Intrafusala

Intrafusala is not a standard term in established anatomy or physiology. When encountered, it is usually treated as a variant spelling or a misspelling of intrafusal, which refers to the intrafusal fibers inside a muscle spindle. In typical wording, intrafusal fibers are specialized muscle fibers contained within the sheath of a muscle spindle, a sensory organ embedded in skeletal muscle.

Muscle spindles lie between or alongside the ordinary (extrafusal) muscle fibers and serve as receptors for muscle stretch. The intrafusal component consists of different fiber types, notably nuclear bag fibers and nuclear chain fibers, which can be dynamically or statically responsive. The central regions of these fibers are surrounded by primary (Ia) and secondary (II) sensory afferents that relay information about length and the rate of change of length to the central nervous system. Efferent gamma motor neurons innervate the contractile ends of intrafusal fibers, modulating their tension and, consequently, their sensitivity to stretch.

Functionally, intrafusal fibers contribute to proprioception and to the regulation of muscle tone through reflex pathways such as the stretch (myotatic) reflex. They help the nervous system detect joint position and movement and adjust motor output accordingly. Intrafusal fibers are distinct from extrafusal muscle fibers, which generate the bulk of muscular force.

Etymology-wise, intrafusal derives from intra- (inside) and fusus (spindle). If a source uses intrafusala, it likely reflects a nonstandard spelling or translation variant and should be cross-checked with authoritative anatomical terminology.