Extrafusal muscle fiber

Extrafusal muscle fiber is a type of muscle fiber that is responsible for the force exerted by contraction of a skeletal muscle. They are innervated by alpha motor neurons and generate tension by contracting, thereby allowing for skeletal movement.

Etymology

The term "extrafusal" is derived from the Latin "extra", meaning "outside", and "fusus", meaning "spindle". This is in contrast to intrafusal muscle fibers, which are located inside the muscle spindle and are involved in sensory perception of muscle stretch.

Structure

Extrafusal muscle fibers are the major muscle fibers in the body and are surrounded by a layer of connective tissue called the endomysium. They are bundled together into groups known as fascicles, which are then grouped together to form a muscle.

Function

The primary function of extrafusal muscle fibers is to generate force for muscle contraction. When stimulated by an alpha motor neuron, the extrafusal muscle fiber contracts, leading to movement of the skeleton. This is in contrast to intrafusal muscle fibers, which do not contribute to the force of muscle contraction but instead serve a sensory role, detecting the amount and rate of change in length of a muscle.

Clinical significance

Abnormalities in extrafusal muscle fibers can lead to a variety of muscular disorders, including muscular dystrophy and myasthenia gravis. In these conditions, the ability of the extrafusal muscle fibers to contract and generate force is impaired, leading to muscle weakness and fatigue.

See also

• Intrafusal muscle fiber
• Muscle contraction
• Alpha motor neuron