What Is a Monosynaptic Reflex?

A monosynaptic reflex has only one synapse in between an outgoing motor response and an incoming sensory; a good example of this would be kicking the leg outward, which is also referred to as a knee jerk. Monosynaptic reflexes are the most basic type of reflex motions. Something to remember is that reflex responses can have both polysynaptic and monosynaptic elements.

Another name that monosynaptic reflex goes by is the stretch reflex. Most monosynaptic reflexes can be found in the ankle, knee, spine, triceps biceps and jaw. The stretch reflex arc has been referred to as a negative feedback loop that exists to maintain healthy muscle lengths.

In a neurological examination, a neurologist may use a reflex hammer to test these different points to help diagnose if a patient has an illness or condition. Using the reflex hammer on the calcaneal, or Achilles tendon, will cause a plantar flexion response from the sciatic nerve. Another method of testing the plantar reflex is called the Babinski response and is done by running a key or the handle end of the hammer from heel to big toe on the bottom of the foot. Tapping on the tricep muscle causes an extension of the elbow. Using the hammer on the patella should cause the leg to kick out as a response from the femoral nerve.