300 BCE 鈥� Aristotle: First ideas on reflexes, actions performed 鈥渨ithout one鈥檚 consciousness鈥�
1600 鈥� Ren茅 Descartes: Reflexes mediated by the nervous system, independent of the soul
1875 鈥� William H. Erb & Friedrich O. Westphal: Demonstrated the clinical value of tendon reflexes
1886 鈥� William Gowers: Published Manual of Diseases of the Nervous System
1896 鈥� Joseph Babinski: Described the plantar reflex
1945 鈥� Robert Wartenberg: Published Examination of Reflexes, standardizing clinical techniques
Reflexes are rapid, automatic responses that reveal the integrity of the nervous system. By tapping a tendon with a reflex hammer, the clinician can observe involuntary movements and assess the connections between muscles, nerves, and the spinal cord. Each reflex 鈥� from the knee-jerk to the Babinski sign 鈥� provides clues about normal function and potential neurological problems.
Testing the Deep Tendon Reflexes is an important part of a neurological exam and general nerve assessment.
The Reflex Arc
Muscles contain sensory receptors called muscle spindles that can detect changes in the length of adjacent muscle fibres. This information enables the brain to control muscular functions such as posture and gait, and to prevent muscle overextension. A muscle reflex test begins with a simple tap to a tendon, stretching the spindles. The resulting signal travels along a sensory neuron to the spinal cord, where it is processed by interneurons. Some of these activate a motor neuron, causing the muscle to contract almost instantaneously; others 鈥� including interneurons called Renshaw cells 鈥� provide inhibitory feedback to prevent excessive contraction and fine-tune the response. Observing these rapid, involuntary muscle twitches or limb movements helps the clinician assess the integrity of neural pathways.
Credit: C么t茅 M-P, Murray LM and Knikou M (2018) Spinal Control of Locomotion: Individual Neurons, Their Circuits and Functions. Front. Physiol. 9:784. doi: 10.3389/fphys.2018.00784
The Grading Scale
Reflexes can be graded on a scale from 0 to 4+ as an aide to determine whether a response is normal, diminished, or exaggerated. Reduced or absent reflexes may indicate peripheral neuropathy, nerve root compression, or lower motor neuron lesions, whereas overly brisk reflexes point to upper motor neuron lesions, spinal cord injury, or certain neurodegenerative disorders.
|
4 |
Very brisk, with clonus (rhythmic oscillations between flexion and extension) |
|
3 |
Brisker than average; possible but not necessarily indicative of disease |
|
2 |
Average; normal |
|
1 |
Somewhat diminished, or requires reinforcement |
|
0 |
Reflex absent |
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