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Published byDerick Winfred Ramsey Modified over 9 years ago
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OBJECTIVES At the end of this lecture the student should be able to: Define different types of muscles Enumerate cellular organization of human skeletal muscular system Enumerate molecular organization of human skeletal muscular system
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Muscular System Functions Body movement Maintenance of posture Respiration Production of body heat Communication Constriction of organs and vessels Heart beat
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Properties of Muscle Contractility – Ability of a muscle to shorten with force Excitability – Capacity of muscle to respond to a stimulus Extensibility – the ability to be stretched or to increase in length Elasticity – the ability to return to normal length after extension or contraction.
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Muscle Tissue Types Skeletal – Attached to bones – Nuclei multiple and peripherally located – Striated, Voluntary Smooth – Walls of hollow organs, blood vessels, eye, glands, skin – Single nucleus centrally located – Not striated, involuntary, Cardiac – Heart – Single nucleus centrally located – Striations, involuntary, intercalated disks
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Skeletal Muscle Most skeletal muscles are connected to at least two bones – Muscles attach directly to bone Or muscles attach indirectly to bone through tendons Muscles produce movement by producing tension between its ends Skeletal Muscle Structure – Cellular Level – Molecular Level
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Skeletal Muscle Structure – Cellular Level A Skeletal muscle fiber is an individual muscle cell Muscle fibers are long and narrow in shape – Sarcolemma The plasma membrane of the muscle cell Surrounds the sarcoplasm – Many nuclei (multi-nucleated) Located in the periphery of the muscle cell just beneath the sarcolemma
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Skeletal Muscle Structure – Cellular Level Each muscle fiber contains various organelles specifically designed to meet the needs of the contractile skeletal muscle fiber – Abundant mitochondria High demand for energy (ATP) required for muscle contraction – Myoglobin Protein with a high affinity for oxygen Transfers oxygen from the blood to the mitochondria of the muscle cell
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Skeletal Muscle Structure – Cellular Level Each muscle fiber contains: Myofibrils – a cylindrical bundle of contractile proteins, which are called Myofilaments, within a muscle fiber – Located in the sarcoplasm of the muscle cell Myofilaments – the contractile protein filaments that make up the Myofibrils – Actin – thin filament – Myosin – thick filament
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Skeletal Muscle Structure – Cellular Level Sarcoplasmic reticulum (SR) – Saclike membranous network of tubules Elaborate form of smooth endoplasmic reticulum – Surrounds each myofibril – Contains terminal cisternae Located where the SR ends, which is near the area where actin and myosin overlap – The SR tubules and terminal cisternae store high concentrations of calcium, which is important in the process of skeletal muscle contraction
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Skeletal Muscle Structure – Cellular Level Transverse tubules (T-tubules) – Closely associated with SR – Connected to the sarcolemma – Penetrate the sarcolemma into the interior of the muscle cell (invaginations) – Bring extracellular materials into close proximity of the deeper parts of the muscle fiber SR and T-tubules Function – Activate skeletal muscle contraction when the muscle cell is stimulated by a nerve impulse – Transmit nerve impulses from the sarcolemma to the myofibirls
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Skeletal Muscle Structure – Molecular Level Sarcomere – Smallest contractile unit of the muscle fiber – Arrangement of Myofilaments Alternating bands of light and dark areas Due to the organization of the actin and myosin – Striated appearance
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The Sarcomere A band I band Z disc sarcomere thick filament (myosin) thin filament (actin) titin (filamentous structural protein) M line H zone
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Sarcomere Components Z-lines = borders of the sarcomere – Perpendicular to long axis of the muscle fiber – Anchor thin myofilaments (actin) M-lines – Perpendicular to long axis of the muscle fiber – Anchor thick myofilaments (myosin)
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Sarcomere Components A-Bands Dark area where actin and myosin overlap Equal to the length of the thick myofilaments (myosin) Contains the H-Zone – Lighter area within the A-Band that contains only myosin – The M-Line is located with in the H-zone I-Bands Light area composed of actin only Contains the Z line, which is the boarder of the sarcomere – Actin is directly attached the Z-Line – Appears as a darker line through the I-Band.
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Skeletal Muscle Structure – Molecular Level Actin – G-actin (globular actin) = the basic component of each actin myofilament Contains myosin binding sites – The actin myofilament consists of two strands of G-actin molecules The two strands of G-action molecules are twisted together with two regulatory proteins: – tropomyosin – troponin
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Skeletal Muscle Structure – Molecular Level Tropomyosin – Rod-shaped protein that occupies the groove between the twisted strand of actin molecules – Blocks the myosin binding sites on the G-actin molecules Troponin – A complex of three globular proteins. One is attached to the actin molecule One is attached to tropomyosin One contains a binding site for calcium
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Skeletal Muscle Structure – Molecular Level Myosin – Crossbridges Composed of a rod-like tail and two globular heads – The tails form the central portion of the myosin myofilament – The two globular headsface outward and in opposite directions Interact with actin during contraction. Contain binding sites for both actin and ATP – The enzyme ATP-ase is located at the ATP binding site for hydrolysis of ATP
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