Muscle Contraction Energy for Movement Muscular System Organization Muscle Contraction Energy for Movement

Functions of the Muscular System Supports the body Makes the bones move Helps maintain constant body temperature Assists movement in cardiovascular and lymphatic vessels Helps protect internal organs and stabilize joints

Structure of Skeletal Muscle Each fascicle is a bundle of muscle fibers Each muscle fiber is a bundle of myofibrils Whole muscle is a bundle of many fasicles Each myofibril is made of many sarcomeres The fascia surrounds the muscle Each sarcomere is made of actin and myosin fibers

Skeletal Muscles Work in Pairs Muscles contract (shorten) or relax Muscle contraction pulls on an attached bone Prime mover = muscle doing the most work Synergists = muscles assisting prime mover Antagonist = muscle with action opposite to prime mover on stationary bone on bone that moves

by direction of muscle fibers by number of attachments Ways to Name Muscles by location by attachment by direction of muscle fibers by shape by number of attachments by action by size

Structure of a Skeletal Muscle Cell cytoplasm, contains organelles and myofibrils plasma membrane bundle of muscle cells (fibers) sarcolemma myofibril sarcoplasm Contains actin and myosin filaments for contraction one myofibril Skeletal muscle cell (fiber) contractile unit one sarcomere Z line Z line extensions of sarcolemma, contact sarcoplasmic reticulum T tubule nucleus Smooth ER, stores calcium sarcoplasmic reticulum

Applying Your Knowledge Synergist Sarcomere Myofibril Antagonist Muscle Fiber A fascicle is a bundle of ________. Which one assists the primer mover? Which one is the contractile unit?

Structure of the Sarcomere Muscle has light and dark bands (striations) corresponding to the placement of myofilaments in the sarcomere.

Sliding Filament Theory of Muscle Contraction Sarcomere shortens when actin filaments slide past myosin filaments and approach one another.

Events at the Neuromuscular Junction Neurotransmitter is released into synaptic cleft between neuron and muscle cell Neurotransmitter binds to receptors on sarcolemma, impulse spreads down T tubules Sarcoplasmic reticulum releases calcium to stimulate contraction

Events at the Sarcomere Attached to tropomyosin at regular intervals Calcium binds to troponin Arranged over myosin binding sites on actin filaments

Events at the Sarcomere ATPase Enzyme Energy from ATPADP + P causes myosin heads to form cross-bridges that pull actin filaments toward the center of the sarcomere.

Applying Your Knowledge Troponin Actin Tropomyosin Myosin Calcium Which is released by the sarcoplasmic reticulum to stimulate contraction? Which one has ATPase activity? Which one binds to calcium? Which one slides past another fiber to shorten the sarcomere?

Whole Muscle Contraction Strength of Contraction depends on number of muscle fibers contracting number of motor units responding number of muscle fibers within a motor unit

Energy for Muscle Contraction anaerobic built up in resting muscle aerobic anaerobic

Slow-and-Fast Twitch Muscle Fibers Slow twitch motor units with fewer fibers many mitochondria myoglobin gives dark color dense capillary beds draw more blood and oxygen Fast twitch motor units with many fibers fewer mitochondria little myoglobin fewer blood vessels Motor units with many fibers