Muscle I-A PDF

GENERAL CONSIDERATION OF STRIATED MUSCLE AND NEUROMUSCULAR JUNCTION -1- E-mail: [email protected] Learning Objectives:  Identify the many roles (functions) of skeletal muscle in the body.  Describe the levels of organization in a skeletal muscle.  Detail...

GENERAL CONSIDERATION OF STRIATED MUSCLE AND NEUROMUSCULAR JUNCTION -1- E-mail: [email protected] Learning Objectives:  Identify the many roles (functions) of skeletal muscle in the body.  Describe the levels of organization in a skeletal muscle.  Detail the components of muscle fibers. “SKELETAL MUSCLES ARE ASSOCIATED WITH THE MOVEMENT OF THE BODY, THESE MOVEMENTS ARE CHARACTERISTIC OF SKELETAL MUSCLE CELLS”  What is the work of the all muscle types? CONTRACTION! “The primary function of muscle is to generate force or movement in response to a physiological stimulus.” Muscle tissue is responsible for most of our interactions with the external world.  Properties of Muscle Excitability: Excitability is equated with responsiveness Contractility: Stimulation of muscle cells generates tension within the cell (contraction), which may cause the cell to shorten Extensibility: A muscle cell must be capable of extending in length in response to the contraction of opposing muscle cells Elasticity: A contracted muscle cell recoils to its resting length when the applied tension is removed.  “The primary function of muscle is to generate force or movement.” Movement: Maintenance of posture Respiration: Heat generation Protection: Digestion: Pumping blood: Mechanical control of the blood vessels of the circulatory system and the airway passages of the respiratory system  MUSCLE CELLS CHEMICAL ENERGY MECHANICAL ENERGY ATP POWER PERISTALTIZM HEART BEAT ACTION POSTURE VASOCONSTRICTION BREATHING SPEAKING All muscles transduce chemical energy released by hydrolysis of ATP into mechanical work.  COMPARISION OF MUSCLE CELLS WORKS IN THE BODY ARE VARIOUS // MUSCLE TYPES ARE VARIOUS Contractile cells of the body can be classified into THREE major groups based on their shape, position of nuclei, presence of striation and whether they are under voluntary or involuntary control. SKELETAL MUSCLE HEART MUSCLE SMOOTH MUSCLE Skeletal Muscle: Interactions With the External Environment. As its name implies, most skeletal muscles are attached to the bones of the skeleton, enabling them to control body movement.  COMPARISION OF SKELETAL, CARDIAC AND SMOOTH MUSCLE CELLS MUSCLE CLASSIFICATION The human body contains three fundamentally different types of muscle adapted to specialized functions. The categories may overlap. Skeletal muscle is Cardiac muscle is specific to Smooth muscle provides responsible for the the heart as the mechanical control of voluntary movement of biomechanical pump organ systems such as the bones that underlie driving the delivery of digestive, urinary, and locomotion. blood to the lungs and reproductive tracts as (It is responsible for large tissues. well as the blood vessels and forceful movements of the circulatory system and also small and and the airway passages delicate movements) of the respiratory system.  COMPARISION OF SKELETAL, CARDIAC AND SMOOTH MUSCLE CELLS MUSCLE CLASSIFICATION The human body contains three fundamentally different types of muscle adapted to specialized functions.  Skeletal Muscle Skeletal muscle is composed of numerous skeletal muscle fibers, blood vessels and nerves, and connective tissue sheets that surround the muscle fibers and connect the muscle to bone. 40% to 50 % of human body mass Skeletal muscles are mainly responsible for locomotion, and voluntary contraction and relaxation. ORGANIZATIONAL LEVELS OF SKELETAL MUSCLE  INTERNAL STRUCTURE OF SKELETAL MUSCLE Brachialis m. WHOLE MUSCLE  INTERNAL STRUCTURE OF SKELETAL MUSCLE Brachialis m. Skeletal muscle is composed of connective tissue and contractile cells. Structure of skeletal muscle INTERNAL STRUCTURE OF SKELETAL MUSCLE The entire muscle is surrounded by an external connective tissue, called EPIMYSIUM Skeletal muscle is made up fascicles, each fascicle is surrounded by a connective tissue, called PERIMYSIUM  INTERNAL STRUCTURE OF SKELETAL MUSCLE In the fascicle, the third connective tissue layer is ENDOMYSIUM separates and electrically isolates each muscle cells from eachother. Epimysium, perimysium and endomysium, three connective tissue layers provide strength and support to muscle. These connective layers bind to muscle cells and merge at the end of muscle continue with tendons.  INTERNAL STRUCTURE OF SKELETAL MUSCLE TT: An invagination of the TC: The sac – like regions of the sarcolemma, has deep SR. Serves as a specialized projections into muscle cells. reservoir of calcium ions. S: The plasma membrane of the T: Composed of three unit, one muscle cell. N: Cellular structure t-tubule lying between that contains genetic adjacent terminal cisternae. material of the cell. M: A cylindrical bundle of contractile filaments within the skeletal muscle cell. Mt: The cytoplasmic organel that is site of ATP synthesis, reffered as “powerhouse “of the cell. C: Intracellular fluid in MC: A contractile cell with SR: Endoplasmic reticulum of the multiple peripheral nuclei and which the organells are muscle cell. It’s interconnecting visible striations, as they are suspended and molecules tubules surround each myofibril. and ions are dissolved. elongated, skeletal muscle cells are ofen reffered muscle fibers.  Sarcoplasmic reticulum (SR) – Intracellular membrane network – Regulation of intracellular [Ca++] Transverse tubules – specialized membrane invaginations T- Tubule STRUCTURE OF MYOFIBRIL The myofibrils are composed of individual contractile proteins, called myoflaments. There are two types of myoflaments, 1. Thin filament 2. Thick filament  Thick Filaments – Myosin  Thin Filaments – Actin – Tropomyosin – Troponin  Under a light microscope, the arrangment of thick and thin filaments in a myofibril creates a repeating pattern of alternating light and dark bands. One repeat of the pattern forms a sarcomere. The repeating units of sarcomeres account for the unique banding pattern seen in striated muscle (which includes both skeletal and cardiac muscle) The sarcomere is the basic contractile unit, and it is delineated by the Z disks. Each sarcomere contains a full A band in the center and one half of two I bands on either side of the A band The repeating units of sarcomeres account for the unique banding pattern seen in striated muscle  Cytoskeletal proteins establish the architecture of the myofibrils, ensuring that the thick and thin filaments are aligned correctly and at proper distances with respect to each other;  Dystrophin  Titin  Nebulin  α-Actinin  Structural proteins: Numerous specialized cytoskeletal proteins rigidly constrain the thick and thin filaments within the framework of a sarcomere and aid in its assembly and maintenance.  a. Actinin: -Actinin binds the ends of thin filaments to the Z disks (Z disks appear as Z lines in micrographs).  b. Titin: Titin is a massive protein (3 million MW). One end is attached to a Z disk, the other to the thick filaments. It forms a spring that limits how much the sarcomere can be stretched. It also centers the thick filaments within the sarcomere.  Nebulin: Nebulin associates with and extends the length of an actin filament. It is believed to act as a molecular ruler that determines thin-filament length during assembly. Dystrophin supports muscle fiber strength, and the absence of dystrophin reduces muscle stiffness, increases sarcolemmal deformability, and compromises the mechanical stability of costameres and their connections to nearby myofibrils.  Skeletal Muscle Physiology of Contraction How does all this functional anatomy work? – 1st – synaptic transmission at the neuromuscular junction – 2nd – excitation-contraction coupling – 3rd – contraction-relaxation cycle Thank You 