![]() ![]() The opposite effect is observed when tension on the annulospiral ring is decreased by contraction of the main muscle mass. Stretching the annulospiral ring activates mechano-sensitive channels, depolarizes the sensory neuron, and increases its firing rate. This change causes compensatory stretching or relaxation of the sensory endings of the annulospiral ring. Changes in the length of fibers within the main muscle mass during contraction or relaxation passively change the tension on the intrafusal fibers through the connective tissue attachment site. (B) A second type of sensory structure, the Golgi mechanoreceptor nerve ending that forms a springlike configuration called the annulospiral ring. Muscle spindles are also innervated by small myelinated neurons called gamma afferents that directly stimulate intrafusal fibers (but not extrafusal muscles) to contract and thereby regulate the tension on the annulospiral ring and flower spray afferents. (A) Two types of sensory neurons (shown in blue) innervate the spindle: (1) the annulospiral ring, or Ia afferents, sensitive to both the absolute muscle length and rate of change in length during contractions and (2) the flower spray, or II afferents, which monitor static length of the muscle. A spindle contains about four nuclear bags and two nuclear chain fibers enclosed in a capsule. ![]() Spindles contain small intrafusal muscles, each with their centrally located nuclei arranged either in a cluster called a nuclear bag or in a nuclear chain. Muscle spindles are small, fusiform structures embedded in skeletal muscles (extrafusal muscle fibers) that monitor the length of the muscle. (B) A second type of sensory structure, the Golgi Golgi tendon organ Ib afferentįIGURE 1 Organization of the muscle spindle and Golgi tendon organ. ![]() ![]() The central portion of the individual intrafusal muscle fiber is encircled by a specialized extrafusal muscle fiber extrafusal muscle fiberįIGURE 1 Organization of the muscle spindle and Golgi tendon organ. The ends of the sheath are attached to adjacent muscle fibers. The first type, the muscle spindle, consists of a group of fine muscle fibers 4 to 10 mm long encapsulated by a fusiform or spindle-shaped connective tissue sheath (Fig. Two types of specialized sensory endings are present within muscle tissue, and they provide feedback control over firing rates of the alpha motor neuron. One of the major sensory inputs to the lower motor neuron is derived from specialized end organs located within the muscle itself. The driving force on lower motor neurons comes from three major sources: (1) sensory pathways from the spinal cord and brain stem that trigger reflex actions, (2) inter-neurons within the spinal cord that interconnect syner-gistic and antagonistic motor neuron pools, and (3) upper motor neurons in the motor cortex and other motor areas in the brain that provide complex motor commands. ![]()
0 Comments
Leave a Reply. |