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There are several theories as to what may trigger gamma motoneurons to increase the reflex's sensitivity. For example, alpha-gamma co-activation might keep the spindles taut when a muscle is contracted, preserving stretch reflex sensitivity even as the muscle fibers become shorter. Otherwise the spindles would become slack and the reflex would ...
The static gamma motor neurons increase their firing, in response to an increase in magnitude of change in length and controls the static sensitivity of the stretch reflex. [8] For this reason, this type of gamma motor neuron is mostly used in the maintenance of postures and slower movements such as lifting a box, rather than activities ...
Dynamic gamma activity is adjusted proactively during movement preparation in order to facilitate execution of the planned action. For example, if the intended movement direction is associated with stretch of the spindle-bearing muscle, Ia afferent and stretch reflex sensitivity from this muscle is reduced.
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.
With activation of gamma neurons, intrafusal muscle fibers contract so that only a small stretch is required to activate spindle sensory neurons and the stretch reflex. There are two types of gamma motor neurons: Dynamic- These focus on Bag1 fibers and enhance dynamic sensitivity. Static- These focus on Bag2 fibers and enhance stretch sensitivity.
This gamma innervation modulates the sensitivity of muscle spindle afferents to stretch. In cat studies, muscle spindle afferent firing rates with gamma fusimotor innervation were shown to be approximately equal to the sum of the gamma motoneuron firing rate and muscle spindle firing rate with no gamma innervation.
Gamma motor neurons innervate intrafusal muscle fibers that control the sensitivity of muscle spindles to stretch. They have smaller cell bodies than alpha motor neurons and do not receive proprioceptive input. [3] They have been shown to reduce in numbers but not size with age. [2]
Joints are controlled by two opposing sets of muscles called extensors and flexors, that work in synchrony for smooth movement.When a muscle spindle is stretched, the stretch reflex is activated, and the opposing muscle group must be inhibited to prevent it from working against the contraction of the homonymous muscle.