Logan Steele
Muscles are what allow us to move. They are made of thousands of small fibres, bundled tightly together, that stretch and press together to move our organs and body. There are about 600 muscles in the human body, and they are categorised into three types of tissue: skeletal, smooth, and cardiac. Skeletal muscles are attached to the bones via tendons and are under our conscious control, meaning they are also known as voluntary muscles. Smooth muscles are involuntary and are found within the walls of organs and structures like the intestines, stomach, and bladder. Cardiac muscle is found only in the walls of the heart and is also involuntary.
Characteristics and Values of Muscles
| Characteristics | Values |
|---|---|
| Definition | A soft tissue, one of the four basic types of animal tissue |
| Number of muscles in the human body | 600 |
| Muscle composition | Thousands of elastic fibres bundled tightly together |
| Muscle movement | Contraction or relaxation |
| Types of movement | Voluntary, controlled by the brain; or involuntary, controlled by other body systems |
| Types of muscle tissue | Skeletal, cardiac, and smooth |
| Skeletal muscle composition | Striated muscle tissue with elongated, multinucleate muscle cells called muscle fibres |
| Skeletal muscle shape | Spindle, flat, triangular, or circular |
| Skeletal muscle fibre types | Type I (slow-twitch) and type II (fast-twitch) |
| Cardiac muscle location | Walls of the heart |
| Smooth muscle location | Walls of hollow organs of the body (except the heart) |
| Muscle health tests | Complete blood count, EMG, MRI, muscle biopsy |
| Muscle health maintenance | Exercise, balanced diet, smart food choices |
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What You'll Learn
- Skeletal muscle is attached to the bones via tendons and is under conscious control
- Cardiac muscle is found in the heart and contracts involuntarily to pump blood
- Smooth muscle is found in the walls of hollow organs and performs essential functions like breathing and digestion
- Muscle fibres are made of contractile proteins called actin and myosin which interact to cause movement
- Muscles are controlled by the brain and nervous system, either voluntarily or involuntarily
Skeletal muscle is attached to the bones via tendons and is under conscious control
There are about 600 muscles in the human body, and they make up a large part of our body mass. An average adult man is made up of 42% skeletal muscle, while an average adult woman is made up of 36%.
Skeletal muscle is a specialised tissue that is attached to bones and allows movement. It is also called striated muscle due to its striped appearance under a microscope. This striated appearance is caused by a pattern of alternating dark A bands and light I bands. Skeletal muscle is attached to the bones via tendons, which can be found all over the body.
The brain, nerves, and skeletal muscles work together to cause movement, and this is collectively known as the neuromuscular system. Skeletal muscles are under conscious control, meaning they are voluntary muscles. When you think about moving a part of your body, the appropriate muscles are activated.
Skeletal muscles are broadly classified into two fibre types: type I (slow-twitch) and type II (fast-twitch). Type I muscles move slowly, like back muscles that help with posture. Type II muscles contract quickly and use short bursts of energy, like the biceps in your upper arm.
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Cardiac muscle is found in the heart and contracts involuntarily to pump blood
A muscle is a soft tissue that is one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Cardiac muscle is a specialised type of tissue that is only found in the heart. It is a powerful muscle that contracts involuntarily to pump blood around the body.
Cardiac muscle tissue, also known as myocardium, forms the middle layers of the heart. It is highly organised and contains many types of cells, including fibroblasts, smooth muscle cells, and cardiomyocytes. The cardiac muscle cells work together to produce the rhythmic, wave-like contractions known as the heartbeat. These contractions are caused by electrical impulses from the nervous system, which result in the release of calcium, which attaches to troponin C. This causes tropomyosin to detach from the myosin-binding sites on actin, allowing actin and myosin to form a cross-bridge and causing the cardiac muscle cell to contract.
The force and frequency of these contractions, known as cardiac output, are determined by the contractile forces of the cardiac muscle and the frequency of their activation. This is influenced by metabolic demand, which can change depending on the body's needs. Regular aerobic exercise can help strengthen cardiac muscle tissue and lower the risk of cardiovascular conditions such as heart attacks and strokes.
Cardiac muscle cells are striated or branched and contain many mitochondria. They are under involuntary control, meaning they contract without conscious intervention. This is in contrast to skeletal muscles, which are under conscious control and are therefore considered voluntary muscles. Smooth muscles are also involuntary and are found within the walls of organs and structures such as the oesophagus, stomach, intestines, and blood vessels.
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Smooth muscle is found in the walls of hollow organs and performs essential functions like breathing and digestion
There are about 600 muscles in the human body, and they have a range of functions, from pumping blood around the body to supporting movement, lifting heavy weights, and even giving birth. Muscles are made of thousands of small fibres woven together, and they produce their own connective tissue.
One type of muscle is smooth muscle, which is located in the walls of hollow organs such as the stomach, urinary bladder, and intestines. Smooth muscle is also found in the uterus, blood vessels, and the respiratory system. It is arranged in layered sheets that contract in waves along the length of the structure.
Smooth muscle is an involuntary muscle, meaning it contracts and relaxes without conscious awareness. Its contractile function is initiated by a Ca2+-calmodulin interaction to stimulate phosphorylation of the light chain of myosin. The triggers for smooth muscle contraction include hormones, neural stimulation by the autonomic nervous system, and local factors. For example, in the walls of visceral organs, stretching the muscle can trigger its contraction (the stretch-relaxation response).
Smooth muscle plays an important role in breathing and digestion. In the respiratory system, it helps the lungs expand and contract during breathing. In the digestive system, it moves waste through the intestines. Smooth muscle can maintain a muscle tone when the organ empties and shrinks, preventing "flabbiness" in the empty organ.
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Muscle fibres are made of contractile proteins called actin and myosin which interact to cause movement
A muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to contract.
Muscles are made of thousands of small fibres woven together. Each bundle of fibres is wrapped in a thin, transparent membrane called a perimysium. An individual muscle fibre is made up of blocks of proteins called myofibrils, which contain a specialised protein called myoglobin. Myofibrils also contain molecules that provide the oxygen and energy required for muscle contraction. Each myofibril contains filaments that fold together when given the signal to contract. This shortens the length of the muscle fibre, which, in turn, shortens the entire muscle if enough fibres are stimulated at the same time.
The three distinct types of muscle cells in vertebrates are: skeletal muscle, which is responsible for all voluntary movements; cardiac muscle, which pumps blood from the heart; and smooth muscle, which is responsible for involuntary movements of organs such as the stomach, intestine, uterus, and blood vessels. Skeletal and cardiac muscles are types of striated muscle tissue, while smooth muscle is non-striated.
Skeletal muscle tissue is striated, consisting of elongated, multinucleate muscle cells called muscle fibres, and is responsible for movements of the body. Skeletal muscles are under conscious control and are, therefore, also known as voluntary muscles. They are attached to bones and allow movement.
Cardiac muscle tissue is found only in the walls of the heart as myocardium and is an involuntary muscle controlled by the autonomic nervous system. Smooth muscle fibres do not contain sarcomeres but use actin and myosin contraction to constrict blood vessels and move the contents of hollow organs in the body.
Muscle fibres are made of contractile proteins called actin and myosin, which interact to cause movement. Actin is a globular protein that combines with other actin globules to form two intertwined strands with positive and negative ends. The double-stranded actin filaments are covered by tropomyosin, which blocks the interaction between myosin and actin when the muscle is inactive. The thick filaments are made from the protein myosin, which has one pair of heavy chains and two pairs of light chains. The myosin heads have an actin-binding site that helps them attach to the thin filaments.
The interaction of actin and myosin provides a basis for molecular models of force generation and contraction in living muscle. The signal for a muscle to contract originates in the nervous system and is transmitted to the muscle at the neuromuscular junction, a point of contact between the motor nerve and the muscle. The complex process leading to muscle contraction, called excitation-contraction coupling, begins when an action potential causes depolarization in the myocyte membrane.
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Muscles are controlled by the brain and nervous system, either voluntarily or involuntarily
A muscle is made up of thousands of elastic fibres bundled tightly together. Each bundle is wrapped in a thin transparent membrane called a perimysium. An individual muscle fibre is made up of blocks of proteins called myofibrils, which contain a specialised protein called myoglobin, and molecules to provide the oxygen and energy required for muscle contraction.
The brain, nerves, and skeletal muscles work together to cause movement—this is collectively known as the neuromuscular system. The nervous system orders the body's muscles to contract. We can deliberately order skeletal muscles to contract, which enables us to perform movements. These voluntary movements are commanded by the motor cortex, the zone of the cerebrum located behind the frontal lobe. The motor cortex sends a neural message that moves through the brain stem along the spinal cord and into the neural network to the muscle being commanded. Stimulated by the neural message, the skeletal muscle contracts.
Voluntary movements are actions that we choose to perform. We use our nervous system to control these movements. Skeletal muscles are also known as voluntary muscles because they are under our conscious control. They work with our bones, tendons, and ligaments to support our weight and move us. Tendons attach skeletal muscles to bones all over our body.
However, not all muscles are under our voluntary control. Some muscles, like those of the stomach wall, are controlled directly by regions deep within the brain, such as the hypothalamus. During digestion, the stomach contracts without our being aware of it. These involuntary contractions ensure that food is digested, even while we sleep.
Other examples of involuntary muscles include the heart, which beats on its own without our input, and smooth muscles, which line the inside of some organs. Smooth muscles perform essential functions such as moving waste through our intestines and helping our lungs expand when we breathe.
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Frequently asked questions
A muscle is a soft tissue made up of thousands of elastic fibres bundled tightly together. Each bundle is wrapped in a thin transparent membrane called a perimysium. There are about 600 muscles in the human body, which support almost every part of the body.
There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Skeletal muscles are attached to the bones and allow movement. Cardiac muscle is found in the heart and beats on its own without our input. Smooth muscle is found within the walls of organs and structures like the intestines, stomach, and bladder.
Muscles work by contracting and relaxing to cause movement. This movement may be voluntary, controlled by our nervous system, or involuntary, done without our conscious awareness. Skeletal and cardiac muscles are types of striated muscle tissue, while smooth muscle is non-striated.
