Sir Andrew Fielding Huxley was an English physiologist and biophysicist. He was born into the prominent Huxley family. After leaving Westminster School in central London, he went to Trinity College, Cambridge, on a scholarship, after which he joined Alan Hodgkin to study nerve impulses. Their eventual discovery of the basis for propagation of nerve impulses earned them the Nobel Prize in Physiology or Medicine in 1963. They made their discovery from the giant axon of the Atlantic squid. Soon after the outbreak of the Second World War, Huxley was recruited by the British Anti-Aircraft Command and later transferred to the Admiralty. After the war he resumed research at the University of Cambridge, where he developed interference microscopy that would be suitable for studying muscle fibres.
The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is composed of similar proteins in the various organisms. It is composed of three main components: microfilaments, intermediate filaments, and microtubules, and these are all capable of rapid growth or disassembly depending on the cell's requirements.
Smooth (soft) muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations. It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit muscle, the whole bundle or sheet of smooth muscle cells contracts as a syncytium.
Microfilaments, also called actin filaments, are protein filaments in the cytoplasm of eukaryotic cells that form part of the cytoskeleton. They are primarily composed of polymers of actin, but are modified by and interact with numerous other proteins in the cell. Microfilaments are usually about 7 nm in diameter and made up of two strands of actin. Microfilament functions include cytokinesis, amoeboid movement, cell motility, changes in cell shape, endocytosis and exocytosis, cell contractility, and mechanical stability. Microfilaments are flexible and relatively strong, resisting buckling by multi-piconewton compressive forces and filament fracture by nanonewton tensile forces. In inducing cell motility, one end of the actin filament elongates while the other end contracts, presumably by myosin II molecular motors. Additionally, they function as part of actomyosin-driven contractile molecular motors, wherein the thin filaments serve as tensile platforms for myosin's ATP-dependent pulling action in muscle contraction and pseudopod advancement. Microfilaments have a tough, flexible framework which helps the cell in movement.
In cell biology, the cleavage furrow is the indentation of the cell's surface that begins the progression of cleavage, by which animal and some algal cells undergo cytokinesis, the final splitting of the membrane, in the process of cell division. The same proteins responsible for muscle contraction, actin and myosin, begin the process of forming the cleavage furrow, creating an actomyosin ring. Other cytoskeletal proteins and actin binding proteins are involved in the procedure.
A myofibril is a basic rod-like organelle of a muscle cell. Skeletal muscles are composed of long, tubular cells known as muscle fibers, and these cells contain many chains of myofibrils. Each myofibril has a diameter of 1–2 micrometres. They are created during embryonic development in a process known as myogenesis.
A sarcomere is the smallest functional unit of striated muscle tissue. It is the repeating unit between two Z-lines. Skeletal muscles are composed of tubular muscle cells which are formed during embryonic myogenesis. Muscle fibers contain numerous tubular myofibrils. Myofibrils are composed of repeating sections of sarcomeres, which appear under the microscope as alternating dark and light bands. Sarcomeres are composed of long, fibrous proteins as filaments that slide past each other when a muscle contracts or relaxes. The costamere is a different component that connects the sarcomere to the sarcolemma.
Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of over 100 μM; its mass is roughly 42 kDa, with a diameter of 4 to 7 nm.
Myosins are a superfamily of motor proteins best known for their roles in muscle contraction and in a wide range of other motility processes in eukaryotes. They are ATP-dependent and responsible for actin-based motility.
The Frank–Starling law of the heart represents the relationship between stroke volume and end diastolic volume. The law states that the stroke volume of the heart increases in response to an increase in the volume of blood in the ventricles, before contraction, when all other factors remain constant. As a larger volume of blood flows into the ventricle, the blood stretches cardiac muscle, leading to an increase in the force of contraction. The Frank-Starling mechanism allows the cardiac output to be synchronized with the venous return, arterial blood supply and humoral length, without depending upon external regulation to make alterations. The physiological importance of the mechanism lies mainly in maintaining left and right ventricular output equality.
Muscle contraction is the activation of tension-generating sites within muscle cells. In physiology, muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in muscle length, such as when holding something heavy in the same position. The termination of muscle contraction is followed by muscle relaxation, which is a return of the muscle fibers to their low tension-generating state.
In physiology, isotropic bands are the lighter bands of skeletal muscle cells. Isotropic bands contain only actin-containing thin filaments. The thin filaments are placed between 2 myosin filaments and contain only the actin filaments of neighboring sarcomeres. Bisecting the I band and serving as an anchoring point for the two adjacent actin filaments is the Z disc. During muscle contraction, the I band will shorten, while an A band will maintain its width.
Hugh Esmor Huxley MBE FRS was a British molecular biologist who made important discoveries in the physiology of muscle. He was a graduate in physics from Christ's College, Cambridge. However, his education was interrupted for five years by the Second World War, during which he served in the Royal Air Force. His contribution to development of radar earned him an MBE.
Myofilaments are the three protein filaments of myofibrils in muscle cells. The main proteins involved are myosin, actin, and titin. Myosin and actin are the contractile proteins and titin is an elastic protein. The myofilaments act together in muscle contraction, and in order of size are a thick one of mostly myosin, a thin one of mostly actin, and a very thin one of mostly titin.
Myosin light-chain kinase also known as MYLK or MLCK is a serine/threonine-specific protein kinase that phosphorylates a specific myosin light chain, namely, the regulatory light chain of myosin II.
Emmeline Jean Hanson was a biophysicist and zoologist known for her contributions to muscle research. Hanson gained her PhD in zoology from Bedford College, University of London before spending the majority of her career at a biophysics research unit at King's College London, where she was a founder member, and later its second Head. While working at Massachusetts Institute of Technology, she, with Hugh Huxley, discovered the mechanism of movement of muscle fibre in 1954, which came to known as "sliding filament theory". This was a groundbreaking research in muscle physiology, and for this BBC nicknamed her "Mrs Muscle" on the 50th anniversary of the discovery.
Rolf Nidergerke was a German physiologist and physician, and one of the discoverers of the sliding filament theory of muscle contraction. He and Andrew Huxley, complimenting the independent works of Hugh Huxley and Jean Hanson, revealed that muscle contraction is due to shortening of the muscle fibres. He studied medicine throughout the Second World War, and obtained his MD degree as the war ended in 1945. After a brief practise in his hometown, he chose a research career. He became associated with Huxley, whom he joined at Cambridge University. Together they published a landmark paper in Nature in 1954, which became the foundation of muscle mechanics.
Ilona Banga (1906–1998) was a Hungarian biochemist known for co-discovering actomyosin and working to characterize how actin and myosin interact to produce muscle contraction. She and her husband József Mátyás Baló discovered the first elastase – an enzyme capable of degrading the protein elastin which gives tissues like veins their flexibility. She also contributed to work that earned Albert Szent-Györgyi the Nobel Prize in Physiology or Medicine in 1937, including by developing methods for the purification and characterization of large quantities of vitamin C. During World War II she saved the equipment of the Institute of Chemistry of the University of Szeged.
Edwin W. Taylor is an adjunct professor of cell and developmental biology at Northwestern University. He was elected to the National Academy of Sciences in 2001. Taylor received a BA in physics and chemistry from the University of Toronto in 1952; an MSc in physical chemistry from McMaster University in 1955, and a PhD in biophysics from the University of Chicago in 1957. In 2001 Taylor was elected to the National Academy of Scineces in Cellular and Developmental Biology and Biochemistry.
Hans Hermann Julius Wilhelm Weber was a German physiologist and biochemist who worked on muscle structure and function. He was among the pioneers who helped establish the mechanism of muscle relaxation and contraction. His daughter Annemarie Weber also continued work in myosin biochemistry.
