Absolute refractory period

Absolute refractory period is a concept in neuroscience and cardiology that refers to the time during which a neuron or cardiac muscle cell is unable to respond to a second stimulus, no matter how strong. This period begins immediately after the initiation of an action potential and lasts until the cell has largely returned to its resting state.

Overview

The absolute refractory period is a critical component of how neurons and cardiac muscle cells function. It ensures that action potentials move in one direction along a neuron, from the dendrites towards the axon terminal, and that cardiac muscle cells contract in a coordinated manner to pump blood effectively.

During the absolute refractory period, a second action potential cannot be initiated, because the voltage-gated sodium channels that initiate the action potential are inactivated. This is a result of the membrane potential being at a high positive value following the depolarization phase of the action potential. The channels remain inactivated until the membrane potential has returned to a negative value during the repolarization phase.

Role in Neurons

In neurons, the absolute refractory period plays a crucial role in the propagation of action potentials. It ensures that action potentials move in one direction along the neuron, from the dendrites towards the axon terminal. This is because the region of the neuron behind the action potential is in its absolute refractory period and therefore cannot be reactivated.

Role in Cardiac Muscle Cells

In cardiac muscle cells, the absolute refractory period is longer than in neurons. This prevents the cells from undergoing tetanus, a sustained contraction that would prevent the heart from effectively pumping blood. The longer refractory period in cardiac muscle cells also ensures that the cells contract in a coordinated manner, allowing the heart to effectively pump blood.

See Also

• Relative refractory period
• Action potential
• Neuron
• Cardiac muscle