For starters, the knee gets top billing in the reflex test for one simple reason: it’s easy to access. You’re sitting on the table in that backless gown, fighting humiliation and cold.

Testing a series of different reflexes gives an indication of the health of your whole nervous system. Now let's follow the path of the knee jerk reflex to see how it works.

They felt the knee jerk — or "patellar-tendon" reflex — in particular could help assess nerve function. Enlarge this image Anton Wintrich introduced this percussion hammer model in 1841.

The knee jerk reflex can be tested by tapping just below the knee causing the lower leg to suddenly jerk forward. You are working the patella tendon. This is the tendon that runs down from the ...