Final answer:
The 'undershoot' or 'hyperpolarizing aftershoot' is a phenomenon in neuronal action potentials when the membrane potential goes below the resting potential due to delayed closure of voltage-gated potassium channels. This hyperpolarization makes the neuron temporarily less excitable. The neuron eventually returns to the resting potential due to other ion channels and pumps.
Step-by-step explanation:
The concept of 'undershoot/hyperpolarizing aftershoot' pertains to the events occurring during and after an action potential within a neuron. When a neuron fires an action potential, after the depolarization phase, the repolarization phase occurs. This is where the membrane potential returns to the resting potential of around -70 mV, brought upon by the outflux of potassium ions (K+) through voltage-gated K+ channels. However, these channels close with a delay after the membrane potential passes -50 mV on its way back down, leading to an overshoot or hyperpolarization below the resting potential (hyperpolarizing aftershoot). This overshoot happens because K+ continues to exit the cell for a short period, making the inside of the cell more negative than it is at resting potential.
The hyperpolarizing aftershoot, also known as an inhibitory postsynaptic potential (IPSP), is crucial in determining how soon a neuron can fire another action potential. When the hyperpolarization occurs, it becomes less likely for an action potential to be generated immediately following the preceding one. As the voltage-gated K+ channels eventually close, non-gated channels and the Na+/K+ pump help restore the resting potential.