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Definition

Reflex tests are simple physical tests of nervous system function.

Purpose

A reflex is a simple nerve circuit. A stimulus, such as a light tap with a rubber hammer, causes sensory neurons (nerve cells) to send signals to the spinal cord. There, the signals are conveyed both to the brain and to nerves that control muscles affected by the stimulus. Without any brain intervention, these muscles may respond to an appropriate stimulus by contracting.

Reflex tests measure the presence and strength of a number of reflexes. In so doing, they help to assess the integrity of the nerve circuits involved. Reflex tests are performed as part of a neurological exam, either a "mini-exam" done to quickly confirm integrity of the spinal cord, or a more complete exam performed to diagnose the presence and location of a spinal cord injury or neuromuscular disease.

Deep tendon reflexes are responses to muscle stretch. The familiar "knee-jerk" reflex is an example of a reflex. This tests the integrity of the spinal cord in the lower back region. The usual set of deep tendon reflexes tested, involving increasingly higher regions of the spinal cord, includes:

• ankle
• knee
• abdomen
• forearm
• biceps
• triceps
• patellar

Another type of reflex test is called the Babinski test, which involves gently stroking the sole of the foot to assess proper development and function of the spine and cerebral cortex.

Precautions

Reflex tests are entirely safe, and no special precautions are needed.

Description

The examiner uses a reflex hammer or rubber mallet to strike different points on the examinee's body, and observes the response. The points chosen for eliciting reflexes are the tendons of specific muscles. Tapping specific sites is intended to provide a quick stretch to the muscle. Muscle spindles, or receptors, mediate the reflex lying within the muscle—not the site of the hammer strike. The examiner may position, or hold, one of the limbs during testing, and may require exposure of the ankles, knees, abdomen, and arms. Reflexes can be difficult to elicit if the individual being examined is paying too much attention to the stimulus. To compensate for this, that person may be asked to perform some muscle contraction, such as clenching teeth or grasping and pulling the two hands apart. When performing the

Babinski reflex test, the examiner will gently stroke the outer soles of the person's feet with the mallet while checking to see whether or not the big toe extends out as a result.

Preparation

The examiner positions the person to be examined in a comfortable position, usually seated on the examination table with legs hanging free. There is no other preparation.

Aftercare

A reflex examination is not invasive. No care after the examination is required.

Complications

The pressure exerted by a reflex hammer is minimal and does not hurt the person being examined. A reflex

Muscle stretch (deep tendon) reflexes
Reflex	Stimulus	Response
SOURCE: Rothstein, J.M., S.H. Roy, and S.L. Wolf. The Rehabilitation Specialist's Handbook, 2nd ed. Philadelphia: F.A. Davis Co., 1998.
Biceps	Tap biceps tendon	Contraction of biceps
Brachioradialis (periosteradial)	Tap styoid process of radius (insertion of brachioradialis)	Flexion of elbow and pronation of forearm
Jaw (maxillary)	Tap mandible in half-open position	Closure of jaw
Patellar	Tap patellar tendon	Extension of leg at knee
Tendocalcaneus	Tap Achilles tendon	Plantar flexion at ankle
Triceps	Tap triceps tendon	Extension of elbow
Wrist extension	Tap wrist extensor tendons	Extension of wrist
Wrist flexion	Tap wrist flexor tendon	Flexion of wrist

examination is not invasive. There are no complications from performing the examination.

Results

Normal results

The strength of the response depends partly on the strength of the stimulus. For this reason, an examiner will attempt to elicit the response with the smallest stimulus possible. Learning the range of normal responses requires some clinical training. Responses should be the same on both sides of the body. A normal response to the Babinski reflex test depends upon the age of the person being examined. In children under the age of one and a half years, the big toe will extend out with or without the other toes. This is due to the fact that the fibers in the spinal cord and cerebral cortex have not been completely covered in myelin, the protein and lipid sheath that aids in processing neural signals. In adults and children over the age of one and a half years, the myelin sheath should be completely formed; and as a result, all the toes will curl under (plantar flexion reflex).

Abnormal results

Weak or absent response may indicate damage to the nerves outside the spinal cord (peripheral neuropathy), damage to the motor neurons just before or just after they leave the spinal cord (motor neuron disease), or muscle disease. Excessive response may indicate spinal cord damage above the level controlling the hyperactive response. Different responses on the two sides of the body may indicate early onset of progressive disease, or localized nerve damage, as from trauma. An adult or older child who responds to the Babinski with an extended big toe may have a lesion in the spinal cord or cerebral cortex.

Health care team roles

A reflex examination is usually conducted by a physician. Neurologists (doctors with specialized training in neurology) often perform reflex tests. Physician assistants, physical therapists, and nurses may also test reflexes as they examine or evaluate individuals.

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KEY TERMS

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Lesion—A pathologic change in body tissue.

Myelin—A substance composed largely of fat that constitutes the sheaths of various nerve fibers throughout the body.

Neurology—The study of nerves.

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L. Fleming Fallon, Jr., MD, PhD, DrPH