Victor Forge
The muscular system is responsible for the movement of the human body. There are about 700 named muscles in the human body, comprising roughly half of a person's body weight. Each of these muscles is a discrete organ constructed of skeletal muscle tissue, blood vessels, tendons, and nerves. There are three types of muscles in the human body: skeletal, cardiac, and smooth muscle. Gross muscle anatomy is the study of the structure and composition of these muscles.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | 700 |
| Muscle composition | Skeletal muscle tissue, blood vessels, tendons, and nerves |
| Types of muscle tissue | Visceral, cardiac, and skeletal |
| Muscle control | Voluntary or involuntary |
| Skeletal muscle composition | Connective tissue, blood vessels, nerves, and microanatomy of a skeletal muscle fiber (cell) |
| Skeletal muscle shape | Striated, multinucleated cells ranging from 10 to 100 micrometers in diameter |
| Skeletal muscle layers | Endomysium, perimysium, and epimysium |
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What You'll Learn
Skeletal muscle composition
Skeletal muscles are the most common type of muscle in the human body, comprising 30% to 40% of total body mass. They are attached to the bones and allow us to perform a wide range of movements and functions. These muscles are voluntary, meaning we have conscious control over how and when they work.
Each skeletal muscle is a discrete organ constructed of skeletal muscle tissue, blood vessels, tendons, and nerves. Skeletal muscle tissue is composed of bundles of muscle fibres called myofibers, which contain several myofibrils. Each myofiber represents a muscle cell, with its basic cellular unit being the sarcomere. Myofibrils are composed of actin (thin filaments), myosin (thick filaments), and support proteins. The arrangement of actin and myosin gives skeletal muscle its microscopic striated appearance.
The skeletal muscle fibres are red and white, and they appear striped or striated. These fibres are made up of endomysium, perimysium, and epimysium, covering the sarcolemma. The sarcolemma is a tubular sheath that encases and defines each muscle fibre, forming a barrier between extracellular and intracellular compartments. The sarcolemma is composed of a plasma membrane and a polysaccharide coating that fuses with tendon fibres.
The primary artery supplying blood to a skeletal muscle generally courses parallel to the longitudinal axis of the muscle fibre. The primary artery gives off tributaries known as feed arteries, which run perpendicular to the primary artery and proceed towards the external connective tissue sheath of the muscle fibre (perimysium). The neuronal innervation of a skeletal muscle typically comprises sensory nerve fibres, motor nerve fibres, and the neuromuscular junction.
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Muscle tissue types
Muscle tissues are pieces of soft tissue that help the body to move, breathe, swallow, and stay alive. There are three types of muscle tissue in the body: skeletal, smooth, and cardiac.
Skeletal muscles are part of the musculoskeletal system and work with bones, tendons, and ligaments to support the body's weight and facilitate movement. Tendons attach skeletal muscles to bones all over the body. Skeletal muscles are voluntary, meaning they move when you want them to. Some skeletal muscles contract quickly and use short bursts of energy (fast-twitch muscles), while others move slowly, like back muscles that assist with posture. Skeletal muscles are also called striated muscles because they appear to have light and dark stripes when viewed under a light microscope.
Cardiac muscle, also known as myocardium, makes up the middle layers of the heart and is not found anywhere else in the body. It is an involuntary muscle that squeezes and relaxes to pump blood through the cardiovascular system. Cardiac muscle has branching fibers, one nucleus per cell, and intercalated disks. The cells are tightly connected, forming an X or Y shape, which helps them resist high blood pressures and the strain of pumping blood.
Smooth muscle, also known as visceral muscle, lines the inside of some organs, including the liver, pancreas, intestines, and blood vessels. It is an involuntary muscle that helps organs contract to move substances through them. When viewed under a microscope, smooth muscle appears smooth and uniform, in contrast to the banded appearance of skeletal and cardiac muscles.
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Muscle movement
Skeletal muscles are voluntary muscles, meaning an individual can control how and when they move. They are also responsible for sustaining body posture and position, maintaining body temperature, storing nutrients, and stabilizing joints. Each skeletal muscle is considered an organ, composed of various tissues, including muscular, connective, nervous, and epithelial tissues. Skeletal muscles are controlled by neurons called somatic motor neurons, which stimulate contraction and the production of force.
The skeletal muscle itself is covered by a layer of connective tissue called the epimysium, which keeps the muscle intact during contraction and extension. The epimysium also connects with the periosteum of the skeletal system to form tendons, which attach to the bones and cause movement when the muscle contracts. Inside the skeletal muscle are large bundles called fascicles, covered by a layer of connective tissue called the perimysium. Skeletal muscle fibres are striated, multinucleated cells, with nuclei located peripherally, adjacent to the sarcolemma, a tubular sheath encasing each muscle fibre.
The three types of muscle tissue in the body are skeletal, cardiac, and visceral (or smooth) muscle. Skeletal muscles are attached to bones and allow for a wide range of movements and functions. Cardiac muscle is found only in the heart and is responsible for pumping blood throughout the body. Visceral muscle is the weakest type of muscle tissue and is found inside organs like the stomach, intestines, and blood vessels. It contracts to move substances through the organ and is controlled by the unconscious part of the brain, making it an involuntary muscle.
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Muscle naming
The human body has about 700 named muscles, which make up roughly half of a person's body weight. Skeletal muscles, which are the most common type of muscle in the body, are named based on several factors, including their location, origin, insertion, number of origins, shape, size, direction, and function. Many muscles derive their names from their anatomical region. For example, the rectus abdominis and transverse abdominis are found in the abdominal region. Some muscles, like the tibialis anterior, are named after the part of the bone they are attached to (in this case, the anterior portion of the tibia).
Skeletal muscles are attached to the bones of the skeletal system and allow for a wide range of movements and functions. They are considered voluntary muscles, meaning that individuals have control over how and when they move. Skeletal muscle mass varies from person to person and is generally higher in males, taller individuals, and those with higher body weight. Muscle mass tends to decrease with age.
Skeletal muscles are composed of skeletal muscle tissue, blood vessels, tendons, and nerves. They are covered by a layer of connective tissue called the epimysium, which helps maintain the integrity of the muscle during contraction and extension. The epimysium also extends and connects with the periosteum of the skeletal system to form tendons. Tendons are tough bands of connective tissue that attach skeletal muscles to bones, enabling muscles to pull on the attached bone and cause movement.
Within the skeletal muscle, there are large bundles called fascicles, which are covered by a layer of connective tissue called the perimysium. Each skeletal muscle fiber is composed of several hundred to several thousand myofibrils, which are made up of actin (thin filaments), myosin (thick filaments), and support proteins. The arrangement of actin and myosin gives skeletal muscle its microscopic striated appearance.
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Muscle disorders
The muscular system is responsible for the movement of the human body. There are about 700 named muscles, making up roughly half of a person's body weight. Each muscle is a discrete organ constructed of skeletal muscle tissue, blood vessels, tendons, and nerves. Muscle tissue is also found inside the heart, digestive organs, and blood vessels. There are three types of muscle tissue: visceral, cardiac, and skeletal.
Neuromuscular disorders are another type of muscle disorder that affects the nerves controlling voluntary muscles and those communicating sensory information to the brain. When nerve cells become unhealthy or die, communication between the nervous system and muscles breaks down, resulting in muscle atrophy. Common symptoms of neuromuscular disorders include muscle weakness, twitching, cramps, and aches and pains. While there is currently no cure for neuromuscular disorders, treatments such as medications, physical therapy, and surgery aim to manage symptoms and enhance patients' quality of life.
Congenital myopathy is another muscle disorder that arises from genetic defects, resulting in muscle weakness and other symptoms. While some muscle disorders have known causes, the origins of others remain unknown, underscoring the complexity of muscle function and the need for ongoing research.
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Frequently asked questions
Gross muscle anatomy refers to the structure and composition of skeletal muscles, which are the most common type of muscle in the human body. Skeletal muscles are responsible for movement and are attached to bones.
There are three types of muscles in the human body: skeletal, cardiac, and smooth or visceral muscle.
Skeletal muscle is considered an organ and is composed of various tissues, including muscular tissue, connective tissue, nervous tissue, and epithelial tissue.
Skeletal muscle serves many functions in the body, including producing movement, sustaining body posture and position, maintaining body temperature, storing nutrients, and stabilizing joints.
Skeletal muscle is under voluntary control, meaning that an individual can control how and when the muscle moves. On the other hand, cardiac and smooth muscle are involuntary and are controlled by the autonomic nervous system.
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