Which of the following is a multipennate muscle:March 2012
**Core Concept**
A multipennate muscle is a type of skeletal muscle with a specific arrangement of muscle fibers and tendons. This arrangement allows for increased muscle strength and power. Multipennate muscles are characterized by a broad origin and a narrow insertion, with multiple tendons (or "pennation") that intersect with the muscle fibers.
**Why the Correct Answer is Right**
The pectoralis major muscle is an example of a multipennate muscle. Its broad origin on the chest (sternum and clavicle) and narrow insertion on the humerus (upper arm bone) allow for powerful movements of the shoulder joint, including flexion, extension, and rotation. The muscle fibers of the pectoralis major are oriented at an angle to the tendon, which enables the muscle to generate a greater force of contraction. This pennate arrangement also helps to increase the muscle's mechanical advantage.
**Why Each Wrong Option is Incorrect**
* **Option A:** The deltoid muscle is a multipennate muscle, but it is not the best example of this type of muscle. While it does have a pennate arrangement, its origin and insertion are not as broad and narrow, respectively, as those of the pectoralis major.
* **Option B:** The biceps brachii muscle is a fusiform muscle, characterized by a cylindrical shape and a uniform diameter along its length. It does not have the pennate arrangement of the pectoralis major.
* **Option C:** The trapezius muscle is a triangular muscle with a broad origin on the spine and a narrow insertion on the clavicle. While it does have a pennate arrangement, its muscle fibers are not oriented at an angle to the tendon in the same way as those of the pectoralis major.
**Clinical Pearl / High-Yield Fact**
When studying skeletal muscles, it's essential to remember that the pennate arrangement of muscle fibers can significantly affect the muscle's mechanical advantage and overall strength. This is why multipennate muscles like the pectoralis major are often more powerful than other types of muscles.
**Correct Answer:** D.