Ch. 6 Checklist Q&A Flashcards
Describe the steps in the synthesis, storage release, and termination of action of the major autonomic transmitters.
A: GENERAL- Two transmitters to note for autonomic system: Acetylcholine and Norepinephrine(aka: Adrenergic).
Transmitter #1 -Acetylcholine (ACh) is the primary transmitter in all autonomic ganglia and at the synapses between parasympathetic postganglionic neurons and their effector cells. Note: acety-CoA is produced in the mitochondria and Choline is transported across the cell membrane. It is the transmitter at postganglionic sympathetic neurons to the thermoregulatory sweat glands. It is also the primary transmitter at the somatic (voluntary) skeletal muscle neuromuscular junction.
SYNTHESIS & STORAGE- Acetylcholine is synthesized in the nerve terminal by the enzyme choline acetyltransferase (ChAT) from acetyl-CoA and choline. The rate-limiting step is probably the transport of choline into the nerve terminal. This transport can be inhibited by the research drug hemicholinium. Acetylcholine is actively transported into its vesicles for storage by the vesicle-associated transporter (VAT). This process can be inhibited by another research drug, vasamicol.
RELEASE OF ACETYLCHOLINE- Release of transmitter stores from vesicles in the nerve ending requires the entry of Ca2+ through Ca2+ channels and triggering of an interaction between soluble N-ethylmaleimide sensitive factor attachment protein receptor proteins.This interaction results in docking of the vesicle to the terminal membrane and with influx of calcium, fusion of the mebranes of the vesicles with the nerve-ending membrandes, the opening of a pore to the extracellular space, and the release of the stored transmitter. The several types of botulinum toxins enzymatically alter synaptobrevin or one of the other docking or fusion proteins to prevent the release process.
TERMINATION OF ACETYLCHOLINE ACTION- The action of acetylchline in the synapse is terminated by metabolism to acetate and chline by the enzyme acetylcholinesterase in the synaptic cleft. The products are not excreted but are recycled in the body. Inhibition of acetylcholinesterase is an important therapeutic effect of several drugs.
Transmitter #2- Norepinephrine (NE) is the primary transmitter at the sympathetic postganglionic neuron-effector cell synapses in most tissues. Norepinephrine is a vasoconstrictor in renal blood vessels. Dopamine plays a minor role.
SYNTHESIS & STORAGE- The synthesis of dopamine and norepinephrine require several steps. After transport across the cell membrane, “outside the vesicle” tyrosine is hydoxylated by tyrosine hydroxylase (the rate-limiting step) to dihydroxyphenylalanine (DOPA), decarboxylated to dopamine and “once inside the vesicle” hydroxylated to norepinephrine. Tyrosine hydroxylae can be inhibited by metyrosine. Norepinephrine and Dopamine are transported into vesicles by the vesicular monoamine transporter (VMAT) and are stored there. Monoamine oxidase (MAO) is present on mitochondria in the adrenergic nerve ending and inactiates a portion of the dopamine and norepinephrine in the cytoplasm. Therefore, MAO inhibitors may increase the store of thes transmitters and other amines in the nerve endings. Vesicular Monoamine Transporter (VMAT) can be inhibited by reserpine, resulting in depletion of transmitter stores.
Describe the steps in the synthesis, storage release, and termination of action of the major autonomic transmitters
A: Adenosine Triphosphate (ATP) and substance P
Name 2 cotransmitter substances
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Name the major types of autonomic receptors and the tissues in which they are found.
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Describe the organ system effects of stimulation of the parasympathetic and sympathetic systems.
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Name examples of inhibitors of acetylcholine and norepinehrine synthesis, storage, and release. Predict the effects of these inhibitors on the function of the major organ systems.
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List the determinants of blood pressure and describe the baroreceptor reflex response for the following pertubations: (1) blood loss (2) administration of a vasodilator (3) a vasoconstrictor (4) a cardiac stimulant (5) a cardiac depressant
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Describe the results of transplantation of the heart (with interruption of its autonomic nerves) on cardiac function.
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Describe the actions of several toxins that affect nerve function: tetrodotoxin, saxitoxin, botulinum toxins, and latrotoxin.
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