Definitions of impulse:

• noun:   the act of applying force suddenly

  Example: "The impulse knocked him over"

• noun:   an impelling force or strength
• noun:   the electrical discharge that travels along a nerve fiber

  Example: "They demonstrated the transmission of impulses from the cortex to the hypothalamus"

• noun:   a sudden desire

  Example: "He bought it on an impulse"

• noun:   an instinctive motive

  Example: "Profound religious impulses"

• noun:   (electronics) a sharp transient wave in the normal electrical state (or a series of such transients)