The nervous system is one of the most complex systems. It controls all
the body’s activities. Having a general understanding of the nervous system
is critical to your being able to analyze and interpret clinical findings. This
chapter reviews the structures and functions, assessment, and diagnostic
studies of the nervous system.
Structures and Functions of Nervous
System
The nervous system is responsible for the control and integration of the
body’s many activities. It is divided into the central nervous system and
peripheral nervous system. The central nervous system (CNS) consists of
the brain, spinal cord, and cranial nerves I and II. The peripheral nervous
system (PNS) consists of cranial nerves III to XII, spinal nerves, and
peripheral components of the autonomic nervous system (ANS).
Cells of Nervous System
The nervous system is made up of 2 types of cells: neurons and supportive
glial cells.
Neurons
Neurons are the primary functional unit of the nervous system. Although
neurons come in many shapes and sizes, they share 3 characteristics:
(1) excitability, or the ability to generate a nerve impulse;
(2) conductivity, or the ability to transmit an impulse; and (3) influence, or
the ability to influence other neurons, muscle cells, or glandular cells.
A typical neuron consists of a cell body, multiple dendrites, and an axon
(Fig. 55.1). The cell body contains the nucleus and cytoplasm. It is the
metabolic center of the neuron. Dendrites are short processes extending
from the cell body. They receive impulses or signals from other neurons
and conduct them toward the cell body. The axon projects varying
distances from the cell body. The axon carries nerve impulses to other
neurons or to end organs, such as smooth and striated muscles and glands.
FIG.
55.1 Structural features of neurons: dendrites, cell body, and axons.
Modified from Thibodeau GA, Patton KT: Anatomy and physiology, ed 8, St Louis,
2013, Mosby.
Many axons in the CNS and PNS are covered by a myelin sheath, a white,
lipid protein substance that acts as an insulator for the conduction of
impulses. Axons may be myelinated or unmyelinated, as in the case of
smaller fibers.
Glial Cells
Glial cells (glia or neuroglia) provide support, nourishment, and protection
to neurons. Glial cells make up about half of the brain and spinal cord mass.
Glial cells are divided into microglia and macroglia. Microglia, specialized
macrophages capable of phagocytosis, protect the neurons. These cells are
mobile within the brain and multiply when the brain is damaged.
Macroglial cells include astrocytes, oligodendrocytes, and ependymal
cells. Astrocytes are found mainly in gray matter. They provide structural
support to neurons. Their delicate processes form the blood-brain
barrier with the endothelium of the blood vessels. They also play a role
in synaptic transmission (conduction of impulses between neurons). When
the brain is injured, astrocytes act as phagocytes for cleaning up neuronal
debris. They help restore the neurochemical milieu and provide support for
repair. Proliferation of astrocytes contributes to the formation of scar
tissue (gliosis) in the CNS.
Oligodendrocytes are specialized cells that produce the myelin sheath of
nerve fibers in the CNS. They are found mainly in the white matter of the
CNS. Ependymal cells line the brain ventricles and aid in the secretion of
cerebrospinal fluid (CSF).
Neuroglia are mitotic and can replicate. In general, when neurons are
destroyed, the tissue is replaced by the proliferation of neuroglial cells.
Most primary CNS tumors involve glial cells. Primary cancers involving
neurons are rare.
Nerve Regeneration
If the axon of the nerve cell is damaged, the cell tries to repair itself.
Damaged nerve cells try to grow back to their original destinations by
sprouting many branches from the damaged ends of their axons. Axons in
the CNS are generally less successful than peripheral axons in
regeneration.1
Schwann cells myelinate the nerve fibers in the PNS. Injured nerve fibers
in the PNS can regenerate by growing within the protective myelin sheath
of the Schwann cells if the cell body is intact and the environment is
optimal.2 The final result of nerve regeneration depends on the number of
axon sprouts that join with the appropriate Schwann cell columns and
reinnervate appropriate end organs.
Neurons have long been thought to be nonmitotic. That is, after being
damaged, neurons could not be replaced. Recent research shows a subset of
glial cells (astrocytes) proliferate after certain injuries in the CNS, and
neurogenesis may occur from stem cells.3 These findings support the
expectation that the patient will have a certain amount of recovery after
injury involving the neurons.
Nerve Impulse
The purpose of a neuron is to initiate, receive, and process messages about
events both within and outside the body. The initiation of a neuronal
message (nerve impulse) involves the generation of an action potential. A
series of action potentials travel along the axon. When the impulse reaches
the end of the nerve fiber, a chemical interaction involving
neurotransmitters transmits the impulse across the
junction (synapse) between nerve cells by. This chemical interaction
generates another set of action potentials in the next neuron. These events
are repeated until the nerve impulse reaches its destination.
Because of its insulating capacity, myelination of nerve axons speeds the
conduction of an action potential. Many peripheral nerve axons have nodes
of Ranvier (gaps in the myelin sheath) that allow an action potential to
travel much faster by jumping from node to node. We call
this saltatory (hopping) conduction. In an unmyelinated fiber, conduction is
slower. The wave of depolarization travels the entire length of the axon,
with each part of the membrane becoming depolarized in turn.
Synapse
A synapse is the structural and functional junction between 2 neurons. It is
where the nerve impulse is transmitted from 1 neuron to another. The
nerve impulse also can be transmitted from neurons to glands or muscles.
The essential structures of synaptic transmission are a presynaptic
terminal, synaptic cleft, and receptor site on the postsynaptic cell
(Fig. 55.2).
Neurotransmitters
Neurotransmitters are chemicals that affect the transmission of impulses
across the synaptic cleft. Excitatory neurotransmitters (e.g., epinephrine,
norepinephrine, glutamate) activate postsynaptic receptors that increase
the chance that an action potential will be generated. Inhibitory
neurotransmitters (e.g., serotonin, γ-aminobutyric acid [GABA], dopamine)
activate postsynaptic receptors to decrease the chance that an action
potential will be generated. For example, endorphins block pain
transmission while substance P makes nerves more sensitive to pain.
FIG. 55.2 Impulse generation between neurons. Synapse shown with neurotransmitters
and receptors.
In general, the net effect (excitatory or inhibitory) depends on the
number of presynaptic neurons releasing neurotransmitters on the
postsynaptic cell. A presynaptic cell that releases an excitatory
neurotransmitter does not always cause the postsynaptic cell to depolarize
enough to generate an action potential.
When many presynaptic cells release excitatory neurotransmitters on a
single neuron, the sum of their input is enough to generate an action
potential. Neurotransmitters continue to combine with the receptor sites at
the postsynaptic membrane until they are inactivated by enzymes, are
taken up by the presynaptic endings, or diffuse away from the synaptic
region. Drugs and toxins can affect neurotransmitters by changing their
function or blocking their attachment to receptor sites on the postsynaptic
membrane. We can use cerebral microdialysis to measure
neurotransmitter levels in the cerebral cortex (see Chapter 56).
Central Nervous System
The components of the CNS include the cerebrum (cerebral hemispheres),
brainstem, cerebellum, and spinal cord.
Spinal Cord
The spinal cord is continuous with the brainstem and exits from the cranial
cavity through the foramen magnum. A cross section of the spinal cord
reveals gray matter that is centrally located in an H shape and surrounded
by white matter. The gray matter contains the cell bodies of voluntary
motor neurons, preganglionic autonomic motor neurons, and association
neurons (interneurons). The white matter contains the axons of the
ascending sensory and descending motor fibers. The myelin surrounding
these fibers gives them their white appearance. The spinal pathways or
tracts are named for the point of origin and the point of destination (e.g.,
spinocerebellar tract [ascending], corticospinal tract [descending]).
Ascending Tracts
In general, the ascending tracts carry specific sensory information to higher
levels of the CNS. This information comes from special sensory receptors in
the skin, muscles and joints, viscera, and blood vessels and enters the spinal
cord by way of the dorsal roots of the spinal nerves. The ascending tracts
are organized by sensory modality and anatomy. The fasciculus gracilis and
the fasciculus cuneatus (often called the dorsal or posterior columns) carry
information about touch, deep pressure, vibration, position sense, and
kinesthesia (appreciation of movement, weight, and body parts).
The spinocerebellar tracts carry information about muscle tension and body
position to the cerebellum for coordination of movement.
The spinothalamic tracts carry pain and temperature sensations.
Other ascending tracts may also carry sensory modalities. The signs and
symptoms of various neurologic diseases suggest there are additional
pathways for touch, position sense, and vibration.
Descending Tracts
Descending tracts carry impulses that are responsible for muscle
movement. Among the most important descending tracts are the
corticobulbar and corticospinal tracts, collectively termed the pyramidal
tract. These tracts carry voluntary impulses from the cerebral cortex to the
cranial and peripheral nerves. Another group of descending motor tracts
carries impulses from the extrapyramidal system (all motor systems except
the pyramidal) concerned with voluntary movement. It includes pathways
originating in the brainstem, basal ganglia, and cerebellum. The motor
output exits the spinal cord by way of the ventral roots of the spinal nerves.
Reflex Arc
A reflex is an involuntary response to stimuli. In the spinal cord, reflex arcs
play an important role in maintaining muscle tone, which is essential for
body posture. The components of a monosynaptic reflex arc (Fig. 55.3) are
a receptor organ, afferent neuron, effector neuron, and effector organ (e.g.,
skeletal muscle). The afferent neuron synapses with the efferent neurons in
the gray matter of the spinal cord. More complex reflex arcs have other
neurons (interneurons) in addition to the afferent neuron influencing the
effector neuron.
Lower and Upper Motor Neurons
Upper motor neurons (UMNs) originate in the cerebral cortex and project
downward. The corticobulbar tract ends in the brainstem, and the
corticospinal tract descends into the spinal cord. These neurons influence
skeletal muscle movement. UMN lesions generally cause weakness or
paralysis, disuse atrophy, hyperreflexia, and increased muscle tone
(spasticity).
Lower motor neurons (LMNs) are the final common pathway through
which descending motor tracts influence skeletal muscle. The cell bodies of
LMNs, which send axons to innervate the skeletal muscles of the arms,
trunk, and legs, are found in the anterior horn of the corresponding
segments of the spinal cord (e.g., cervical segments contain LMNs for the
arms). LMNs for skeletal muscles of the eyes, face, mouth, and throat are
found in the corresponding segments of the brainstem. These cell bodies
and their axons make up the somatic motor components of the cranial
nerves. LMN lesions generally cause weakness or paralysis, denervation
atrophy, hyporeflexia or areflexia, and decreased muscle tone (flaccidity).
Brain
The brain has 3 major intracranial components: cerebrum, brainstem, and
cerebellum.
Cerebrum
The cerebrum is composed of the right and left cerebral hemispheres. It is
divided into 4 lobes: frontal, temporal, parietal, and occipital (Fig. 55.4).
The functions of the cerebrum are multiple and complex (Table 55.1).
The frontal lobe controls higher cognitive function, memory
retention, voluntary eye movements, voluntary motor movement, and
motor functions involved in speech production (Broca’s area). The temporal
lobe integrates somatic, visual, and auditory data and contains Wernicke’s
receptive speech area. (Language and potential functional deficits are
described with strokes in Chapter 57 [see Table 57.4]).
The parietal lobe interprets spatial information and contains the sensory
cortex. Processing of sight takes place in the occipital lobe.
The division of the cerebrum into lobes is useful to delineate portions of
the neocortex (gray matter), which makes up the outer layer of the cerebral
hemispheres. Neurons in specific parts of the neocortex are essential for
various highly complex and sophisticated functions, such as language,
memory, and appreciation of visual-spatial relationships.
The basal ganglia, thalamus, hypothalamus, and limbic system are also in
the cerebrum. The basal ganglia are a group of structures found centrally in
the cerebrum and midbrain. Most of them are on both sides of the
thalamus. The function of the basal ganglia includes the initiation,
execution, and completion of voluntary movements, learning, emotional
response, and automatic movements associated with skeletal muscle
activity (e.g., swallowing saliva, blinking, swinging the arms while walking).
The thalamus lies directly above the brainstem (Fig. 55.5). It is the major
relay center for sensory input from the body, face, retina, and cochlear and
taste receptors. Motor relay nuclei in the thalamus connect the cerebellum
and basal ganglia to the frontal cortex.
The hypothalamus is just below the thalamus and slightly in front of the
midbrain. It exerts a direct influence on release of hormones from the
anterior pituitary gland. It has a rich capillary connection to the pituitary
gland to aid in the transport of hormones. These hormones include thyroid-
stimulating hormone, growth hormone, luteinizing hormone, and prolactinreleasing hormone, which play a role in regulating reproductive function. In
contrast, the supraoptic and paraventricular neurons travel directly
through the pituitary stalk to the posterior pituitary, where they release
vasopressin and oxytocin. The hypothalamus contains the satiety center
that regulates appetite. With input from the limbic system, it also regulates
body temperature, water balance (through influence on vasopressin
secretion), circadian rhythm, and expression of emotion. The limbic
system is found near the inner surfaces of the cerebral hemispheres. It is
concerned with emotion, aggression, feeding behavior, and sexual
response.
Brainstem
The brainstem includes the midbrain, pons, and medulla (Fig. 55.5).
Ascending and descending fibers to and from the cerebrum and cerebellum
pass through the brainstem. The nuclei of cranial nerves III through XII are
in the brainstem. The vital centers concerned with respiratory, vasomotor,
and heart function are in the medulla.
Also in the brainstem is the reticular formation, a diffusely arranged
group of neurons and their axons that extends from the medulla to the
thalamus and hypothalamus. The functions of the reticular formation
include relaying sensory information, influencing excitatory and inhibitory
control of spinal motor neurons, and controlling vasomotor and respiratory
activity. The reticular activating system (RAS) is a complex system that
requires communication among the brainstem, reticular formation, and
cerebral cortex. The RAS regulates arousal and sleep-wake transitions. The
brainstem also contains the centers for sneezing, coughing, hiccupping,
vomiting, sucking, and swallowing.
Cerebellum
The cerebellum is in the posterior cranial fossa below the occipital lobe. It
coordinates voluntary movement and maintains trunk stability and
equilibrium. The cerebellum receives information from the cerebral cortex,
muscles, joints, and inner ear. It influences motor activity through axonal
connections to the thalamus, motor cortex, and brainstem nuclei and their
descending pathways.
FIG. 55.5 Major divisions of the CNS.
Ventricles and Cerebrospinal Fluid
The ventricles are 4 interconnected fluid-filled cavities. The lower part of
the fourth ventricle becomes the central canal in the lower part of the
brainstem. The spinal canal extends centrally through the full length of the
spinal cord.
Cerebrospinal fluid (CSF) is made largely in the choroid plexuses of the
brain within the ventricles. It circulates within the subarachnoid space that
surrounds the brain, brainstem, and spinal cord, cushioning the brain and
spinal cord. CSF flows from the cranial cavity to the spinal cavity, carrying
nutrients through both passive diffusion and active transport. We make CSF
at an average rate of about 500 mL/day. The ventricles and central canal
are filled with an average of 150 mL at any given time. Changes in the rate
of CSF production or absorption can occur, leading to a change in the
volume within the ventricles and central canal. Excessive buildup of CSF
results in a condition known as hydrocephalus.
CSF circulates throughout the ventricles and seeps into the subarachnoid
space surrounding the brain and spinal cord. It is absorbed primarily
through the arachnoid villi (tiny projections into the subarachnoid space)
into the intradural venous sinuses and eventually into the venous system.
The analysis of CSF composition provides useful diagnostic information
related to certain nervous system diseases. We often measure CSF pressure
in patients with actual or suspected intracranial injury. Increased
intracranial pressure, indicated by increased CSF pressure, can force
downward (central) herniation of the brain and brainstem. The signs
marking this event are part of the herniation syndrome (see Chapter 56).
Peripheral Nervous System
The PNS includes all the neuronal structures that lie outside the CNS. It
consists of the spinal and cranial nerves, their associated ganglia
(groupings of cell bodies), and portions of the ANS.
Spinal Nerves
The spinal cord can be seen as a series of spinal segments, each on top of
another with no visible boundaries. In addition to the cell bodies, each
segment has a pair of dorsal (afferent) sensory nerve fibers or roots and
ventral (efferent) motor fibers or roots. They innervate a specific region of
the body. This combined motor-sensory nerve is called a spinal nerve (Fig.
55.6). The cell bodies of the voluntary motor system are in the anterior
horn of the spinal cord gray matter. The cell bodies of the autonomic
(involuntary) motor system are in the anterolateral part of the spinal cord
gray matter. The cell bodies of sensory fibers are in the dorsal root ganglia
just outside the spinal cord. On exiting the spinal column, each spinal nerve
divides into ventral and dorsal rami, a collection of motor and sensory
fibers that eventually goes to peripheral structures (e.g., skin, muscles,
viscera).
FIG. 55.6 Cross section of spinal cord showing attachments of spinal nerves and coverings
of the spinal cord.
A dermatome is the area of skin innervated by the sensory fibers of a
single dorsal root of a spinal nerve (Fig. 55.7). The dermatomes give a
general picture of somatic sensory innervation by spinal segments.
A myotome is a muscle group innervated by the primary motor neurons of a
single ventral root. The dermatomes and myotomes of a given spinal
segment overlap with those of adjacent segments because of the
development of ascending and descending collateral branches of nerve
fibers.
Cranial Nerves
The cranial nerves (CNs) are the 12 paired nerves composed of cell bodies
with fibers that exit from the cranial cavity. Unlike the spinal nerves, which
always have both afferent sensory and efferent motor fibers, some CNs are
only sensory, some only motor, and some both.
Table 55.4 (later in this chapter) outlines the motor and sensory
components of the CNs. Fig. 55.8 shows the position of the CNs in relation
to the brain and spinal cord. Just as the cell bodies of the spinal nerves are
found in specific segments of the spinal cord, cell bodies (nuclei) of the CNs
found in specific segments of the brainstem. Exceptions are the nuclei of
the olfactory and optic nerves. The primary cell bodies of the olfactory
nerve are in the nasal epithelium. The cell bodies of the optic nerve are in
the retina.
Autonomic Nervous System
The autonomic nervous system (ANS) is divided into the sympathetic and
parasympathetic systems. The ANS governs involuntary functions of heart
muscle, smooth muscle, and glands through both efferent and afferent
pathways. The 2 systems function together to maintain a relatively
balanced internal environment. The preganglionic cell bodies of
the sympathetic nervous system (SNS) are found in spinal segments T1
through L2. The major neurotransmitter released by the postganglionic
fibers of the SNS is norepinephrine. The neurotransmitter released by the
preganglionic fibers is acetylcholine.
FIG. 55.7 Dermatomes of the body.
From Herlihy B: The human body in health and illness, ed 4, St Louis, 2011,
Saunders.
The preganglionic cell bodies of the parasympathetic nervous
system (PSNS) are found in the brainstem and sacral spinal segments (S2
through S4). Acetylcholine is the neurotransmitter released at both
preganglionic and postganglionic nerve endings.
SNS stimulation activates the mechanisms required for the “fight-orflight” response that occurs throughout the body (Fig. 55.9). In contrast, the
PSNS is geared to act in localized and discrete regions. It conserves and
restores the body’s energy stores. The ANS provides dual and often
reciprocal innervation to many structures. For example, the SNS increases
the rate and force of heart contraction and the PSNS decreases the rate and
force.
Cerebral Circulation
Knowing the distribution of the brain’s major arteries is essential for
understanding and evaluating the signs and symptoms of cerebrovascular
disease and trauma. The brain’s blood supply arises from the internal
carotid arteries (anterior circulation) and the vertebral arteries (posterior
circulation). They are shown in Fig. 55.10.
The internal carotid arteries provide blood flow to the anterior and
middle portions of the cerebrum. The vertebral arteries join to form the
basilar artery, which branches to supply the middle and lower parts of the
temporal lobes, occipital lobes, cerebellum, brainstem, and part of the
diencephalon. The main branch of the basilar artery is the posterior
cerebral artery. The circle of Willis is formed by communicating arteries
that join the basilar and internal carotid arteries (Fig. 55.11). The circle of
Willis plays a key role in cerebral blood flow. Interestingly, only 40% of us
have a well-formed, complete circle of Willis. Everyone else has a degree of
variation.4
Superior to the circle of Willis, 3 pairs of arteries supply blood to the left
and right hemispheres. The anterior cerebral artery feeds the medial and
anterior portions of the frontal lobes. The middle cerebral artery feeds the
outer portions of the frontal, parietal, and superior temporal lobes. The
posterior cerebral artery feeds the medial portions of the occipital and
inferior temporal lobes. Venous blood drains from the brain through the
dural sinuses, which form channels that drain into the 2 jugular veins.
Blood-Brain Barrier
The blood-brain barrier is a physiologic barrier between blood capillaries
and brain tissue. This barrier protects the brain from harmful agents, while
allowing nutrients and gases to enter. The structure of brain capillaries
differs from that of other capillaries, so substances that normally pass into
most tissues are prevented from entering brain tissue. Lipid-soluble
compounds enter the brain easily. Water-soluble and ionized drugs enter
the brain and the spinal cord slowly. Thus the blood-brain barrier affects
the penetration of drugs. Only certain drugs can enter the CNS from the
bloodstream.
Protective Structures
Meninges
The meninges consist of 3 protective membranes that surround the brain
and spinal cord: the dura mater, arachnoid, and pia mater (Fig. 55.12). The
thick dura mater forms the outermost layer. The falx cerebri is a fold of the
dura that separates the 2 cerebral hemispheres. It slows expansion of brain
tissue in conditions such as a rapidly growing tumor or acute hemorrhage.
The tentorium cerebelli is a fold of dura that separates the cerebral
hemispheres from the posterior fossa (which contains the brainstem and
cerebellum).
The arachnoid layer is a fragile, web-like membrane that lies between the
dura mater and pia mater (the vascular innermost layer of the meninges).
The area between the arachnoid layer and pia mater (subarachnoid
space) is filled with CSF. Structures such as arteries, veins, and cranial
nerves passing to and from the brain and skull must pass through the
subarachnoid space. A larger subarachnoid space in the region of the third
and fourth lumbar vertebrae is the area used to obtain CSF during a lumbar
puncture.
Skull
The skull protects the brain from external trauma. It is composed of 8
cranial bones and 14 facial bones. Although the top and sides of the inside
of the skull are fairly smooth, the bottom surface is uneven. It has many
ridges, prominences, and foramina (holes through which blood vessels and
nerves enter the intracranial vault). The largest hole is the foramen
magnum, through which the brainstem extends to the spinal cord. The
foramen magnum is the only major space for the expansion of brain
contents when increased intracranial pressure occurs.
Vertebral Column
The vertebral column protects the spinal cord, supports the head, and
provides flexibility. The vertebral column is made up of 33 individual
vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral (fused into 1), and 4
coccygeal (fused into 1). Each vertebra has a central opening through which
the spinal cord passes. A series of ligaments holds the vertebrae together.
Intervertebral discs occupy the spaces between vertebrae, allowing
movement of the column. Fig. 55.13 shows the natural curvature of the
spinal column and its relation to the trunk.
Gerontologic Considerations: Effects of Aging
on Nervous System
Aging affects several parts of the nervous system. In the CNS, the gradual
loss of neurons in certain areas of the brainstem, cerebellum, and cerebral
cortex begins in early adulthood. With loss of neurons, the ventricles widen
or enlarge, brain weight decreases, cerebral blood flow decreases, and CSF
production declines.
In the PNS, degenerative changes in myelin cause a decrease in nerve
conduction. Coordinated neuromuscular activity, such as maintaining BP in
response to changing from a lying to a standing position, is altered with
aging. As a result, older adults are more likely to have orthostatic
hypotension. Similarly, coordination of neuromuscular activity to maintain
body temperature becomes less efficient with aging. Older adults are less
able to adapt to extremes in environmental temperature and are more
vulnerable to both hypothermia and hyperthermia.
Other relevant changes associated with aging include decreases in
memory, vision, hearing, taste, smell, vibration, position sense, muscle
strength, and reaction time. Sensory changes, including decreases in taste
and smell perception, may result in decreased dietary intake in the older
adult. Reduced hearing and vision can result in perceptual
confusion.5Problems with balance and coordination can put the older adult
at risk for falls.6 Changes in assessment findings result from age-related
changes in the nervous system (Table 55.2). Changes should not be
attributed to aging without considering other underlying causes.
Assessment of Nervous System
Subjective Data
Important Health Information
Past Health History
When performing a neurologic examination, first determine if an
emergency exists. For example, does the patient have decreasing level of
consciousness? The neurologic assessment is done when an abnormality is
identified during screening or can be expected based on patient history. Is
the patient a reliable historian and able to give detailed information? If not,
interview someone with first-hand knowledge of the patient’s history and
current problem. Avoid suggesting symptoms or asking leading questions.
Second, the mode of onset and course of the illness are especially
important aspects of the history. Often these facts alone can reveal the
nature of a neurologic disease process. Obtain all pertinent data in the
history of the present illness, especially data related to the characteristics
and progression of the symptoms. In some cases, the history may include
birth injury (e.g., cerebral palsy from hypoxia) and/or other neurologic
insults, such as a traumatic brain injury, stroke, or degenerative disease.
Growth and developmental history can be important in determining if
nervous system dysfunction was present at an early age. Specifically, ask
about major developmental tasks, such as walking and talking.
Medications
Obtain a careful medication history, especially the use of sedatives, opioids,
tranquilizers, and mood-elevating drugs. Many other drugs can cause
neurologic side effects. Ask the patient to describe the medication regimen
to determine adherence to prescribed therapies.
Surgery or Other Treatments
Ask about any surgery involving any part of the nervous system, such as
head, spine, or sensory organs. If a patient had surgery, determine the date,
cause, procedure, recovery, and current status. Note any history of eye
surgery to determine the relevance of abnormal pupil assessment.
Functional Health Patterns
Key questions to ask a patient with a neurologic problem are outlined
in Table 55.3.
Health Perception–Health Management Pattern
Ask about the patient’s health practices that affect the nervous system, such
as substance use, smoking, adequate nutrition, BP management, safe
participation in physical and recreational activities, and use of seat belts or
helmets. Ask about hospitalizations for neurologic problems.
If the patient has an existing neurologic problem, assess how it affects
daily living and the ability to perform self-care. After a careful review of
information, ask someone who knows the patient well whether they notice
any mental or physical changes in the patient. The patient with a neurologic
problem may not be aware of it or may be a poor historian.
Nutritional-Metabolic Pattern
Neurologic problems can result in poor nutrition. Problems related to
chewing, swallowing, facial nerve paralysis, and muscle coordination could
make it difficult for the patient to ingest adequate nutrients. Certain
vitamins, such as thiamine (B1), niacin, and pyridoxine (B6), are essential
for the health of the CNS. Deficiencies in any of these can result in
nonspecific problems, such as depression, apathy, neuritis, weakness,
mental confusion, and irritability. Cobalamin (vitamin B12) deficiency can
occur in older adults, who may have problems with vitamin absorption
from supplements as well as natural food sources, such as meat, fish, and
poultry. Untreated, cobalamin deficiency can cause mental function decline.
In the patient with brain injury, early nutritional support can markedly
improve outcomes.7
Elimination Pattern
Bowel and bladder problems often are associated with neurologic
problems, such as stroke, head injury, spinal cord injury, MS, and dementia.
To plan appropriate interventions, determine if the bowel or bladder
problem was present before or after the current neurologic event. Urinary
retention and incontinence of urine and feces are the most common
elimination problems associated with a neurologic problem or its
treatment. For example, nerve root compression (as occurs in cauda equina
conditions) leads to a sudden onset of incontinence. Record key details,
such as number of episodes, accompanying sensations or lack of sensations,
and measures to control the problem.
Activity-Exercise Pattern
Many neurologic disorders can cause problems in the patient’s mobility,
strength, and coordination. These problems can affect the patient’s usual
activity and exercise patterns and can increase the risk for falls.6 Assess the
person’s activities of daily living because neurologic diseases can affect the
ability to perform motor tasks, which increases the risk for injury.
Sleep-Rest Pattern
Sleep pattern changes can be both a cause and a response to neurologic
problems. Pain and reduced ability to change position because of muscle
weakness and paralysis could interfere with sleep quality. Hallucinations
resulting from dementia or drugs can interrupt sleep. Carefully assess and
record the patient’s sleep pattern and bedtime routines.
Cognitive-Perceptual Pattern
Because the nervous system controls cognition and sensory integration,
many neurologic problems affect these functions. Consider culture, age, and
education when assessing communication because they play a role in our
interaction with others. Assess memory, language, calculation ability,
problem-solving ability, insight, and judgment. Ask the patient hypothetical
questions such as, “What is a reasonable price for a cup of coffee?” or “What
would you do if you saw a car crash outside your house?” Consider if the
patient’s plans and goals match the physical and mental capabilities. Note
the presence of factors affecting intellectual capacity, such as cognitive
impairment, hallucinations, delusions, and dementia.
Assess a person’s ability to use and understand language.
Appropriateness of responses is a useful indicator of cognitive and
perceptual ability. Determine the patient’s understanding and ability to
carry out needed treatments. Neurologic-related cognitive changes can
interfere with the patient’s understanding of the disease and adherence to
related treatment.
Pain is common with many neurologic problems and is often the reason a
patient seeks care. Carefully assess the patient’s pain. (Pain and pain
assessment are discussed in Chapter 8.)
Self-Perception–Self-Concept Pattern
Neurologic diseases can drastically change a patient’s control over life and
create dependency on others for meeting daily needs. The patient’s
physical appearance and emotional control can be affected. Sensitively ask
about the patient’s evaluation of self-worth, perception of abilities, body
image, and general emotional pattern.
Role-Relationship Pattern
Physical impairments, such as weakness and paralysis, can alter or limit
participation in usual roles and activities. Cognitive changes can
permanently alter a person’s ability to maintain previous roles. These
changes can dramatically affect the patient and caregiver. Ask the patient if
a role change has occurred (e.g., spouse or breadwinner) because of
neurologic problems and determine how long it has lasted. Caregivers
should take part in decision making when neurologic deficits prevent the
patient from decisions that will affect the role.
Sexuality-Reproductive Pattern
Assess the person’s ability to take part in sexual activity. Many neurologic
disorders can affect sexual response. Cerebral lesions may inhibit the
desire phase or the reflex responses of the excitement phase. The
hypothalamus stimulates the pituitary gland to release hormones that
influence sexual desire. Brainstem and spinal cord lesions may partially or
completely interrupt the desire or ability to have intercourse. Neuropathies
and spinal cord lesions may prevent reflex activities of the sexual response
or affect sensation and decrease desire. Despite neurologically related
changes in sexual function, many persons can achieve satisfying expression
of intimacy and affection.
Coping–Stress Tolerance Pattern
The physical sequelae of a neurologic problem can strain a patient’s coping
ability. Often the problem is chronic, and the patient must learn new coping
skills. Assess if the patient’s coping skills are adequate to deal with the
stress of this problem. Also assess the patient’s support system.
Value-Belief Pattern
Many neurologic problems have serious, long-term, life-changing effects.
Determine what these effects are because they can strain the patient’s
belief system. Assess if any religious or cultural beliefs could affect the
treatment plan.
Objective Data
Physical Examination
The standard neurologic examination helps determine the presence,
location, and nature of nervous system disease (Fig. 55.14). The
examination assesses 6 categories of function: mental status, cranial nerve
function, motor function, sensory function, cerebellar function, and
reflexes.8 Develop a consistent pattern of completing the neurologic
examination to remember to include each element for every patient
examination.
Mental Status
Assessment of mental status (cerebral function) gives a general impression
of how the patient is functioning. It involves determining complex and highlevel cerebral functions governed by many areas of the cerebral cortex.
Complete most of the mental status examination during your interaction
with the patient. For example, assess language and memory when asking
the patient for details of the illness and significant past events. Consider the
patient’s age, cultural background, and level of education when evaluating
mental status.
The components of the mental status examination include:
• General appearance and behavior: This includes level of
consciousness (awake, asleep, comatose), motor activity, body
posture, dress and hygiene, facial expression, and speech pattern.
This assessment begins when you first see the patient. A patient who
has deficits in self-care as shown by poor grooming is more likely to
have other cognitive deficits.
• Cognition: Note orientation to time, place, person, and situation, as
well as memory, general knowledge, insight, judgment, problem
solving, and calculation. Common questions are “Who were the last 3
presidents?” “What do people use to cut paper?” “Can you count
backward from 100 by 7s?”8 Often a structured mental status
questionnaire is used to evaluate these functions and provide
baseline data for evaluating changes over time. Common tools
include the Mini-Mental State Examination (MMSE) (see Table
59.10) and Montreal Cognitive Assessment (MoCA).9 Delirium is an
acute and transient disorder of cognition that can be seen at any
time during a patient’s illness. As discussed in Chapter 59, delirium
is often an early indicator of various illnesses (see Table 59.16). The
Confusion Assessment Method tool is used to assess for delirium
(see Table 59.18).
• Mood and affect: Note any agitation, anger, depression, or euphoria,
and the appropriateness of these states. Use suitable questions to
reveal the patient’s feelings.
Cranial Nerves
Olfactory nerve
Chronic rhinitis, sinusitis, and heavy smoking may decrease the sense of
smell. Problems with the ability to smell may be associated with a tumor
involving the olfactory bulb or the result of a basilar skull fracture that has
damaged the olfactory fibers as they pass through the delicate cribriform
plate of the skull. Anosmia (loss of sense of smell) is an early sign in
Parkinson’s disease and Alzheimer’s disease.10
Optic nerve
Visual field defects may arise from lesions of the optic nerve, optic chiasm,
or tracts that extend through the temporal, parietal, or occipital lobes.
Visual field changes resulting from brain lesions include hemianopsia (half
of the visual field is affected), quadrantanopia (one fourth of the visual field
is affected), bitemporal hemianopsia (bilateral peripheral vision is affected),
or monocular vision. It may be hard to test acuity if the patient does not
read English or is aphasic.
Oculomotor, trochlear, and abducens nerves
Because the oculomotor (CN III), trochlear (CN IV), and abducens (CN VI)
nerves help move the eye, they are tested together (Table 55.4). With
weakness or paralysis of an eye muscle, the eyes do not move together, and
the patient has a disconjugate gaze. Note the presence and direction
of nystagmus (fine, rapid jerking movements of the eyes), even though this
condition most often indicates vestibulocerebellar problems.
Because the oculomotor nerve exits at the top of the brainstem at the
tentorial notch, it can be compressed easily by expanding mass lesions.
When this occurs, sympathetic input to the pupil is unopposed; the pupil
changes shape and becomes dilated. The lack of pupillary constriction is an
early sign of central herniation (see Chapter 56).
Two abbreviations we often used to record the reaction of the pupils
are PERRL (Pupils are Equal [in size], Round, and Reactive to Light)
and PERRLA (Pupils are Equal, Round, and Reactive to Light
and Accommodation). The PERRLabbreviation is appropriate when
accommodation cannot be assessed, as in an unconscious patient.
Convergence and accommodation are tested by having the patient focus on
the examiner’s finger as it moves toward the patient’s nose.
Another function of the oculomotor nerve is to keep the eyelid open.
Damage to the nerve can cause ptosis (drooping eyelid), pupillary
abnormalities, and eye muscle weakness.
Motor System
The motor system examination includes assessment of strength, tone,
coordination, and symmetry of the major muscle groups. Test muscle
strength by asking the patient to push and pull against the resistance of
your arm as it opposes flexion and extension of the patient’s muscle. Ask
the patient to offer resistance at the shoulders, elbows, wrists, hips, knees,
and ankles. Mild weakness of the arm is demonstrated by downward
drifting of the arm or pronation of the palm (pronator drift). The pronator
drift test is especially sensitive when the patient has a potential for
vasospasm or increasing edema in 1 hemisphere of the cerebrum. Ask the
patient to close the eyes and hold the arms out with palms facing up (like
they are holding a large pizza). The patient should hold this position for 30
seconds. Downward drift with palm pronation indicates a problem in the
opposite motor cortex. Note any weakness or asymmetry of strength
between the same muscle groups of the right and left sides.
Test muscle tone by passively moving the limbs through their range of
motion. You should identify a slight resistance to these movements.
Abnormal tone is described as hypotonia (flaccidity)
or hypertonia (spasticity). Note any involuntary movements, such as tics,
tremor, myoclonus (spasm of muscles), athetosis (slow, writhing,
involuntary movements of extremities), chorea (involuntary, purposeless,
rapid motions), and dystonia (impairment of muscle tone).
Test cerebellar function by assessing balance and coordination. A good
screening test for both balance and muscle strength is to observe the
patient’s stature (posture while standing) and gait. Note the pace and
rhythm of the gait. Observe for normal symmetric and oppositional arm
swing. The patient’s ability to ambulate helps to determine the level of
nursing care needed and the risk for falling.
The finger-to-nose test (having the patient alternately touch the nose,
then touch the examiner’s finger) and the heel-to-shin test (having the
patient stroke the heel of 1 foot up and down the shin of the opposite leg)
assess coordination and cerebellar function. Reposition your finger while
the patient is touching the nose so that the patient must adjust to a new
distance each time your finger is touched. These movements should be
performed smoothly and accurately. Other tests include asking the patient
to pronate and supinate both hands rapidly and to do a shallow knee bend,
first on 1 leg and then on the other. Note dysarthria or slurred speech
because it is a sign of incoordination of the speech muscles.
Sensory System
In the somatic sensory examination, several modalities are tested. Each
modality is carried by a specific ascending pathway in the spinal cord
before it reaches the sensory cortex. As a rule, perform the examination
with the patient’s eyes closed and avoid providing the patient with clues.
Ask “How does this feel?” rather than “Is this sharp?” In the routine
neurologic examination, sensory testing of the anterior torso, posterior
torso, and all extremities is sufficient. However, if a problem is identified in
sensory function, the boundaries of that dysfunction should be carefully
delineated along the dermatome.
Touch, pain, and temperature
Light touch is usually tested first using a cotton wisp or light pinprick.
Gently touch each extremity and ask the patient to indicate when they feel
the stimulus. Test pain by alternately touching the skin with the sharp and
dull end of a pin. Tell the patient to respond “sharp” or “dull.” Evaluate each
limb separately.
Extinction is assessed by simultaneously touching both sides of the body
symmetrically. Normally, the simultaneous stimuli are both perceived
(sensed). An abnormal response occurs when the patient perceives the
stimulus on only 1 side. The other stimulus is extinguished.
Test the sensation of temperature by applying tubes of warm and cold
water to the skin and asking the patient to identify the stimuli with the eyes
closed. If pain sensation is intact, you do not have to assess temperature
sensation because the same ascending pathways carry both sensations.
Vibration sense
Assess vibration sense by applying a vibrating tuning fork to the fingernails
and bony prominences of the hands, legs, and feet. Ask the patient if the
vibration or “buzz” is felt. Then ask the patient to indicate when the
vibration ceases.
Position sense
Assess position sense (proprioception) by placing your thumb and
forefinger on either side of the patient’s forefinger or great toe and gently
moving his or her digit up or down. Ask the patient to close the eyes and
state the direction in which the digit is moved.
Another test of proprioception is the Romberg test. Ask the patient to
stand with feet together and then close his or her eyes. If the patient can
maintain balance with the eyes open but sways or falls with the eyes closed
(i.e., a positive Romberg test), vestibulocochlear dysfunction or disease in
the posterior columns of the spinal cord may be present. Be aware of
patient safety during this test.
Cortical sensory functions
Several tests evaluate cortical integration of sensory perceptions (which
occurs in the parietal lobes). Explain these tests to the patient before
performing them, while his or her eyes are still open. Assess two-point
discrimination by placing the 2 points of a calibrated compass on the tips of
the fingers and toes. The minimum recognizable separation is 4 to 5 mm in
the fingertips and a greater degree of separation elsewhere. This test is
important in diagnosing diseases of the sensory cortex and PNS.
FIG. 55.16 The examiner strikes a swift blow over a stretched tendon to elicit a stretch
reflex. A, Biceps reflex. B, Patellar reflex.
Test graphesthesia (ability to feel writing on skin) by having the patient
identify numbers traced on the palm of the hands. Test stereognosis (ability
to perceive the form and nature of objects) by having the patient close the
eyes and identify the size and shape of easily recognized objects (e.g., coins,
keys, safety pin) placed in the hands.
Reflexes
Tendons have receptors that are sensitive to stretch. A reflex contraction of
the skeletal muscle occurs when the tendon is stretched. In general, we test
the biceps, triceps, brachioradialis, patellar, and Achilles tendon reflexes.
Initiate a simple muscle stretch reflex by briskly tapping the tendon of a
stretched muscle, usually with a reflex hammer (Fig. 55.16). Measure the
response (muscle contraction of the corresponding muscle) on a 0 to 5
scale as follows: 0 = absent reflex; 1 = weak response, seen only with
reinforcement; 2 = normal response; 3 = brisk response; 4 = hyperreflexia
with nonsustained clonus; and 5 = hyperreflexia with sustained
clonus. Clonus, an abnormal response, is a continued rhythmic contraction
of the muscle with continuous application of the stimulus.
Elicit the biceps reflex, with the patient’s arm partially flexed and palm up,
by placing your thumb over the biceps tendon in the antecubital space and
striking the thumb with a hammer. The normal response is flexion of the
arm at the elbow or contraction of the biceps muscle that you can feel with
your thumb.
Elicit the triceps reflex by striking the triceps tendon above the elbow
while the patient’s arm is flexed. The normal response is extension of the
arm or visible contraction of the triceps.
Elicit the brachioradialis reflex by striking the radius 3 to 5 cm above the
wrist while the patient’s arm is relaxed. The normal response is flexion and
supination at the elbow or visible contraction of the brachioradialis muscle.
Elicit the patellar reflex by striking the patellar tendon just below the
patella. The patient can be sitting or lying as long as the leg being tested
hangs freely. The normal response is extension of the leg with contraction
of the quadriceps.
Gently dorsiflex the patient’s foot at the ankle. Elicit the Achilles tendon
reflex by striking the Achilles tendon while the patient’s leg is flexed at the
knee. The normal response is plantar flexion at the ankle.
A focused assessment is used to evaluate the status of previously
identified neurologic problems and to monitor for signs of new problems. A
focused assessment of the neurologic system is shown in the box on p.
1294.
Diagnostic Studies of Nervous System
Many diagnostic studies are available to assess the nervous system
(Tables 55.7, 55.8, 55.9, and 55.10). CSF analysis provides information
about a variety of CNS diseases. Normal CSF is clear, colorless, odorless, and
free of red blood cells. It contains little protein. Normal CSF values are
listed in Table 55.7. CSF may be obtained through lumbar puncture (LP) or,
on occasion, ventriculostomy.
During LP, the HCP aspirates CSF through a needle inserted into the L3-4
or L4-5 interspace. A manometer attached to the needle is used to obtain
CSF pressure. CSF is withdrawn in a series of tubes and sent for analysis. LP
is contraindicated in the presence of increased intracranial pressure
because of the risk for downward herniation from CSF removal or if there is
infection at the intended puncture site. Nursing care of the patient
undergoing LP is outlined in Table 55.8.
Biopsies of nerve, muscle, brain, and arterial tissues are useful in
diagnosing several disorders (e.g., tumors, infectious disease, degenerative
diseases, temporal artery for arteritis). A brain biopsy is usually done using
a stereotactic procedure.
CNS, Central nervous system; LMN, lower motor neuron.