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Skeletal muscle is the most common type of muscle in the human body, accounting for 30% to 50% of total body mass. These muscles are attached to the bones and are under voluntary control. They are composed of skeletal muscle fibers, blood vessels, nerve fibers, and connective tissue. Skeletal muscle fibers are red and white and have a striped or striated appearance under a microscope. This striated appearance is caused by repeating bands of the proteins actin and myosin that are present along the length of myofibrils. Cardiac muscles are also striated, but they are involuntary muscles and are only found in the heart.
| Characteristics | Values |
|---|---|
| Definition | Muscle tissue that features repeating functional units called sarcomeres |
| Types | Skeletal muscle, cardiac muscle |
| Skeletal muscle composition | Skeletal muscle fibers, blood vessels, nerve fibers, connective tissue |
| Skeletal muscle appearance | Striped or striated |
| Skeletal muscle function | Breathing, movement, posture maintenance |
| Skeletal muscle control | Voluntary |
| Cardiac muscle location | Walls of the heart |
| Cardiac muscle function | Pump blood throughout the body, maintain blood pressure |
| Cardiac muscle control | Involuntary |
| Cardiac muscle appearance | Striated |
| Cardiac muscle composition | Branched, intercalated disks, one nucleus per cell |
| Fiber types | Type 1 (red fibers), Type 2 (white fibers) |
| Type 1 characteristics | Greater content of myoglobin, more mitochondria, higher capillary density, greater blood flow, depend on aerobic respiration, function in postural or sustained activity |
| Type 2 characteristics | Rich in glycogen, smaller mitochondrial population, more efficient under anaerobic respiration |
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What You'll Learn
Skeletal muscle is striated and the most common muscle type in the body
Skeletal muscle, also known as striated muscle, is the most common muscle type in the body, making up between 30% and 50% of total body mass. Skeletal muscles are attached to the skeleton and are under voluntary control, meaning that we can decide how and when they move. They consist of flexible muscle fibres that range from less than half an inch to just over 3 inches in diameter. Skeletal muscle fibres are multinucleated and contain many nuclei, unlike cardiac and smooth muscle cells, which have a single nucleus.
Skeletal muscle is composed of bundles of myofibres, which are the multinucleated cells of muscle. These myofibres are formed from the fusion of developmental myoblasts in a process known as myogenesis, resulting in long multinucleated cells. Skeletal muscle cells are much longer than other types of muscle tissue cells. Each muscle fibre contains sarcolemma, sarcoplasm, and sarcoplasmic reticulum. The functional unit of a muscle fibre is called a sarcomere, and these are visible under a microscope, giving skeletal muscle its striated appearance.
The primary function of skeletal muscle is contraction, which enables breathing, movement, and posture maintenance. Skeletal muscle also functions as an endocrine organ by secreting myokines, which are believed to mediate the health benefits of exercise. Myokines are secreted into the bloodstream after muscle contraction, with Interleukin 6 (IL-6) being the most studied example. Skeletal muscle is also responsible for producing body heat, contributing to 85% of the body's heat.
Skeletal muscle is able to regenerate effectively due to the presence of satellite cells, which are dormant in healthy skeletal muscle tissue. The regeneration process occurs in three phases: the inflammatory response, the activation, differentiation, and fusion of satellite cells, and the maturation and remodelling of newly formed myofibrils. This process is initiated by the necrosis of damaged muscle fibres, which induces an inflammatory response.
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Cardiac muscle is striated and found in the heart
Muscle tissue is classified into three types according to structure and function: skeletal, smooth, and cardiac. Striated muscle tissue is a muscle tissue that features repeating functional units called sarcomeres. Under the microscope, sarcomeres are visible along muscle fibres, giving a striated appearance to the tissue. The two types of striated muscle are skeletal muscle and cardiac muscle.
Cardiac muscle, also called heart muscle or myocardium, is one of the three major categories of muscles found within the human body, the others being smooth muscle and skeletal muscle. Cardiac muscle forms the contractile walls of the heart. The cells of cardiac muscle, known as cardiomyocytes, also appear striated under the microscope. Cardiac muscle is short, branched, appears striated, and has a single central nucleus. It contracts to pump blood and is found only in the heart.
The heart is made up of three layers—pericardium, myocardium, and endocardium. The endocardium is not cardiac muscle and is comprised of simple squamous epithelial cells and forms the inner lining of the heart chambers and valves. The pericardium is a fibrous sac surrounding the heart, consisting of the epicardium, pericardial space, parietal pericardium, and fibrous pericardium. The cardiac muscle is responsible for the contractility of the heart and, therefore, the pumping action. The cardiac muscle must contract with enough force and blood to supply the metabolic demands of the entire body.
Cardiac muscle cells are located in the walls of the heart, appear striped (striated), and are under involuntary control. They contain many mitochondria which provide the energy needed for the cell in the form of adenosine triphosphate (ATP), making them highly resistant to fatigue. Each cardiomyocyte needs to contract in coordination with its neighbouring cells, working to efficiently pump blood from the heart. If this coordination breaks down, then the heart may not pump at all, such as during abnormal heart rhythms like ventricular fibrillation.
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Skeletal muscle fibres are red and white
Skeletal muscle, also known as striated muscle, is the major tissue component in the body, accounting for 40% to 50% of body weight. It is composed of skeletal muscle fibres, blood vessels, nerve fibres, and connective tissue. Skeletal muscle fibres are of two types: Type 1, or red fibres, and Type 2, or white fibres.
Type 1 muscle fibres are referred to as red fibres due to their greater content of myoglobin and higher number of mitochondria. They also have a higher capillary density and greater blood flow. These fibres depend on aerobic respiration and are used in postural or sustained activities. Type 1 fibres are slower to contract but are more resistant to fatigue.
Type 2 muscle fibres, or white fibres, are rich in glycogen and have a smaller number of mitochondria. They are more efficient under anaerobic respiration and are used in shorter bouts of high-intensity exercise. White fibres contract faster but fatigue more quickly.
The different types of skeletal muscle fibres work together to enable breathing, movement, and posture maintenance. The regeneration process of skeletal muscle is facilitated by satellite cells, which are dormant in healthy skeletal muscle tissue. This regeneration process can occur in three phases: the inflammatory response, the activation, differentiation, and fusion of satellite cells, and the maturation and remodelling of newly formed myofibrils.
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Skeletal muscle can be controlled consciously
Skeletal muscle, which accounts for 40-50% of body weight, is the only voluntary muscle tissue in the human body and can be controlled consciously. It is composed of skeletal muscle fibers, blood vessels, nerve fibers, and connective tissue. Skeletal muscle fibers are striated, multinucleated cells ranging from 10 to 100 micrometers in diameter and several centimeters long. They are found in muscles attached to the skeleton, such as those in the arms, legs, neck, back, and trunk.
The function of skeletal muscle is to contract in response to a stimulus, causing the connected bones to move closer to each other. This results in movements such as speaking, walking, or writing. Skeletal muscles also play a role in sustaining body posture and position, maintaining body temperature, storing nutrients, and stabilizing joints.
The appearance of skeletal muscle tissue under a microscope is striated due to the repeating functional units called sarcomeres. Each muscle fiber contains sarcolemma, sarcoplasm, and sarcoplasmic reticulum. The sarcolemma is a tubular sheath that encases and defines each muscle fiber, forming a barrier between extracellular and intracellular compartments. The sarcomere is the basic functional unit of a muscle fiber, composed of actin and myosin myofilaments.
Skeletal muscle can be classified into different fiber types, such as Type 1 (red fibers) and Type 2 (white fibers), based on functional properties, contraction velocity, resistance to fatigue, and oxidative capacities. Type 1 fibers have greater endurance capabilities due to their higher mitochondrial content and blood flow, while Type 2 fibers are more suited for anaerobic respiration and are often used for powerful but short-duration movements.
The conscious control of skeletal muscle is made possible by neural inputs from motor neurons. Each motor neuron controls several muscle cells, and when stimulated, they release calcium ions from the sarcoplasmic reticulum, leading to muscle contraction. Disorders affecting the nerves that control skeletal muscles, such as neuromuscular disorders, can result in muscle weakness or an inability to control these voluntary movements.
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Skeletal muscle can regenerate better than cardiac muscle
Skeletal muscle and cardiac muscle are two types of striated muscle tissue. Striated muscle tissue features repeating functional units called sarcomeres, which are visible along muscle fibres under a microscope, giving a striated appearance.
Skeletal muscle is under direct voluntary control and is wrapped in epimysium, allowing structural integrity during contractions. Skeletal muscle fibres occur in muscles attached to the skeleton. Skeletal muscle can regenerate better than cardiac muscle due to the presence of satellite cells, which are a type of stem cell. These satellite cells are dormant in healthy skeletal muscle tissue and are stimulated to divide and repair damaged muscle fibres when the muscle is damaged. The regeneration process can be divided into three phases: the inflammatory response, the activation, differentiation, and fusion of satellite cells, and the maturation and remodelling of newly formed myofibrils.
Cardiac muscle cells, on the other hand, are located in the walls of the heart and are under involuntary control. These muscle cells respond to signals from the autonomic nervous system to increase or decrease the heart rate. Unlike skeletal muscle, cardiac muscle cells do not have equivalent regenerative cells like satellite cells. When cardiac muscle cells die, they are replaced by scar tissue, which cannot contract. This accumulation of scar tissue leads to a loss of contractile power in the heart, impacting its ability to pump blood effectively.
While cardiac muscle does exhibit some minor regeneration capabilities, it is primarily through stem or progenitor cell contribution rather than the cell cycle re-entry of differentiated cardiomyocytes. The limited regenerative capacity of cardiac muscle is a focus of research, with a combination of pharmacological approaches, tissue engineering, and cell transplantation being explored as potential therapies to enhance regeneration.
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Frequently asked questions
Striated muscles are muscles that feature repeating functional units called sarcomeres, which give them a striped appearance under a microscope.
The two types of striated muscle are skeletal muscle and cardiac muscle.
Skeletal muscles are the most common type of muscle in the body. They are attached to the bones and are under voluntary control.
Cardiac muscles are found in the walls of the heart and are under involuntary control. Their contractions pump blood throughout the body and maintain blood pressure.
There are two main categories of skeletal muscle fibres: extrafusal and intrafusal. Intrafusal fibres are further divided into nuclear chain and nuclear bag fibres, collectively known as the muscle spindle.
