Logan Steele
Muscle theory refers to the sliding filament theory, which explains how muscles contract. It is a cycle of repetitive events that cause a thin filament to slide over a thick filament, generating tension in the muscle. The theory was developed in 1954 by Andrew Huxley and Rolf Niedergerke, and Hugh Huxley and Jean Hanson. The sliding filament theory is fundamental to muscle physiology, which involves an electrical stimulus that causes a mechanical response in the form of a contraction.
| Characteristics | Values |
|---|---|
| What is muscle theory? | The mechanism of muscle contraction. |
| Types of muscles | Skeletal, smooth, and cardiac. |
| Muscle contraction | Muscle shortening and muscle contraction are not synonymous. |
| Muscle contraction variables | Length and tension. |
| Muscle contraction process | Excitation-contraction coupling. |
| Sliding filament theory | A muscle fiber contracts when myosin filaments pull actin filaments closer together, shortening sarcomeres within a fiber. |
| Muscle contraction types | Concentric and eccentric. |
| Muscle contraction function | Muscle contraction provides animals with flexibility, allowing them to move. |
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Muscle contraction
Mammals have three types of muscles: skeletal, cardiac, and smooth. Skeletal muscles are attached to bones and give the body structure and strength. Cardiac muscle comprises the walls of the heart, allowing blood to be pumped through the vasculature. Smooth muscle is found throughout the body in the blood vessels, gastrointestinal tract, bronchioles, uterus, and bladder.
Striated muscles, such as skeletal and cardiac muscles, are made up of many individual muscle fibres. Inside these muscle fibres are smaller units called myofibrils, which are made of parallel thin and thick filaments. These filaments are arranged longitudinally in small units known as sarcomeres, which give the muscle a striated appearance under microscopy. The thick filaments are made from the protein myosin, and the thin filaments are composed of actin.
The sliding filament theory, developed in 1954 by Andrew Huxley and Rolf Niedergerke, and also by Hugh Huxley and Jean Hanson, explains the process of muscle contraction. According to this theory, myosin filaments use energy from ATP to "walk" along the actin filaments, pulling them closer together and generating tension in the muscle. This action shortens the sarcomeres within a fibre, and when all the sarcomeres in a muscle fibre shorten, the fibre contracts.
The process of muscle contraction is initiated by a signal from the nervous system, which travels through the nervous system to the muscle. This signal causes an action potential that depolarizes the myocyte membrane, resulting in an increase in cytosolic calcium called a calcium transient. This increase in calcium activates calcium-sensitive contractile proteins that then use ATP to cause cell shortening and muscle contraction.
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Types of muscles
Muscle theory is a complex and fascinating area of study, and understanding the types of muscles and their functions is an important part of this. There are three main types of muscle tissue in mammals: skeletal, smooth, and cardiac.
Skeletal Muscle
Skeletal muscles are attached to bones and enable the body's movements. They are responsible for the voluntary movements of bones and almost all movement of substances within the body, such as blood and food, is the result of skeletal muscle contraction. Skeletal muscle contractions are neurogenic, requiring input from motor neurons. The contraction occurs when protein filaments within each skeletal muscle fibre slide past each other, as described by the sliding filament theory. This process can be observed during a bicep curl, where a concentric contraction of the biceps causes the arm to bend at the elbow. Skeletal muscles can be further classified into Type I and Type IIx fibres. Type I fibres are slow-twitch fibres that contract slowly with low force but can keep contracting for long periods without fatigue, making them ideal for long-distance runners. Type IIx fibres, on the other hand, contract very quickly and produce a lot of force, enabling activities like sprinting, but they fatigue quickly.
Smooth Muscle
Smooth muscle is found in the walls of hollow organs, such as the intestines, uterus, and stomach. Unlike skeletal muscle, smooth muscle contractions are myogenic and are not under conscious control. Smooth muscle contractions are initiated by the muscle cells themselves, although they can be modulated by stimuli from the autonomic nervous system.
Cardiac Muscle
Cardiac muscle is found in the walls of the heart and is also under the control of the autonomic nervous system. Cardiac muscle cells have one central nucleus and are rectangular in shape. Cardiac muscle contractions are involuntary, strong, and rhythmical. Similar to smooth muscle contractions, they are myogenic and are initiated by the muscle cells themselves.
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Muscle tissue
There are three types of muscle tissue: skeletal, smooth, and cardiac. Skeletal muscles are attached to bones and give the body structure and strength. They are under voluntary control, meaning they move when you think about moving that part of the body. Cardiac muscle makes up the middle layers of the heart and is found nowhere else in the body. It contracts involuntarily to pump blood through the cardiovascular system. Smooth muscle tissue lines some organs, like the liver, pancreas, intestines, uterus, and stomach, and is also under involuntary control.
The physiological concept of muscle contraction is based on two variables: length and tension. Muscle contraction is not synonymous with muscle shortening. Tension can be produced without changes in muscle length, as when holding a sleeping child in your arms. Upon termination of muscle contraction, muscle relaxation occurs, allowing the muscle to contract again.
The sliding filament theory describes the process of muscle contraction. Actin and myosin filaments slide past each other to produce a contraction. This theory was developed independently by Andrew Huxley and Rolf Niedergerke, and by Hugh Huxley and Jean Hanson in 1954.
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Muscle fibres
The arrangement of these filaments gives the muscle tissue a striped or striated appearance, which is particularly noticeable in skeletal and cardiac muscles. Skeletal muscles are attached to bones and are responsible for voluntary movements such as walking, bending, and picking up objects. They also enable the growth of muscles through a combination of muscle cell growth and the addition of new protein filaments. Cardiac muscles, on the other hand, are only found in the heart and have their own unique rhythm due to the presence of pacemaker cells.
The contraction of muscle fibres occurs through a process known as excitation-contraction coupling, which involves the movement of various ions and molecules that ultimately result in the sliding of the thin filaments over the thick filaments. This sliding filament theory was developed in 1954 and describes the mechanism of muscle contraction, where the thin filament slides over the thick filament, generating tension in the muscle. The speed of contraction depends on how quickly myosin's ATPase hydrolyzes ATP to produce cross-bridge action. Fast fibres hydrolyze ATP much faster than slow fibres, resulting in quicker contraction and higher tension development.
There are several types of muscle fibres, including slow oxidative (SO), fast oxidative (FO), and fast glycolytic (FG). These types differ in their speed of contraction and their energy-generating mechanisms. Type 1 or slow-twitch fibres contract slowly and use oxygen to generate energy through aerobic respiration. Type 2 or fast-twitch fibres, on the other hand, can be further divided into subtypes based on their energy generation methods and the presence or absence of mitochondria.
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Muscle relaxation
Muscle theory refers to the mechanism of muscle contraction and relaxation. The physiological concept of muscle contraction is based on two variables: length and tension. Muscle shortening and contraction are not synonymous. Tension within the muscle can be produced without changes in the length of the muscle, as when holding a dumbbell in the same position or holding a sleeping child in your arms.
The first step in this practice is to create tension in specific muscle groups and notice what tension feels like in that body part. The second step is to release the tension and notice what a relaxed muscle feels like as the tension drains away. This technique involves alternately tensing and relaxing 14 different muscle groups, in a specific order, generally beginning with the lower extremities and ending with the face, abdomen, and chest. It can be practised seated or lying down, and in comfortable clothing, in a quiet place free of distractions.
While inhaling, contract one muscle group (e.g. upper thighs) for 5-10 seconds, then exhale and release the tension. Give yourself 10-20 seconds to relax, then move on to the next muscle group. While releasing the tension, focus on the changes in feeling when the muscle group is relaxed. Imagery may be helpful here, such as imagining that stressful feelings are flowing out of your body.
PMR has been used to control stress and anxiety, relieve insomnia, and reduce symptoms of certain types of chronic pain. It was developed by Dr Edmund Jacobson in the 1920s and published in 1938. It can be learned by nearly anyone and requires only 10-20 minutes per day to practice.
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