Muscle Shapes and Fascicle Arrangements

Parallel Muscle (Fusiform)

Fascicles run along the long axis of the muscle and taper at each end (spindle-shaped); majority of skeletal muscles are parallel (biceps brachii)

Parallel Muscle (Non-Fusiform)

Fascicles run along the long axis but the muscle is NOT tapered at the ends (sartorius)

Circular Muscle (Sphincter)

Concentrically arranged muscle fibers that surround an opening; contracted = shrinks/closes; when relaxed = enlarges (orbicularis oris)

Convergent Muscle

Fascicles spread over a wide area but converge to a single common attachment point (pectoralis major)

Pennate Muscle

Fascicles blend into a tendon running through the central length of the muscle; fibers pull at an angle so the tendon moves less far, but force is greater. (three subtypes: unipennate, bipennate, multipennate)

Unipennate Muscle

Fascicles are located on only one side of the central tendon (extensor digitorum of forearm)

Bipennate Muscle

Fascicles are located on both sides of the central tendon (rectus femoris of thigh)

Multipennate Muscle

Muscle fibers wrap around the tendon, sometimes forming individual fascicles, creating multiple 'feather' arrangements (deltoid)