In a class experiment, the strength of a neural stimulus and the resulting muscle contraction are ...

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A neuronal membrane is said to be depolarized if the transmembrane potential is reduced to less than the resting potential of −70 mV. If, for any reason, the membrane at a node of Ranvier becomes depolarized to −55 mV, a dramatic change occurs in the membrane. This change is called an action potential. (As you will see later, this depolarization is usually caused by an action potential that has just occurred at an adjacent node of Ranvier.) An action potential is called an “all-or-none” event because a depolarization to between −70 mV and −55 mV has no effect. Any depolarization to −55 mV, or any other amount up to 0, will produce identical action potentials. The potential difference of −55 mV is therefore called the threshold potential. Threshold potentials can vary slightly, depending on the type of neuron, but they are usually close to −55 mV. When the transmembrane potential at a node of Ranvier reaches threshold, special structures in the membrane called voltage-gated sodium channels open and make the membrane very permeable to sodium ions. The sodium ions on the outside of the axon suddenly rush into the axon, driven by their concentration gradient and the potential difference across the membrane. Within a millisecond or less, enough positively charged sodium ions have crossed the membrane to make the potential difference across the membrane in that tiny region of the axon +35 mV.

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By any chance would you know this question. I think it is D but I still want to make sure.

An Olympic downhill skier, attempting to win a bronze medal, is midway through the race. Which row now describes accurately the effects of the sympathetic nervous system on the skier's body components?

a) Blood vessles in the skin constrict, sphincters of the digestive tract contracted, bronchioles dilated
b) Blood vessles in the skin constricted, sphincters of the digestive tract relaxed, bronchioles constricted
c) Blood vessles in the skin dilated, sphincters of the digestive tract contracted, bronchioles constricted
d) Blood vessles in the skin dilated, sphincters of the digestive tract relaxed, bronchioles dilated

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