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Muscle spindles are fusiform (spindle-shaped), and the specialized fibers that make up the muscle spindle are called intrafusal muscle fibers. The regular muscle fibers outside of the spindle are called extrafusal muscle fibers. Muscle spindles have a capsule of connective tissue, and run parallel to the extrafusal muscle fibers unlike Golgi ...
A muscle spindle, with γ motor and Ia sensory fibers. A type Ia sensory fiber, or a primary afferent fiber, is a type of afferent nerve fiber. [1] It is the sensory fiber of a stretch receptor called the muscle spindle found in muscles, which constantly monitors the rate at which a muscle stretch changes.
The stretch reflex is accomplished through several different structures. In the muscle, there are muscle spindles, whose intrafusal muscle fibers lie parallel to the muscle and sense changes in length and velocity. The afferent sensory neuron is the structure that carries the signal from the muscle to the spinal cord.
Muscle spindle, sensory receptors within the belly of a muscle, which primarily detect changes in the length of this muscle; Pulmonary stretch receptors, mechanoreceptors found in the lungs; Chordotonal organ, in insects
Intrafusal muscle fibers are skeletal muscle fibers that serve as specialized sensory organs (proprioceptors). [ 1 ] [ 2 ] They detect the amount and rate of change in length of a muscle . [ 1 ] They constitute the muscle spindle , [ 2 ] and are innervated by both sensory (afferent) and motor (efferent) fibers.
Striking of the patellar tendon with a reflex hammer just below the patella stretches the muscle spindle in the quadriceps muscle. [2] [3] This produces a signal which travels back to the spinal cord and synapses (without interneurons) at the level of L3 or L4 in the spinal cord, completely independent of higher centres. [4]
Spindles are conventionally thought of as encoding muscle length, velocity, and acceleration, however there is evidence to suggest that they respond to the force and yank (the first time-derivative of force) exerted on intrafusal muscle. Spindles are also composed of bag- and chain-type fibers, with dynamic and static stretch responses ...
Primary endings of muscle spindles "respond to the size of a muscle length change and its speed" and "contribute both to the sense of limb position and movement". [72] Secondary endings of muscle spindles detect changes in muscle length, and thus supply information regarding only the sense of position. [72]