosis |
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If the concentration of ACh becomes too high (as in long-acting organophosphates) what might you expect to see?
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1 - Parasympathetic Effects
2- CNS effects 3 - NMJ = twitching |
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How does an excess of ACh lead to respiratory arrest and death?
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- Massive [ACh]
- Stimulation of nAChrs at NMJs of diaphragm - Desensitisation - NMJs do not function - No contraction of diaphragm - Stop breathing |
