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Muscular System
Muscular System

Muscular System

Systema musculare

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Types of Muscle Tissue

The muscular system is composed of the contractile tissues of the body. Muscular contractions are necessary for processes such as locomotion, the pumping of blood from the heart, and the movement of food through the digestive system. There are three types of muscle tissue in the body.

- Skeletal muscle is the muscle tissue that is generally attached to bones and extends across joints, although some skeletal muscles are attached to other structures such as cartilage. It is under voluntary control and has a striated appearance under microscopy.

- Cardiac muscle is the muscle tissue found in the heart. It is under involuntary control and has a striated appearance under microscopy.

- Smooth muscle is the muscle tissue found in the walls of organs and blood vessels. It is under involuntary control and has a non-striated appearance under microscopy.

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Groups of Skeletal Muscles

The majority of the named muscles in the body are of the skeletal muscle type. Skeletal muscles are categorized into four distinct groups based on the orientation and arrangement of their muscle fibers.

- Parallel skeletal muscle consists of muscle fibers that are arranged in parallel to the line of pull during muscle contraction. They can be subcategorized based on their shape into quadrilateral (e.g., pronator quadratus), strap-like (e.g., sartorius), and fusiform (e.g., biceps brachii) muscles.

- Convergent skeletal muscle consists of muscle fibers that have a wide origin, but whose fibers converge in order to attach to a narrow tendon (e.g., pectoralis major).

- Circular skeletal muscle consists of muscle fibers that are arranged in a circular manner (e.g., orbicularis oculi). They are found at points of openings, where their contraction leads to closure of that opening.

- Pennate skeletal muscle consists of muscle fibers that are attached to the sides of a tendon in a manner that is very similar to a feather. They can be subcategorized, based on their shape, into unipennate (e.g., flexor pollicis longus), bipennate (e.g., rectus femoris), and multipennate (e.g., deltoid) muscles.

Naming of Skeletal Muscles

In addition to the four groups of muscles named about, the names of many skeletal muscles, which are Greek or Latin in origin, also give an indication to their characteristic features. Such characteristics include:

- location (e.g., external intercostal muscles, which are located between the ribs);

- sites of attachment (e.g., sternocleidomastoid muscles, which attaches to the sternum, clavicle, and mastoid process of the temporal bone);

- shape (e.g., deltoid muscle, which refers to the Greek letter delta, which is triangular);

- size (e.g., pectoralis major and pectoralis minor muscles, where “major” means large, and “minor” means small);

- fiber direction (e.g., rectus abdominis muscle, where “rectus” is Latin for “straight”);

- number of heads, or sites of origin (e.g., biceps brachii muscle has two heads and triceps brachii muscle has three heads);

- action (e.g., flexor carpi ulnaris muscle, which bends the carpus, or wrist).

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