An all-or-nothing impulse code ("digital" code) is based on pulses that are either all the way
on, or all the way off. They code excitation and inhibition by the number of pulses sent per second.
Strong excitation elicits (trigger) many impulses per second. Weak excitation produces few impulses
per second, and inhibition can stop completely the impulses. Figure 1 illustrates the relation between
the strength of stimulation and the number of all-or-nothing impulses represented by the vertical lines
riding on the horizontal line representing resting potential.
Figure 1. The all-or-nothing code which
axons use. The higher that rate of impulses (impulses/second), the stronger the excitation the axon
got
An ordinary light switch is an all-or-nothing device. It is either all the way on or all the way off. Image a light turned on just briefly. It give a flash or pulse of light. Flashing light infrequently gives little light. The faster (more frequently) it is flashed, the more light it gives. The CDs you play record the sound by converting it into pulses. The stronger the sound pressure at any given moment the more pulses
See also graded, analog code