What two parameters affect the speed of nervous transmission?What specific effec

Question

What two parameters affect the speed of nervous transmission?What specific effect would the following have on nerve transmission? Where on the nerve (specific region) would the effect occur? Why would this effect occur?
A. All extracellular Calcium was destroyed.
B. All post-synaptic neurotransmitter binding sites were destroyed.
C. All post-synaptic neurotransmitter sites were occupied with a non-transmitter substance which did not mimic the action of the neurotransmitter.
D. Sodium was depleted around the axon................really stuck:(

Explanation / Answer

A. No extracellular calcium would mean that no calcium is available to enter the presynaptic nerve cell. The direct effect would be that the action potential arriving at the terminal would have not have the effect of allowing calcium into the nerve cell, because no calcium is available. Because of this, acetylcholine vesicles would not be triggered to fuse with the presynaptic membrane and be released into the synaptic cleft. Ultimately, no extracellular calcium means no acetylcholine release from neurons. B. If all post-synaptic neurotransmitter binding sites are destroyed, then the neurotransmitter specific for those sites will not be able to bind. So even though the neurotransmitter will have entered the synaptic cleft, there will be no effect (no nerve transmission). C. If all postsynaptic neurotransmitter sites were occupied with non-transmitter substance, then the neurotransmitter specific for those sites would have limited access to bind. This occurs in the synaptic cleft. In fact, this is exactly how many poisons and pharmaceuticals work, by blocking access to a binding site, though usually only transiently, with varying half-lifes depending upon the drug/poison. Inevitably, the effect of the neurotransmitter would be limited, and thus nerve transmission would be impeded. The degree of the inhibition would be dependent on the amount of non-neurotransmitter present and the half-life of this substance. Although, some substances are capable of irreversible binding, and thus are much more deleterious. D.If sodium is depleted, then there will be no action potential generated along the axon and to the nerve terminal. Positively charged sodium is located on the outside of the axon, and potassium on the inside. The outside of the axon is positively charged relative to the inside. If no sodium is available, then there is no depolarization, because positively charged sodium is not available to enter the sodium ion channel. Usually, sodium would enter the axon through these channels and cause a change inside the axon in which the relative charge would become more positive when it was previously more negative. This depolarization would happen along the length of the axon until reaching the nerve terminal. But with no sodium, no nerve transmission is possible, as depolarization is not possible.

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