Chapter 8 Muscular System_Slides_Handout

Chapter 8 Muscular System_Slides_Handout - Functions of the...

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1 Chapter 8: The Muscular System Functions of the Muscular System Produces movement Maintains posture Stabilizes joints Generates heat Types of Muscles Smooth muscle 1 nucleus; no striations; involuntary in the walls of hollow organs (viscera) Cardiac muscle (myocardium) 1 nucleus; striations; involuntary only in the heart Skeletal muscle multinucleate; striated; voluntary attached by tendons to bones Muscle Fibers Muscle cells = muscle 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 of Skeletal Muscle 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
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2 Skeletal Muscle Attachments Muscles attach to bones, cartilages, The epimysium blends into a connective tissue attachments, which could be either a (an): tendon : cord-like aponeuroses : sheet-like Structure of a Muscle Fiber Sarcolemma : specialized plasma membrane Sarcoplasmic Reticulum (SR): specialized smooth endoplasmic reticulum stores Ca 2+ (for muscle contractions) Sarcomere : the 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) is 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 + the muscle fibers stimulated by that neuron Neuromuscular Junction Terms Neurotransmitter : a chemical released by a neuron to stimulate another cell Acetylcholine (ACh) for skeletal muscle Excitability/Irritability : 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 Function of the Neuromuscular Junction
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3 Muscle Contraction Nerve impulse down 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 Muscle Contraction Contraction of muscle begins as the myosin head bends
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Chapter 8 Muscular System_Slides_Handout - Functions of the...

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