Organization of Skeletal Muscle Fibers
While the muscle fibers of the fascicles lie parallel to one another, the fascicles themselves can vary in their relationship to one another and to their tendons. The different patterns of arrangement of the fasciles produce four different types of skeletal muscles: parallel muscles, convergent muscles, pennate muscles, and sphincter muscles.
- Parallel muscles
The fascicles of parallel muscles run parallel to the direction of the muscle, thus these muscles on a whole function similarly to a single muscle fiber. Most skeletal muscles in the body are parallel muscles; although they can be seen in a variety of shapes such as flat bands, spindle shaped, and some can have large protrusions in their middle known as the belly of the muscle.
- ex: Triceps, biceps
- Convergent muscles
The fibers in convergent muscles fan out from a common point of attachment. Covering a broad surface these fibers allow for more versatile types of movement. These muscles do not pull as hard on their corresponding tendons as their parallel muscle counterparts however due to the fibers not all pulling in the same direction, even pulling in different directions at opposite ends.
- ex: Pectoralis muscles
- Pennate muscles
In a pennate muscle one or more tendons run through the body of the muscle with the fascicles forming an oblique angle to the tendons. Because the fascicles pull on the tendons at an angle they do not move the tendon as far as their parallel muscle counterparts. Despite this they generate greater tension due to their possessing a greater amount of muscle fibers than similarly sized parallel muscles.
- ex: Rectus femoris
- Sphincter muscles
The fibers of the sphincter or circular muscles are arranged concentrically around an opening or recess. As the muscle contracts, the opening it circumvents gets smaller, for this reason these muscles are often found at the entrances and exits of external and internal passage ways.
- ex: Orbicularis oris
Read more about this topic: Skeletal Muscle, Muscle Fibers
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