lOMoARcPSD|35378278 MUSCULAR SYSTEM MUSCULAR TISSUE makes up 40–50% of total adult body weight. producing body movements stabilizing body positions storing and moving substances within the body, generating heat MYOLOGY is the scientific study of muscles? (myo-: muscle; - logy: study of). TYPES OF MUSCULAR TISSUE 1. Skeletal Muscle Tissue 2. Cardiac Muscle Tissue 3. Smooth Muscle Tissue 1. Skeletal Muscle Tissue Located: moves most of the bones of the skeletons. Striated: Alternating light and dark protein bands works mainly in a voluntary manner. 2. Cardiac Muscle Tissue Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 Located: Forms most of the heart wall. Striated, but its action is involuntary. This built-in rhythm is termed auto rhythmicity. 3. Smooth Muscle Tissue Located: in the walls of hollow internal structures, such as blood vessels, airways, and most organs in the abdominopelvic cavity. It is also found in the skin, attached to hair follicles. lacks the striations with involuntary action. some smooth muscle tissue, such as the muscles that propel food through your gastrointestinal tract, has auto rhythmicity. PROPERTIES OF MUSCULAR TISSUE 1. Electrical excitability Autorhythmic electrical signals Chemical stimuli 2. Contractility 3. Extensibility 4. Elasticity 1. Electrical excitability the ability to respond to certain stimuli by producing electrical signals called action potentials (impulses). Action potentials in muscles are referred to as muscle action potentials; those in nerve cells are called nerve action potentials. Autorhythmic electrical signals Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 arising in the muscular tissue itself, as in the heart’s pacemaker. Chemical stimuli such as neurotransmitters released by neurons, hormones distributed by the blood, or even local changes in pH. 2. Contractility the ability of muscular tissue to contract forcefully when stimulated by an action potential. 3. Extensibility is the ability of muscular tissue to stretch, within limits, without being damaged. 4. Elasticity the ability of muscular tissue to return to its original length and shape after contraction or extension. PARTS OF A SKELETAL MUSCLE Fascia it is a dense sheet or broad band of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscles and other organs of the body. Fascia allows free movement of muscles; carries nerves, blood vessels, and lymphatic vessels; and fills spaces between muscles. THREE LAYERS OF CONNECTIVE TISSUE Epimysium Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 The outermost layer of dense, irregular connective tissue, encircling the entire muscle. Perimysium surrounds groups of 10 to 100 or more muscle fibers, separating them into bundles called fascicles. Many fascicles are large enough to be seen with the naked eye. They give a cut of meat its characteristic “grain”; if you tear a piece of meat, it rips apart along the fascicles. Endomysium Penetrates the interior of each fascicle and separates individual muscle fibers from one another. Epimysium – it is a thick dense connective tissue that surrounds the entire skeletal muscle. Fascicle – bundle of skeletal muscle that is surrounded by perimysium. Perimysium – thin but dense connective tissue that wraps fascicles. Muscle fiber – elongated, multinuclear cells composed of several myofibrils. Endomysium – delicate connective tissue that surrounds muscle fiber. Myofibril – long, cylindrical filament bundles in the sarcoplasm of myocytes. NERVES AND BLOOD SUPPLY Somatic Motor Neuron stimulates skeletal muscle to contract. MICROSCOPIC ANATOMY OF A SKELETAL MUSCLE FIBER Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 Muscle Fiber – structural and functional unit of a skeletal muscle. Diameter:10 to 100 m.* Length: average -10 cm (4 in.) although some are as long as 30 cm (12 in.) SARCOLEMMA, TRANSVERSE TUBULES, AND SARCOPLASM Sarcolemma (sarc- flesh; -lemma- sheath) the plasma membrane of a muscle cell. Transverse (T) tubules, tiny invaginations of the sarcolemma, tunnel in from the surface toward the center of each muscle fiber. Sarcoplasm the cytoplasm of a muscle fiber. Composition: Glycogen – large molecule composed of many glucose molecule; can be used for ATP synthesis. Myoglobin – red-colored protein; found only in muscle, binds oxygen molecules that diffuse into muscle fibers from interstitial fluid. MYOFIBRILS AND SARCOPLASMIC RETICULUM MYOFIBRILS (myo- muscle; -fibrilla little fiber) Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 appears like little threads inside the sarcoplasm; it is the contractile organelles of skeletal muscle. 2m in diameter and extend the entire length of a muscle fiber. Their prominent striations make the entire skeletal muscle fiber appear striped (striated). SARCOPLASMIC RETICULUM A fluid-filled system of membranous sacs which encircles the entire myofibrils. TERMINAL CISTERNS dilated end sacs of the sarcoplasmic reticulum butt against the T tubule from MYOFILAMENTS Myofilaments or filaments small protein structures within the myofibrils Thin filaments are 8 nm in diameter and 1–2 m long and composed mostly of the protein actin, Thick filaments are 16 nm in diameter and 1–2 m long and composed mostly of the protein myosin. Both thin and thick filaments are directly involved in the contractile process. Overall, there are two thin filaments for every thick filament in the regions of filament overlap. The filaments inside a myofibril do not extend the entire length of a muscle fiber. Instead, they are arranged in compartments called sarcomeres Sarcomeres are the basic functional units of a myofibril. COMPONENTS OF SARCOMERE Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 Z discs – narrow, plate-shaped regions of dense protein material separate one sarcomere from the next. Thus, a sarcomere extends from one Z disc to the next Z disc. A band – the darker middle part of the sarcomere which extends the entire length of the thick filaments. -Toward each end of the A band is a zone of overlap, where the thick and thin filaments lie side by side. I band – Is a lighter, less dense area that contains the rest of the thin filaments but no thick filaments and a Z disc passes through the center of each I band. H zone – located in the center of each A band contains thick but not thin filaments. M line – so named because it is at the middle of the sarcomere; at the center of the H zone. Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 MUSCLE PROTEIN Muscle Proteins (1) contractile proteins, which generate force during contraction; Myosin is the main component of thick filaments and functions as a motor protein in all three types of muscle tissue; shaped like two golf clubs twisted together. Motor proteins pull various cellular structures to achieve movement by converting the chemical energy in ATP to the mechanical energy of motion. Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 The myosin tail (twisted golf club handles) points toward the M line in the center of the sarcomere. Tails of neighboring myosin molecules lie parallel to one another, forming the shaft of the thick filament. The two projections of each myosin molecule (golf club heads) are called myosin heads. The heads project outward from the shaft in a spiraling fashion, each extending toward one of the six thin filaments that surround each thick filament. Actin Individual actin molecules join to form an actin filament that is twisted into a helix. On each actin molecule is a myosin-binding site, where a myosin head can attach. (2) regulatory proteins, which help switch the contraction process on and off; (3) structural proteins, which keep the thick and thin filaments in the proper alignment, give the myofibril elasticity and extensibility, and link the myofibrils to the sarcolemma and extracellular matrix. REGULATORY PROTEINS Tropomyosin and troponin are also part of the thin filament. In relaxed muscle, myosin is blocked from binding to actin because strands of tropomyosin cover the myosin-binding sites on actin. The tropomyosin strands in turn are held in place by troponin molecules. You will soon learn that when calcium ions (Ca2) bind to troponin, it undergoes a change in shape; this change moves tropomyosin away from myosin-binding sites on actin and muscle contraction subsequently begins as myosin binds to actin. STRUCTURAL PROTEIN structural proteins, which contribute to the alignment, stability, elasticity, and extensibility of myofibrils. Several key structural proteins are titin, -actinin, myomesin, nebulin, and dystrophin. Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 STRUCTURE OF THICK AND THIN FILAMENTS Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 Sliding filament mechanism of muscle contraction, as it occurs in two adjacent sarcomeres. Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 THE SLIDING FILAMENT MECHANISM Muscle contraction occurs because myosin heads attach to and “walk” along the thin filaments at both ends of a sarcomere, progressively pulling the thin filaments toward the M line. As a result, the thin filaments slide inward and meet at the center of a sarcomere. They may even move so far inward that their ends overlap. As the thin filaments slide inward, the Z discs come closer together, and the sarcomere shortens. However, the lengths of the individual thick and thin filaments do not change. Shortening of the sarcomeres causes shortening of the whole muscle fiber, which in turn leads to shortening of the entire muscle. THE CONTRACTION CYCLE Sarcomeres exert force and shorten through repeated cycles during which the myosin heads attach to actin (cross-bridges), rotate, and detach. During the power stroke of contraction, cross-bridges rotate and move the thin filaments past the thick filaments toward the center of the sarcomere. Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 The role of Ca2 in the regulation of contraction by troponin and tropomyosin. (a) During relaxation, the level of Ca2in the sarcoplasm is low, only 0.1 M (0.0001 mM), because calcium ions are pumped into the sarcoplasmic reticulum by Ca2 active transport pumps. (b) A muscle action potential propagating along a transverse tubule opens Ca2 release channels in the sarcoplasmic reticulum, calcium ions flow into the cytosol, and contraction begins. An increase in the Ca2 level in the sarcoplasm starts the sliding of thin filaments. When the level of Ca2 in the sarcoplasm declines, sliding stops. Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 CARDIAC MUSCLE TISSUE The principal tissue in the heart wall Between the layers of cardiac muscle fibers, the contractile cells of the heart, are sheets of connective tissue that contain blood vessels, nerves, and the conduction system of the heart. Cardiac muscle fibers have the same arrangement of actin and myosin and the same bands, zones, and Z discs as skeletal muscle fibers. intercalated discs are unique to cardiac muscle fibers. These are microscopic structures that are irregular transverse thickenings of the sarcolemma that connect the ends of cardiac muscle fibers to one another. Cardiac muscle tissue has an endomysium and perimysium, but lacks an epimysium. SMOOTH MUSCLE TISSUE visceral (single-unit) smooth muscle tissue (more common type). It is found in the skin and in tubular arrangements that form part of the walls of small arteries and veins and of hollow organs such as the stomach, intestines, uterus, and urinary bladder. Like cardiac muscle, visceral smooth muscle is autorhythmic. multiunit smooth muscle tissue, consists of individual fibers, each with its own motor neuron terminals and with few gap junctions between neighboring fibers. Stimulation of one visceral muscle fiber causes contraction of many adjacent fibers, but stimulation of one multiunit fiber causes contraction of that fiber only. Multiunit smooth muscle tissue is found in the walls of large arteries, in airways to the lungs, in the arrector pili muscles that attach to hair follicles, in the muscles of the iris that adjust pupil diameter, and in the ciliary body that adjusts focus of the lens in the eye. Smooth muscle tissue (a) One autonomic motor neuron synapses with several visceral smooth muscle fibers, and action potentials spread to neighboring fibers through gap junctions. Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 (b) Three autonomic motor neurons synapse with individual multiunit smooth muscle fibers; stimulation of one multiunit fiber causes contraction of that fiber only. (c) Relaxed and contracted smooth muscle fiber. Visceral smooth muscle fibers connect to one another by gap junctions and contract as a single unit. Multiunit smooth muscle fibers lack gap junctions and contract independently. Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 THE MUSCULAR SYSTEM The function of most muscles is to produce movements of body parts. A few muscles function mainly to stabilize bones so that other skeletal muscles can execute a movement more effectively. This chapter presents many of the major skeletal muscles in the body, most of which are found on both the right and left sides. We will identify the attachment sites and innervation (the nerve or nerves that stimulate contraction) of each muscle described. Relationship of skeletal muscles to bones. Muscles are attached to bones by tendons at their origins and insertions. Skeletal muscles produce movements by pulling on bones. Bones serve as levers, and joints act as fulcrums for the levers. Here the lever– fulcrum principle is illustrated by the movement of the forearm. Note where the load (resistance) and effort are applied in (b). Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 Lever structure and types of levers. • based on the placement of the fulcrum, effort, and load (resistance). LEVERS AND FULCRUMS In producing movement, bones act as levers, and joints function as the fulcrums of these levers. A lever is a rigid structure that can move around a fixed point called a fulcrum Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 A lever is acted on at two different points by two different forces: the effort (E), which causes movement; The effort is the force exerted by muscular contraction. the load or resistance, which opposes movement; the load is typically the weight of the body part that is moved or some resistance that the moving body part is trying to overcome (such as the weight of a book you might be picking up). TYPES OF LEVERS 1. first-class levers. The fulcrum is between the effort and the load. 2. second-class levers. The load is between the fulcrum and the effort. 3. third-class levers. The effort is between the fulcrum and the load. Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 NAME MEANING Based on the Direction Rectus Parallel to midline Transverse Perpendicular to midline Oblique Diagonal to midline NAME MEANING Based on the Direction Rectus Parallel to midline Transverse Perpendicular to midline Oblique Diagonal to midline NAME MEANING Based on the Size Maximus Largest Minus Smallest Longus Long Brevis Short Latissimus Widest Longissimus Longest Magnus Large Major Larger Minor Smaller Vastus Huge Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 *************************************** Group of Muscles by FUNCTION 1. Prime Mover/Agonist - Primary responsibility is producing a particular motion. 2. Antagonists - Muscles that oppose a particular movement. 3. Synergists - Muscles that help prime movers and stabilize motion 4. Fixators - Synergist that immobilize a bone. Naming Skeletal Muscles by SIZE 1. 2. 3. 4. Maximus = Large Minimus = Small Longus = Long Brevis = Short Naming Skeletal Muscles by DIRECTION 1. Midline of body = Axis of the bone 2. Rectus = Parallel 3. Transversus = Perpendicular Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 4. Oblique = At some angle Naming Skeletal Muscles by NUMBER OF ORIGINS 1. BI-ceps – Have 2 origins 2. TRI-ceps – Have 3 origins 3. QUAD-riceps – Have 4 origins Naming Skeletal Muscles by TYPE OF MOTION Naming the Skeletal Muscle by LOCATION OF ATTACHEMENT POINT(S) OF ORIGIN + POINT OF INSERTION Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 Naming the Skeletal Muscle by SHAPE Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 IMPORTANT MUSCLES IN THE HUMAN BODY Muscles That Move the Tongue Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 Muscles of the Anterior Neck Muscles That Move the Head Muscles of the Posterior Neck and the Back Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 Muscles That Position the Pectoral Girdle Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 Intrinsic Muscles of the Hand Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 Muscles of the Thigh Gluteal Region Muscles That Move the Femur Muscles That Move the Feet and Toes Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 WHOLE BODY Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 PRINCIPAL SUPERFICIAL SKELETAL MUSCLES. Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 Downloaded by ryan plussi (nasiah.dmitry@falkcia.com) lOMoARcPSD|35378278 MUSCLES OF THE HEAD THAT PRODUCE FACIAL EXPRESSIONS Downloaded by ryan plussi (nasiah.dmitry@falkcia.com)
