impulse

In mechanics, the product of a force and the time over which it acts. An impulse applied to a body causes its momentum to change and is equal to that change in momentum. It is measured in newton seconds (N s).

For example, the impulse J given to a football when it is kicked is given by:

J = Ft

where F is the kick force in newtons and t is the time in seconds for which the boot is in contact with the ball.

impulse

In biology, a means of carrying information between different parts of the body. Nerve impulses travel at speed along nerve cells (neurones). A sequence of impulses carries information.

A stimulus from the environment may cause impulses to be sent from the receptor receiving the stimulus, along a sensory neurone, and to the brain or spinal cord. For example, a touch receptor in the skin of a finger will send impulses that tell the brain an object has been touched. Alternatively, information may be carried from the brain or spinal cord to a muscle or gland along a motor neurone. For example, the information may be carried in a sequence of impulses which causes the contraction of a muscle which causes the finger to be moved away from the object.

A simple example of these processes involving all steps from stimulus to muscle response occurs in any reflex arc.

Although a nerve impulse is an electrical effect, it is not electricity, which travels down wire at much greater speeds. A nerve impulse is an area of a neurone which has an altered electrical potential, commonly described as an area of depolarization. Depolarization is produced by the movement of mineral ions across the cell surface membrane of the neurone.