Knee tendon reflexes disappear

Knee jump reflex refers to brisk tapping of the knee tendon when the knee is half flexed and the calf is free to sag, causing the quadriceps to contract, causing the calf to react to a sharp forward kick. This reflection is a tendon reflection. The sensor is a muscle spindle that can sense mechanical stimuli. Muscle spindles are generally muscle fibers arranged in parallel, shaped like a shuttle, with both ends attached to tendons (or extrafuscular muscle fibers), and connective tissue capsules outside. The sac contains 2 to 12 specialized muscle fibers, the middle of which is full of cell nuclei, without striations, and can feel stretch stimulation. There are horizontal stripes at both ends and there is contraction. When tapping the tendon below the knee joint, due to rapid muscle tension, the intrafusal muscle fibers contract, stimulating the muscle shuttle sensory part to issue nerve impulses, and the afferent nerve fibers located in the femoral nerve are transmitted to the spinal cord (lumbar 2 ～ 4). Tendon reflexes are single synaptic reflexes, in which afferent nerve fibers are directly connected to the cell body of efferent neurons. The impulses are transmitted by the outgoing fibers located in the femoral nerve to the motor endplate of the effector quadriceps, which causes the stretched muscles to contract and the calf to extend forward. This reflex is usually affected by the high-level parts of the central nervous system, and the strength and delay of its response can reflect the functional state of the central nervous system. It is used clinically to check for diseases of the central nervous system. Patients with disappeared knee tendon reflexes were more likely to have impaired glucose tolerance than patients with normal knee tendon reflexes (P <0.01). The disappearance of the knee tendon reflex can be a means to prompt clinicians to detect patients with reduced glucose tolerance early.

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