NationMaster - Encyclopedia: Intrafusal muscle fibers

Intrafusal muscle fibers are muscle fibers 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 the contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. ... 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. Ia fibers essentially supply proprioceptive information about the rate of change of its respective muscle: the derivative of the muscle's length (or position).

The second of the two main groups of stretch receptors are the II fibers, and they are non-adapting, meaning that they keep responding even when the muscle has stopped changing its length. Their firing rate is directly related to the muscle's instantaneous length, or position. This information would indicate the position one's leg once it has stopped moving.

It is by the sensory information from these two intrafusal fiber types that one is able to judge the position of their muscle, and the rate at which it is changing.

The nervous system of an animal coordinates the activity of the muscles, monitors the organs, constructs and also stops input from the senses, and initiates actions. ... (See also sense) A sensory system is a part of the nervous system that consists of sensory receptors, neural pathways, and those parts of the brain responsible for processing the information. ... The somatosensory system is the sensory system of somatic sensation. ... Cross-section through cervical spinal cord. ... The medial lemniscus, also known as Reils band or Reils ribbon, is a pathway in the brainstem, that carries sensory information from the gracile and cuneate nuclei to the thalamus. ... This article needs to be cleaned up to conform to a higher standard of quality. ... Pressure (symbol: p) is the force per unit area acting on a surface in a direction perpendicular to that surface. ... See Oscillator (disambiguation) for particular types of oscillation and oscillators. ... Proprioception (from Latin proprius, meaning ones own and perception) is the sense of the position of parts of the body, relative to other neighbouring parts of the body. ... The spinothalamic tract is the sensory pathway in the body that transmits pain, temperature, itch and crude touch. ... Pain is an unpleasant sensation which may be associated with actual or potential tissue damage and which may have physical and emotional components. ... Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ... In a sensory system, a sensory receptor is a structure that recognizes a stimulus in the internal or external environment of an organism. ... A Pacinian corpuscle is a structure that functions as a mechanoreceptor. ... Meissners corpuscles (discovered by the anatomist Georg Meissner (1829-1903) are a type of mechanoreceptor and more specifically, a tactile corpuscle(corpusculum tactus). ... Merkel nerve endings are mechanoreceptors found in the skin and mucosa of vertebrates that provide touch information to the brain. ... Ruffini Endings are one of the four main cutaneous mechanoreceptors. ... NERVE ENDINGS SUCK PENIS!!! ... A hair follicle is part of the skin that grows hair by packing old cells together. ... Organ of Golgi (neurotendinous spindle) from the human tendo calcaneus. ... A muscle spindle is a specialized muscle structure innervated by both sensory and motor neuron axons. ... Intrafusal fibers are muscle fibers that comprise the muscle spindle. ... A nociceptor is a sensory receptor that responds only after a high level of stimuli or a level enough to hurt the individual. ... A thermoreceptor is a sensory receptor that responds to heat and cold. ...