The preganglionic fibers of the sympathetic nervous system extend from the
spinal cord to the ganglionic fiber. These are relatively short. However, sympa-
thetic postganglionic fibers are long from the ganglion to the body cells.
Neurological pathways in the parasympathetic nervous system originate from
cranial nerves III, VII, IX, and X from the brain stem and the sacral segments S2,
S3, and S4 from the spinal cord. This is why the parasympathetic nervous system
is also known as the craniosacral division of the autonomic nervous system.
Preganglionic fibers are long from the spinal cord to the ganglion and the
postganglionic fibers are short from the ganglion to the body cells.
Central Nervous System Stimulants
Medication is given to stimulate the central nervous system in order to induce a
therapeutic response. These include medications that treat narcolepsy, attention
deficit disorder (ADD), obesity, and reversal of respiratory distress.
There are four major groups of medications that stimulate the central ner-
vous system. These are amphetamines, caffeine, analeptics, and anorexiants.
Amphetamines stimulate the cerebral cortex of the brain. Caffeine also stimu-
lates the cerebral cortex and stimulates respiration by acting on the brain
stem and medulla. Analeptics have an effect on the brain stem and medulla as
caffeine does. Anorexiants inhibit appetite by stimulating the cerebral cortex and
the hypothalamus.
Amphetamines, analeptics, and anorexiants are commonly referred to as
“uppers” when used to prevent sleep. Anorexiants and amphetamines can pro-
duce psychological dependence and the body can become tolerant to its effect if
abused. Abruptly discontinuing these medications may result in withdrawal
symptoms including depression. Amphetamines are also taken to decrease
weight and increase energy enabling the patient to perform work quickly with-
out rest.
Analeptics are substances which stimulate breathing and heart activity. Methyl-
phenidate (Ritalin) is an analeptic often prescribed for children with Attention
Deficit Hyperactivity Disorder (ADDHD).
Amphetamines, analeptics, and anorexiants stimulate the release of the neuro-
transmitters norepinephrine and dopamine from the brain and from the periph-
eral nerve terminals of the sympathetic nervous system. The result is euphoria
and increased alertness. The patient can also experience sleeplessness, restless-
ness, tremors, and irritability; cardiovascular problems (increased heart rate, pal-
pitations, dysrhythmias and hypertension). Some examples of anorexiants and
CHAPTER 15 Nervous System Drugs^271