Deep tendon reflexes (DTRs) are involuntary muscle contractions that occur when a tendon is suddenly stretched. These rapid, automatic responses are a fundamental part of the nervous system’s function. Assessing DTRs provides insights into the health and integrity of the neural pathways connecting muscles to the spinal cord and brain, offering general indicators of nervous system health.
The Science of Reflexes
Deep tendon reflexes operate through a simple neural pathway called a reflex arc. This arc begins when a tendon tap stretches the muscle, activating sensory receptors. These receptors send a signal along a sensory neuron to the spinal cord.
In the spinal cord, the sensory neuron directly connects with a motor neuron, bypassing conscious brain processing. This motor neuron transmits an impulse back to the stretched muscle, causing it to contract. This circuit allows for immediate reactions to stimuli, bypassing the slower process of brain-mediated thought.
Getting Ready to Check Reflexes
Checking deep tendon reflexes usually requires a reflex hammer, designed for precise tendon taps. While ideal, a hand edge or stethoscope side can sometimes be used to elicit a response. Ensure the individual is relaxed and comfortable before checking reflexes.
Position the limb to slightly stretch the muscle and expose the tendon for a clear response. For example, for the patellar reflex, have the person sit with legs dangling freely. Distraction techniques, like the Jendrassik maneuver (clinching teeth or interlocking hands and pulling), can enhance difficult-to-elicit reflexes by reducing conscious inhibition.
Checking Common Deep Tendon Reflexes
Patellar Reflex
To check the patellar reflex, have the person sit with their lower legs dangling freely, relaxing the quadriceps muscle. Locate the patellar tendon just below the kneecap. Strike this tendon briskly with the broad end of the reflex hammer.
The expected response is an involuntary extension or kicking motion of the lower leg. The tap should be firm enough to stretch the tendon without discomfort. This reflex assesses the L2, L3, and L4 spinal nerve roots.
Achilles Reflex
For the Achilles reflex, have the person kneel on a chair with feet dangling, or lie supine with hip externally rotated and knee flexed. Gently dorsiflex the foot to slightly stretch the Achilles tendon, located at the back of the ankle. Strike the Achilles tendon directly with the broad end of the reflex hammer.
A normal response is plantarflexion, where the foot points downwards. This reflex evaluates the S1 and S2 spinal nerve roots. Ensure the foot is relaxed and unweighted for an accurate response.
Biceps Reflex
To check the biceps reflex, position the person’s arm with their elbow flexed at 90 degrees and forearm relaxed. Place your thumb firmly over the biceps tendon in the antecubital fossa (elbow crease). Strike your thumb with the narrow end of the reflex hammer.
The expected response is slight elbow flexion and visible biceps muscle contraction. This reflex assesses the C5 and C6 spinal nerve roots. The tap should be precise and directed through your thumb to the tendon.
Triceps Reflex
For the triceps reflex, have the person’s arm dangle loosely or support it with the elbow flexed at 90 degrees. Locate the triceps tendon on the back of the upper arm, just above the elbow. Strike the triceps tendon directly with the narrow end of the reflex hammer.
A normal response is elbow extension or a slight straightening of the arm due to triceps muscle contraction. This reflex evaluates the C6, C7, and C8 spinal nerve roots. Maintaining arm relaxation is important for an accurate response.
Brachioradialis Reflex
To assess the brachioradialis reflex, position the person’s arm with the forearm resting on their lap or supported, hand slightly pronated (palm down). Locate the brachioradialis tendon by palpating the radius bone 1 to 2 inches above the wrist on the thumb side. Strike this area directly with the narrow end of the reflex hammer.
The expected response is slight forearm flexion and supination (turning palm upwards), or visible brachioradialis muscle contraction. This reflex assesses the C5 and C6 spinal nerve roots. A relaxed forearm is important for observing the response.
Understanding Your Reflex Responses
Deep tendon reflexes are graded on a scale from 0 to 4+:
0: No response.
1+: Diminished or weak response.
2+: Normal or average response.
3+: Brisk or exaggerated response.
4+: Hyperactive response, often with clonus (rapid, involuntary muscle contractions and relaxations).
Absent or diminished reflexes (hyporeflexia) can suggest issues like peripheral nerve damage or muscle disorders. Exaggerated reflexes (hyperreflexia) might indicate problems with upper motor neurons, which control movement. These interpretations are general indicators requiring a broader medical context.
Self-checking reflexes is for informational purposes only and not a substitute for professional medical diagnosis. If you have concerns about your reflex responses or notice abnormalities, seek evaluation from a qualified healthcare professional.