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The human body has more than 600 muscles, which help us do everything from breathing to moving our bodies. These muscles are made of thousands of small fibres woven together, and they store and release energy that the body uses as part of its metabolism. Skeletal muscles, which are the most common type of muscle, are attached to the bones of the skeletal system and make up around 30-40% of a person's body weight. They are under voluntary control and are powered by the oxidation of fats and carbohydrates. In contrast, smooth and cardiac muscles are involuntary muscles that are controlled by the autonomic nervous system.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | More than 600 |
| Percentage of body weight | 30-40% |
| Muscle tissue types | Visceral, cardiac, and skeletal |
| Skeletal muscle composition | Actin and myosin filaments (myofilaments) |
| Skeletal muscle fibres | Red and white |
| Skeletal muscle appearance | Striated (striped) |
| Skeletal muscle functions | Producing movement, maintaining body posture, controlling body temperature, and stabilizing joints |
| Energy storage in muscles | Myoglobin, Creatine phosphate, ATP, and Glycogen |
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What You'll Learn
Skeletal muscle stores energy and nutrients
Skeletal muscles are the most common type of muscle in the human body, accounting for between 30% and 40% of total body mass. They are attached to the bones of the skeletal system and are responsible for physical movement, posture, and breathing.
Skeletal muscles store energy and nutrients. They serve as a storage site for essential substrates such as carbohydrates and amino acids. Skeletal muscles are a primary site for glucose uptake and storage, and they also store amino acids as protein. These amino acids are released when they are needed elsewhere in the body.
Skeletal muscles use a combination of voluntary and involuntary movements to work with the body's systems and functions. They play a crucial role in breathing, speaking, swallowing, digestion, waste elimination, movement, maintaining posture, and stabilising joints.
To maintain their function, skeletal muscle fibres contain several important energy molecules. Myoglobin, a red pigment found in muscles, stores oxygen in a manner similar to hemoglobin in the blood, allowing muscles to continue aerobic respiration even when oxygen levels are low. Creatine phosphate is another chemical that helps keep muscles working by donating its phosphate group to ADP, converting it back into ATP, and providing extra energy to the muscle.
Additionally, skeletal muscle fibres contain energy-storing glycogen, a large macromolecule made of linked glucoses. During muscle activity, glucose is broken off from glycogen molecules to provide an internal fuel supply. When muscles run out of energy, they quickly tire and lose their ability to contract. Therefore, maintaining adequate energy levels in skeletal muscles is essential for optimal physical performance.
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Cardiac muscle stores energy
The human body has more than 600 muscles that help with everything from moving the body to staying alive. The heart is the only organ that is also a muscle. It is made of a special type of muscle tissue called cardiac muscle.
Cardiac muscle is one of the three major categories of muscles in the human body, the other two being smooth muscle and skeletal muscle. Cardiac muscle is striated and under involuntary control. The heart is made up of three layers—the pericardium, myocardium, and endocardium. The myocardium, or cardiac muscle, is responsible for the contractility of the heart and, therefore, the pumping action. The primary function of cardiac muscle is to pump blood into circulation by generating sufficient force.
Cardiac energy is produced in the mitochondria. The mitochondria’s primary function is to generate the energy needed for cardiac metabolism. The primary energy source for cardiac muscles is adenosine triphosphate (ATP), which is used to fuel the contraction of the heart muscles. Cardiac metabolism is a highly concerted plethora of chemical reactions leading to the conversion of substrates for energy production in the form of ATP to sustain cell function and allow contraction.
Cardiac muscle can store excessive glucose as glycogen, which, in turn, provides an essential source of energy for maintaining myocardial performance during periods of reduced substrate and oxygen supplies. The heart is the most energy-consuming muscle in the body, and too little of an energy source can lead to heart failure or other cardiac issues.
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Smooth muscle stores energy
The human body has more than 600 muscles, which help us perform a variety of functions, from moving our bodies to breathing and staying alive. There are three types of muscle tissue in the body: visceral, cardiac, and skeletal. Smooth muscle is one of the three major types of vertebrate muscle tissue, the others being skeletal and cardiac muscle. Smooth muscle is present throughout the body and serves a variety of functions. It is found in the stomach, intestines, bladder, uterus, arteries, veins, and lymph vessels. It helps with digestion, nutrient collection, toxin removal, and the regulation of blood pressure and tissue oxygenation.
Smooth muscle is an involuntary muscle, controlled by the autonomic nervous system. It can contract phasically with rapid contraction and relaxation, or tonically with slow and sustained contraction. Smooth muscle contraction is caused by the sliding of myosin and actin filaments over each other, a process known as crossbridge cycling. The energy for this process is provided by the hydrolysis of ATP, which is a molecule that stores energy. Myosin functions as an ATPase, utilizing ATP to produce a molecular conformational change and generate movement. The shape of smooth muscle is fusiform, which is round in the center and tapering at each end.
Smooth muscle has greater elastic properties than striated muscle, which is important in organ systems like the urinary bladder, where the preservation of contractile tone is essential. Smooth muscle can maintain high tension at low energy consumption, a state known as the latch state. It has the ability to sustain force at low energy costs due to the presence of certain myosin crossbridges, termed latch-bridges, that cycle very slowly. This allows smooth muscle to efficiently store and utilize energy, making it an important component of the body's energy management system.
Additionally, muscle fibers contain several energy-storing molecules, such as myoglobin, creatine phosphate, and glycogen, which help to keep muscles functioning. Myoglobin, a red pigment found in muscles, stores oxygen and allows muscles to continue aerobic respiration even when oxygen levels are low. Creatine phosphate provides extra energy to the muscle by donating its phosphate group to ADP, converting it back into ATP. Glycogen, a large macromolecule made of linked glucoses, serves as an internal fuel supply for active muscles. These energy molecules work together to ensure that smooth muscles have the necessary energy to perform their vital functions in the body.
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Muscle fatigue and oxygen debt
The human body has over 600 muscles, which help with everything from breathing and speaking to moving and pumping blood through the heart. These muscles are made up of thousands of small fibres woven together, which stretch and press together to move the body and its organs.
Oxygen debt, also known as Excess Post-exercise Oxygen Consumption (EPOC), refers to the amount of additional oxygen required by the body to restore its normal metabolic processes after engaging in intense or prolonged physical activity. During muscle contraction, the body primarily uses ATP for energy. When oxygen availability is limited, the body relies on a cycle of anaerobic glycolysis and fermentation to produce ATP, leading to an accumulation of lactic acid in the muscles. This increase in lactic acid causes temporary muscle fatigue. To clear this lactic acid and restore normal ATP and creatine phosphate levels, the body needs to consume more oxygen, creating an oxygen debt.
Myoglobin, a red pigment found in muscles, contains iron and stores oxygen in a manner similar to hemoglobin in the blood. The oxygen from myoglobin allows muscles to continue aerobic respiration in the absence of oxygen. Another chemical that helps to keep muscles working is creatine phosphate, which donates its phosphate group to ADP to turn it back into ATP to provide extra energy to the muscle.
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Skeletal muscle anatomy
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 of the skeletal system 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. Nerves in our somatic nervous system send signals to make them function. For example, when we reach for a book on a shelf, we are using the skeletal muscles in our neck, arm, and shoulder.
Skeletal muscles are named based on various factors, including their location, origin, insertion, number of origins, shape, size, direction, and function. Many muscles derive their names from their anatomical region. For instance, the rectus abdominis and transverse abdominis are found in the abdominal region. Some muscles, like the tibialis anterior, are named after the bone they are attached to. Other muscles use a combination of these factors, like the brachioradialis, which is named after a region (brachial) and a bone (radius).
Skeletal muscles contribute to the maintenance of homeostasis in the body by generating heat. Muscle contraction requires energy, and when ATP is broken down, heat is produced. This heat is noticeable during exercise, when sustained muscle movement raises body temperature, and in cases of extreme cold, when shivering produces random skeletal muscle contractions to generate heat. Skeletal muscles also play a role in metabolism by storing and releasing energy.
Each skeletal muscle is an organ that consists of various integrated tissues, including skeletal muscle fibres, blood vessels, nerve fibres, and connective tissue. They have three layers of connective tissue, called "mysia," that enclose them and provide structure. Each muscle is wrapped in a sheath of dense, irregular connective tissue called the epimysium, which allows the muscle to contract and move powerfully while maintaining its structural integrity. Skeletal muscle fibres are red and white, and they appear striated or striped, hence their other name, striated muscles.
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Frequently asked questions
Muscles are pieces of soft tissue throughout your body that help you do everything from holding your body still to running a marathon. There are more than 600 muscles in the human body, making up around 35-40% of body weight in healthy young adults.
There are three types of muscles: skeletal, smooth, and cardiac. Skeletal muscles are the most common type and are attached to the bones of the skeletal system. Smooth muscles are under involuntary control and are found in the walls of blood vessels and structures such as the urinary bladder, intestines, and stomach. The heart is made up of cardiac muscles, which are responsible for its rhythmic contractions.
Muscles use a combination of voluntary and involuntary movements to work with nearly all the body's systems and functions. They store and release energy that the body uses as part of its metabolism. Muscle fibres contain several important energy molecules such as myoglobin, creatine phosphate, and glycogen, which provide energy to the muscles.
