The epidural block occurs when the anesthetic is injected into the outer cov-
ering (dura mater) of the spinal cord near the sacrum.
The saddle block is given at the lower end of the spinal column to block the
perineal area for procedures such as childbirth.
The caudal block is placed near the sacrum.
The patient may experience headaches and hypotension as a result of these
procedures because of a change in cerebrospinal fluid pressure when the needle
is inserted into the spine. The patient should remain in the supine position fol-
lowing the procedure and increase fluid intake.
Autonomic Nervous System
The autonomic nervous system—also known as the visceral system—involun-
tarily regulates smooth muscles and glands including the heart, respiratory sys-
tem, GI tract, peristalsis (digestion), bladder, and eyes.
The autonomic nervous system has two sets of nerves. These are the sensory
neurons (afferent) and the motor neurons (efferent). Sensory neurons send
impulses to the central nervous system, which are transmitted to the brain where
they are interpreted. The brain then sends a response to the motor neuron’s brain
through the spinal cord that directs specific organ cells to respond to the sensory
neuron’s impulse.
Previously in this chapter you learned that the autonomic nervous system has
two branches. These are the sympathetic branch and parasympathetic branch. Both
branches act on the same organ cells but in an opposite way. The sympathetic
branch stimulates a response and the parasympathetic branch depresses a response
by the organ cell. Together, they keep the organ in balance (homeostasis).
The sympathetic branch stimulates a response using norepinephrine, a neuro-
transmitter. Medications that mimic the effect of norepinephrine are called
adrenergic drugs or sympathomimetics (mimic sympathetic nervous system
actions) (see chart). These drugs are also known as adrenergic agonists because
they start a response at the adrenergic receptor sites. There are four types of
adrenergic receptors. These are alpha 1 , alpha 2 , beta 1 , and beta 2. (see chart)
The parasympathetic branch depresses a response using adrenergic block-
ers—also known as sympatholytics. Lytic means to stop effect. Adrenergic
blockers prevent the norepinephrine response at the adrenergic receptor sites.
The parasympathetic branch is sometimes referred to as the cholinergic sys-
tem because an acetylcholine neurotransmitter is used to innervate muscle cells
at the end of the neuron. Acetylcholine stimulates receptor cells to produce a
CHAPTER 15 Nervous System Drugs^281