Body & HealthFact

The knee-jerk reflex simply bypasses your brain.

The tap on the patellar tendon stretches the muscle, a sensory neuron reports it to the spinal cord and synapses directly onto a motor neuron – one single synapse, segment L3 or L4. About 18 milliseconds pass between stretch and twitch. The brain only learns about it afterwards.

Useful: Reflexes are local short circuits: they skip the detour through your head.

Source: en.wikipedia.org

NervenReflexe

Difficulty:

Question on this card

How many synapses lie in the main path of the knee-jerk reflex?

None
One
About ten
Over a hundred, in the brain

Show the answer

Correct: One

It is monosynaptic: sensory neuron and motor neuron connect directly, at segment L3/L4.

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