Victor Forge
The human body is made up of over 600 muscles, which are pieces of soft tissue that help the body to move and function. There are three types of muscles: skeletal, cardiac, and smooth. Skeletal muscles are attached to bones and allow the body to move; cardiac muscles are specific to the heart; and smooth muscles are located in various internal structures, including the digestive tract, uterus, and blood vessels. Skeletal muscles are voluntary, meaning a person can control how and when they move. In contrast, cardiac and smooth muscles are involuntary and controlled by the autonomic nervous system. Muscle contraction can be described in terms of two variables: length and tension. For example, an isometric contraction of a muscle generates tension without changing length, such as when gripping an object. Understanding the structure and function of muscles is essential for maintaining overall health and well-being.
| Characteristics | Values |
|---|---|
| Definition | Muscle contraction is the tightening, shortening, or lengthening of muscles when an activity is performed. |
| Muscle Relaxation | When a muscle contraction ends, muscle relaxation occurs, which is the return of muscle fibres to a low-tension state. |
| Types | Isotonic, Isometric, Concentric, Eccentric, Passive Stretch |
| Isotonic Contraction | The tension in the muscle remains constant despite a change in muscle length. |
| Isometric Contraction | Muscle tension changes but muscle length remains the same. |
| Concentric Contraction | Muscle tension is sufficient to overcome the load, and the muscle shortens as it contracts. |
| Eccentric Contraction | The muscle remains tight but lengthens, for example, when lowering something heavy. |
| Passive Stretch | The muscle is passively lengthened, for example, when leaning down to touch your toes. |
| Variables | Length and tension |
| Muscle Types | Skeletal, cardiac, and smooth |
| Muscle Composition | Actin, Myosin, Troponin, Calcium |
| Mechanism | Excitation-contraction coupling, Sliding Filament Theory |
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What You'll Learn
Types of muscles
The human body has more than 600 muscles that help us move, breathe and stay alive. There are three types of muscles in the body: skeletal, cardiac, and smooth muscle.
Skeletal muscles are the most common type of muscle in the body and make up between 30% and 40% of our total body mass. They are attached to bones and allow us to perform a wide range of movements and functions. These muscles are voluntary, meaning we control how and when they move. Skeletal muscles consist of flexible muscle fibres that range from less than half an inch to just over 3 inches in diameter. Each muscle can contain thousands of fibres. Skeletal muscles are also known as striated muscles because they look striped under a microscope.
Cardiac muscle, or myocardium, makes up the middle layers of the heart and is the only organ in the body that is also a muscle. The contraction of cardiac muscle is involuntary, strong, and rhythmical.
Smooth muscle tissue lines some of our organs, although most organs are also made of other types of tissue. Smooth muscle contractions are myogenic, meaning they are initiated by the muscle cells themselves instead of being stimulated by an outside event.
Muscle contractions can be described in terms of two variables: length and tension. Isometric contractions generate tension without changing length, while isotonic contractions keep tension constant despite a change in muscle length. Concentric contractions occur when muscle tension is sufficient to overcome the load, and the muscle shortens as it contracts. Eccentric contractions happen when the tension generated while isometric is insufficient to overcome the external load, and the muscle fibres lengthen as they contract.
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Muscle contractions
The physiological concept of muscle contraction is based on two variables: length and tension. While muscle shortening and contraction are not synonymous, tension within the muscle can be produced without changes in length, such as when holding a dumbbell or a sleeping child in one's arms.
There are three types of muscle contractions: isometric, isotonic, and eccentric. An isometric contraction occurs when muscle tension changes without any change in muscle length. An example of this is carrying something in your arms in front of you, where the muscle is held at a set length without any shortening or lengthening. An isotonic contraction is when muscle tension remains constant despite changes in muscle length. This occurs when the force of contraction matches the total load on the muscle. A concentric contraction, which is a type of isotonic contraction, occurs when muscle tension is sufficient to overcome the load, causing the muscle to shorten as it contracts. An eccentric contraction happens when a muscle is actively lengthened during normal activity, such as walking or lowering a heavy object.
The mechanism of muscle contraction can be summarised in three steps. First, a message is sent from the nervous system to the muscular system, triggering chemical reactions. Second, these chemical reactions lead to muscle fibres reorganising themselves in a way that shortens the muscle, resulting in contraction. Finally, when the nervous system signal ceases, the chemical process reverses, and the muscle fibres rearrange, leading to muscle relaxation.
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Muscle composition
There are three main types of muscle in the body: skeletal, smooth, and cardiac. Skeletal muscle is the specialised tissue that attaches to bones and allows movement. It represents the largest body-composition component in humans, accounting for more than 40% and 30% of total body mass in men and women, respectively. Each skeletal muscle is made up of hundreds or thousands of muscle fibres bundled together and wrapped in a connective tissue covering. Skeletal muscle consists of approximately 90% muscle fibres and 10% connective and fat tissues. The connective tissue surrounding each muscle fibre is called the endomysium, while the perimysium surrounds bundles of muscle fibres, and the epimysium surrounds the entire muscle.
Smooth muscle is located in various internal structures, including the digestive tract, uterus, and blood vessels. It is also known as involuntary muscle because its movements occur without conscious awareness. Smooth muscle is arranged in layered sheets that contract in waves along the length of the structure. Cardiac muscle is specific to the heart and, like smooth muscle, operates involuntarily.
The composition of muscle fibres can vary depending on the species, breed, gender, age, physical activity, environmental temperature, and feeding practices. Muscle composition can be influenced by nutritional and environmental factors, and maintaining healthy muscles requires regular exercise and a nutritious, balanced diet. Protein, carbohydrates, and fat are essential for building and strengthening muscles.
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Muscle functions
The human body has over 600 muscles that help us perform a variety of functions, from moving our bodies to breathing and staying alive. Muscles are made of thousands of small fibres woven together, and these fibres stretching and pressing together is what moves our organs and body.
Types of Muscle
There are three types of muscles in the human body: skeletal, smooth, and cardiac. Skeletal muscles are attached to bones and give the body structure and strength. They are the only muscles that can be consciously controlled. They contract in response to a stimulus, producing movement, sustaining body posture and position, maintaining body temperature, storing nutrients, and stabilising joints. Skeletal muscles comprise approximately 40% of the human body weight.
Smooth muscles, on the other hand, are found in the walls of organs and blood vessels and are responsible for involuntary movements such as digestion and breathing. Cardiac muscle, as the name suggests, is found only in the heart and is responsible for pumping blood around the body.
Types of Muscle Contractions
Muscle contractions can be categorised into four types: isometric, isotonic, concentric, and eccentric. Isometric contractions occur when the tension in the muscle changes without any change in muscle length. Isotonic contractions, on the other hand, are when the tension in the muscle remains constant despite changes in muscle length. Concentric contractions happen when the muscle tension is sufficient to overcome the load, causing the muscle to shorten as it contracts. Lastly, eccentric contractions occur when the muscle is actively lengthened during normal activity, such as walking or lowering a heavy object.
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Muscle disorders
There are three types of muscles in the body: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles that control movement and function. They make up 30% to 40% of total body mass and are attached to bones, allowing for a wide range of movements. Skeletal muscle fibres contract, allowing the muscles to move bones and perform different movements. Skeletal muscles can also be controlled by the somatic nervous system.
Cardiac and smooth muscles are involuntary muscles controlled by the autonomic nervous system. Smooth muscles are found in the urinary system, for example, helping to rid the body of waste and toxins. Cardiac muscles are found in the heart and are responsible for heart contractions.
Some examples of muscle disorders include congenital myopathy, mitochondrial disorders, neuromuscular disorders, and muscular dystrophy. Neuromuscular disorders affect the nerves that control voluntary muscles and the nerves that communicate sensory information to the brain. When nerve cells become unhealthy or die, communication between the nervous system and muscles breaks down, leading to muscle weakness and atrophy. Muscular dystrophy causes weakness and the wasting away of muscle tissue.
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Frequently asked questions
Muscle contraction is the process by which muscles fibres slide past each other to produce movement.
There are three types of muscle contractions: isometric, isotonic, and eccentric.
Isometric contractions generate tension without changing length. For example, when you grip an object, the joints of your hand do not move, but your muscles generate sufficient force to prevent the object from being dropped.
During isotonic contractions, the tension in the muscle remains constant despite a change in muscle length. This occurs when a muscle's force of contraction matches the total load on the muscle.
Eccentric contractions occur when the tension generated while isometric is insufficient to overcome the external load on the muscle and the muscle fibres lengthen as they contract.
