Victor Forge
The human body is an intricate machine, with over 600 muscles that work in harmony to keep us alive and moving. These muscles are made of thousands of small fibres that stretch and press together, allowing us to perform a wide range of movements and functions. There are three main types of muscle tissue: skeletal, cardiac, and smooth muscle. Skeletal muscles, attached to our bones, enable us to move and maintain posture. Cardiac muscles, found in the heart, are responsible for pumping blood and keeping us alive. Smooth muscles, located in our organs, help with various functions like digestion and breathing. Together, these muscle tissues form the foundation of our physicality, working tirelessly to keep our bodies functioning optimally.
| Characteristics | Values |
|---|---|
| Number of muscles in the body | More than 600 |
| Muscle tissue types | 3 (skeletal, cardiac, and smooth) |
| Skeletal muscle composition | 30-40% of total body mass |
| Skeletal muscle appearance | Striated |
| Skeletal muscle control | Voluntary |
| Cardiac muscle appearance | Striated |
| Cardiac muscle control | Involuntary |
| Cardiac muscle location | Middle layers of the heart |
| Smooth muscle appearance | Non-striated |
| Smooth muscle control | Involuntary |
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What You'll Learn
Skeletal muscle is the most common type of muscle in the body
There are more than 600 muscles in the human body, which is made up of thousands of small fibres woven together. These fibres stretching and pressing together is what moves your organs or body. There are three types of muscle tissue in the body: skeletal, cardiac, and smooth muscle.
Skeletal muscles are also known as muscle fibres and are much longer than other types of muscle tissue. They are attached by tendons to the bones of a skeleton. Skeletal muscle cells are striated, having a striped appearance due to the arrangement of the sarcomeres. They contain multiple fascicles, or bundles of muscle fibres. Each individual fibre and each muscle is surrounded by a type of connective tissue layer of fascia.
Skeletal muscles play a vital role in everyday activities. They are used to breathe, eat, and move your bones. They also function as an endocrine organ by secreting myokines, a wide range of cytokines and other peptides that act as signalling molecules. Myokines are secreted into the bloodstream after muscle contraction. Interleukin 6 (IL-6) is the most studied myokine, but other muscle contraction-induced myokines include BDNF, FGF21, and SPARC.
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Cardiac muscle is an involuntary muscle
There are three types of muscle tissue in the human body: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles, meaning that we can control how and when they move and work. Cardiac and smooth muscle, on the other hand, are involuntary muscles controlled by the autonomic nervous system.
Cardiac muscle, also known as myocardium or heart muscle, is the involuntary muscle tissue that constitutes the main tissue of the heart wall. It forms a thick middle layer (myocardium) between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium). The endocardium is not cardiac muscle but is made up of simple squamous epithelial cells that form the inner lining of the heart chambers and valves. The pericardium, on the other hand, is a fibrous sac surrounding the heart. The myocardium forms the bulk of the heart and is made up of individual cardiac muscle cells or cardiomyocytes, which are joined by intercalated discs. These discs contain gap junctions and desmosomes that allow the cardiomyocytes to contract together synchronously, enabling the heart to work as a pump.
Cardiac muscle cells are striated, branched, and contain many mitochondria. They are surrounded by an extracellular matrix produced by supporting fibroblast cells. Each cell contains myofibrils, specialized protein contractile fibers of actin and myosin that slide past each other during contraction. The generation of a cardiac action potential is involuntary and proceeds via a process known as excitation-contraction coupling (ECC). This process involves electrical stimulation triggering the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum. The rise in calcium causes the cell's myofilaments to slide past each other, resulting in contraction.
The coordinated contraction of cardiac muscle cells is vital for the heart's pumping action. When the sheets of muscle contract in a coordinated manner, they allow the ventricle to squeeze in several directions simultaneously – longitudinally, radially, and with a twisting motion. This complex movement ensures that the maximum possible amount of blood is pumped out of the heart with each heartbeat.
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Smooth muscle is non-striated and involuntary
There are three types of muscle tissue in the human body: skeletal, cardiac, and smooth muscle. Smooth muscle is non-striated and involuntary.
Skeletal muscles are the most common type of muscle in the body and are attached to the bones. They are under voluntary control, meaning that a person can control how and when these muscles work. Smooth muscle, on the other hand, is found in the walls of hollow visceral organs, such as the liver, pancreas, intestines, blood vessels, digestive tract organs, urinary bladder, and uterus. They are non-striated, meaning their structure is less organized than striated muscles, and they are under involuntary control.
The involuntary muscles are controlled by the autonomic nervous system, which means they work without conscious thought. For example, muscles in the urinary system help rid the body of waste and toxins, and smooth muscles in the gut are responsible for the churning of the stomach.
Smooth muscle contractions are relatively slow, but they can contract over a much greater range of lengths than striated muscles. They can also maintain contractions for longer periods. The ratio of thin to thick filaments is much higher in smooth muscle than in striated muscle.
The specialized function of smooth muscle has been of particular interest to researchers, especially in the context of diseases prevalent in industrialized societies, such as hypertension, asthma, and gastrointestinal motility disorders.
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Skeletal muscles rarely work alone
There are over 600 muscles in the human body, and skeletal muscles are the most common type, comprising 30% to 40% of total body mass. They are attached to the bones by tendons, which are cords made of tough connective tissue, and allow us to perform a wide range of movements and functions.
Skeletal muscles are also classified into compartments. For instance, the quadriceps muscles contain around 52% type I fibres, while the soleus is composed of about 80% type I fibres. The orbicularis oculi muscle of the eye contains only about 15% type I fibres. These muscle fibres are formed from the fusion of developmental myoblasts in a process known as myogenesis, resulting in long multinucleated cells. Each muscle can contain thousands of fibres, and these fibres contract to allow the muscles to move bones.
Additionally, skeletal muscles are voluntary muscles, meaning you control how and when they work. They are connected to the somatic nervous system, which sends signals to make them function. For example, if you reach for a book on a shelf, you are using skeletal muscles in your neck, arm, and shoulder.
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Skeletal muscle is made of thousands of fibres
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. Skeletal muscles are voluntary muscles, meaning we control how and when they move and work.
Each skeletal muscle is an organ that consists of various integrated tissues, including skeletal muscle fibres, blood vessels, nerve fibres, and
Skeletal muscle fibres are flexible and range from less than half an inch to just over 3 inches in diameter. They usually span the length of the muscle and are surrounded by three layers of connective tissue called mysia, which enclose them, provide structure to the muscle, and compartmentalise the muscle fibres within the muscle. The outermost layer of tissue surrounding the entire muscle is called the epimysium. The middle layer, which surrounds bundles of muscle fibres, is called the perimysium. The innermost layer, which surrounds individual muscle fibres, is called the endomysium.
The tension created by the contraction of the muscle fibres is transferred through the connective tissue layers, to the tendon, and then to the periosteum to pull on the bone for movement of the skeleton.
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