Psychiatric Mental Health Nursing by Videbeck

alertness. Some psychotropic drugs block histamine,
resulting in weight gain, sedation, and hypotension.

ACETYLCHOLINE

Acetylcholine is a neurotransmitter found in the brain,
spinalcord, and peripheral nervous system partic-
ularly at the neuromuscular junction of skeletal mus-
cle. It can be excitatory or inhibitory. It is synthesized
from dietary choline found in red meat and vegetables
and has been found to affect the sleep/wake cycle
and to signal muscles to become active. Studies have
shown that people with Alzheimer’s disease have de-
creased acetylcholine-secreting neurons, and people
with myasthenia gravis (a muscular disorder in which
impulses fail to pass the myoneural junction, which
causes muscle weakness) have reduced acetylcholine
receptors.

GLUTAMATE

Glutamate is an excitatory amino acid that, at high
levels, can have major neurotoxic effects. Glutamate
has been implicated in the brain damage caused by
stroke, hypoglycemia, sustained hypoxia or ischemia,
and some degenerative diseases such as Huntington’s
or Alzheimer’s.

GAMMA-AMINOBUTYRIC ACID (GABA)

GABA, an amino acid, is the major inhibitory neuro-
transmitter in the brain and has been found to mod-
ulate other neurotransmitter systems rather than to
provide a direct stimulus (Shank, Smith-Swintonky,
& Twyman, 2000). Drugs that increase GABA func-

24 Unit 1 CURRENTTHEORIES ANDPRACTICE

Table 2-1

MAJORNEUROTRANSMITTERS

Type Mechanism of Action Physiologic Effects

Dopamine

Norepinephrine

(noradrenaline)

Epinephrine (adrenaline)

Serotonin

Histamine

Acetylcholine

Neuropeptides

Glutamate

Gamma-aminobutyric

acid (GABA)

Controls complex movements, motivation, cognition;

regulates emotional response

Causes changes in attention, learning and memory,

sleep and wakefulness, mood

Controls fight-or-flight response

Controls food intake, sleep and wakefulness, temper-

ature regulation, pain control, sexual behaviors,

regulation of emotions

Controls alertness, gastric secretions, cardiac stimu-

lation, peripheral allergic responses

Controls sleep and wakefulness cycle; signals mus-

cles to become alert

Enhance, prolong, inhibit, or limit the effects of prin-

cipal neurotransmitters

Results in neurotoxicity if levels are too high

Modulates other neurotransmitters

Excitatory

Excitatory

Excitatory

Inhibitory

Neuromodulator

Excitatory or inhibitory

Neuromodulators

Excitatory

Inhibitory

tion, such as benzodiazepines, are used to treat anx-

iety and induce sleep.

BRAIN IMAGING TECHNIQUES

At one time, the brain could be studied only through

surgery or autopsy. Over the past 25 years, how-

ever, several brain imaging techniques developed

now allow visualization of the brain’s structure and

function. These techniques are useful for diagnos-

ing some disorders of the brain and have helped to

correlate certain areas of the brain with specific

functions. Brain imaging techniques also are useful

in research to find the causes of mental disorders.

Table 2-2 describes and compares several of these

diagnostic techniques.

Types of Brain Imaging Techniques

Computed tomography(CT, also called computed

axial tomography or CAT scan) is a procedure in

which a precise x-ray beam takes cross-sectional im-

ages (slices) layer by layer. A computer reconstructs

the images on a monitor and also stores the images

on magnetic tape or film. CT can visualize the brain’s

soft tissues; so CT is used to diagnose primary tu-

mors, metastases, and effusions and to determine the

size of the ventricles of the brain. Some people with

schizophrenia have been shown to have enlarged ven-

tricles; this finding is associated with a poorer prog-

nosis and marked negative symptoms (see Chap. 14)

(Fig. 2-5). The person undergoing a CT scan must lie

motionless on a stretcher-like table for about 20 to

40 minutes as the stretcher passes through a “ring”

while the serial x-rays are taken.