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NAME: ADEBAYO ZULAIHA ADERONKE DEPARTMENT; PHYSIOLOGY MATRIC NO; 14/MHS01/003 COURSE; ANA 203 (HISTOLOGY OF BASIC TISSUES) LEVEL; 200 ASSIGNMENT Write an essay on the histology of muscle as a tissue and state its types. ANSWER HISTOLOGY OF THE MUSCLE TISSUE Muscle is a soft tissue found in most animals. It is characterized based on its functional property, which is the ability of its cells to contract. The Muscle tissue is the fourth basic tissue type. All muscle tissues are derived from the mesodermal layer of embryonic germ cells in a process called myogenesis and they differentiate by a gradual process of cell lengthening with abundant synthesis of the myofibrillar proteins, actin and myosin. They are primarily responsible for maintaining and changing posture, locomotion, as well as movement of internal organs, such as the contraction of the heart and the movement of food through the digestive system via peristalsis. Muscle cells are generally refered to as ‘muscle fibers’ and are arranged in parallel arrays allowing them to function together effectively. Muscles are predominantly powered by the oxidation of fats and carbohydrates, but anaerobic chemical reactions are also used, particularly by fast twitch fibers. The term muscle is derived from the latin word musculus meaning little mouse perhaps because of the shape of certain muscles or because contracting muscles look like mice moving under the skin. TYPES OF MUSCLE TISSUE There are three types of muscle tissue which are distinguished on the basis of morphologic and functional characteristics, with the structure of each adapted to its physiologic role. T 1. SKELETAL MUSCLE This type of muscle constitutes the muscle that is attached to the skeleton and controls motor movements and posture. It is a striated muscle. Skeletal muscle fibers are a multinucleated syncytium formed by the fusion of individual small muscle cells or myoblasts, during development. They are filled with myofibrils of which are made up of myofilaments myosin (thick filament) and actin (thin filament). Individual contractile units are called sacromeres. A myofibril consists of many sacromeres. Longitudinal sections of skeletal muscle contains alternating pattern of dark and light bands called A(anisotropic) and I(isotropic) band. The I band is bisected by a dense zone called the Z line to which the thin filaments of the I band are attached. The nuclei are located peripherally, immediately under the plasma. The thickness of each fiber is uniform throughout its length and they do not branch out. Skeletal/ voluntary muscle is divided into two; a) Slow twitch These muscles are also called red muscles. They are dense in capillaries and rich in mitochondria and myoglobin, giving the muscle its red colour. It can carry more oxygen and sustain aerobic activity using fats or carbohydrates as fuel. They contract for a long period of time but with little force. b) Fast twitch They contract quickly and powerfully but fatigue very rapidly, sustaining only short, anaerobic bursts of activities before muscle contraction becomes painful. They contribute most to the muscle strength and have greater potential for increase in mass. Fast twitch muscle/ Type II have three subtypes IIa, IIx, IIb that vary in contractile speed and force generated. 2. CARDIAC MUSCLE This is the type of muscle found in the heart and at the base of the venae cava as they enter into the heart. Cardiac muscle also exhibit striation due to the presence of actin and myosin filaments arranged into sacromeres. Cardiac muscle cells have only one or two nuclei that are centrally located. They are joined to one another in a linear array. The boundary between two cells abutting each other is called an intercalated disc. Cardiac muscle fibers branch and anastomose with one another. Although made up of individual fibers, heart acts as a functional syncytium during contraction for the efficient pumping of blood. 3. SMOOTH MUSCLE This is the intrinsic muscle of the internal organs and blood vessels. It is also found in the iris and ciliary body of the eye and associated with hair follicles. No striations are present due to the different arrangement of actin and myosin filaments. Smooth muscles are specialised for slow, prolonged contraction. Smooth muscle fibers are generally arranged in bundles or sheets. Each fiber is fusiform in shape with tapered end. The single nucleus is located in the central part of the fiber of which has a cork screw shape in longitudinal section due to contraction of the muscle fiber during fixation. Fibers do not branch.They range enormously in size, from 20 to 500mm. Smooth muscle fibers lie over one another in a staggered fashion. Smooth muscle has the ability to secrete connective tissue matrix.