Human Physiology/The Nervous System

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Central Nervous System

The central nervous system is the control center for the body. It regulates organ function, higher thought, and

movement of the body. The central nervous system consists of the brain and spinal cord.

Generation & propagation of an action potential

Electrical characteristics of a neurochemical action potential.

The Nerve Impulse

When a nerve is stimulated the resting potential changes. Examples of such stimuli are pressure, electricity,

chemicals, etc. Different neurons are sensitive to different stimuli(although most can register pain). The stimulus

causes sodium ion channels to open. The rapid change in polarity that moves along the nerve fiber is called the

"ACTION POTENTIAL." This moving change in polarity has several stages:

Depolarization

The upswing is caused when positively charged sodium ions(Na+) suddenly rush through open sodium gates

into a nerve cell.The membrane potential of the stimulated cell undergoes a localized change from-65

millivolts to 0 in a limited area. As additional sodium rushes in, the membrane potential actually reverses its

polarity so that the outside of the membrane is negative relative to the inside. During this change of polarity

the membrane actually develops a positive value for a moment(+40 millivolts). The change in voltage

stimulates the opening of additional sodium channels (called a voltage-gated ion channel). This is an example

of a positive feedback loop.

Repolarization