Organizational Patterns of Skeletal Muscle Fibers

Fascicles

Bundles of Muscle Fibers

Types of organization of fascicles

Circular, Parallel, Convergent, & Pennate

Circular muscles

concentrically arranged fascicles

• Create a sphincter; control material passage through an opening

Parallel muscles

fascicles run parallel to muscle’s long axis

• Sometimes have an expanded central belly; high endurance

Convergent muscles

fascicles merge toward a common attachment site

• Can pull in varying directions, but not as hard as parallel muscles

Pennate muscles:

fascicles organized as if part of a large feather

• Fibers pull at an angle to the tendon

• Generate more tension but don’t pull their tendons as far as parallel muscles

Three subtypes of Pennate muscles

• Unipennate – fascicles on same side of tendon

• Bipennate – fascicles on both sides of tendon; most common

• Multipennate – branches of tendon within muscle, and fascicles arranged around both sides of each tendon branch