Question

What is it when an impulse returns to stimulate tissure that was previously depolarized?

Answer 1

The refractory period is the time following the depolarization of a neuron or muscle cell when it cannot generate another action potential, allowing the cell to reset its ion balances. Sodium potassium ATPase actively moves sodium (Na+) out and potassium (K+) in to re-establish the resting potential, preventing immediate re-stimulation.

Step-by-step explanation:

The phenomenon you are describing, when an impulse returns to stimulate tissue that was previously depolarized, typically refers to the refractory period. The refractory period is a critical phase in the action potential of a neuron or muscle cell after it has been activated, or depolarized. During this time, the cell “recharges” and prepares for a new impulse, meaning the cell membrane cannot generate another action potential immediately. This process involves the sodium potassium ATPase which actively transports sodium (Na+) out of the cell and potassium (K+) into the cell, re-establishing the resting membrane potential. Due to the refractory period, the cell briefly becomes unresponsive to further stimulation, and this allows the orderly transmission of impulses without backflow, ensuring proper functioning of nerve and muscle tissues. When considering how an electric current along the cell membrane is created, it’s essential to note that any stimulus changing the membrane's permeability can cause depolarization. This change in permeability allows sodium (Na+) to enter the cell, making the inside membrane positive. Afterward, potassium (K+) helps to repolarize the cell, returning it to its resting potential.

Answer 2

An impulse returning to previously stimulated tissue typically happens during the refractory period when a neuron or muscle cell cannot generate another action potential and is transitioning back to its resting state.

Step-by-step explanation:

When an impulse returns to stimulate tissue that was previously depolarized, this generally refers to a phenomenon that occurs during or immediately after the refractory period. This refractory period is a critical phase immediately following the transmission of an impulse in a nerve or muscle, in which a neuron or muscle cell regains its ability to transmit another impulse. During a refractory period, the cell's membrane is momentarily unable to generate another action potential, allowing voltage-sensitive ion channels to return to their resting configurations. The sodium-potassium ATPase actively moves Na+ out of the cell and K+ back into the cell, resulting in repolarization, wherein the membrane returns to its resting state and can be depolarized again.

Specifically, the inrush of Na+ during depolarization neutralizes the inside of the membrane and may render it slightly positive. Afterward, the closure of Na+ channels and the outflow of K+ underpin repolarization, taking the cell back to its resting potential. In the context of the heart, this sequence of depolarization and repolarization is what enables the heart muscles to contract rhythmically, propelling blood throughout the circulatory system.