brain, spinal cord, and nerve disorders
Neurologic Examination
Motor Nerves
Motor nerves carry impulses from the brain and spinal cord to voluntary muscles (muscles controlled by conscious effort), such as muscles of the arms and legs. Muscle weakness or paralysis of a muscle may indicate damage to any of the following: The muscle itself A motor nerve The nerve's connection to the muscle ( Overview of Neuromuscular Junction Disorders ) The brain The spinal cord Doctors look for abnormalities such as the following: A decrease in muscle size (wasting, or atrophy) An increase in muscle size Tremor (rhythmic shaking of a body part) and other unintended (involuntary) muscle movements Muscle twitching An increase (spasticity or rigidity) or a decrease in muscle tone Weakness , particularly which body parts are affected (pattern of weakness) Loss of dexterity (the ability to use the hands skillfully and nimbly) The doctor inspects the muscles for size, unusual movements, tone, strength, and dexterity. A muscle wastes away (atrophies) when the muscle or the nerves supplying it are damaged or when the muscle has not been used for months for other reasons (such as being in a cast). A muscle may increase in size (hypertrophy) because it is working harder to compensate for the weakness of another muscle. Muscles can appear to increase is size when normal muscle tissue is replaced by abnormal tissue, as occurs in Amyloidosis and some inherited muscle disorders (such as Muscles may move without the person meaning them to (involuntarily). The following are examples of Overview of Movement Disorders : Fasciculationsare tiny, subtle muscle twitches, which may look ripples under the skin. Fasciculations may indicate nerve damage to the affected muscle. Myoclonus None Tourette Syndrome and Other Tic Disorders in Children and Adolescents None Chorea, Athetosis, and Hemiballismus None Chorea, Athetosis, and Hemiballismus None Chorea, Athetosis, and Hemiballismus None Dystonia None Involuntary movements may indicate damage in the areas of the brain (basal ganglia) that control motor coordination. To evaluate muscle tone, doctors first ask the person to completely relax muscles in a limb. Then doctors move the person’s limb to determine how much the relaxed muscle involuntarily resists being moved—called muscle tone. How muscle tone reacts to being moved suggests possible causes, as follows: Uneven muscle tone that suddenly increases as the relaxed muscle is moved (spasticity): Possibly due to a Overview of Stroke or Evenly increased muscle tone: Possibly due to a disorder of the basal ganglia, such as Parkinson Disease (PD) None Severely reduced muscle tone (flaccidity): Possibly due to a disorder of the nerves outside of the brain and spinal cord ( Overview of the Peripheral Nervous System ), such a Flaccidity may be present for a short time after an injury that causes paralysis, such as a spinal cord injury. When flaccidity results from such a spinal cord injury, muscle tone often gradually increases over days to weeks, eventually resulting in spasticity. If people are afraid or confused during the examination, they may not be able to relax the muscles. In such cases, muscle tone may vary, making it hard for doctors to evaluate. Doctors test muscle strength by asking the person to push or pull against resistance or to do maneuvers that require strength, such as walking on the heels and tiptoes or rising from a chair. Doctors then rate muscle strength from 0 (no muscle contraction) to 5 (full strength). Sometimes Weakness is evident when a person uses one limb more than another. For example, a right-handed person may gesture mostly with the left hand during a conversation. A weak arm may swing less while walking or drift downward when the arms are held up and the eyes are closed. Knowing which body parts are weak (the pattern of weakness) can help doctors identify what the problem is, as in the following cases: The shoulders and hips are weaker than the hands and feet: The cause may be a disorder that affects muscles (myopathy). Myopathies tend to affect the largest muscles first. People may have difficulty raising their arms to comb their hair, climbing stairs, or getting up from a seated position. The hands and feet are weaker than the shoulders, arms, and thighs: The problem is often a Polyneuropathy (the malfunction of many peripheral nerves throughout the body). Polyneuropathies tend to affect the longest nerves first (those going to the hands and feet). People may have a weak grip and have trouble with fine finger movements (dexterity). People may have difficulty fastening a button, opening a safety pin, or tying their shoes. Weakness is limited to one side of the body: Doctors suspect a disorder affecting the opposite side of the brain, such as a Overview of Stroke . Weakness occurs below a certain level of the body: The cause may be a Overview of Spinal Cord Disorders . For example, an injury to the part of the spine in the chest (thoracic spine) causes the legs but not the arms to be paralyzed. An injury in or above the neck causes paralysis of all four limbs. Muscle weakness may also occur in other patterns, such as the following: Weakness occurs in only one relatively small area: This type of weakness suggests that only one or a few peripheral nerves are damaged. In such cases, weakness may also impair dexterity. Weakness becomes apparent only when muscles that are used to do the same activity over and over become weak more quickly than usual. For example, people who once could use a hammer well become weak after hammering for several minutes. Myasthenia Gravis can cause this type of weakness. Weakness accompanied by increased muscle tone (making arms or legs stiff) and exaggerated reflexes suggest a problem in the central nervous system. Weakness accompanied by decreased muscle tone (making arms or legs feel loose or floppy), decreased or absent reflexes, and intermittent twitching in the muscle suggest a problem in the peripheral nervous system. 