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The stiffness of death. The rigidity of a body after death. Rigor mortis is a good example of a Latin term (one in this case that was coined in the 19th century) remaining intact in contemporary medical usage (and crime writing).

Rigor mortis is due to a biochemical change in the muscles that occurs several hours after death, though the time of its onset after death depends on the ambient temperature. The biochemical basis of rigor mortis is hydrolysis in muscle of ATP, the energy source required for movement. Without ATP, myosin molecules adhere to actin filaments and the muscles become rigid.

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The heart automaticity is a fundamental physiological function in higher organisms. The spontaneous activity is initiated by specialized populations of cardiac cells generating periodical electrical oscillations. The exact cascade of steps initiating the pacemaker cycle in automatic cells has not yet been entirely elucidated. Nevertheless, ion channels and intracellular Ca²⁺ signaling are necessary for the proper setting of the pacemaker mechanism.

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Various theories have been proposed to explain increases in muscle extensibility observed after intermittent stretching. Most of these theories advocate a mechanical increase in length of the stretched muscle. More recently, a sensory theory has been proposed suggesting instead that increases in muscle extensibility are due to a modification of sensation only. Studies that evaluated the biomechanical effect of stretching showed that muscle length does increase during stretch application due to the viscoelastic properties of muscle.

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Muscle contractility and cell motility play a vital role in various physiological and pathological processes, ranging from animal locomotion to cardiovascular function to myopathies and heart failure. Actin-activated myosin II motors power muscle contraction and non-muscle-cell motility. Actin-myosin-derived contractility has been most extensively studied in striated muscle (skeletal and cardiac muscles), but it is also the foundation for smooth muscle contraction and non-muscle-cell motility. Recent advances in biology and medicine have significantly enriched our understanding of the molecular mechanisms underlying muscle contractility and cell motility.

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Calcium triggers contraction by reaction with regulatory proteins that in the absence of calcium prevent interaction of actin and myosin. Two different regulatory systems are found in different muscles. In actin-linked regulation troponin and tropomyosin regulate actin by blocking sites on actin required for complex formation with myosin; in myosin-linked regulation sites on myosin are blocked in the absence of calcium. The major features of actin control are as follows: there is a requirement for tropomyosin and for a troponin complex having three different subunits with different functions; the actin displays a cooperative behavior; and a movement of tropomyosin occurs controlled by the calcium binding on troponin.

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Myosin requires huge amounts of ATP when muscles are exerted. When you start running, the supply of ATP in your muscles lasts only about a second. Then, the muscle cells shift to phosphocreatine, a backup source of energy, which can be converted quickly into about 10 seconds worth of ATP. Then, if you are still running full tilt, your muscles start using glycogen, a molecule that stores glucose. This lasts for a minute or two, building up toxic acids as the sugar is used up. Then, the sprint is over and you have pushed your muscles to the limit

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Actin, protein that is an important contributor to the contractile property of muscle and other cells. It exists in two forms: G-actin (monomeric globular actin) and F-actin (polymeric fibrous actin), the form involved in muscle contraction.
In muscle, two long strands of beadlike actin molecules are twisted together to form a thin filament, bundles of which alternate and interdigitate with bundles of thick filaments formed of myosin, the most abundant protein found in muscle. When a signal for muscle contraction is sent along a nerve to a muscle cell, actin and myosin are activated.

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When a muscle contracts, the actin is pulled along myosin toward the center of the sarcomere until the actin and myosin filaments are completely overlapped. In other words, for a muscle cell to contract, the sarcomere must shorten. However, thick and thin filaments—the components of sarcomeres—do not shorten. Instead, they slide by one another, causing the sarcomere to shorten while the filaments remain the same length. The sliding filament theory of muscle contraction was developed to fit the differences observed in the named bands on the sarcomere at different degrees of muscle contraction and relaxation. The mechanism of contraction is the binding of myosin to actin, forming cross-bridges that generate filament movement

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Skeletal muscle, also called voluntary muscle, in vertebrates, most common of the three types of muscle in the body. Skeletal muscles are attached to bones by tendons, and they produce all the movements of body parts in relation to each other. Unlike smooth muscle and cardiac muscle, skeletal muscle is under voluntary control. Similar to cardiac muscle, however, skeletal muscle is striated; its long, thin, multinucleated fibres are crossed with a regular pattern of fine red and white lines, giving the muscle a distinctive appearance

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Cardiac muscle, also known as heart muscle, is the layer of muscle tissue which lies between the endocardium and epicardium. These inner and outer layers of the heart, respectively, surround the cardiac muscle tissue and separate it from the blood and other organs. Cardiac muscle is made from sheets of cardiac muscle cells. These cells, unlike skeletal muscle cells, are typically unicellular and connect to one another through special intercalated discs.

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Smooth muscle, also called involuntary muscle, muscle that shows no cross stripes under microscopic magnification. It consists of narrow spindle-shaped cells with a single, centrally located nucleus. Smooth muscle tissue, unlike striated muscle, contracts slowly and automatically. It constitutes much of the musculature of internal organs and the digestive system.

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Tetany is a symptom. Like many symptoms, it can be brought on by a variety of conditions. This means that it’s sometimes difficult to find what’s causing this symptom. While there are effective treatments for the condition, preventing it often depends on pinpointing what caused it in the first place.Overly stimulated nerves cause involuntary muscle cramps and contractions, most often in the hands and feet. But these spasms can extend throughout the body, and even into the larynx, or voice box, causing breathing problems.

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Tetanus: An often fatal infectious disease that is caused by the bacterium Clostridium tetani, which usually enters the body through a puncture, a cut, or an open wound. Tetanus leads to profound painful spasms of muscles, including 'locking' of the jaw so that the mouth cannot open, and death. The C. tetani bacteria releases a toxin that affects the motor nerves, which stimulate the muscles. Prevention involves immediately cleaning and covering any open wound and getting a tetanus vaccination

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In the tonic phase the body becomes entire rigid, and in the clonic phase there is uncontrolled jerking. Tonic-clonic seizures may or may not be preceded by an aura, and are often followed by headache, confusion, and sleep. They may last mere seconds, or continue for several minutes. Also known as a grand mal seizure.spasm. ... a sudden, abnormal, involuntary muscular contraction, consisting of a continued muscular contraction (tonic spasm) or of a series of alternating muscular contractions and relaxations (clonic spasm

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Otherwise known as muscle cramps, spasms occur when a muscle involuntary and forcibly contracts and cannot relax. These are very common and can affect any muscle. Typically, they involve part or all of a muscle, or several muscles in a group. The most common sites for muscle spasms are the thighs, calves, foot arches, hands, arms, abdomen and sometimes along the ribcage. When occurring in the calves, especially, such cramps are known as “charley horses.”

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Muscle fatigue is a symptom that decreases your muscles’ ability to perform over time. It can be associated with a state of exhaustion, often following strenuous activity or exercise. When you experience fatigue, the force behind your muscles’ movements decrease, causing you to feel weaker.
While exercise is a common cause of muscle fatigue, this symptom can be the result of other health conditions, too.

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5 Basic functions of the muscular system

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5 Basic functions of the muscular system

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The muscular system creates movement. The primary function of muscular system is to produce voluntary gross and fine movements. ...

It protects the organs. ...

The cardiac muscle pumps blood. ...

Smooth muscle aids digestion. ...

Smooth muscle ensures blood flow.

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fascia is the body’s connective tissue. It is a head to toe, inside to out, all-encompassing and interwoven system of fibrous connective tissue found throughout the body. Your fascia provides a framework that helps support and protect individual muscle groups, organs, and the entire body as a unit.

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, tissue that attaches a muscle to other body parts, usually bones. Tendons are the connective tissues that transmit the mechanical force of muscle contraction to the bones; the tendon is firmly connected to muscle fibres at one end and to components of the bone at its other end. Tendons are remarkably strong, having one of the highest tensile strengths found among soft tissues.