Dominic Stone
The human body has over 600 muscles that help us do everything from breathing and pumping blood to lifting heavy weights and giving birth. Muscles are pieces of soft tissue made of thousands of small fibres woven together. These fibres contract and press together to move our organs and body. There are three types of muscles in the body: skeletal, smooth and cardiac. Skeletal muscles are voluntary muscles, meaning we control how and when they move. Smooth and cardiac muscles are involuntary muscles that our autonomic nervous system controls.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | 600+ |
| Muscle composition | Thousands of small fibres woven together |
| Types of muscle tissue | Skeletal, cardiac, smooth |
| Muscle movement | Contraction, relaxation |
| Types of movement | Voluntary, involuntary |
| Muscle control | Brain, nerves, somatic nervous system |
| Muscle function | Movement, support, pumping blood |
| Muscle appearance | Striated, non-striated |
| Muscle layers | Epimysium, perimysium, endomysium |
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What You'll Learn
Muscle types: skeletal, cardiac, and smooth
There are over 600 muscles in the human body, which can be categorised into three types of muscle tissue: skeletal, cardiac, and smooth.
Skeletal Muscle
Skeletal muscles are attached to bones via tendons and are responsible for movement and posture. They are voluntary muscles, meaning you can control their movement. Skeletal muscles are the most common type of muscle in the human body, accounting for 30-40% of total body mass. They consist of thousands of muscle fibres that are bundled together, giving them a striped or striated appearance. Skeletal muscles can be further classified into two fibre types: type I (slow-twitch) and type II (fast-twitch). Type I muscles are slow oxidative, dense with capillaries, and rich in mitochondria and myoglobin, giving them a red colour. Type II muscles, on the other hand, contract very quickly and produce a lot of force but tire quickly.
Cardiac Muscle
Cardiac muscle tissue, also known as myocardium, is found only in the walls of the heart. It is an involuntary muscle, meaning it contracts without conscious intervention, controlled by the autonomic nervous system. Cardiac muscle is striated, containing sarcomeres in highly regular arrangements of bundles. It connects at irregular angles known as intercalated discs. Cardiac muscle propels blood and ensures proper oxygenation of each cell in the body.
Smooth Muscle
Smooth muscle is non-striated and involuntary. It is found within the walls of various organs and structures, including the oesophagus, stomach, intestines, lungs, blood vessels, and skin. Smooth muscle uses contractile force to propel various contents across the lumen of multiple organ systems. Smooth muscle cells are often rounded in the centre and tapered off at the sides, and they are arranged in sheets rather than spindles, giving them a smooth appearance.
These three types of muscles work together to facilitate movement and perform vital functions that keep the human body alive.
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Muscle composition: muscle fibres and tissue
Muscles are pieces of soft tissue made up of thousands of small fibres woven together. These fibres stretch and press together to move the organs and different parts of the body. There are over 600 muscles in the human body, comprising 30% to 40% of total body mass.
There are three types of muscle tissue in vertebrates: skeletal, cardiac, and smooth muscle. Skeletal muscle is the most common type of muscle in the body. It is attached to bones by tendons and is under voluntary control, meaning that it moves when you think about moving that part of the body. Skeletal muscle cells are much longer than the other types of muscle tissue and are also known as muscle fibres. They are striated, having a striped appearance due to the arrangement of the sarcomeres. Each muscle fibre is composed of several hundred to several thousand myofibrils, which are made up of actin (thin filaments), myosin (thick filaments), and support proteins. The arrangement of actin and myosin gives skeletal muscle its microscopic striated appearance and creates functional units called sarcomeres. Skeletal muscles can be further categorised into two fibre types: type I (slow-twitch) and type II (fast-twitch).
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. Cardiac muscle is striated like skeletal muscle, containing sarcomeres in highly regular arrangements of bundles. While skeletal muscles are arranged in regular, parallel bundles, cardiac muscle connects at branching, irregular angles known as intercalated discs.
Smooth muscle is non-striated and involuntary. It is found within the walls of organs and structures such as the oesophagus, stomach, intestines, bronchi, uterus, urethra, bladder, blood vessels, and the arrector pili in the skin that control the erection of body hair.
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Muscle movement: voluntary and involuntary
Muscles are pieces of soft tissue that enable movement in the body. There are over 600 muscles in the human body, comprising 30% to 40% of total body mass. These muscles are made up of thousands of small fibres woven together, allowing them to stretch and press together to move the body and its organs.
Muscles perform two types of movements: voluntary and involuntary. Voluntary movements are actions that an individual consciously controls and chooses to perform. These movements are controlled by the somatic nervous system and include skeletal muscles, which attach to bones and allow for a wide range of movements. Examples of voluntary movements include flicking a thumb to scroll through an article on a phone and sprinting around a track.
Involuntary movements occur automatically without conscious thought and are controlled by the autonomic nervous system. They include smooth and cardiac muscles, which are found in the internal organs and help with essential bodily functions such as digestion and circulation. For example, the heart beating and the movement of ribs during breathing are involuntary movements.
While most muscles fall clearly into one of these two categories, reflexes represent a grey area. Reflexes are a form of non-conscious activation of skeletal muscles, yet they arise through the activation of the central nervous system.
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Muscle function: from pumping blood to lifting weights
The human body has more than 600 muscles that help us do everything from moving our bodies to breathing and staying alive. Muscles are pieces of soft tissue made of thousands of small fibres woven together. These fibres stretching and pressing together is what moves our organs and body.
There are three types of muscle tissue in vertebrates: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles, meaning we control how and when they move. They are attached to bones and allow us to perform a wide range of movements and functions. Skeletal muscles make up between 30% and 40% of our total body mass. They also help with maintaining body temperature, storing nutrients, and stabilising joints.
Cardiac and smooth muscle are involuntary muscles controlled by the autonomic nervous system. Cardiac muscle is found only in the walls of the heart and stimulates its own contractions to form our heartbeat. Smooth muscle is found within the walls of organs and structures such as the oesophagus, stomach, intestines, bronchi, uterus, urethra, bladder, blood vessels, and the arrector pili in the skin.
Muscles perform two types of movements: voluntary and involuntary. Voluntary movements are actions we control. We use our nervous system to control these movements, such as flicking a thumb or sprinting. Involuntary movements happen automatically without thinking, such as the beating of our heart and breathing.
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Muscle disorders: myopathy, cramps, and more
Muscles are pieces of soft tissue that enable movement in the body. There are over 600 muscles in the human body, which is why muscle injuries and health conditions affecting them are common. Skeletal muscles are the most common type of muscle in the body and comprise 30% to 40% of total body mass. They are attached to bones and allow us to perform a wide range of movements and functions.
Muscles are made of thousands of small fibres woven together, which contract and stretch to enable movement. There are three types of muscle tissue in vertebrates: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles, meaning we control how and when they move. Cardiac and smooth muscles are involuntary muscles controlled by the autonomic nervous system.
Muscle Disorders
Myopathies are a group of disorders that primarily affect the skeletal muscle structure, metabolism, or channel function. They usually present with muscle weakness and pain, interfering with daily life activities. Myopathies are derived from the Greek words "myo" for muscle and "pathy" for suffering, meaning muscle disease. Muscle weakness can be either non-progressive or very slowly progressive, and it can be intermittent with other normal periods of strength. Myopathies can also cause muscle cramps, stiffness, spasms, and fatigue.
Myopathies can be caused by a disruption in muscle tissue integrity and metabolic stability, which may be triggered by inherited genetic diseases, metabolic errors, certain drugs and toxins, bacterial or viral infections, inflammation, and hormonal irregularities. Risk factors for myopathy include having a family history of the disease, being male, having an autoimmune, metabolic, or endocrine disorder, and exposure to certain medications or toxins.
Other muscle disorders include cramps, which are sudden and involuntary contractions of the muscles. Muscle cramps can be caused by dehydration, overuse of muscles, or mineral deficiencies such as low potassium or magnesium levels.
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Frequently asked questions
Muscles are pieces of soft tissue made of thousands of small fibres woven together. They help the body perform a wide range of movements and functions, from holding your body still to running a marathon.
Muscles work by contracting and relaxing to cause movement. This movement may be voluntary, controlled by the somatic nervous system, or involuntary, controlled by the autonomic nervous system.
There are three types of muscle tissue in vertebrates: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles, while cardiac and smooth muscles are involuntary.
Skeletal muscles include shoulder muscles, hamstring muscles, abdominal muscles, biceps, triceps, and quadriceps.
Smooth muscles are found in the digestive tract, uterus, bladder, blood vessels, and eyes. They help with processes such as digestion, giving birth, and focusing your vision.
