Final answer:
The statement in question is false; an action potential will not be fired if the membrane potential at the axon hillock is subthreshold. Action potentials require reaching a specific threshold to initiate, and they operate on an all-or-nothing basis without variation in size.
Step-by-step explanation:
The statement that if the membrane potential at the axon hillock becomes subthreshold, an action potential will be fired is False. Action potentials operate on an all-or-nothing principle, where a minimum threshold must be reached to initiate the action potential. The threshold is typically about -55 mV, which is more positive than the resting membrane potential. Once this threshold is exceeded, the neuron will fire an action potential, which will propagate along the axon. If the membrane potential does not reach this threshold, no action potential will be triggered, making the process analogous to a digital event.
In the process of depolarization at the axon hillock, voltage-gated Na+ channels play a critical role. When the threshold is reached, these channels open and allow Na+ ions to flow into the cell, which rapidly depolarizes the membrane, resulting in an action potential reaching a peak at approximately +30 mV. Following this, K+ channels open, allowing the membrane to repolarize and eventually return to the resting potential. Significantly, action potentials cannot vary in size; a stronger stimulus will not create a bigger action potential but might lead to a higher frequency of action potentials.