Logan Steele
The human muscle system is a complex network of muscles, tendons, and bones that work together to facilitate movement, posture, and balance. There are over 600 muscles in the human body, and they can be categorised into three main types: skeletal ?(striated)? muscle, smooth muscle, and cardiac muscle. Skeletal muscles, attached to bones by tendons, enable voluntary movements and contribute to joint stability. Smooth muscles, found within internal organs, aid in processes like digestion and breathing. Cardiac muscle, unique to the heart, contracts and relaxes to pump blood through the cardiovascular system. Muscle health is vital, as issues like long-term pain or weakness can indicate serious conditions, including muscular dystrophy, which affects muscle strength and function.
| Characteristics | Values |
|---|---|
| Number of muscles in the body | More than 600 |
| Types of muscles | Skeletal, Smooth, Cardiac |
| Skeletal muscle composition | Muscle cells, Muscle fibers, Myofibrils, Sarcomeres |
| Muscle movement | Muscles move by shortening their length, pulling on tendons, and moving bones closer to each other |
| Muscle control | Voluntary and Involuntary |
| Muscle functions | Movement, posture, balance, breathing, heart function, digestion |
| Muscle pain | Long-term muscle pain and weakness can be signs of serious issues |
| Muscle diseases | Muscular dystrophy, more than 30 types |
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What You'll Learn
Skeletal muscles
The development of skeletal muscles begins in embryogenesis with the differentiation of the para-axial mesoderm into somites, which then differentiate into dermomyotome and sclerotome. After birth, satellite cells act as stem cells and contribute to the further growth and development of skeletal muscles. Skeletal muscles are powered predominantly by the oxidation of fats and carbohydrates, and they also act as a storage source for amino acids used by organs to synthesize proteins.
There are more than 600 skeletal muscles in the human body, and they make up around 40% of body weight in healthy young adults. Males typically have more skeletal muscle mass than females, and muscle mass decreases with age. Skeletal muscles are an important part of the musculoskeletal system, working with bones, tendons, and ligaments to support body weight and enable movement.
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Smooth muscles
Smooth muscle is one of the three main types of muscle, the others being skeletal and cardiac muscle. It is a type of muscle tissue that works automatically and is found throughout the body. Smooth muscle is controlled by the autonomic nervous system and is not striated, meaning it has no sarcomeres and therefore no bands or stripes. It is divided into two subgroups: single-unit and multi-unit smooth muscle.
Single-unit smooth muscle, also known as visceral smooth muscle, is myogenic, meaning it can contract regularly without input from a motor neuron. It is found in the walls of most internal organs, blood vessels excluding large elastic arteries, the urinary tract, and the digestive tract. It is not found in the heart, which has cardiac muscle.
Multi-unit smooth muscle, on the other hand, is neurogenic, meaning its contraction must be initiated by an autonomic nervous system neuron. It is found in the trachea, in the iris of the eye, and lining the large elastic arteries.
Smooth muscle cells are spindle-shaped with a wide middle and tapering ends. They can tense and relax and have greater elastic properties than striated muscle. This quality is important in organ systems like the intestines and urinary bladder, where smooth muscle helps with digestion, nutrient collection, and the removal of toxins.
Smooth muscle also plays a vital role in the regulation of blood pressure and tissue oxygenation, as well as in the dilation and constriction of pupils in the eyes.
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Cardiac muscles
The human body has more than 600 muscles, which help us move, breathe and survive. The muscular system can be broadly divided into three types of muscle: skeletal, smooth and cardiac.
Cardiac muscle, also called myocardium, is one of the three major categories of muscles in the body. It is the only type of muscle that has its own cardiac tissue, and it only develops in the heart. It is made up of sarcomeres that allow for contractility. The heart is made up of three layers: the pericardium, the myocardium, and the endocardium. The myocardium is the thick middle layer, surrounded by a thin outer layer called the epicardium (or visceral pericardium) and an inner endocardium.
Cardiac muscle cells (cardiomyocytes) are striated, branched, and contain many mitochondria. Each cell contains a single, centrally located nucleus surrounded by a cell membrane known as the sarcolemma. The sarcolemma contains voltage-gated calcium channels, which skeletal muscle does not possess. Cardiac muscle cells contain branched fibres connected via intercalated discs that contain gap junctions and desmosomes. These interconnections allow the cardiomyocytes to contract together synchronously to enable the heart to work as a pump.
Cardiac muscle tissue gets its strength and flexibility from its interconnected cardiac muscle cells, or fibres. Cardiomyocytes are the individual cells that make up the cardiac muscle. Their primary function is to contract, which generates the pressure needed to pump blood through the circulatory system. Cardiac muscle is involuntary, meaning it contracts and relaxes automatically, without a person's conscious control.
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Voluntary and involuntary movements
The human body has more than 600 muscles, which help us perform a wide range of movements and functions, from moving our body to breathing and staying alive. The muscular system can be broadly divided into skeletal (striated) muscle, smooth muscle, and cardiac muscle. Skeletal muscles are voluntary muscles, while smooth and cardiac muscles are involuntary.
Voluntary muscles are those that you can control consciously, such as those in your arms and legs. They move when you think about moving that part of your body. These muscles are responsible for movements that require conscious thought and control, such as lifting, walking, or writing. They contract quickly and powerfully, allowing us to perform rapid and intense movements. However, this also means that they can tire easily and need rest after intense use. Voluntary muscles work when the brain sends signals through nerves, allowing movement when you decide to move.
Involuntary muscles, on the other hand, function automatically without conscious effort. They manage essential functions that are vital for survival, such as controlling heartbeats, breathing, and digestion. The heart, for example, is an involuntary muscle as it beats on its own without your input. Smooth muscles, which line the inside of some organs, are also involuntary. They perform essential tasks like moving waste through the intestines and helping the lungs expand when breathing. Involuntary muscles are highly resistant to fatigue and contract slowly and rhythmically, allowing them to maintain long-term functions without tiring.
Some actions, like breathing, can be both voluntary and involuntary. You can control your breath, but it also happens automatically.
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Muscle contractions
The human body has more than 600 muscles that help us move, breathe, and perform other vital functions. The muscular system can be broadly divided into three types of muscles: skeletal, smooth, and cardiac.
Skeletal Muscles
Skeletal muscles are the most common type of muscle in the body, comprising 30% to 40% of our total body mass. They are attached to bones by tendons and allow us to perform various movements and functions. These muscles are under our voluntary control, meaning we decide how and when they work. Skeletal muscles consist of flexible muscle fibers that contract (tighten) to enable movement. Each muscle can contain thousands of fibers, and these fibers usually span the length of the muscle.
Smooth Muscles
Smooth muscle tissue lines some of our organs, and while most organs are made of other types of tissue as well, smooth muscles play essential roles. They are found in the blood vessels, gastrointestinal tract, bronchioles, uterus, and bladder. Smooth muscles are involuntary, meaning their contractions are initiated by the muscle cells themselves rather than external stimuli.
Cardiac Muscles
The heart is the only organ that is also a muscle, made of a special type of muscle tissue called cardiac muscle. Cardiac muscle is a striated muscle fiber, like skeletal muscle, but it is under involuntary control. It comprises the walls of the heart and contracts to pump blood through our bodies.
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Frequently asked questions
The muscle system, or muscular system, refers to the muscles of the human body that work the skeletal system and are concerned with movement, posture, and balance.
Skeletal muscles are the most common type of muscle in the body and are attached to bones by tendons. They are voluntary muscles, meaning you control how and when they work. They make up 30-40% of your total body mass.
Smooth muscles are involuntary muscles that line the inside of some organs. They perform essential functions like moving waste through the intestines and helping the lungs expand during breathing.
Cardiac muscles are the muscles that make up the heart. They are striated, like skeletal muscles, but their fibres are laterally connected and their movement is involuntary. The heart is the only organ that is also a muscle.
Muscle pain, weakness, and other symptoms can be signs of serious issues. Muscle injuries and conditions are common. Muscular dystrophy, for example, is a group of disorders associated with progressive muscle weakness and loss of mass, affecting movement and daily activities.
