A muscle with fascicles that insert into only one side of the tendon is categorized as
A) parallel.
B) bipennate.
C) convergent.
D) unipennate.
E) circular.
The Correct Answer and Explanation is :
The correct answer is D) unipennate.
Explanation:
A muscle with fascicles (the bundles of muscle fibers) that insert into only one side of the tendon is categorized as unipennate. The term “pennate” comes from the Latin word penna, which means “feather”. In this muscle type, the muscle fibers are arranged at an angle to the tendon, much like the barbs of a feather. The primary advantage of this structure is that it allows for a greater number of muscle fibers in a given area, which increases the force generated by the muscle.
The unipennate arrangement involves the muscle fibers being aligned on one side of a central tendon, like the structure of a feather where the fibers point toward a single central tendon. This type of muscle structure is often found in muscles that require strength over range of motion. Examples of muscles with unipennate arrangements include the extensor digitorum longus (which extends the toes) and the flexor pollicis longus (which flexes the thumb).
Comparison to Other Muscle Types:
- Parallel muscles (Option A): These muscles have fibers running parallel to the length of the muscle. An example of a parallel muscle is the sartorius in the thigh. Parallel muscles generally have a greater range of motion but do not generate as much force as pennate muscles.
- Bipennate muscles (Option B): In bipennate muscles, the fascicles insert into both sides of the tendon, resembling the structure of a feather with two “barbs”. An example of this is the rectus femoris.
- Convergent muscles (Option C): These muscles have a broad origin and converge into a single tendon. The pectoralis major in the chest is an example.
- Circular muscles (Option E): These muscles are arranged in concentric rings, such as the orbicularis oris around the mouth, and their primary function is to close or constrict an opening.
By arranging muscle fibers in a unipennate pattern, the muscle can generate a greater force in a smaller area compared to parallel muscle fibers.
Let me generate an image to help visualize this.
Here is an illustration showing the structure of a unipennate muscle, where the muscle fibers insert into one side of the tendon, similar to the structure of a feather. This helps to visualize how the fibers are arranged to maximize force production.