JACOPIN / SCIENCE PHOTO LIBRARY JACOPIN / SCIENCE PHOTO LIBRARY
Neuromuscular spindle and proprioception. The proprioception is the perception of the position of the different parts of the body in space. It is performed via sensorial receptors (proprioceptors) detecting the position of the body, the length and the tension of the muscles and tendons, the position and the movement of articulations. The muscles spindles are the proprioceptors that inform the organism on the variation of the muscles' length ; they are present in most skeletal muscles. It is specialized muscles cells (intrafusal myocytes) disseminated among the ordinary skeletal muscle cells (extrafusal myocytes). Various nervous fibers entering in contact with the neuromuscular spindle : beta motor neurons (in connection with an extrafusal myocyte) and gamma (in connection with the intrafusal myocytes) regulating the muscular contraction, sensitive fibers of type I and II winded around the central part of intrafusorial myocytes. The sensitive fibers send to the central nervous system the proprioceptive information : speed of the variation of the muscle length for the fibers, degree of the muscle stretching for the fibers II. Only the fibers of type II are represented here (in yellow). The neuromuscular spindle is at the origin of myotatic reflexes, such as the patellar reflex of leg extension when produced by a sharp tap to the tendon below the patella. See.
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