Neural Circuits

Factors Affecting Speed of Impulse

Some simple neuronal circuits (arrows are direction of action potentials)

A presynaptic cell sends an action potential (yellow) to a postsynaptic cell with a low threshold and the postsynaptic cell responds with it's own action potential.

A presynaptic cell sends a message (green) to a postsynaptic cell with a high threshold. As long as the presynaptic action potentials are far apart in time, the postsynaptic cell does not respond. When the signals occur rapidly, the postsynaptic cell responds. This is temporal summation.

Two presynaptic cells send a simultaneous message to a postsynaptic cell with a high threshhold and it responds with an action potential. This is spatial summation.

The effects of temporal and spatial summation can be mixed together (look for the two stimuli that occur close together).

Inhibitory nerve cells (dark) can decrease the response of another cell.

A) No inhibition; B) lateral inhibition

Lateral Inhibition 2D: = Resting; = Stimulus (light); = Full excitation; = Small inhibition; = Large inhibition

More Lateral Inhibition Cartoons. Good for edge and movement detection!