Each muscle spindle is built around 3-10 small intrafusal muscle fibres attached to the sheaths of the surrounding extrafusal
skeletal muscle fibres, the ends of which are excited by small gamma efferent motor nerve fibres.
Muscle spindles are found within the belly of muscles, embedded in extrafusal
For example, stretch-shortening cycle fatigue appears to influence both extrafusal
and intrafusal muscle, which may describe a form of neural fatigue (Avela and Komi, 1998; Avela et al.
First, the bulk of the muscle is made of extrafusal
fibers (synonymous with skeletal muscle fiber), which are innervated by alpha motor neurons; when extrafusal
fibers contract, the muscle shortens.
Estudos com imunoistoquimica realizados anterior ao desenvolvimento da doenca clinica mostraram evidencias de infeccao de fibras musculares extrafusal
e fibrocitos ocasionais no sitio de inoculacao.
If botulinum toxin is administered over a prolonged period of time, however, true muscle atrophy can occur, both in the extrafusal
and intrafusal muscle fibers within the muscle spindle organ.
Auditory cues did not specifically help in this experiment, but humans are capable of activating [alpha] motor neurons because the final common pathways are directly innervating the extrafusal
skeletal muscles in gross movement and in strong muscle contractions.
reported that a liquid diet and unilateral extraction cause a reduction in the diameter of extrafusal
, and later intrafusal, fibers.
When the release of acetylcholine is blocked, the denervation of the extrafusal
and intrafusal muscle fibers occurs.