A myotatic reflex where tapping the patellar tendon causes involuntary knee extension, serving as both a crucial medical test and an exemplar of basic neural circuitry.

Knee-reflex

The knee-reflex, also known as the patellar reflex or knee-jerk response, represents one of the most well-known examples of a monosynaptic reflex in human physiology. This involuntary response occurs when the patellar tendon below the kneecap is struck, resulting in a sudden extension of the leg at the knee joint.

Anatomical Mechanism

The reflex arc involves several key components:

The patellar tendon connecting the quadriceps muscle to the tibia
Muscle spindles in the quadriceps muscle
Sensory neurons carrying signals to the spinal cord
Motor neurons returning signals to the quadriceps
The quadriceps muscle that executes the movement

Clinical Significance

Healthcare providers regularly test the knee-reflex as part of a neurological examination. The response provides valuable information about:

Spinal cord function at L2-L4 levels
peripheral nervous system integrity
Overall neuromuscular junction health

Abnormal responses may indicate:

Hyperreflexia (enhanced response): suggesting upper motor neuron lesions
Hyporeflexia (reduced response): indicating peripheral neuropathy or lower motor neuron issues

Historical Context

First described by Wilhelm Heinrich Erb and Carl Friedrich Otto Westphal in 1875, the knee-reflex has become an iconic symbol of medical examination procedures. Its discovery helped establish the fundamental principles of reflex arc physiology and contributed significantly to our understanding of the nervous system.

Research Applications

The knee-reflex serves as a model system for studying:

Basic neural circuits
motor control mechanisms
synaptic transmission
neuroplasticity

In Popular Culture

The knee-reflex has entered popular consciousness as a metaphor for automatic, unthinking responses, often referenced in discussions of behavioral conditioning and instinctive reactions.

Related Clinical Tests

The examination of the knee-reflex is typically performed alongside other deep tendon reflexes including:

These tests collectively provide a comprehensive assessment of neurological function and spinal cord integrity.