Sympathetic and parasympathetic effects and adrenergic and cholinergic receptor physiology tested on USMLE Step 1.
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- What neurotransmitter is released by all preganglionic autonomic neurons (both sympathetic and parasympathetic)?
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Acetylcholine- What receptor type do preganglionic autonomic fibers act on at the ganglion?
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Nicotinic acetylcholine receptors- What neurotransmitter is released by most postganglionic sympathetic neurons onto target organs?
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Norepinephrine- What neurotransmitter is released by postganglionic parasympathetic neurons onto target organs?
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Acetylcholine- What is a notable exception among postganglionic sympathetic fibers that releases acetylcholine instead of norepinephrine?
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Sympathetic fibers innervating sweat glands- What receptor type do postganglionic sympathetic fibers act on at sweat glands?
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Muscarinic acetylcholine receptors- What is released directly into the bloodstream by the adrenal medulla in response to sympathetic stimulation?
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Epinephrine (and some norepinephrine)- Why is the adrenal medulla considered a modified sympathetic ganglion?
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It is directly innervated by preganglionic sympathetic fibers releasing acetylcholine onto nicotinic receptors, without a postganglionic neuron in between- What is the primary physiologic effect of alpha-1 adrenergic receptor activation on vascular smooth muscle?
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Vasoconstriction- What second messenger system does the alpha-1 receptor signal through?
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Gq, activating phospholipase C to increase IP3 and diacylglycerol and raise intracellular calcium- What is the primary physiologic effect of alpha-2 adrenergic receptor activation at presynaptic sympathetic nerve terminals?
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Inhibition of further norepinephrine release, providing negative feedback- What second messenger system does the alpha-2 receptor signal through?
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Gi, inhibiting adenylate cyclase and decreasing cAMP- What is the primary physiologic effect of beta-1 adrenergic receptor activation in the heart?
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Increased heart rate and contractility- What second messenger system does the beta-1 receptor signal through?
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Gs, activating adenylate cyclase and increasing cAMP- What is the primary physiologic effect of beta-2 adrenergic receptor activation on bronchial and vascular smooth muscle?
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Bronchodilation and vasodilation (relaxation of smooth muscle)
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