1-8. NERVE IMPULSE TRANSMISSION

A nerve impulse is an electro-negative wave that travels over the cell's membrane. To understand the way in which a nerve impulse travels, follow this example of a hand touching a match:

a. The hand touches a lighter match -- stimulus.

b. A dendrite receives the impulse from the skin. The impulse is then transmitted over each neuron as follows:

(1) Cell body.

(2) Axon.

(3) Axon terminals.

Figure 1-5. The transmission of a nerve impulse.

(4) Synapse. Synapse is the junction between two neurons where the electrical activity in one neuron influences the excitability of the second neuron. At this point (the synapse), a chemical reaction occurs.

(a) Acetylcholine (excitor). This is the chemical transmitter of a nerve impulse across a synapse. Acetylcholine is a nerve transmitter stored in synaptic vesicles. This transmitter is the major neurotransmitter in the efferent divisions of the peripheral nervous system.

(b) Acetylcholinesterase (inhibitor). Also called cholinesterase, this enzyme is located on the postsynaptic membrane that destroys acetylcholine.

c. The impulse continues to the next dendrite, in a chain reaction.

d. The hand jerks away -- response.