A neurological reflex is an automatic, involuntary muscle contraction that occurs immediately after a sensory stimulus, bypassing the brain for a rapid response. The reflex arc is a simple pathway involving a sensory neuron, a synapse in the spinal cord, and a motor neuron. Charting these reflexes is a fundamental component of a comprehensive neurological examination. This assessment provides immediate insight into the functional integrity of specific spinal cord segments and the peripheral nerves, helping clinicians localize potential damage within the central or peripheral nervous systems.
The Key Reflexes Assessed
The most frequently assessed reflexes are the deep tendon reflexes (DTRs), evaluated by tapping the tendon to induce a stretch. In the upper extremities, the Biceps reflex is tested at the elbow (C5 and C6 spinal nerve roots). The Triceps reflex, tested just above the elbow, reflects the function of the C7 and C8 nerve roots.
Moving to the lower body, the Patellar reflex (knee-jerk) is elicited by tapping the tendon below the kneecap and involves the L2 through L4 spinal segments. The Achilles reflex (ankle-jerk) is tested at the heel and is associated with the S1 nerve root.
Standardized Technique for Elicitation
Achieving a consistent and accurate reflex response begins with proper patient positioning and relaxation, as muscle tension can inhibit the reflex arc. The limb being tested must be completely limp and positioned to ensure the target tendon is slightly stretched. For example, the knee should be flexed at a right angle with the foot dangling freely to test the patellar reflex.
The reflex hammer should be held loosely and used with a brisk, swinging motion to deliver a quick, direct tap to the tendon, similar to a pendulum. Let the hammer bounce off the tendon immediately rather than pressing or pushing into the area. This technique ensures a momentary stretch of the muscle spindle, which is the necessary stimulus to activate the reflex arc.
If a reflex appears diminished or absent, a reinforcement technique can be used to temporarily increase the excitability of the reflex pathway. The most common method, the Jendrassik maneuver, involves asking the patient to interlock their fingers and pull them apart vigorously while testing the lower extremity reflexes. This distant isometric contraction momentarily overrides inhibitory central control, often revealing a subtle reflex response that was previously masked.
Decoding the Grading Scale
The charted reflex response is quantified using the standardized five-point NINDS Myotatic Reflex Scale, ranging from 0 to 4+. The score of 2+ is defined as a normal, average, or expected response and serves as the reference point for all other grades. A score of 0 indicates a complete absence of a reflex, even with reinforcement maneuvers.
A grade of 1+ describes a diminished or low-normal response, meaning the reflex is present but noticeably less vigorous than average. Conversely, a 3+ is charted when the response is brisker than average. The highest score, 4+, signifies a very brisk or hyperactive response, often accompanied by clonus. Clonus presents as rhythmic, involuntary muscle contractions following the initial reflex, signaling a significant neurological issue.
Understanding Clinical Significance
The numerical grades assigned during reflex charting help distinguish between two broad categories of nervous system dysfunction. Hyporeflexia (scores of 0 or 1+) suggests a problem within the two-neuron reflex arc itself, typically indicating a lower motor neuron lesion. This can occur due to damage to the peripheral nerve or the spinal nerve root where the reflex originates, such as in peripheral neuropathy or muscle diseases.
In contrast, hyperreflexia (scores of 3+ or 4+) generally points to an issue with upper motor neuron control. This type of lesion occurs in the brain or spinal cord above the level of the reflex arc, removing the normal inhibitory influence the brain exerts on the spinal cord. Conditions such as stroke, multiple sclerosis, or spinal cord injury are often characterized by hyperreflexia. Asymmetry between the left and right sides is often considered a more concerning sign than a globally high or low score, as it strongly suggests a focal neurological problem.