SECTION 12 Problems Related to Movement and Coordination
60
Assessment: Nervous System
Kristen J. Costello
http://evolve.elsevier.com/Lewis/medsurg/
CONCEPTUAL FOCUS
Cognition Intracranial Regulation
Functional Ability Sensory Perception
LEARNING OUTCOMES
1. Compare the functions of neurons and glial cells. 7. Obtain significant subjective and objective data related to
2. Explain the anatomic location and functions of the the nervous system from a patient.
cerebrum, brainstem, cerebellum, spinal cord, peripheral 8. Perform a physical assessment of the nervous system using
nerves, and cerebrospinal fluid. the appropriate techniques.
3. Identify the major arteries supplying the brain. 9. Discern normal from abnormal findings of a physical
4. Describe the functions of the 12 cranial nerves. assessment of the nervous system.
5. Compare the functions of the 2 divisions of the autonomic 10. Describe the purpose, significance of results, and nursing
nervous system. responsibilities related to diagnostic studies of the nervous
6. Link the age-related changes in the neurologic system to system.
the differences in assessment findings.
KEY TERMS
autonomic nervous system (ANS) meninges
blood-brain barrier neurons
central nervous system (CNS) neurotransmitters
cerebrospinal fluid (CSF) peripheral nervous system (PNS)
cranial nerves (CNs) reflex
dermatome synapse
glial cells upper motor neurons (UMNs)
lower motor neurons (LMNs)
The nervous system is one of the most complex systems. It STRUCTURES AND FUNCTIONS OF NERVOUS
controls all the body’s activities. Having a good understanding
of the nervous system is critical to be able to analyze and inter-
SYSTEM
pret clinical findings. This chapter reviews the structures and The nervous system is responsible for the control and integra-
functions, assessment, and diagnostic studies of the nervous tion of the body’s many activities. It is divided into the central
system. nervous system and peripheral nervous system. The central
1461
,1462 SECTION 12 Problems Related to Movement and Coordination
or to end organs, such as smooth and striated muscles and
glands.
Dendrites Many axons in the CNS and PNS are covered by a myelin
Golgi apparatus sheath. It is a white, lipid protein substance that acts as an insu-
Mitochondrion Neuron cell lator for impulse conduction. Axons may be myelinated or
Nucleolus body (soma)
unmyelinated, as in the case of smaller nerve fibers.
Nucleus
Glial Cells
Nissl bodies
Glial cells (glia, neuroglia) provide support, nourishment, and
Axon hillock protection to neurons. Glial cells make up about half of the brain
and spinal cord mass. Glial cells are divided into microglia and
Axon
macroglia. Microglia are specialized macrophages capable of
phagocytosis. They protect the neurons. These cells are mobile
Schwann cell within the brain. They multiply when the brain is damaged.
Macroglial cells include astrocytes, oligodendrocytes, and
ependymal cells. Astrocytes are found mainly in gray matter.
Myelin sheath They provide structural support to neurons. Their delicate pro-
cesses form the blood-brain barrier with the endothelium of the
Collateral axon
blood vessels. They play a role in synaptic transmission (impulse
conduction between neurons). When the brain is injured, astro-
cytes act as phagocytes for cleaning up neuronal debris. They
Node of Ranvier 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 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. They aid in cere-
brospinal fluid (CSF) secretion.
Telodendria
Synaptic knobs Nerve Regeneration
Fig. 60.1 Structural features of neurons: dendrites, cell body, and If the axon of the nerve cell is damaged, the cell tries to repair
axons. (Modified from Thibodeau GA, Patton KT: Anatomy and physiol-
ogy, ed 8, St Louis, 2013, Mosby.)
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 suc-
nervous system (CNS) consists of the brain, spinal cord, and cessful than peripheral axons in regeneration.1
cranial nerves I and II. The peripheral nervous system (PNS) Schwann cells myelinate the nerve fibers in the PNS. Injured
consists of cranial nerves III to XII, spinal nerves, and periph- nerve fibers in the PNS can regenerate by growing within the
eral components of the autonomic nervous system (ANS). protective myelin sheath of the Schwann cells if the cell body is
intact and the environment is optimal.2 The final result of nerve
Cells of Nervous System regeneration depends on the number of axon sprouts that join
The nervous system is made up of 2 types of cells: neurons and with the appropriate Schwann cell columns and reinnervate
supportive glial cells. appropriate end organs.
Neurons have long been thought to be nonmitotic. That is,
Neurons after being damaged, neurons could not be replaced. Recent
Neurons are the main functional unit of the nervous system. research shows a subset of astrocytes proliferate after some CNS
Neurons come in many shapes and sizes. They share 3 char- injuries, and neurogenesis may occur from stem cells.3 These
acteristics: (1) excitability, or the ability to generate a nerve findings support the fact that the patient will have a certain
impulse; (2) conductivity, or the ability to transmit an impulse; amount of recovery after injury involving the neurons.
and (3) the ability to influence other neurons, muscle cells, or
glandular cells. Nerve Impulse
A typical neuron consists of a cell body, multiple dendrites, The purpose of a neuron is to initiate, receive, and process
and an axon (Fig. 60.1). The cell body contains the nucleus and messages about events both within and outside the body. The
cytoplasm. It is the metabolic center of the neuron. Dendrites initiation of a neuronal message (nerve impulse) involves the
are short processes extending from the cell body. They receive generation of an action potential. A series of action potentials
impulses or signals from other neurons and conduct them travel along the axon. When the impulse reaches the end of the
toward the cell body. The axon projects varying distances from nerve fiber, a chemical interaction involving neurotransmitters
the cell body. The axon carries nerve impulses to other neurons transfers the impulse across the junction (synapse) between
, CHAPTER 60 Assessment: Nervous System 1463
postsynaptic cell to depolarize enough to generate an action
potential.
When many presynaptic cells release excitatory neurotrans-
Neuron mitters on a single neuron, the sum of their input is enough
to generate an action potential. Neurotransmitters continue to
Dendrites combine with the receptor sites at the postsynaptic membrane
until they are inactivated by enzymes, taken up by the presynap-
tic endings, or diffuse away from the synaptic region. Drugs and
Axon toxins can affect neurotransmitters by changing their function
Electrical impulses or blocking their attachment to receptor sites on the postsynap-
tic membrane. Cerebral microdialysis can be used to measure
Neurotransmitter neurotransmitter levels in the cerebral cortex (see Chapter 61).
molecules
Central Nervous System
The components of the CNS include the cerebrum (cerebral
Synapse
hemispheres), brainstem, cerebellum, and spinal cord.
Spinal Cord
Receptor
The spinal cord is continuous with the brainstem and exits
from the cranial cavity through the foramen magnum. A cross
Fig. 60.2 Impulse generation between neurons. Synapse shown with section of the spinal cord reveals gray matter that is centrally
neurotransmitters and receptors.
located in an H shape and surrounded by white matter. The
gray matter contains the cell bodies of voluntary motor neu-
nerve cells. This chemical interaction generates another set of rons, preganglionic autonomic motor neurons, and association
action potentials in the next neuron. These events are repeated neurons (interneurons). The white matter contains the axons of
until the nerve impulse reaches its destination. the ascending sensory and descending motor fibers. The myelin
Because of its insulating capacity, myelination of axons surrounding these fibers gives them their white appearance. The
speeds the conduction of an action potential. Many peripheral spinal pathways or tracts are named for the point of origin and
nerve axons have nodes of Ranvier (gaps in the myelin sheath) the point of destination (e.g., spinocerebellar tract [ascending],
that allow an action potential to travel much faster by jumping corticospinal tract [descending]).
from node to node. We call this saltatory (hopping) conduction. Ascending tracts. In general, the ascending tracts carry
In an unmyelinated fiber, conduction is slower. The wave of specific sensory information to higher levels of the CNS. This
depolarization travels the entire length of the axon, with each information comes from special sensory receptors in the skin,
part of the membrane becoming depolarized in turn. muscles and joints, viscera, and blood vessels. It enters the
spinal cord by way of the dorsal roots of the spinal nerves.
Synapse The ascending tracts are organized by sensory modality and
A synapse is the structural and functional junction between 2 anatomy. The fasciculus gracilis and the fasciculus cuneatus
neurons. It is where the nerve impulse is transmitted from one (dorsal or posterior columns) carry information about touch,
neuron to another. The nerve impulse also can be transmitted deep pressure, vibration, position sense, and kinesthesia
from neurons to glands or muscles. The essential structures of (appreciation of movement, weight, and body parts). The
synaptic transmission are a presynaptic terminal, synaptic cleft, spinocerebellar tracts carry information about muscle tension
and receptor site on the postsynaptic cell (Fig. 60.2). and body position to the cerebellum for coordination of
movement. The spinothalamic tracts carry pain and temperature
Neurotransmitters sensations.
Neurotransmitters are chemicals that affect the transmission of Other ascending tracts may also carry sensory information.
impulses across the synaptic cleft. Excitatory neurotransmitters The signs and symptoms of various neurologic problems sug-
(e.g., epinephrine, norepinephrine, glutamate) activate postsyn- gest there are other pathways for touch, position sense, and
aptic receptors that increase the chance that an action potential vibration.
will be generated. Inhibitory neurotransmitters (e.g., serotonin, Descending tracts. Descending tracts carry impulses that
γ-aminobutyric acid [GABA], dopamine) activate postsynaptic are responsible for muscle movement. Important descending
receptors to decrease the chance that an action potential will tracts are the corticobulbar and corticospinal tracts, collectively
be generated. For example, endorphins block pain transmission termed the pyramidal tract. These tracts carry voluntary
while substance P makes nerves more sensitive to pain. impulses from the cerebral cortex to the cranial and peripheral
In general, the net effect (excitatory or inhibitory) depends nerves. Another group of descending motor tracts carries
on the number of presynaptic neurons releasing neurotrans- impulses from the extrapyramidal system (all motor systems
mitters on the postsynaptic cell. A presynaptic cell that releases except the pyramidal) concerned with voluntary movement. It
an excitatory neurotransmitter does not always cause the includes pathways originating in the brainstem, basal ganglia,
60
Assessment: Nervous System
Kristen J. Costello
http://evolve.elsevier.com/Lewis/medsurg/
CONCEPTUAL FOCUS
Cognition Intracranial Regulation
Functional Ability Sensory Perception
LEARNING OUTCOMES
1. Compare the functions of neurons and glial cells. 7. Obtain significant subjective and objective data related to
2. Explain the anatomic location and functions of the the nervous system from a patient.
cerebrum, brainstem, cerebellum, spinal cord, peripheral 8. Perform a physical assessment of the nervous system using
nerves, and cerebrospinal fluid. the appropriate techniques.
3. Identify the major arteries supplying the brain. 9. Discern normal from abnormal findings of a physical
4. Describe the functions of the 12 cranial nerves. assessment of the nervous system.
5. Compare the functions of the 2 divisions of the autonomic 10. Describe the purpose, significance of results, and nursing
nervous system. responsibilities related to diagnostic studies of the nervous
6. Link the age-related changes in the neurologic system to system.
the differences in assessment findings.
KEY TERMS
autonomic nervous system (ANS) meninges
blood-brain barrier neurons
central nervous system (CNS) neurotransmitters
cerebrospinal fluid (CSF) peripheral nervous system (PNS)
cranial nerves (CNs) reflex
dermatome synapse
glial cells upper motor neurons (UMNs)
lower motor neurons (LMNs)
The nervous system is one of the most complex systems. It STRUCTURES AND FUNCTIONS OF NERVOUS
controls all the body’s activities. Having a good understanding
of the nervous system is critical to be able to analyze and inter-
SYSTEM
pret clinical findings. This chapter reviews the structures and The nervous system is responsible for the control and integra-
functions, assessment, and diagnostic studies of the nervous tion of the body’s many activities. It is divided into the central
system. nervous system and peripheral nervous system. The central
1461
,1462 SECTION 12 Problems Related to Movement and Coordination
or to end organs, such as smooth and striated muscles and
glands.
Dendrites Many axons in the CNS and PNS are covered by a myelin
Golgi apparatus sheath. It is a white, lipid protein substance that acts as an insu-
Mitochondrion Neuron cell lator for impulse conduction. Axons may be myelinated or
Nucleolus body (soma)
unmyelinated, as in the case of smaller nerve fibers.
Nucleus
Glial Cells
Nissl bodies
Glial cells (glia, neuroglia) provide support, nourishment, and
Axon hillock protection to neurons. Glial cells make up about half of the brain
and spinal cord mass. Glial cells are divided into microglia and
Axon
macroglia. Microglia are specialized macrophages capable of
phagocytosis. They protect the neurons. These cells are mobile
Schwann cell within the brain. They multiply when the brain is damaged.
Macroglial cells include astrocytes, oligodendrocytes, and
ependymal cells. Astrocytes are found mainly in gray matter.
Myelin sheath They provide structural support to neurons. Their delicate pro-
cesses form the blood-brain barrier with the endothelium of the
Collateral axon
blood vessels. They play a role in synaptic transmission (impulse
conduction between neurons). When the brain is injured, astro-
cytes act as phagocytes for cleaning up neuronal debris. They
Node of Ranvier 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 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. They aid in cere-
brospinal fluid (CSF) secretion.
Telodendria
Synaptic knobs Nerve Regeneration
Fig. 60.1 Structural features of neurons: dendrites, cell body, and If the axon of the nerve cell is damaged, the cell tries to repair
axons. (Modified from Thibodeau GA, Patton KT: Anatomy and physiol-
ogy, ed 8, St Louis, 2013, Mosby.)
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 suc-
nervous system (CNS) consists of the brain, spinal cord, and cessful than peripheral axons in regeneration.1
cranial nerves I and II. The peripheral nervous system (PNS) Schwann cells myelinate the nerve fibers in the PNS. Injured
consists of cranial nerves III to XII, spinal nerves, and periph- nerve fibers in the PNS can regenerate by growing within the
eral components of the autonomic nervous system (ANS). protective myelin sheath of the Schwann cells if the cell body is
intact and the environment is optimal.2 The final result of nerve
Cells of Nervous System regeneration depends on the number of axon sprouts that join
The nervous system is made up of 2 types of cells: neurons and with the appropriate Schwann cell columns and reinnervate
supportive glial cells. appropriate end organs.
Neurons have long been thought to be nonmitotic. That is,
Neurons after being damaged, neurons could not be replaced. Recent
Neurons are the main functional unit of the nervous system. research shows a subset of astrocytes proliferate after some CNS
Neurons come in many shapes and sizes. They share 3 char- injuries, and neurogenesis may occur from stem cells.3 These
acteristics: (1) excitability, or the ability to generate a nerve findings support the fact that the patient will have a certain
impulse; (2) conductivity, or the ability to transmit an impulse; amount of recovery after injury involving the neurons.
and (3) the ability to influence other neurons, muscle cells, or
glandular cells. Nerve Impulse
A typical neuron consists of a cell body, multiple dendrites, The purpose of a neuron is to initiate, receive, and process
and an axon (Fig. 60.1). The cell body contains the nucleus and messages about events both within and outside the body. The
cytoplasm. It is the metabolic center of the neuron. Dendrites initiation of a neuronal message (nerve impulse) involves the
are short processes extending from the cell body. They receive generation of an action potential. A series of action potentials
impulses or signals from other neurons and conduct them travel along the axon. When the impulse reaches the end of the
toward the cell body. The axon projects varying distances from nerve fiber, a chemical interaction involving neurotransmitters
the cell body. The axon carries nerve impulses to other neurons transfers the impulse across the junction (synapse) between
, CHAPTER 60 Assessment: Nervous System 1463
postsynaptic cell to depolarize enough to generate an action
potential.
When many presynaptic cells release excitatory neurotrans-
Neuron mitters on a single neuron, the sum of their input is enough
to generate an action potential. Neurotransmitters continue to
Dendrites combine with the receptor sites at the postsynaptic membrane
until they are inactivated by enzymes, taken up by the presynap-
tic endings, or diffuse away from the synaptic region. Drugs and
Axon toxins can affect neurotransmitters by changing their function
Electrical impulses or blocking their attachment to receptor sites on the postsynap-
tic membrane. Cerebral microdialysis can be used to measure
Neurotransmitter neurotransmitter levels in the cerebral cortex (see Chapter 61).
molecules
Central Nervous System
The components of the CNS include the cerebrum (cerebral
Synapse
hemispheres), brainstem, cerebellum, and spinal cord.
Spinal Cord
Receptor
The spinal cord is continuous with the brainstem and exits
from the cranial cavity through the foramen magnum. A cross
Fig. 60.2 Impulse generation between neurons. Synapse shown with section of the spinal cord reveals gray matter that is centrally
neurotransmitters and receptors.
located in an H shape and surrounded by white matter. The
gray matter contains the cell bodies of voluntary motor neu-
nerve cells. This chemical interaction generates another set of rons, preganglionic autonomic motor neurons, and association
action potentials in the next neuron. These events are repeated neurons (interneurons). The white matter contains the axons of
until the nerve impulse reaches its destination. the ascending sensory and descending motor fibers. The myelin
Because of its insulating capacity, myelination of axons surrounding these fibers gives them their white appearance. The
speeds the conduction of an action potential. Many peripheral spinal pathways or tracts are named for the point of origin and
nerve axons have nodes of Ranvier (gaps in the myelin sheath) the point of destination (e.g., spinocerebellar tract [ascending],
that allow an action potential to travel much faster by jumping corticospinal tract [descending]).
from node to node. We call this saltatory (hopping) conduction. Ascending tracts. In general, the ascending tracts carry
In an unmyelinated fiber, conduction is slower. The wave of specific sensory information to higher levels of the CNS. This
depolarization travels the entire length of the axon, with each information comes from special sensory receptors in the skin,
part of the membrane becoming depolarized in turn. muscles and joints, viscera, and blood vessels. It enters the
spinal cord by way of the dorsal roots of the spinal nerves.
Synapse The ascending tracts are organized by sensory modality and
A synapse is the structural and functional junction between 2 anatomy. The fasciculus gracilis and the fasciculus cuneatus
neurons. It is where the nerve impulse is transmitted from one (dorsal or posterior columns) carry information about touch,
neuron to another. The nerve impulse also can be transmitted deep pressure, vibration, position sense, and kinesthesia
from neurons to glands or muscles. The essential structures of (appreciation of movement, weight, and body parts). The
synaptic transmission are a presynaptic terminal, synaptic cleft, spinocerebellar tracts carry information about muscle tension
and receptor site on the postsynaptic cell (Fig. 60.2). and body position to the cerebellum for coordination of
movement. The spinothalamic tracts carry pain and temperature
Neurotransmitters sensations.
Neurotransmitters are chemicals that affect the transmission of Other ascending tracts may also carry sensory information.
impulses across the synaptic cleft. Excitatory neurotransmitters The signs and symptoms of various neurologic problems sug-
(e.g., epinephrine, norepinephrine, glutamate) activate postsyn- gest there are other pathways for touch, position sense, and
aptic receptors that increase the chance that an action potential vibration.
will be generated. Inhibitory neurotransmitters (e.g., serotonin, Descending tracts. Descending tracts carry impulses that
γ-aminobutyric acid [GABA], dopamine) activate postsynaptic are responsible for muscle movement. Important descending
receptors to decrease the chance that an action potential will tracts are the corticobulbar and corticospinal tracts, collectively
be generated. For example, endorphins block pain transmission termed the pyramidal tract. These tracts carry voluntary
while substance P makes nerves more sensitive to pain. impulses from the cerebral cortex to the cranial and peripheral
In general, the net effect (excitatory or inhibitory) depends nerves. Another group of descending motor tracts carries
on the number of presynaptic neurons releasing neurotrans- impulses from the extrapyramidal system (all motor systems
mitters on the postsynaptic cell. A presynaptic cell that releases except the pyramidal) concerned with voluntary movement. It
an excitatory neurotransmitter does not always cause the includes pathways originating in the brainstem, basal ganglia,
