Compare and contrast the 3 types of skeletal muscle . Understand and apply themes in how muscles are named •
The correct answer and explanation is:
Skeletal muscles can be classified into three main types: skeletal, cardiac, and smooth muscles. Each type has distinct characteristics suited for its function in the body.
1. Skeletal Muscle
Skeletal muscle is the most common type of muscle found in the human body. It is attached to bones and facilitates movement by contracting and relaxing. These muscles are voluntary, meaning they are controlled consciously. Skeletal muscle fibers are striated, meaning they have a striped appearance under a microscope due to the regular arrangement of actin and myosin filaments. These fibers are multinucleated because they develop from the fusion of multiple precursor cells. Skeletal muscle contraction is rapid, but it can tire quickly due to the use of energy. Examples of skeletal muscles include the biceps, quadriceps, and hamstrings.
2. Cardiac Muscle
Cardiac muscle is found only in the heart. Unlike skeletal muscle, it is involuntary, meaning it is controlled by the autonomic nervous system and not consciously. Cardiac muscle is also striated, but the fibers are branched and interconnected, forming a network that allows coordinated contractions. The fibers contain a single nucleus, and the muscle has special junctions called intercalated discs, which help transmit electrical signals quickly, ensuring the heart beats as a coordinated unit. Cardiac muscle contractions are rhythmic and do not tire as skeletal muscle does.
3. Smooth Muscle
Smooth muscle is found in the walls of internal organs like the stomach, intestines, bladder, and blood vessels. Unlike skeletal and cardiac muscle, smooth muscle fibers are non-striated, appearing smooth under a microscope. This muscle type is involuntary and controlled by the autonomic nervous system. The fibers have a single nucleus and can contract for long periods without tiring. Smooth muscle contracts more slowly than skeletal and cardiac muscles, but it is more sustained. For example, the smooth muscle in the intestines contracts to move food through the digestive system.
Naming of Muscles
Muscles are typically named based on their function, location, size, shape, orientation of fibers, and number of origins. For example:
- Location: The temporalis muscle is named for its position near the temporal bone.
- Shape: Muscles like the deltoid (triangular) are named for their shape.
- Size: Gluteus maximus refers to the largest muscle in the buttocks, while gluteus minimus is smaller.
- Number of origins: The biceps brachii has two heads, while the triceps has three.
In summary, skeletal, cardiac, and smooth muscles differ in their location, function, and structure. Their naming conventions reflect key attributes, such as shape, size, and number of muscle origins.