Action Potential
Definition
An action potential is a rapid electrical impulse that travels along the membrane of a neuron (nerve cell). It occurs when there is a sudden change in the electrical charge across the membrane, caused by the movement of positively charged ions (sodium and potassium) into and out of the cell. Depolarization begins when sodium channels open, allowing positively charged sodium ions to rush into the cell, making the inside more positive. This must reach a threshold of excitation—the critical level of depolarization—before the neuron fully fires. After the peak of the action potential, potassium channels open and potassium exits the cell, leading to hyperpolarization, a temporary state where the inside of the neuron becomes more negative than its resting potential. This process allows neurons to communicate with other cells, such as muscles or glands, enabling the body to respond to stimuli.
Example
Imagine you touch a hot stove accidentally. Sensory receptors in your skin detect the heat and generate an action potential. This electrical signal travels through sensory neurons to your spinal cord, where it is transmitted to motor neurons. These motor neurons send an action potential back to your muscles, causing them to contract and pull your hand away from the stove. Without action potentials, you wouldn’t be able to react quickly enough to avoid injury. The action potential is only triggered when the sensory neuron's membrane depolarizes past the threshold of excitation; otherwise, the signal fails to continue.
Why It Matters
Action potentials are essential for communication within the nervous system. They allow your body to respond rapidly to changes in the environment, such as avoiding danger or reacting to sensory inputs. Without action potentials, you couldn’t move, think, or feel. They ensure that signals travel efficiently and accurately throughout the body, making them a fundamental aspect of how the brain and nervous system function. Understanding depolarization, threshold, and hyperpolarization also helps explain how drugs, disorders, or injuries can disrupt neural signaling and affect everything from reflexes to mood and cognition.
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