Rnsg 233 Chapter 43 Assessment of
the Nervous System study guide
➢ Structures and Functions of Nervous System
• Central nervous system (CNS)
o Brain
o Spinal cord
o Cranial nerves I and III
• Peripheral nervous system (PNS)
o Cranial nerves III to XII
o Spinal nerves
o Autonomic nervous system (ANS)
• Neurons
o Primary functional unit
o Characterized by
▪ Excitability: Ability to generate a nerve impulse
▪ Conductivity: Ability to transmit an impulse
▪ Influence: Ability to influence other neurons, muscle cells,
or glandular cells by transmitting nerve impulses to them
o function: carries impulses to other neurons or other organs
o Myelin sheath: a white, lipid substance that acts as an insulator for
the conduction of impulses
o Nonmitotic
• Glial cells: (glia or neuroglia) provide support, nourishment, and protection to neurons. Glial cells constitute
almost half of the brain and spinal cord mass and are 5 to 10 times more numerous than neurons
o Microglia: specialized macrophages capable of phagocytosis,
protect the neurons. These cells are mobile within the brain
and multiply when brain is damaged.
o Macroglia:
▪ Astrocytes: (Most Abundant) Found primarily in gray
matter and provide structural support to neurons. are
found primarily in gray matter and provide structural
support to neurons. Their delicate processes form the
blood-brain barrier with the endothelium of the blood
vessels. Play a role in synaptic transmission (conduction
of impulses between neurons). When the brain is
injured, astrocytes act as phagocytes for 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. VOLUNATARY MOTOR NEURONS
▪ Oligodendrocytes: Specialized cells that produce
the myelin sheath of nerve fibers in the CNS and are
`primarily found in the white matter of the
CNS. (Schwann cells myelinate the nerve fibers
in the periphery.)
▪ Ependymal cells: line the brain ventricles and aid in
the secretion of CSF
o Mitotic: Neuroglia are mitotic and can replicate. When
destroyed, the tissue is replaced by proliferation of
neuroglial cells.
o AFFERENT- AFFECTS SOMETHING
o EFFERENT- EFFECT FROM SOMETHING.
• Nerve regeneration (repair)
, Rnsg 233 Chapter 43 Assessment of
the Nervous System study guide
o Attempt to grow back by sprouting many branches from
the damaged ends of their axons
o PNS more successful than CNS
• Injured nerve fibers in the PNS can regenerate by growing within the protective myelin sheath of the
supporting Schwann cells if the cell body is intact. 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.
• Nerve impulse: Purpose is to initiate, receive, and process messages about events both within and outside
the body. Initiation involves the generation of an action potential. Once an action potential is initiated, a
series of action potentials travels along the axon. When the impulse reaches the end of the nerve fiber, it
is transmitted across the junction between nerve cells (synapse) by a chemical interaction involving
neurotransmitters. This chemical interaction generates another set of action potentials in the next
neuron. Events are repeated until the nerve impulse reaches its destination.
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 without traversing the insulated membrane segment.
Called saltatory (hopping) conduction. In an unmyelinated fiber, the wave of depolarization travels the entire
length of the axon, with each portion of the membrane becoming depolarized in turn.
o Action potential
o Synapse: Is the structural and functional junction between two neurons. The point at which nerve impulse is
transmitted from one neuron to another. The nerve impulse can also be transmitted from neurons to glands
or muscles. The essential structures of synaptic transmission are a presynaptic terminal, a synaptic cleft, and
a receptor site on the postsynaptic cell
o Neurotransmitters: Chemicals that affect the transmission of impulses across the synaptic cleft.
Excitatory neurotransmitters activate postsynaptic receptors that increase the likelihood that an
action potential will be generated.
Inhibitory neurotransmitters activate postsynaptic receptors that inhibit the likelihood that an action potential
will be generated.
The net effect (excitatory or inhibitory) depends on the number of presynaptic neurons that are releasing
neurotransmitters on the postsynaptic cell.
Neurotransmitters can be affected by drugs and toxins, which can modify their function or block their
attachment to receptor sites on the postsynaptic membrane.
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.
With the use of cerebral microdialysis neurotransmitter levels can now be measured in the cerebral cortex
o Myelin increases speed of conduction.
• Spinal cord: 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 is surrounded by
white matter.
o Gray and white matter: Contains the cell bodies of voluntary motor neurons, preganglionic autonomic
motor neurons, and association neurons (interneurons). It contains the axons of the ascending sensory and
the descending (suprasegmental) motor fibers. 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,
corticospinal tract (descending)
o Ascending tracts: Carry specific sensory information to higher levels of the CNS.
- Info 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 fasciculus gracilis and the fasciculus cuneatus carry info and transmit impulses concerned with touch,
deep pressure, vibration, position sense, and kinesthesia (appreciation of movement, weight, and body parts).
, Rnsg 233 Chapter 43 Assessment of
the Nervous System study guide
- Spinocerebellar tracts carry info about muscle tension & body position to cerebellum for coordination of movement.
- Spinothalamic tracts carry pain and temperature sensations.
o Descending tracts: Carry impulses that are responsible for muscle movement.
- Most important descending tracts are the corticobulbar and corticospinal tracts, termed the pyramidal tract.
- These tracts carry volitional (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.
o Lower and upper motor neurons
- Lower motor neurons (LMNs): Final common pathway through which
descending motor tracts influence skeletal muscle. Cell bodies of LMNs,
which send axons to innervate the skeletal muscles of the arms, trunk,
and legs, are located in the anterior horn of the corresponding
segments of the spinal cord
LMNs for skeletal muscles of eyes, face, mouth, & throat are located 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 cause weakness or paralysis, denervation atrophy,
hyporeflexia or areflexia, & decreased muscle tone (flaccidity).
- 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 cause weakness or paralysis, disuse atrophy, hyperreflexia,
and increased muscle tone (spasticity).
o Reflex arc: in the spinal cord, reflex arcs play an important role in
maintaining muscle tone, which is essential for body posture.
Components of a monosynaptic reflex arc are a receptor organ,
an afferent neuron, an effector neuron, and an effector organ
(skeletal muscle).
Afferent neuron synapses with the efferent neuron in the
gray matter of the spinal cord.
• Brain: Cerebrum, brainstem,
and cerebellum
o Cerebrum: Right & left
cerebral hemispheres. Divided into 4 lobes: frontal, temporal, parietal, and occipital
the Nervous System study guide
➢ Structures and Functions of Nervous System
• Central nervous system (CNS)
o Brain
o Spinal cord
o Cranial nerves I and III
• Peripheral nervous system (PNS)
o Cranial nerves III to XII
o Spinal nerves
o Autonomic nervous system (ANS)
• Neurons
o Primary functional unit
o Characterized by
▪ Excitability: Ability to generate a nerve impulse
▪ Conductivity: Ability to transmit an impulse
▪ Influence: Ability to influence other neurons, muscle cells,
or glandular cells by transmitting nerve impulses to them
o function: carries impulses to other neurons or other organs
o Myelin sheath: a white, lipid substance that acts as an insulator for
the conduction of impulses
o Nonmitotic
• Glial cells: (glia or neuroglia) provide support, nourishment, and protection to neurons. Glial cells constitute
almost half of the brain and spinal cord mass and are 5 to 10 times more numerous than neurons
o Microglia: specialized macrophages capable of phagocytosis,
protect the neurons. These cells are mobile within the brain
and multiply when brain is damaged.
o Macroglia:
▪ Astrocytes: (Most Abundant) Found primarily in gray
matter and provide structural support to neurons. are
found primarily in gray matter and provide structural
support to neurons. Their delicate processes form the
blood-brain barrier with the endothelium of the blood
vessels. Play a role in synaptic transmission (conduction
of impulses between neurons). When the brain is
injured, astrocytes act as phagocytes for 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. VOLUNATARY MOTOR NEURONS
▪ Oligodendrocytes: Specialized cells that produce
the myelin sheath of nerve fibers in the CNS and are
`primarily found in the white matter of the
CNS. (Schwann cells myelinate the nerve fibers
in the periphery.)
▪ Ependymal cells: line the brain ventricles and aid in
the secretion of CSF
o Mitotic: Neuroglia are mitotic and can replicate. When
destroyed, the tissue is replaced by proliferation of
neuroglial cells.
o AFFERENT- AFFECTS SOMETHING
o EFFERENT- EFFECT FROM SOMETHING.
• Nerve regeneration (repair)
, Rnsg 233 Chapter 43 Assessment of
the Nervous System study guide
o Attempt to grow back by sprouting many branches from
the damaged ends of their axons
o PNS more successful than CNS
• Injured nerve fibers in the PNS can regenerate by growing within the protective myelin sheath of the
supporting Schwann cells if the cell body is intact. 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.
• Nerve impulse: Purpose is to initiate, receive, and process messages about events both within and outside
the body. Initiation involves the generation of an action potential. Once an action potential is initiated, a
series of action potentials travels along the axon. When the impulse reaches the end of the nerve fiber, it
is transmitted across the junction between nerve cells (synapse) by a chemical interaction involving
neurotransmitters. This chemical interaction generates another set of action potentials in the next
neuron. Events are repeated until the nerve impulse reaches its destination.
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 without traversing the insulated membrane segment.
Called saltatory (hopping) conduction. In an unmyelinated fiber, the wave of depolarization travels the entire
length of the axon, with each portion of the membrane becoming depolarized in turn.
o Action potential
o Synapse: Is the structural and functional junction between two neurons. The point at which nerve impulse is
transmitted from one neuron to another. The nerve impulse can also be transmitted from neurons to glands
or muscles. The essential structures of synaptic transmission are a presynaptic terminal, a synaptic cleft, and
a receptor site on the postsynaptic cell
o Neurotransmitters: Chemicals that affect the transmission of impulses across the synaptic cleft.
Excitatory neurotransmitters activate postsynaptic receptors that increase the likelihood that an
action potential will be generated.
Inhibitory neurotransmitters activate postsynaptic receptors that inhibit the likelihood that an action potential
will be generated.
The net effect (excitatory or inhibitory) depends on the number of presynaptic neurons that are releasing
neurotransmitters on the postsynaptic cell.
Neurotransmitters can be affected by drugs and toxins, which can modify their function or block their
attachment to receptor sites on the postsynaptic membrane.
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.
With the use of cerebral microdialysis neurotransmitter levels can now be measured in the cerebral cortex
o Myelin increases speed of conduction.
• Spinal cord: 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 is surrounded by
white matter.
o Gray and white matter: Contains the cell bodies of voluntary motor neurons, preganglionic autonomic
motor neurons, and association neurons (interneurons). It contains the axons of the ascending sensory and
the descending (suprasegmental) motor fibers. 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,
corticospinal tract (descending)
o Ascending tracts: Carry specific sensory information to higher levels of the CNS.
- Info 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 fasciculus gracilis and the fasciculus cuneatus carry info and transmit impulses concerned with touch,
deep pressure, vibration, position sense, and kinesthesia (appreciation of movement, weight, and body parts).
, Rnsg 233 Chapter 43 Assessment of
the Nervous System study guide
- Spinocerebellar tracts carry info about muscle tension & body position to cerebellum for coordination of movement.
- Spinothalamic tracts carry pain and temperature sensations.
o Descending tracts: Carry impulses that are responsible for muscle movement.
- Most important descending tracts are the corticobulbar and corticospinal tracts, termed the pyramidal tract.
- These tracts carry volitional (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.
o Lower and upper motor neurons
- Lower motor neurons (LMNs): Final common pathway through which
descending motor tracts influence skeletal muscle. Cell bodies of LMNs,
which send axons to innervate the skeletal muscles of the arms, trunk,
and legs, are located in the anterior horn of the corresponding
segments of the spinal cord
LMNs for skeletal muscles of eyes, face, mouth, & throat are located 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 cause weakness or paralysis, denervation atrophy,
hyporeflexia or areflexia, & decreased muscle tone (flaccidity).
- 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 cause weakness or paralysis, disuse atrophy, hyperreflexia,
and increased muscle tone (spasticity).
o Reflex arc: in the spinal cord, reflex arcs play an important role in
maintaining muscle tone, which is essential for body posture.
Components of a monosynaptic reflex arc are a receptor organ,
an afferent neuron, an effector neuron, and an effector organ
(skeletal muscle).
Afferent neuron synapses with the efferent neuron in the
gray matter of the spinal cord.
• Brain: Cerebrum, brainstem,
and cerebellum
o Cerebrum: Right & left
cerebral hemispheres. Divided into 4 lobes: frontal, temporal, parietal, and occipital
