Published on Jan 19, 2023 - 6 min read
Read this article to understand the composition and function of human muscles and their effect on growth and development.
Every human wants a muscular physique and knowing the properties of muscles improves the understanding of how to make them stronger. Muscles in humans and animals are a type of tissue composed of contractile cells and fibers that affect the movement of an organ or part of the body. The characteristic feature of muscular tissue is its ability to shorten or contract. Muscle units, which are known as sarcomeres, are long and thin so that the shortening which occurs at the time of contraction may be as effective as possible. Muscles possess the properties of irritability, conductivity, and elasticity. Muscle tissue contains little intercellular material, so muscle fibers lie close together.
A muscle is a contractile part of the human body consisting of muscle tissue, which affects the movements of parts of the body.
A typical muscle consists of a central fleshy portion or belly and its attachments. One end, called the head, is attached to a fixed structure termed the origin, while the other is attached to a movable part called the insertion.
Some muscles are spindle-shaped, while others form flat sheets or bands. Muscles may be attached directly utilizing tough cords of connective tissue (tendons) or broad flat sheets (aponeuroses). The connective tissue enclosing a muscle is called epimysium, which is continuous with the deep fascia.
Striated muscles are also known as striated, voluntary, and skeletal muscles. Skeletal muscles are attached to the bone, such as in the hands, legs, and neck. Wherever there is a voluntary movement, these muscles are under the direct supervision of the brain and a person's conscious control. It consists of long cells called fibers, varying in length from 30 mm (millimeter) or more and 10 to 40 µm (micrometer) in diameter. The cytoplasm of muscles is known as sarcoplasm, and numerous myofibrils are present inside the sarcoplasm. The cytoplasmic cell membrane is known as sarcolemma. The nucleus is at the edge of the cell.
Each myofibril is regularly striped across, and it has alternate light and dark bands throughout its length so that the light and dark bands come next to each other. The light band is known as myosin, and the dark band is known as actin.
The outermost sheath of fibrous tissue that surrounds a skeletal muscle is the epimysium or the perimysium externum.
Muscle fibers are grouped into fasciculi bundles (bundles of muscle fibers), each surrounded by a sheath called the perimysium. The threads within a fasciculus are covered and held together by delicate reticular fibrils forming the endomysium.
Voluntary muscles obtain their blood supply from small vessels that enter the muscular tissue and subdivide into capillaries that permeate throughout between individual muscle cells to ensure adequate blood supply. These muscles are worked by branches from the peripheral cerebrospinal nervous system. It is because of this that skeletal muscles are under conscious control. At the ends of the muscles, the connective tissue sheaths are drawn out to form tendons attached to the periosteum covering the bone. At a tendon insertion, collagen fibers of the periosteum are embedded in the bone substance, giving it a firm anchorage.
Smooth muscles are also involuntary, plain, visceral, unstriped, and non-striated, and they consist of elongated fusiform or spindle-shaped cells with a central nucleus. The cells are arranged in layers or sheets but may also occur as isolated units in connective tissue. The cells do not show any stripes and have no sheath but are bound together by connective tissue to form the walls of various organs. Smooth muscles obtain their blood supply from small vessels that enter the tissue and subdivide into capillaries that permeate throughout. Smooth muscles receive their nerve supply from the autonomic nervous system and function without conscious control.
Smooth muscles are found principally in the internal organs (viscera), such as the digestive tract, respiratory passages, urinary and genital ducts, urinary bladder and gallbladder, and the walls of the blood vessels.
Smooth muscles bring about the actions of the internal organs by peristalsis. The distribution of cells in circular and longitudinal muscle layers allows an antagonistic action.
Cardiac muscle is also known as heart muscle or myocardium, and it consists of short, cylindrical, branched fibers that anastomose with adjacent fibers forming a continuous network or syncytium. The fibers have no sheath but are bound together by connective tissue. They have centrally placed nuclei. Microscopic stripes occur in the cardiac muscles due to the arrangement of myofibrils. At intervals, prominent bands or intercalated discs cross the fibers, cutting off successive cells. The myocardium is supplied by a pair of coronary arteries that arise within the right and left aortic sinuses at the base of the aorta. It is drained by a pair of coronary veins. Certain fibers, called Purkinje fibers, form the impulse-conducting system of the heart. The cardiac muscle is not under the control of the will but contracts automatically in a rhythmic manner 72 times a minute throughout life. However, the rate of these rhythmic contractions is controlled by nerves from the autonomic nervous system that quicken or slow down its action. The fibers branch and join with each other so that impulses are spread throughout the myocardium.
Voluntary muscles consist of cylindrical fibers. Involuntary muscles consist of elongated fusiform or spindle-shaped cells. Cardiac muscles consist of short, cylindrical, branched fibers.
Voluntary muscle fibers have their nuclei at the edges. Involuntary and cardiac muscle fibers have centrally located nuclei.
Voluntary muscles are attached to the skeletal tissue. Involuntary muscles are found principally in the internal organs (viscera). Cardiac muscle is located in the heart wall only.
Voluntary muscles are enclosed in a sheath called the epimysium. Involuntary and cardiac muscles do not have any sheath but are bound together by connective tissue.
Voluntary muscles are worked by branches of the peripheral cerebrospinal nervous system. The autonomic nervous system works involuntary and cardiac muscles.
Voluntary muscles can be contracted and relaxed as wished. Involuntary muscles function without conscious control but under the supervision of the brain. Cardiac muscle can contract automatically in a rhythmic manner throughout life, although the rate of contraction is controlled by the brain.
Voluntary muscles are striped in regular dark and light bands. Involuntary muscles are not stripped. Microscopic stripes occur in the cardiac muscle due to the arrangement of myofibrils.
The rate of contraction in voluntary muscles is very quick, while in involuntary muscles, it is prolonged. Cardiac muscle contracts in a rhythmic manner, and the rate of contraction is controlled by the brain.
Voluntary muscle fibers have multiple nuclei, while involuntary and cardiac muscle cells have a single nucleus.
Disconnecting a voluntary muscle from the nervous supply completely paralyzes it. Deprivation from the nervous supply has slight effects on involuntary muscles. The cardiac muscle is able to contract rhythmically independent of any nerve supply; the autonomic nervous system only modifies the rate of contraction.
The following factors affect muscle growth:
The diet must contain food containing high biological value (HBV) proteins that have all the essential amino acids. Such foods include meat, fish, eggs, milk, cheese, etc. An appropriate supply of calcium (Ca), phosphorus (P), iodine (I2), and iron (Fe) are required for the healthy growth of muscles. Calcium is found in milk, eggs, and green vegetables, and phosphorus is found in meat, fish, and egg yolk. Iron is found in liver, eggs, flour, and green vegetables, and iodine is in sea fish and iodized table salt. Lack of salt (NaCl) causes muscle cramps, and lack of iron affects muscle myoglobin formation. Vitamins A, B, C, and D are essential for the healthy development of muscles. Vitamin A is found in butter, margarine, fish liver oils, milk, carrot, etc. Vitamin B is present in meat, milk, cereals, cheese, yeast, etc. Vitamin C is found in citrus fruits, blackcurrants, green vegetables, potatoes, and tomatoes. Vitamin D is found in animal fat and fish oils, and irradiated margarine.
A sufficient amount of hormone somatotropin must be released from the pituitary for the healthy development of muscles. This hormone increases the growth rate and maintains size once it attains maturity. Hormone thyroxine is also crucial as it controls metabolism.
Regular exercise makes a muscle stronger and enables it to bear stress and pressure. Exercise causes increased blood supply to the muscles. Since the blood carries necessary nutrients, exercise results in increased growth. Rest is important to allow the products of anaerobic respiration to be restored. During vigorous exercise, anaerobic respiration occurs in the muscles, and oxygen debt occurs. During rest, the body returns to its original condition.
Muscles possess the properties of irritability, conductivity, and elasticity. Muscle tissue contains little intercellular material, so muscle fibers lie close together. An appropriate supply of nutrients is required for the healthy growth of body muscles. The hormone also plays an important role; it increases the growth rate. Regular exercise makes a muscle stronger and enables it to bear stress and pressure. Exercise causes increased blood supply to the muscles.
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19 Jan 2023 - 6 min read
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