Muscles: A Comprehensive Overview PDF

MUSCLES CONTENTS ◦Smooth muscles ◦Cardiac muscles ◦Skeletal muscles ◦Red and white fibers ◦Deep and superficial fascia ◦Functions of muscles MUSCLES ◦Muscle cells are specialized contractile cells also called fibers. ◦Three types of muscle tissues are identified, smooth, cardiac and skeletal,...

MUSCLES CONTENTS ◦Smooth muscles ◦Cardiac muscles ◦Skeletal muscles ◦Red and white fibers ◦Deep and superficial fascia ◦Functions of muscles MUSCLES ◦Muscle cells are specialized contractile cells also called fibers. ◦Three types of muscle tissues are identified, smooth, cardiac and skeletal, each differing in structure, location and physiological functions. SMOOTH MUSCLES ◦Not striated. ◦Long, slender, spindle shaped cell containing a single nucleus. ◦Not connected to the bones. ◦Usually form sheets in the walls of the hollow organs e.g., blood vessels, GIT. ◦Because of its location in the walls of hollow organs, the smooth muscle also entitles as visceral muscles. ◦It is also called involuntary muscles because it is not under conscious control. CARDIAC MUSCLES ◦Found only in the walls of the heart. ◦Short, cylindrical segments (cells) joined end to end by intercellular junction. ◦Each segment contain one nucleus located in the central region of the cell. ◦Show cross-striations due to presence of alternating dark and light bands. ◦They give off branches which make junctions with the branches of neighboring cells and thus convert the whole myocardium into a network. ◦They are also involuntary muscles. SKELETAL MUSCLES ◦Long, cylindrical multinucleated cells. ◦Cell membrane of the muscle fiber is called sarcolemma while the cytoplasm is referred as sarcoplasm. ◦Sarcoplasm contain many mitochondria and a large number of thread-like elements called myofibrils. ◦The myofibrils are further composed of thin and thick myofilaments called actin and myosin filaments respectively. ◦Overlapping of thick myosin filaments and a thin actin filaments produce the dark bands while the actin filaments alone appear as the light bands. RED, WHITE AND INTERMEDIATE MUSCLE FIBERS ◦The sarcoplasm of skeletal muscle fibers contains variable amount of proteins called myoglobin which takes up oxygen from the erythrocytes, stores it and transport it to the mitochondria of the muscle cells. ◦Depend upon its amount, the skeletal muscle fibers are classified as: RED FIBERS ◦Smaller diameter ◦Relatively abundant myoglobin ◦Numerous mitochondria ◦Well-suited for prolonged and steady contractions. ◦Also called slow-twitch fiber. WHITE FIBERS ◦Larger diameter ◦Less myoglobin ◦Fewer mitochondria ◦Able to contract more rapidly. ◦Also called fast twitch fiber. Intermediate fibers exhibit intermediate characteristics. IMPORTANT TERMS ◦Muscle fiber: single muscle cell surrounded by endomysium. Muscle cells are called muscle fibers. ◦Myofilaments: macromolecular structure of contractile proteins. ◦Myofibril: complex organelle composed of bundles of myofilaments. ◦Sarcomere: the smallest., single contracting unit of the segment. ◦Sarcolemma: plasma or cell membrane of muscle. ◦Sarcoplasm: cytoplasm of muscle cell with large amount of glycogen and myoglobin. ◦Myoglobin: red pigmented oxygen binding protein. ◦Contraction depends on two kinds of myofilaments: 1. Actin 2. myosin CONNECTIVE TISSUE ASSICIATED WITH SKELETAL MUSCLES ◦The skeletal muscles are protected , strengthened and attached to other structures by connective tissue. ◦The connective tissue is found in: 1. Fascia 2. Connective tissue components of muscles FASCIA ◦The term fascia is applied to sheath or band of fibrous connective tissue that lies beneath the skin or forms an investment for muscles and various organs of body. ◦Two types 1. Superficial fascia 2. Deep fascia SUPERFICIAL FASCIA ◦Also called hypodermis lies just beneath the skin. ◦Covers the whole body but varies in thickness in different regions. ◦Consists of two layers 1. outer fatty layer 2. inner fibrous layer. ◦Outer layer contain fatty tissues. ◦Varies in amount in different regions in body. ◦The fats is absent in the eyelids, nose, external ear. ◦Inner layer consists mainly of fibrous connective tissue. ◦Usually this layer is thin. ◦The superficial fascia conducts the blood vessels, nerves and lymphatics of the skin. ◦ In face and neck it contains skeletal muscles. Fatty layer of fascia serves two main functions: 1. It act as a store of energy for metabolic use. 2. Being non-conductor, the fatty layer function as an insulation that serves to prevent the loss of body heat. DEEP FASCIA ◦Lies beneath the superficial fascia. ◦Rough and inelastic sheath, made up of several layers of dense fibrous connective tissue. ◦In the limbs the deep fascia forms the tight sleeves and from its deep surface arise fibrous sheets which penetrate between muscles as intermuscular septa. ◦Formation of such compartments serves two main functions. 1. The muscles are separated into functioning groups. 2. Contraction of muscles within the inelastic walls of the osteofascial compartments puts pressure on the deep veins of the limbs and thus aid in return of the venous blood toward the heart.  CONNECTIVE TISSUE COMPONENTS OF MUSCLES. ◦In the skeletal muscle, every muscle fiber in ensheathed by a delicate layer of connective tissue, this layer is called endomysium. ◦The muscle fibers are arranged parallel to each other in bundles called fasciculi. ◦Each fasciculus is surrounded by relatively denser connective tissue called perimysium. ◦Finally the entire muscle is wrapped with a substantial quantity of fibrous tissue called epimysium. ◦Generally the connective tissue components of the muscle fuse together and extend beyond the muscle cells as a cord like structure called a tendon, which serves to attach a muscle to a structure (usually a bone) located some distance away from the muscle tissue. ◦In some muscles flat sheets of fibrous connective tissue penetrate into muscle substance, forming septa to which the muscle fibers are attached. ◦Being a cord-like structure, the attachment of a tendon is restricted to a small area on a bone. PARTS OF A MUSCLE ◦A skeletal muscle generally consists of a fleshy part and two ends. ◦A fleshy part (also called belly or gaster) of a muscle is made up of contractile striated muscles. ◦The ends are composed of fibrous tissue. ◦The belly of a muscle can be made to grow in thickness by regular exercise of that muscle. ◦It is customary to call one end of a muscle as origin and the other as insertion. ◦Origin is that end of the muscle, which is attached to a structure (bone or cartilage) that usually remains fixed during muscle contraction. ◦Insertion is attached to non-fixed structure that moves as a result of contraction of the muscle. MUSCULAR ATTCHMENTS ◦Cartilage ◦Fascia ◦Tendons ◦Ligaments ◦Articular capsules of joints ◦Intermuscular septa LURICATING MECHANISM ◦Synovial bursa is a closed sac of synovial membrane. ◦The delicate walls of flat sac are separated from each other merely by film of synovial fluid. ◦Synovial bursa also found in subcutaneous, submuscular and interligamentous locations. SYNOVIAL SHEATH ◦It is a tubular bursa enveloping a tendon. ◦Each synovial sheath consists of two concentric layers of synovial membrane. ◦Inner layer is called visceral layer while the outer layer is celled parietal layer. ◦The two layers are separated by the film of synovial fluid. FUNCTIONS OF MUSCLES ◦The core function of muscle is convert chemical energy (ATP) into mechanical force. ◦Producing movements ◦Maintaining posture and body position ◦Stabilizing joint ◦Maintaining body temperature by generating heat during muscle contraction. PROPERTIES OF MUSCLES 1. Excitability- ability to response a stimulus which may be delivered from a motor neuron or a hormone. 2. Contractibility: ability of muscle cell to forcefully shorten. 3. Extensibility: ability to be stretched. Lack of extensibility is celled spasticity. Elasticity: ability to recoil or bounce back to the muscle’s original length after being stretched.