Encyclopedia of Health and Medicine

272 The Nervous System
neuron. Hormones may also function as neurotransmitters.
The appropriate balance of neurotransmitters is
essential for neurologic function, as some neurotransmitters
are excitory (allow nerve impulses to
move from one neuron to another) and others are
inhibitory (block nerve impulses). Neurotransmitters
have specific functions. The BLOOD–BRAIN BAR-
RIER allows the NERVOUS SYSTEM to maintain
different levels of neurotransmitters in the BRAIN
and in the body. Acetylcholine, for example, is
essential in the brain for functions of cognition
and memory. A diminished level of acetylcholine
in the brain is among the hallmark characteristics
of ALZHEIMER’S DISEASE. DOPAMINE is critical for
movement; PARKINSON’S DISEASE develops when the
cells in the brain that produce dopamine die.
Dopamine also facilitates nerve impulses that activate
the brain’s pleasure centers. Monoamine oxidase
(MAO), serotonin, and NOREPINEPHRINE are
key to mood. ANTIDEPRESSANT MEDICATIONS act by
altering the balance of these three chemicals in
the brain. In the body, acetylcholine conducts
electrical impulses between neurons and MUSCLE
cells to facilitate movement. EPINEPHRINE and norepinephrine
conduct electrical impulses in the
HEART.
For further discussion of neurotransmitters
within the context of the structures and functions
of the nervous system, please see the overview
section, “The Nervous System.”
See also AGING, NEUROLOGIC CHANGES THAT OCCUR
WITH; HORMONE.
organic brain syndrome A collective term for
disorders of cognition (thought and logic) and
memory that arise from physical changes that take
place in the BRAIN. Numerous neurologic and
metabolic disorders can cause organic brain syndrome,
as can head trauma and INFECTION, such as
ENCEPHALITIS. Organic brain syndrome sometimes
becomes an ambiguous diagnosis when there are
few distinct or apparent causes to explain mental
deterioration in people who are elderly. However,
the physical changes that occur in the brain to
produce organic brain syndrome are more common
in old age though are not inevitable aspects
of aging.
ALZHEIMER’S DISEASE
ENCEPHALITIS
hepatic NEUROPATHY
HYDROCEPHALY
long-term ALCOHOLISM
PARKINSON’S DISEASE
COMMON DISORDERS ASSOCIATED
WITH ORGANIC BRAIN SYNDROME
STROKE
TRANSIENT ISCHEMIC ATTACK (TIA)
DEMENTIA
HEART ATTACK
HUNTINGTON’S DISEASE
HYPOXIA
MENINGITIS
SEPTICEMIA
substance abuse
TRAUMATIC BRAIN INJURY (TBI)
Symptoms and Diagnostic Path
The presentation and severity of symptoms varies
with the underlying condition and other health
factors. Symptoms extend over time and often
worsen with time. Key symptoms include
• confusion, disorientation, and DELIRIUM
• difficulty carrying out tasks that require
thought, logic, and reasoning such as shopping
or traveling to and from home
• diminished ability to interact with others in
social settings
• diminished ability to independently carry out
activities of daily living such as bathing, dressing,
and preparing meals
• lapses of memory, especially inability to
remember recent events
The diagnostic path begins with a ROUTINE MED-
ICAL EXAMINATION to assess health overall and a
NEUROLOGIC EXAMINATION to evaluate brain function
and cognitive abilities. Because symptoms can
result from electrolyte imbalance, HORMONE disturbances,
high or low BLOOD GLUCOSE (sugar) levels,
and other factors, the routine medical examination
typically includes a complete blood count
(CBC) and other blood tests. The doctor may also
conduct a basic cardiovascular evaluation, including
ELECTROCARDIOGRAM (ECG) and measurement of
BLOOD PRESSURE. A number of health conditions
that can cause cognitive disturbances become
more common with advanced age, some of which
are easily treatable such as HYPOTHYROIDISM, HYPER-
TENSION, ADRENAL INSUFFICIENCY, and cardiac
ARRHYTHMIA. The doctor may also conduct diagnostic
imaging procedures such as COMPUTED TOMOGRA-