Chapter 60 ● Assessment of Neurologic Function LEARNING OBJECTIVES ● On completion of this chapter, the learner will be able to: 1. Describe the structures and functions of the central and peripheral nervous systems. 2. Differentiate between pathologic changes that affect motor control and those that affect sensory pathways. 3. Compare the functioning of the sympathetic and parasympathetic nervous systems. 4. Describe the significance of physical assessment to the diagnosis of neurologic dysfunction. 5. Describe changes in neurologic function associated with aging and their impact on neurologic assessment findings. 6. Describe diagnostic tests used for assessment of suspected neuro- logic disorders and the related nursing implications. 1820 Chapter 60 Assessment of Neurologic Function 1821 Nurses in many types of practice settings encounter patients impulses away from the cell body. Nerve cell bodies occurring in with altered neurologic function. Disorders of the nervous system clusters are called ganglia or nuclei. A cluster of cell bodies with can occur at any time during the life span and can vary from mild, the same function is called a center (eg, the respiratory center). self-limiting symptoms to devastating, life-threatening disorders. Neuroglial cells, another type of nerve cell, support, protect, and The nurse must be skilled in the assessment of the neurologic sys- nourish neurons. tem whether the assessment is generalized or focused on specific areas of function. Assessment in either case requires knowledge Neurotransmitters of the anatomy and physiology of the nervous system and an understanding of the array of tests and procedures used to diag- Neurotransmitters communicate messages from one neuron to nose neurologic disorders. Knowledge about the nursing impli- another or from a neuron to a specific target tissue. Neurotrans- cations and interventions related to assessment and diagnostic mitters are manufactured and stored in synaptic vesicles. They testing is also essential. enable conduction of impulses across the synaptic cleft. The neuro- transmitter has an affinity for specific receptors in the post- synaptic bulb. When released, the neurotransmitter crosses the Anatomic and Physiologic Overview synaptic cleft and binds to receptors in the postsynaptic cell mem- The nervous system consists of two divisions: the central nervous brane. The action of a neurotransmitter is to potentiate, termi- system (CNS), including the brain and spinal cord, and the pe- nate, or modulate a specific action and can either excite or inhibit ripheral nervous system, made up of the cranial and spinal nerves. the target cell’s activity. There are usually multiple neurotrans- The peripheral nervous system can be further divided into the mitters at work in the neural synapse. There are various types of somatic, or voluntary, nervous system, and the autonomic, or in- neurotransmitters (Bradley et al., 2000; Hickey, 2003); major voluntary, nervous system. The function of the nervous system is neurotransmitters are described in Table 60-1. to control all motor, sensory, autonomic, cognitive, and behav- Many neurologic disorders are due, at least in part, to an ioral activities. The nervous system has approximately 10 million imbalance in neurotransmitters—that is, a lack of gamma- sensory neurons that send information about the internal and ex- aminobutyric acid (GABA) and acetylcholine in Huntington’s ternal environment to the brain and 500,000 motor neurons that disease (Bradley et al., 2000), low serotonin levels in some forms control the muscles and glands. The brain itself contains more of epilepsy (Blows, 2000), and a decrease in dopamine in Parkin- than 20 billion nerve cells that link the motor and sensory path- son’s disease. In fact, probably all brain functions are modulated ways, monitor the body’s processes, respond to the internal and through neurotransmitter receptor site activity, including mem- external environment, maintain homeostasis, and direct all psy- ory and other cognitive processes. chological, biologic, and physical activity through complex There are two types of receptors: direct and indirect. Direct chemical and electrical messages (Bradley, Daroff, Fenichel & receptors are also known as inotropic because they are linked to Marsden, 2000). ion channels and allow passage of ions when opened. They can be excitatory or inhibitory and are rapid-acting (measured in milliseconds). Indirect receptors affect metabolic processes in the ANATOMY OF THE NERVOUS SYSTEM cell, which can take from seconds to hours to occur. Receptor Cells of the Nervous System sites are an expanding area of research because they are often the target for the action and development of new medications. These The basic functional unit of the brain is the neuron (Fig. 60-1). medications either block or stimulate neurotransmitters at re- It is composed of a cell body, a dendrite, and an axon. The den- ceptor sites and thus provide relief from symptoms (Blows, drite is a branch-type structure with synapses for receiving elec- 2000). Receptor sites are also sites for the action of addictive trochemical messages. The axon is a long projection that carries drugs. Glossary agnosia: loss of ability to recognize objects delirium: transient loss of intellectual func- rigidity: increase in muscle tone at rest char- through a particular sensory system; may tion, usually due to systemic problems acterized by increased resistance to passive be visual, auditory, or tactile dendrite: portion of the neuron that con- stretch ataxia: inability to coordinate muscle move- ducts impulses toward the cell body reflex: an automatic response to stimuli ments, resulting in difficulty in walking, dysphagia: difficulty swallowing Romberg test: test for cerebellar dysfunction talking, and performing self-care activities flaccid: displaying lack of muscle tone; limp, requiring the patient to stand with feet autonomic nervous system: division of the floppy together, eyes closed and arms extended; nervous system that regulates the involun- myelography (myelogram): x-ray study of inability to maintain the position, with tary body functions the spinal cord after injection of a contrast either significant stagger or sway, is a axon: portion of the neuron that conducts agent into the subarachnoid space positive test impulses away from the cell body parasympathetic nervous system: division spasticity: sustained increase in tension of a Babinski reflex (sign): a reflex action of the of the autonomic nervous system active muscle when it is passively lengthened or toes, indicative of abnormalities in the primarily during nonstressful conditions, stretched motor control pathways leading from the controlling mostly visceral functions sympathetic nervous system: division of cerebral cortex photophobia: inability to tolerate light the autonomic nervous system with pre- clonus: abnormal movement marked by al- position (postural) sense: awareness of posi- dominantly excitatory responses, the ternating contraction and relaxation of a tion of parts of the body without looking “fight-or-flight” system muscle occurring in rapid succession at them; also referred to as proprioception tone: tension present in a muscle at rest 1822 Unit 14 NEUROLOGIC FUNCTION Nucleus Myelin sheath Axon Node Neurolemma Synaptic Dendrites terminals FIGURE 60-1 Neuron. Another important area of ongoing research is diagnostic test- sure by the corpus callosum. The outside surface of the hemi- ing that can detect abnormal levels of neurotransmitters in the spheres has a wrinkled appearance that is the result of many brain. Positron emission tomography (PET), for example, can de- folded layers or convolutions called gyri, which increase the sur- tect dopamine, serotonin, and acetylcholine (Gjedde et al., face area of the brain, accounting for the high level of activity car- 2001). Single photon emission computed tomography (SPECT) ried out by such a small-appearing organ. The external or outer is similar to PET. Both PET and SPECT are discussed in more portion of the cerebrum (the cerebral cortex) is made up of gray detail later in this chapter. matter approximately 2 to 5 mm in depth; it contains billions of neurons/cell bodies, giving it a gray appearance. White matter The Central Nervous System makes up the innermost layer and is composed of nerve fibers and neuroglia (support tissue) that form tracts or pathways connect- ANATOMY OF THE BRAIN ing various parts of the brain with one another (transverse and as- The brain is divided into three major areas: the cerebrum, the sociation pathways) and the cortex to lower portions of the brain brain stem, and the cerebellum. The cerebrum is composed of two and spinal cord (projection fibers). The cerebral hemispheres are hemispheres, the thalamus, the hypothalamus, and the basal gan- divided into pairs of frontal, parietal, temporal, and occipital glia. Additionally, connections for the olfactory (cranial nerve I) lobes. The four lobes are as follows (see Fig. 60-2): and optic (cranial nerve III) nerves are found in the cerebrum. The brain stem includes the midbrain, pons, medulla, and con- • Frontal—the largest lobe. The major functions of this lobe nections for cranial nerves II and IV through XII. The cerebel- are concentration, abstract thought, information storage lum is located under the cerebrum and behind the brain stem or memory, and motor function. It also contains Broca’s (Fig. 60-2). The brain accounts for approximately 2% of the total area, critical for motor control of