Logan Steele
The human body has over 600 muscles that help us perform a wide range of functions, from involuntary actions like breathing and pumping blood to voluntary movements like walking and running. Our muscles are made of thousands of small fibres woven together, and they contract and relax to allow our bodies to move. They also help to stabilise joints, maintain posture, and protect our bones and organs by absorbing shock and reducing friction. The brain, nerves and skeletal muscles work together to cause movement, and this is known as the neuromuscular system.
| Characteristics | Values |
|---|---|
| Number of muscles in the body | Over 600 |
| Muscle composition | Thousands of elastic fibres bundled together |
| Types of movements | Voluntary, involuntary |
| Types of muscles | Skeletal, smooth, cardiac |
| Functions | Pumping blood, supporting movement, giving birth, controlling heartbeat, breathing, digestion, temperature regulation, vision, producing movement, sustaining body posture, stabilising joints, protecting bones and organs, etc. |
| Muscle disorders | Muscle weakness, pain, paralysis, neuropathy, atrophy, etc. |
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What You'll Learn
Types of muscle: skeletal, smooth and cardiac
The human body has over 600 muscles, which account for around 40% of a person's weight. They are pieces of soft tissue that help us move, breathe, swallow, and stay alive. The brain, nerves, and muscles work together to cause movement, and this is known as the neuromuscular system.
There are three types of muscle tissue in the human body: skeletal, smooth, and cardiac. Each type has a unique structure and a specific role.
Skeletal muscles are attached to bones and allow movement. They are the only muscles that can be consciously controlled. When these muscles contract, they cause the bones to move. Any action that a person consciously undertakes—such as running, chewing, or writing—involves the use of skeletal muscles. They also move and support other structures. Skeletal muscles have a striated appearance and are composed of long cells called muscle fibres, which are bundled together and supplied by blood vessels.
Smooth muscles are located in the walls of hollow visceral organs, such as the liver, pancreas, stomach, bladder, and intestines. They are also found in the uterus, blood vessels, and the eye. Smooth muscles are arranged in layered sheets that contract in waves along the length of the structure, allowing organs to expand and relax as needed. They facilitate peristaltic waves that move swallowed food and nutrients. In the eye, they change the shape of the lens to bring objects into focus. Smooth muscles are under involuntary control.
Cardiac muscle is found only in the heart and is responsible for pumping blood around the body. It is strong and acts involuntarily, contracting in response to signals from the nervous system to form our heartbeat. The contraction of cardiac muscle is rhythmical, and like skeletal muscle, it has a striated appearance.
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How muscles work: contract and relax
The human body has over 600 muscles, which help with a myriad of functions, from involuntary actions like breathing, swallowing, and pumping blood to voluntary ones like walking, running, and writing. The brain, nerves, and skeletal muscles work together to cause movement, and this is collectively known as the neuromuscular system.
Muscles work by either contracting or relaxing to cause movement. This movement may be voluntary, meaning the movement is consciously made, or involuntary, done without our conscious awareness. The principal functionality of muscle is rooted in its ability to contract and relax. The foundation for muscle contraction is the sarcomere, found in all muscle cells. Each muscle fiber is composed of several hundred to several thousand myofibrils, which contain actin (thin filaments) and myosin (thick filaments). Myosin, a motor protein, powers the muscle to contract by "grabbing" onto actin and "flexing". When myosin releases actin, the muscle relaxes.
The neuromuscular system works as follows: the brain sends a message to the motor neurons, which triggers the release of the chemical acetylcholine from the presynaptic terminals. The muscle responds to acetylcholine by contracting. Skeletal muscles are the only muscles that can be consciously controlled. They are attached to bones, and contracting these muscles causes movement of those bones. Most skeletal muscle contraction is under voluntary control, receiving neural inputs that allow for conscious control of the muscles. However, some movements are reflexive, such as withdrawing a hand from a source of heat.
Smooth muscle, found in the digestive tract, uterus, and blood vessels, is arranged in layered sheets that contract in waves along the structure. Cardiac muscle, found only in the heart, stimulates its own contractions to form our heartbeat. Signals from the nervous system control the rate of contraction.
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Neuromuscular system: how the brain, nerves and muscles work together
The neuromuscular system is a complex network of joints, muscles and nerves that work together to provide a link between thoughts and actions. The system includes all the muscles in the body and the nerves connecting them. The brain, nerves and skeletal muscles work together to cause movement.
The brain sends messages to the muscles through the nerves, which tell the muscle fibres to contract, making the muscles move. This is done through electrical impulses that are sent from the brain to the muscles. The neurons that make up these pathways are called motor neurons. Each muscle fibre is innervated by a single motor neuron, but a single motor neuron may innervate from a few to thousands of muscle fibres, depending on the function of a given muscle. The point of contact between the motor neuron and the muscle is called the neuromuscular junction.
The neuromuscular system is involved in all functions of the body, from heartbeat and breathing to running and jumping. Skeletal muscles are the only muscles that can be consciously controlled. They are attached to bones, and contracting these muscles causes movement of those bones. Any action that a person consciously undertakes involves the use of skeletal muscles, such as running, chewing or writing.
There are about 600 muscles in the human body, which can be categorised into three types: skeletal, smooth and cardiac. Smooth muscle is located in various internal structures including the digestive tract, uterus and blood vessels. Cardiac muscle is specific to the heart and is strong and acts involuntarily.
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Muscle disorders: myopathy, atrophy, dystrophies, myopathies, and more
Muscle disorders, or myopathies, are an alteration in the ability to contract muscles efficiently. Myopathies are diseases that attack muscle fibres, causing weakness, pain, or even paralysis. They can be caused by a variety of factors, including autoimmune, metabolic, or endocrine disorders, as well as exposure to certain medications or toxins. The most common inherited myopathies are muscular dystrophies, which are characterised by progressive degeneration of muscle tissue due to abnormal or insufficient structural support proteins.
There are several types of muscular dystrophies, including Duchenne, Becker, limb-girdle, and Steinert myotonic dystrophy. These diseases lead to loss of strength, increasing disability, and possible deformity. They can be treated with specific medications or by managing the underlying disease causing the myopathy. Toxin-related myopathies can be treated by removing the offending agent or medication.
Muscle atrophy is another disorder that can occur due to nutrition issues, age, or genetics. It is characterised by weakness and the wasting away of muscle tissue. Treatment may include physical therapy or functional electric stimulation.
Other types of myopathies include endocrine myopathies, which are caused by hormone disorders of the thyroid, parathyroid, adrenal, or pituitary glands, and critical illness myopathy, which is transmitted from parents to children. Distal myopathies are muscle diseases that begin in the feet and/or hands, unlike most other dystrophies that affect the arms and legs. Metabolic myopathies are caused by defects in genes that code for enzymes needed for normal muscle function and movement, often resulting in exercise intolerance and exertional muscle pain.
Myopathies are rare diseases that require a multidisciplinary approach for correct diagnosis, monitoring, and treatment. While there is no curative treatment for hereditary myopathies, 70-80% of inflammatory myopathies can be treated successfully.
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Muscle nutrition: glucose, calcium, magnesium, potassium, sodium
The human body has about 600 muscles that help us move, speak, chew, swallow, breathe, and digest food. They also control heartbeat, temperature regulation, and vision. Skeletal muscles are the only muscles that can be consciously controlled. They are attached to bones, and contracting these muscles causes movement of those bones.
Muscles are made of thousands of small fibres woven together. These fibres stretching and pressing together is what moves our organs and body. To work properly, muscle tissue needs particular minerals, electrolytes, and other dietary substances. Glucose from carbohydrates in our diet fuels our muscles.
Calcium is a critical electrolyte for muscle function. It is also important for bone and teeth formation and clotting. Low calcium levels can result in high phosphorus levels, which can lead to muscle spasms. Calcium has an inverse relationship with phosphorus. A high intake of calcium, along with magnesium and potassium, through an increased consumption of fruits and vegetables, may improve blood pressure levels and reduce coronary heart disease and stroke.
Magnesium is another important electrolyte for muscle function. It may lower blood pressure by acting like a natural calcium channel blocker. It also regulates intracellular calcium, sodium, potassium, and pH, as well as left ventricular mass, insulin sensitivity, and arterial compliance. Magnesium supplementation has been shown to improve physical performance.
Potassium is an essential electrolyte for the maintenance of intracellular fluid, as well as the regulation of muscle and heart contractions. A healthy diet should include a higher ratio of potassium to sodium.
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Frequently asked questions
Muscles are pieces of soft tissue that help the body to move, breathe, swallow, and stay alive. There are over 600 muscles in the human body.
Muscles work by contracting and relaxing to cause movement. This movement may be voluntary (conscious) or involuntary (unconscious). The brain, nerves, and skeletal muscles work together to cause movement, which is known as the neuromuscular system.
There are three types of muscle: skeletal, smooth, and cardiac. Skeletal muscles are attached to bones and can be consciously controlled. Smooth muscle is located in the digestive tract, uterus, and blood vessels, and moves involuntarily. Cardiac muscle is specific to the heart and also moves involuntarily.
The main function of muscles is to allow movement, including gross movement (large, coordinated motions) and fine movement. They also help with breathing, speaking, chewing, swallowing, digestion, heartbeat, temperature regulation, vision, and giving birth. Muscles protect the bones and organs by absorbing shock and reducing friction in the joints. They also store and release energy.
If muscles are damaged, it can impact movement, speech, and other functions. Muscle disorders may cause weakness, pain, or paralysis. Muscle atrophy can occur due to nutrition issues, age, and genetics.
