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muscle spindle
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Diagram of a mammalian muscle spindle showing its structure within muscle tissue, including extrafusal and intrafusal muscle fibers, motor and sensory nerve endings, sheath, and lymph, with labeled components illustrating sensory reception in human and mammal anatomy.
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muscle spindle

anatomy
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Diagram of a mammalian muscle spindle showing its structure within muscle tissue, including extrafusal and intrafusal muscle fibers, motor and sensory nerve endings, sheath, and lymph, with labeled components illustrating sensory reception in human and mammal anatomy.
mammalian muscle spindle A mammalian muscle spindle, showing both extrafusal and intrafusal fibers.

A muscle spindle is a sensory receptor found within skeletal muscles that detects changes in muscle length and tension. These spindles are composed of specialized muscle fibers called intrafusal fibers, enclosed in a connective tissue sheath. They are arranged parallel to the main muscle fibers and play a crucial role in proprioception, which is the body's awareness of its position and movement in space.123

When a muscle stretches, the intrafusal fibers within the muscle spindle are also stretched, increasing the frequency of nerve impulses sent to the central nervous system. This information allows the nervous system to make rapid adjustments, such as triggering a reflex contraction to counteract the stretch and maintain posture or stability. Muscle spindles are essential for coordinated movements and preventing overstretching of muscles.13

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3 Britannica Sources
  1. mechanoreception - Muscle spindles
  2. human nervous system - Muscle spindles
  3. muscle spindle

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