Muscle (muscle)

Muscle is a soft tissue found in most organisms. Muscles enable organisms to move by contracting and relaxing in response to voluntary and involuntary signals from the nervous system.

Structure

Muscles are composed of muscle fibers, which are the basic units of contraction. Each muscle fiber is a single, elongated cell that contains multiple nuclei. Muscle fibers are grouped together into bundles, or fascicles, which are surrounded by a layer of connective tissue called the perimysium. The entire muscle is then wrapped in another layer of connective tissue known as the epimysium.

Types of Muscle

There are three types of muscle in the human body: skeletal muscle, cardiac muscle, and smooth muscle.

• Skeletal muscle is attached to bones and causes movements of the body. These muscles are striated and voluntary.
• Cardiac muscle makes up the walls of the heart and is responsible for pumping blood throughout the body. This muscle is also striated, but involuntary.
• Smooth muscle is found in the walls of organs and structures such as the esophagus, stomach, intestines, bronchi, uterus, urethra, and blood vessels. Unlike skeletal and cardiac muscle, smooth muscle is not striated and is involuntary.

Function

The primary function of muscle is to produce force and cause motion. Muscles perform a variety of roles in the body, including maintaining posture, stabilizing joints, and generating heat during activity.

Diseases and Disorders

There are many diseases and disorders that can affect the muscles, including muscular dystrophy, myasthenia gravis, and rhabdomyolysis. These conditions can result in a variety of symptoms, such as muscle weakness, pain, and paralysis.

See Also

• Muscle contraction
• Muscle hypertrophy
• Muscle atrophy