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 electri...