Type Ia Sensory Fiber also called Primary Afferent Type 1A Fiber or Group II sensory fibers is a component of a muscle fiber's muscle spindle which keeps track of the how fast a muscle stretch changes (the velocity of the stretch). Global view of a neuromuscular junction: 1. ... A muscle spindle is a specialized muscle structure innervated by both sensory and motor neuron axons. ...

In order to control movements, the nervous system must receive continuous sensory information from muscles and joints. For this purpose the body has specialized sensory receptors called proprioceptors. Muscle spindles are a type of proprioceptor, and they are located inside the muscle itself. They are sensitive to muscle length because they are in parallel with the contractile fibers. This change in length of the spindle is transduced (transformed into electric membrane potentials) by two types of sensory afferents, Type Ia (primary) and Type II (secondary). The cell bodies of these sensory neurons are located in dorsal root ganglia located next to the spinal cord. 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. ... This article is about a joint in zootomical anatomy. ... In a sensory system, a sensory receptor is a structure that recognizes a stimulus in the internal or external environment of an organism. ... Proprioception (from Latin proprius, meaning ones own and perception) is the sense of the relative position of neighbouring parts of the body. ... This article or section is in need of attention from an expert on the subject. ... The Spinal cord nested in the vertebral column. ...

The two kinds of sensory fibers are different in respect to the kind of potentials they generate. Type Ia fibers respond only to the rate of change in muscle length, as well to change in length. Type II fibers respond only to changes in length. Both types of fiber have a non-linear response to muscle length, i.e., they respond more strongly to small changes in length (less than 1 mm) and reach a plateau at highers lengths.

In addition, the spindle also has a motor efferent innervation carried by gamma motor neurons, which is used by the nervous system to modify the spindle's sensitivity. 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. ...

Ia afferents from the muscle spindle terminate on the proximal dendrites of motor neurones.

See also

• Proprioception
• Motor system
• Muscle
• Muscle spindle
• Reflex action
• Phasic stretch reflex
• Tonic stretch reflex
• Type II sensory fiber

Proprioception (from Latin proprius, meaning ones own and perception) is the sense of the relative position of neighbouring parts of the body. ... Structure of a skeletal muscle Muscle is one of the four tissue types. ... It has been suggested that this article or section be merged into Muscular system. ... A muscle spindle is a specialized muscle structure innervated by both sensory and motor neuron axons. ... The mechanism of the reflex arc A reflex action is an automatic (involuntary) neuromuscular action elicited by a defined stimulus. ...

External links

• Lecture notes from John D.C. Lambert on neurophysiology.