3 Types of Proprioceptors :
a) Muscle Spindles:
These are proprioceptors in skeletal muscles that monitor changes in the length of skeletal muscles and participate in skeletal reflexes. This also allows the brain to set the overall level of Muscle Tone . Muscle spindles consist of several slowly adapting sensory nerve endings that wrap around 3-10 specialized muscle fibres called Intrafusal Muscle Fibres . A connective tissue capsule encloses the sensory nerve endings and intrafusal fibres and anchors the spindle to the endomysium and perimysium. They are interspersed among most skeletal muscle fibres and align parallel to them. Muscles that produce finely controlled movements have abundant spindles while muscles of more forceful movements have fewer. The only muscles that lack muscle spindles are tiny muscles of the middle ear. Muscle Spindle Function : measure muscle length – how much a muscle is being stretched. Sudden or prolonged stretch of central areas of the intrafusal muscle fibres stimulates the nerve endings. Impulses then propagate to the CNS arriving quickly at the somatic sensory area of the cerebral cortex allowing perception of limb positions and movements. Concurrently, impulses from the spindles propagate to the cerebellum where the input is used to coordinate muscle contractions.
b) Tendon Organs (Golgi) GTO
Located at the junction of a tendon and a muscle. Tendon organs protect tendons and associated muscles from damage due to excessive tension with tendon reflexes. These tendon organs consist of a thin connective tissue capsule enclosing a few tendon fascicles (bundles of collagen fibres). One or more sensory nerve endings penetrate the capsule and entwine among and around the collagen fibres of the tendon. As tension is applied to the muscle, the tendon organs generate nerve impulses to the CNS providing information about muscle tension. Tendon reflexes decrease muscle tension by causing muscle relaxation.
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