Intrafusal fibers are musclefibers that comprise the muscle spindle. These fibers are walled off from the rest of the muscle by a collagen sheath. This sheath has a spindle or "fusiform" shape, hence the name "intrafusal." While the intrafusal fibers are wrapped with sensor receptors, their counterpart, extrafusal fibers are the ones responsible for the power-generating component of muscle and are innervated by motor neurons. A top-down view of skeletal muscle Muscle is a contractile form of tissue. ... For the meaning of fiber in nutrition, see dietary fiber. ... [[A muscle spindle is a specialized muscle structure innervated by both sensory and motor neuron axons. ... Tropocollagen triple helix. ... Receptor may refer to: In telecommunication, a receiver. ... In vertebrates, motoneurons (also called motor neurons) are efferent neurons that originate in the spinal cord and synapse with muscle fibers to facilitate muscle contraction and with muscle spindles to modify proprioceptive sensitivity. ...
The first of the two main group of stretch receptors wrapping the intrafusal fibers are the Ia fiber, which are the largest and fastest fibers, and they fire when the muscle is stretching. They are characterized by their rapid adaption, because as soon as the muscle stops changing length, the Ia stop firing and adapt to the new length.
The second of the two main groups of stretch receptors are the II fibers, and they are slow-adapting, responding while the muscle is stretching and continuing this response .
Somatic fibers innervate skeletal muscle while autonomic fibers innervate cardiac muscle of the heart and smooth muscle of the visceral organs and glands.
Upon adequate stimulation, the motoneuron releases a flood of neurotransmitters that bind to postsynaptic receptors and triggers a response in the musclefiber.
This is why muscle relaxants work by acting on the nerves that innervate muscles (by decreasing their electrophysiological activity) or on cholinergic neuromuscular junctions, rather than on the muscles themselves.
Share your thoughts, questions and commentary here
Want to know more? Search encyclopedia, statistics and forums:
Press Releases |
The Wikipedia article included on this page is licensed under the
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m