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Transcript of Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier...
Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
Anatomy and Physiology
Chapter 12: Physiology of the Muscular System
Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
General FunctionsMovement of the body and its
partsHeat productionPosture
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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
Function of Skeletal Muscle Tissue Characteristics of skeletal muscle cells
Excitability (irritability)—ability to be stimulated
Contractility—to contract/shorten, & produce movement
Extensibility—to extend/stretch, to return to their resting length
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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
Function of Skeletal Muscle Tissue
Muscle cells are called fibers because of their threadlike shape Contain many mitochondria and several
nuclei Sarcomere
Each myofibril consists of many sarcomeres Segment of myofibril between two
successive Z disks Contractile unit of muscle fibers
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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
Function of Skeletal Muscle Tissue Sarcolemma—plasma membrane of muscle
fibers Sarcoplasmic reticulum (SR)
T tubules—network of tubules and sacs found within muscle fibers
Continually pumps calcium and stores the ions for later release
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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 8
Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
Function of Skeletal Muscle Tissue T tubules
Transverse tubules extend across the sarcoplasm
Membrane has ion pumps that continually transport Ca++ ions
Allow electrical impulses
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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
Myofilaments Each myofibril contains thousands of
thick and thin myofilaments 4 protein molecules make up
myofilaments Myosin
thick filament Myosin “heads” attracted to actin
Form cross bridges when attached to actin
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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
4 different kinds of protein cont..2.) Actin—protein that forms thin filament
3.) Tropomyosin—protein that blocks the active sites on actin molecules
4.) Troponin—protein that holds tropomyosin molecules in place
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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
Mechanism of contraction Excitation and contraction
1. Skeletal muscle fiber remains at rest
2. Stimulated by a motor neuron• Neuromuscular junction(NMJ)—motor
neurons connect to the sarcolemma at the motor endplate
• “NMJ” is a synapse where neurotransmitter transmit signals
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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
Excitation and contraction (cont)
Acetylcholine: neurotransmitter released into the synaptic cleft
1. Stimulates the receptors
2. Initiates an impulse in sarcolemma
3. Triggers the release of calcium ions
4. Calcium binds to troponin, which expose active sites on actin
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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 20
Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 21
Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
Sliding filament model/theory
Active sites on actin are exposed, myosin heads bind to them
Myosin heads bend and “pull” the thin filaments past them
Each head releases, binds to the next active site, and pulls again
The entire myofibril shortens
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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
Whole Muscle Contraction
A single muscle fiber has an “all or nothing” response
But a whole muscle can vary its force of contraction.
Two characteristics of a whole muscle allow this
• Motor unit
• Recruitment
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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
Function of Skeletal Muscle Organs Motor unit
Motor unit= motor neuron + the muscle fibers it attaches
Could be a couple of fibers or an entire fascicle
• Recruitment: Smaller the number of fibers in a motor
unit, the more precise are the available movements
Larger the number of fibers in a motor unit, the more powerful the contraction available
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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
Energy sources for muscle contraction
ATP yields the energy required for muscular contraction
Muscle fibers resynthesize ATP from the breakdown of creatine phosphate (CP)
• Catabolic pathways Aerobic pathway
Presence of O2 from blood Slower than anaerobic pathway Supplies energy for the long term rather than
the short term
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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
Catabolic pathways (cont)
Anaerobic pathway Little to no O2 is available Very rapid, providing energy during
first minutes of maximal exercise Formation of lactic acid
Requires oxygen to convert back to glucose,
Soreness producing of an “oxygen debt” excess post-exercise oxygen consumption
(EPOC)27
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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 29
Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
Responses of a Whole Muscle
• Twitch: Single muscle response in which muscle contracts and then fully relaxes
• Tetanus: Sustained muscle contraction caused by repeated stimulation
• Smooth, sustained contraction
• Tonus: Normal, continuous state of partial muscle contraction
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Speeds of response depends on which fibers are stimulated:Type I: slow-twitch (weakest force,
longest time)
Type II: fast-twitch (2 divisions)type IIa: intermediate speedtype IIb: fastest (greatest force, shortest time)
Skeletal Muscle Fiber Types
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Isotonic vs. Isometric contractions
Isotonic contraction: “same tension” Contraction where tone/tension of
muscle is the same as the length changes
Concentric—muscle shortens as it contracts
Eccentric—muscle lengthens while contracting
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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc.
Isometric contraction
Isometric: “same length” o muscle length stays the same
while muscle tension increases
Most body movements occur as a result of both types of contractions
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