The resting potential of a cell is roughly –70mV. When the potential rises above this level, the cell is considered "depolarized." When the potential delves below this level, the cell is considered "hyperpolarized." If the cell is depolarized above –55mV, the threshold potential, then an action potential is triggered.

Hyperpolarization occurs because potassium channels are slow to open and close, and thus the cell polarizes itself beyond its usual membrane potential. After an action potential depolarizes a cell there is a build-up of positive charge in the cell interior. The late opening of potassium channels causes an abrupt rush of potassium out of the cell, propelled by its electrochemical gradient. This rush lowers the cell potential below its normal resting state, resulting in hyperpolarization. The cell then returns to its resting state via repolarization. Sodium is removed from the cell and potassium is reintroduced through action of the sodium-potassium pump.

The question states that the person is malnourished. This means that he/she is not getting enough nutrients and energy to fuel the body, which directly affects the production of ATP. The correct answer will be a protein that requires energy to transport the molecules (active transport).

Out of the three proteins presented in the question, only one uses ATP to transport molecules: the sodium-potassium pump. It requires ATP because the pump transports sodium (Na) and potassium (K) ions against their respective concentration gradients. The leak channels and the voltage-gated channels use facilitated diffusion and the electrochemical gradients of the ions as the driving force for transport.

Eventually, as ion concentrations fluctuate in the individual, all three types of proteins may be affected, but only as an indirect consequence. Malnourishment will directly affect the available ATP, reducing functionality of the sodium-potassium pump.

The sodium-potassium pump moves sodium to the outside of the cell and potassium to the inside of the cell. Since the pump moves the ions in opposite directions, the pump is classified as an antiporter. If the ions moved in the same direction it would be classified as a symporter.

Threshold potential is defined as the potential that must be reached in order for an action potential to be initiated by a neuron. Threshold potential is around -55mV in humans, which is slightly higher than the resting potential of -70mV. Once this threshold is reached, the electrical signal will propagate as the membrane depolarizes to a positive potential.

Sub-threshold stimuli, such as stimulus causing depolarization to -65mV, will not trigger action potentials. Muscle contractions can result from action potentials or provide sensory feedback, but the contractions themselves do not play a role in initiating action potentials.

The resting membrane potential is approximately –70mV, while the threshold potential is roughly –55mV. When a neuron receives a stimulus, the binding of neurotransmitters elicits small, localized influxes of sodium known as postsynaptic potentials. These small potentials must sum together in order to raise the local region of the neuron to –55mV. Once this threshold potential is reached, an action potential is generated and the neuron perpetuates the signal.

The activity of the sodium-potassium pump creates an electrochemical gradient. There are more sodium ions outside the cell and more potassium ions inside the cell. Recall from diffusion that molecules will always want to go from a region of high concentration to a region of low concentration; therefore, diffusion will drive sodium ions into the cell and potassium ions out of the cell.

However, these ions can only traverse through the cell membrane through specialized channels, called leak channels. The sodium leak channels will facilitate the movement of sodium ions into the cell and potassium leak channel will facilitate the movement of potassium ions out of the cell. The sodium-potassium pump and the leak channels move ions in opposite directions, which is why the pump requires ATP input and the leak channels are examples of passive diffusion.

All muscle types (cardiac, skeletal, and smooth), require sodium to enter the cell to initiate an action potential. The action potential then travels down the axon, elicits neurotransmitters, activates calcium channels, and causes the muscle to contract. In order to initiate the action potential, sodium must enter the cell in large quantity. This depolarizes the cell above the action potential threshold. If the cell does not reach the action potential threshold, then there will be no action potential and no muscle contraction.

The question states that the neuron has a resting membrane potential and threshold stimulus of and , respectively. The researcher must apply at least of external stimulus to generate an action potential. Remember that each action potential is an all or nothing phenomenon. The neuron has to experience a single stimulus of or higher to generate an action potential. Even though the researcher applies a cumulative external stimuli of (sum of voltages from trials 1 through 5) the neuron will not generate an action potential during any single trial.

The refractory period, a phase in which action potentials cannot be fired, is the result of hyperpolarization, during which the membrane potential drops below –70mV. The membrane potential is at this –70mV level while the threshold, which needs to be reached to fire action potential, is slightly higher at –50mV. During the period of extreme hyperpolarization, an action potential will not form.

Temporal summation refers to the phenomenon that an individual neuron will fire with such a high frequency that previous changes in potential have not yet normalized before a new one begins. This summative effect can cause the generation of an action potential, once the threshold potential is surpassed.

Spatial summation refers to the simultaneous activation of several unique neurons to affect another. Numerous individual inputs sum together on the target neuron to stimulate an action potential.