Lewis: Medical-Surgical Nursing, 8th Edition

Chapter 56: Nursing Assessment: Nervous System

Key Points – Printable

STRUCTURES AND FUNCTIONS OF NERVOUS SYSTEM
•	The human nervous system is a highly specialized system responsible for the control and integration of the body’s many activities.
•	The nervous system can be divided into the central nervous system (CNS) and parts of the peripheral nervous system (PNS). 
o	The CNS consists of the brain and spinal cord.
o	The PNS consists of the cranial and spinal nerves and the autonomic nervous system (ANS).

Cells of Nervous System
•	The nervous system is made up of two types of cells: neurons and neuroglia.
•	Neurons come in many different shapes and sizes, but they all share common characteristics: excitability, or the ability to generate a nerve impulse; conductivity, or the ability to transmit the impulse to other portions of the cell; and the ability to influence other neurons, muscle cells, and glandular cells by transmitting nerve impulses to them.
•	Neuroglia, or glial cells, provide support, nourishment, and protection to neurons.
•	Nerve impulses originate within a neuron as an action potential that moves along the body of the cell (axon) until it reaches the end of the nerve fiber. From there, it is transmitted across the junction between nerve cells by a chemical interaction, and then the impulse will move across the next neuron as an action potential.
o	A synapse is the structural and functional junction between two neurons. It is the point at which the nerve impulse is transmitted from one neuron to another or from neuron to glands or muscles.
o	A neurotransmitter is a chemical agent involved in the transmission of an impulse across the synaptic cleft.

Central Nervous System
 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 and is surrounded by white matter.
o	Specific ascending and descending pathways in the white matter can be identified.
o	In general, the ascending tracts carry specific sensory information to higher levels of the CNS.
o	Descending tracts carry impulses that are responsible for muscle movement.
•	Lower motor neurons are the final common pathway through which descending motor tracts influence skeletal muscle, the effector organ for movement. The cell bodies of these cells are located in spinal cord and the axons innervate the skeletal muscles.
Brain
•	The brain consists of the cerebral hemispheres, cerebellum, and brainstem.
•	The cerebrum is composed of the right and left hemispheres. Both hemispheres can be further divided into four major lobes, each with specific functions.
o	The frontal lobe controls higher cognitive function, memory retention, voluntary eye movements, voluntary motor movement, and expressive speech
o	The temporal lobe contains Wernicke’s area, which is responsible for receptive speech and for integration of somatic, visual, and auditory data.
o	The parietal lobe is composed of the sensory cortex, controlling and interpreting spatial information.
o	Processing of sight takes place in the occipital lobe.
•	The basal ganglia, thalamus, hypothalamus, and limbic system are also located in the cerebrum.
•	The brainstem includes the midbrain, pons, and medulla. The vital centers concerned with respiratory, vasomotor, and cardiac function are located in the medulla.
•	The cerebellum coordinates voluntary movement and to maintain trunk stability and equilibrium.
•	Cerebrospinal fluid (CSF) circulates within the subarachnoid space that surrounds the brain, brainstem, and spinal cord. This fluid provides cushioning for the brain and spinal cord, allows fluid shifts from the cranial cavity to the spinal cavity, and carries nutrients.

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.
•	The spinal nerve contains a pair of dorsal (afferent) sensory nerve fibers and ventral (efferent) motor fibers, which innervate a specific region of the neck, trunk, or limbs. This combined motor-sensory nerve is called a spinal nerve.
•	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 have only afferent and some only efferent fibers; others have both.
•	The ANS governs involuntary functions of cardiac muscle, smooth (involuntary) muscle, and glands. The ANS is divided into two components: sympathetic and parasympathetic nervous systems.

Protective Structures
•	The blood-brain barrier is a physiologic barrier between blood capillaries and brain tissue. The structure of brain capillaries differs from that of other capillaries. Some substances that normally pass readily into most tissues are prevented from entering brain tissue.
•	The meninges are three layers of protective membranes that surround the brain and spinal cord.
•	The skeletal system provides protection and support to the nervous system. The bony skull protects the brain from external trauma; the vertebral column protects the spinal cord, supports the head, and provides flexibility. 

GERONTOLOGIC CONSIDERATIONS: EFFECTS OF AGING ON NERVOUS SYSTEM
•	There are a number of changes in the nervous system associated with aging that affect the nervous system, including a loss of neurons occurring in certain areas of the brainstem, cerebellum, and cerebral cortex.
•	These changes place the older adult at risk for a number of changes in muscle strength, memory, vision, hearing, taste, smell, reaction time, and functional ability.

Assessment OF NERVOUS SYSTEM
Subjective Data
•	The mode of onset and the course of the illness are especially important aspects of the history. Often the nature of a neurologic disease process can be described by these facts alone. You should obtain all pertinent data in the history of the present illness, especially data related to the characteristics and progression of the symptoms. 
•	Additional health history information consists of assessment of past health history, medications, surgery or other treatments, family health history, psychosocial history, risk factor identification, and a review of systems using functional health patterns. 
•	Special attention should be given to obtaining a careful medication history, especially the use of sedatives, opioids, tranquilizers, and mood-elevating drugs.

Objective Data
•	The physical examination assesses six categories of functions: mental status, function of CNs, motor function, cerebellar function, sensory function, and reflex function.
•	Because the nervous system controls cognition and sensory integration, many neurologic disorders affect these functions. The nurse should assess memory, language, calculation ability, problem-solving ability, insight, and judgment.
•	Motor system assessment includes the assessment of strength, tone, coordination, and symmetry of major muscle groups.
•	A complete sensory assessment involves testing for touch, pain, temperature, vibration and position sense, and discrimination.

Diagnostic Studies OF NERVOUS SYSTEM
•	CSF analysis provides information about a variety of CNS diseases. Lumbar puncture is the most common method of obtaining CSF for analysis.
•	Cerebral angiography is indicated when vascular lesions or tumors are suspected.
•	Several types of electrographic studies are used to evaluate the function of the nervous system. 
o	Electroencephalography (EEG) involves the recording of the electrical activity of the surface cortical neurons of the brain.
o	Electromyography (EMG) is a recording of electrical activity associated with innervation of skeletal muscle.
o	Nerve conduction and evoked potential studies involve recordings of electrical activity associated with particular nerve conduction pathways.