The human nervous system is an intricate and complex network of fibers that impenetrates the entire body and functions in complicated and often mysterious ways. Sophisticated imaging and laboratory tests do not always provide sufficient information about how the nerves are functioning -- or not functioning, as the case may be. The neurological exam is a series of simple questions and tests that provide crucial information about a person’s nervous system. It is an inexpensive, noninvasive way of getting a glimpse at how the nerves function and finding clues about what might be wrong.

The neurological examination is divided into several components, each focusing on a different part of the nervous system:

• mental status
• cranial nerves
• motor system
• sensory system
• the deep tendon reflexes
• coordination and the cerebellum
• gait

The exam requires skill, patience, and intelligence on the part of the physician, and – just as important – cooperation from the patient. Incomplete or inaccurate exams can lead to incorrect diagnoses.

Mental status
The mental status examination is a series of detailed but simple questions designed to test a patient’s cognitive ability, including their:

• state of consciousness (patient’s awareness and responsiveness to their environment and to their own senses);
• appearance and general behavior;
• mood;
• content of thought; and
• intellectual resources (orientation with reference to time, place, and person; comprehension; ability to pay attention; insight; memory; judgment; abstract reasoning power; speech and language function; and intellectual capacity).

The questions involve asking the patient to remember objects that had been listed earlier in the course of the exam; repeat sentences; solve simple mathematical problems; copy a three-dimensional type of drawing; draw a clock and place the numbers appropriately at a particular time; etc. When speech and language are tested, the examiner listens to the character of the speech, the fluency (the smoothness of speech), the patient’s ability to understand and carry out simple or complex commands, and the patient’s ability to read and write.

In addition to the specific questions that make up the actual mental status exam, the neurologist gathers information simply from observing the patient’s general behavior while they’re in the examining room.

Many neurological diseases, such as dementia, cause changes in intellectual status or emotional responsiveness, and specific personality features have been identified for many nervous system disorders. These changes and features can be detected during the mental status portion of the neurological exam.

The mental status exam is especially important when the other parts of the neurological exam reveal nothing abnormal. Sometimes, slight changes in memory or other intellectual resources may be the only indication that anything is wrong. Evaluating a person’s intellectual capacity can also be helpful in determining a course of treatment and making a prognosis.

Cranial nerves
The cranial nerves are a set of 12 nerves that relay messages between the brain and the head and neck region. They govern the motor and sensory functions of the various parts of the face, including vision, smell, and movements in the tongue and vocal cords.

The cranial nerve exam involves testing the function of all 12 sets of cranial nerves. It’s an essential part of the neurological exam, as it helps localize central nervous system dysfunction and aids in diagnosing systemic disease. Some of the functions that are commonly tested as part of the cranial nerve exam include: eyelid strength and function; visual function; peripheral vision; papillary light reflexes; eye muscle movements; strength of facial musculature; the gag reflex; tongue and lip movements; ability to smell and taste; hearing; and sensation in the face, head, and neck.

Motor system
The motor system includes the brain and spinal cord motor pathways, plus all the motor nerves and muscles throughout the body. Abnormalities in the motor system can often be detected by inspecting the patient’s muscles, assessing muscular strength and tone, and looking for a variety of characteristic signs.

Patients are usually asked to undress, so that the neurologist can look at their muscles and note any atrophy (shrinkage), twitching, or abnormal movements. Tests are done to evaluate strength in all the major muscle groups.

Testing what is known as the Babinski response is an important part of testing the motor system. The neurologist strokes or scratches, heel-to-toe, the outer side of the sole of the foot. The toes fanning upward indicate that there is some sort of brain or spinal cord injury. Normally, except in infants under 2 years old, the toes curl downward. A variety of neurological disorders can lead to the Babinski response.

Sensory system
All sensations depend on impulses that are excited by stimulation of receptors located in the skin, muscles, tendons, and so on, and then sent along nerve fibers to the central nervous system (the brain and spinal cord). The sensory exam is designed to determine areas of abnormal sensation, the quality and type of sensation impairment, and the degree and extent of tissue involvement.

A routine sensory exam involves testing a number of different types of sensation, such as pain, temperature, pressure, and position. For example, a pinprick may be used to test a person’s response to pain. The examiner may compare the response in different parts or opposite sides of the body. A cold or warm object may be used to test the sense of temperature. To test position, the patient might be asked to close their eyes while the examiner moves the patient’s big toe up and down and asks the patient which direction the toe is moving. The neurologist might have the patient identify objects placed in their hand while their eyes are closed or identify numbers or letters "written" on their body.

The sensory exam should always be repeated in order to confirm the results. How the patient responds depends in large part on how alert or tired they are, so the sensory exam should probably be done early on in the course of the neurological exam before the patient loses patience or grows weary. The results of the sensory exam also depend on how aware and intelligent the patient is, and sometimes repeating the exam provides more accurate results.

Deep tendon reflexes
A reflex is an action performed involuntarily in response to impulses that have been sent to the central nervous system. Alterations in a person’s reflexes are often the first sign of neurological dysfunction. Observing a patient’s reflexes is the most objective part of the neurological exam, since the reflexes are not under voluntary control and testing them does not depend on the patient’s cooperation, attitude, or intelligence.

Hundreds of reflexes have been identified, but the neurological exam generally involves testing only the deep tendon reflexes. Deep tendon reflexes, also known as muscle stretch reflexes, are reflexes elicited in response to stimuli to tendons. When the correct area of the muscle tendon is tapped with a soft rubber hammer, the muscle fibers contract. By noting whether the response to the tapping is normal or not, the neurologist can assess whether there might be any injuries to the nervous system pathways that produce the deep tendon reflex.

Coordination and the cerebellum
The cerebellum is the part of the brain responsible for voluntary movement and motor coordination, including posture. Testing coordination provides clues about conditions that affect the cerebellum.

The neurologist may ask the patient to move their finger from their nose to the neurologist’s finger, going back and forth from nose to finger, touching the tip of each. The patient may be asked to tap their fingers together quickly in a coordinated fashion or move their hands one on top of the other, back and forth, as smoothly as they can. The coordination in the lower limbs can be tested by having the patient rub one heel up and down smoothly over the other shin.

Gait
Most of us take our ability to walk for granted. But as simple as it may seem, walking is a very intricate physiological process. How we walk – our gait - is influenced by a number of bodily mechanisms and many different types of nervous system reflexes. The body has to be held erect; all the limbs, head, and trunk need to be held in the right position; the individual has to be oriented to all the different parts of their body and where they are in space; all of the various parts of motor control involved with moving need to be integrated; and so on. Because walking depends on so many different parts of the nervous system, it can be affected by a variety of neurological disorders.

By observing a person’s gait, the neurologist can gather important clues about what might be wrong. The patient is usually asked to walk in a number of different ways, such as heel-to-toe in a straight line, turning abruptly, walking on their toes, walking on their heels, and running.

References
Haerer, A.F., 1992, The Neurological Exam, J.B. Lippincott Co., Philadelphia.