How Nerves Communicate Within Your Body

MEDICAL ANIMATION TRANSCRIPT: A typical neuron consists of a cell body, plasma membrane extensions called dendrites, an elongated fiber known as an axon, and an axon hillock, the trigger zone that releases a nerve impulse. The axon hillock maintains an excitation limit, or threshold, which determines whether or not a neuron will generate a nerve impulse. A nerve impulse is an electrical signal conducted by a neuron, causing a response in another neuron or target cell. When a neuron is at rest, its membrane is polarized because there are more positive ions outside the cell and more negative ions inside the cell, which creates a charge difference across the membrane. Active transport mechanisms called sodium-potassium pumps carry more sodium and less potassium ions across the membrane to maintain this charged difference. Even in a resting neuron, there is the potential for the charged difference to create an electrical current. This is called a resting membrane potential. When an electrical current flows through a dendrite, this is called a local membrane potential. When a dendrite detects a stimulus, a sodium channel in its plasma membrane opens and lets sodium into the neuron. This influx of positive ions reverses the charge across a particular section of the membrane in a process called depolarization. To repolarize the membrane, potassium channels open and release potassium out of the neuron. Nearby, a sodium-potassium pump transports excess sodium amount and brings potassium in, which restores the resting membrane potential. The flow of reversing charges along the dendrite's membrane produces a wavelike electrical current toward the neuron's trigger zone. If the strength of the current meets or exceeds the threshold at the trigger zone, an electrical signal called an action potential or nerve impulse will occur. In a nerve impulse, the trigger zone sends an electrical signal down the axon toward the space between neurons called a synapse or to a target cell membrane.

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