What is a Tendon Reflex?
When the tendon is tapped briskly, it quickly pushes in on the tendon and places a tiny, but quick stretch on the muscle attached to that tendon. The Patellar tendon is the easiest to see and describe. You always do a tendon test when the muscle is slightly stretched, so usually this is done while sitting with knee bent at 90 degrees and the lower leg able to swing freely. When the tap is done, just below the kneecap, the normal reaction of the quadriceps is to contract. When it does it causes the knee to extend (the lower leg to swing out). The nerve loop that controls a tendon reflex is a stretch receptor that travels up to the spinal cord and immediately loops over to a motor nerve that travels down and activates the proper muscle. The reflexes may be dulled by depressant medications, low metabolic states like low magnesium, severe depression, or hypothyroidism. Also in low thyroid states, the reflexes not only will be lessened, but they will be delayed. Reflexes may be accentuated
