Chapter 8 Muscular System_SP_09

Chapter 8 Muscular System_SP_09 - The Muscular System...

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1 Chapter 8: The Muscular System The Muscular System Functions: Produces movement Maintains posture Stabilizes joints Generates heat Types of Muscles Voluntary: skeletal muscle Muscle Cells/Fibers Fascicles : bundles of muscle fibers Muscle fiber consists of myofibrils Each myofibril is made of 2 kinds of myofilaments Actin Myosin Muscle Fibers Connective Tissue Wrappings Endomysium : deepest layer – around a single muscle fiber Perimysium : – around a fascicle of fibers Epimysium : – covers entire skeletal muscle Fascia : – on the outside of the epimysium Skeletal Muscle Attachments Muscles attach to bones, The epimysium blends into a connective tissue attachments, which could be either a (an): tendon : cord-like aponeuroses : sheet-like
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2 Structure of a Muscle Fiber Sarcolemma : specialized plasma membrane Sarcoplasmic Reticulum (SR): – specialized smooth endoplasmic reticulum – stores Ca 2+ (for muscle contractions) Sarcomere : contracting unit of muscle – alternating bundles of actin & myosin filaments give a striated appearance Cross Bridges Cross bridges form when the paddle-like extension on the myosin filament heads attach to the actin filaments Nerve Stimulus to Muscles A nerve impulse (an action potential): a spreading wave of electrical charge across a cell membrane Skeletal muscles must be stimulated by a motor nerve to contract Motor unit : 1 motor neuron + muscle fibers stimulated by that neuron Neuromuscular Junction Terms Neurotransmitter : a chemical released by the axonal terminal vesicles of a neuron to stimulate another cell – e.g. Acetylcholine (ACh) for skeletal muscle Excitability/Irritability : the ability to transmit an electrical current along the cell membrane Contractibility : the capacity of a muscle fiber to undergo shortening to become thicker Neuromuscular Junction An association site Muscle Contraction Nerve impulse down a motor neuron triggers synaptic vesicles to release ACh into synaptic cleft ACh binds to receptors on the motor end plate of the receiving muscle fiber starts an action potential SR in muscle cell releases its stored Ca 2+ into the cytoplasm Ca 2+ shifts 2 protein complexes, troponin tropomyosin , on the actin filament, exposing the myosin binding sites myosin heads bind to actin, forming cross bridges
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3 Muscle Contraction Contraction of muscle begins as the myosin head bends toward the center of the sarcomere sliding the actin with it New ATP molecules cause the myosin to disassociate from the actin, releasing Ca 2+ to be pumped back into SR ATP is required for both contraction & relaxation of
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Chapter 8 Muscular System_SP_09 - The Muscular System...

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