(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.
MAJOR COMPONENTS OF THE CENTRAL NERVOUS SYSTEM
a. Brain. The brain fills the cranium and weighs about three pounds in the
average adult. The brain is shaped like a mushroom. The brain consists of four
principal parts: the brain stem, the diencephalon, the cerebrum, and the cerebellum.
The diencephalon, also known as the forebrainstem, includes the thalamus and
Figure 1-6. Principal parts of the brain.