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Description : Check out this medical presentation on Pathology, which is titled "The Muscular System", to know about the Muscular System (Anatomy and Physiology).

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Published on : Aug 03, 2021 | Views : 3765 | Downloads : 16

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Slide 1-

The Muscular System BIO 137 Anatomy & Physiology I
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Functions of Muscular Tissue Like nervous tissue, muscles are excitable or "irritable” they have the ability to respond to a stimulus Unlike nerves, however, muscles are also: Contractible (they can shorten in length) Extensible (they can extend or stretch) Elastic (they can return to their original shape)
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(b) Cardiac muscle (c) Visceral smooth muscle (a) Skeletal muscle Three Types of Muscular Tissue
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Three Types of Muscular Tissue
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Muscular System Skeletal muscle is the only organ of the muscular system Skeletal muscle is composed of skeletal muscle tissue and also contains nervous tissue, blood vessels and connective tissue Half of the body’s weight is muscle tissue Skeletal muscle = 40% in males, 32% in females Cardiac muscle = 10%
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Deep fascia Surrounds entire skeletal muscle and extends beyond its length Epimysium Closely surrounds skeletal muscle, binds fascicles together Perimysium Surrounds each fascicle Endomysium Surrounds each muscle fiber (cell) Four different connective tissue coverings Skeletal muscle fibers (cells) are arranged into bundles called fascicles Fascicles are bound by connective tissue
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A muscle, a fasciculus, and a fiber all visualized Organization of Muscle Tissue
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Organization of a fasciculus Organization of Muscle Tissue
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Organization of a muscle fiber Organization of Muscle Tissue
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Connective Tissue Coverings Fascia Surrounds an individual skeletal muscle, separating it from other muscles Fascia may extend beyond the ends of the muscle to become a tendon Fascia may connect muscle to muscle and is called an aponeurosis
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Organization of Muscle Tissue Many large muscle groups are encased in both a superficial and a deep fascia Real Anatomy, John Wiley and Sons
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Characteristics of Skeletal Muscle Tissue Long, thin contractile fibers that are Striated Striations due to arrangement of thick and thin filaments Under voluntary control Attached to the bones of the skeleton by tendons Allow for movement, facial expressions, breathing, swallowing, writing, talking and singing, posture, heat production, joint stability
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Skeletal Muscle Arrangement A single muscle cell is a muscle fiber Fibers are made up of myofibrils Myofibrils are made up of thick and thin filaments Sarcolemma – muscle cell membrane Sarcoplasm muscle cell cytoplasm
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Skeletal Muscle Cells Myofibrils are striated Striations due to arrangement of thick and thin filaments Seen as alternating areas of light and dark bands The length of each myofibril is divided into repeating units called sarcomeres A sarcomere is the functional unit of skeletal muscle
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Sarcomere Arrangement
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Sarcomere Structure Sarcomere exists from Z-line to Z-line A-Band is dark middle band Overlapping think and thin filaments I-Band – ends of A-Band, thin filaments only Z-line is in the middle if the I-Band Myosin filaments are held to the Z-line by titin proteins
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Microscopic anatomy of a skeletal muscle fiber I band Z disc Z disc I band A band H zone (c) (d) (e) Thin (actin) filament Thick (myosin) filament Thin (actin) filament Elastic (titin) filaments Z disc Z disc M line M line Sarcomere Thick (myosin) filament I band thin filaments only H zone thick filaments only M line thick filaments linked by accessory proteins Outer edge of A band thick and thin filaments overlap
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Thick Filament Structure Composed of many myosin molecules Each myosin molecule has a tail region and 2 globular heads (crossbridges)
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Thin Filament Structure Composed of actin protein 2 strands of globular actin molecules twisted into a helix Actin filaments have binding sites for myosin cross bridges Tropomyosin protein spirals around actin helix Troponin protein (3 subunits) is attached to actin and holds tropomyosin in place Call this the troponin-tropomyosin complex
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Specialized Organelles of Skeletal Muscle Sarcoplasmic Reticulum (SR) – a type of ER Surrounds each myofibril, running parallel to it Stores calcium, when stimulated, calcium diffuses into sarcoplasm Transverse Tubules (TT) Extends into sarcoplasm as invaginations continuous with sarcolemma T tubules run between cisternae of SR Filled with extracellular fluid Cisternae of SR and TT form a triad near where thick and thin filaments overlap
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Relationship of the sarcoplasmic reticulum and T tubules to myofibrils of skeletal muscle Myofibril Myofibrils Triad Tubules of sarcoplasmic reticulum Sarcolemma Sarcolemma Mitochondrion I band I band A band H zone Z disc Z disc Part of a skeletal muscle fiber (cell) T tubule Terminal cisterna of the sarcoplasmic reticulum M line
Slide 24-

Skeletal Muscle Contraction
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Motor Neuron Nerve cell that innervates skeletal muscle tissue Dendrite Receives information Axon Transmits information Has vesicles containing neurotransmitter that will stimulate or inhibit muscle contraction Neuromuscular Junction -Site where branch of motor neuron (motor nerve ending) comes in contact with sarcolemma of skeletal muscle fiber A type of synapse
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NMJ Motor end-plate Sarcolemma of muscle fiber directly beneath motor nerve ending Contains an abundance of mitochondria and nuclei
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Neuromuscular Junction
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Synapse Junction between the axonal end of one neuron and the dendrite of another neuron OR membrane of another cell type Synaptic cleft Separation that exists between the axonal ending of the motor nerve and the sarcolemma of the muscle cell fiber The axon ending contains vesicles of neurotransmitter
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Neurotransmitter Chemical substance released from vesicles in the motor nerve ending (axonal ending) Acetylcholine (Ach) is the neurotransmitter released by motor neurons When stimulated by a nerve impulse, Ach is released, travels across the synaptic cleft and binds receptors on the motor end plate Stimulates contraction
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Sliding Filament Theory A sarcomere is the functional unit of skeletal muscle When a skeletal muscle contracts, sarcomeres shorten This is described by the sliding filament theory
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Sliding Filament Theory Sarcomeres shorten because thick and thin filaments slide past one another Thin filaments move towards the center of the sarcomere from both ends
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The Sliding-Filament Mechanism The “sliding” of actin on myosin (thick filaments on thin filaments) can be broken down into a 4 step process
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Physiology of Skeletal Muscle Contraction: Neurotransmitter Release Motor impulse is initiated in the brain Travels through the brain and spinal cord to a motor nerve ending Motor nerve endings (axons) depolarize Calcium enters the axonal endings Calcium causes the release of acetylcholine into the neuromuscular junction (synaptic cleft)
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Physiology of Skeletal Muscle Contraction: Depolarization ACh binds receptors on motor end plate Depolarizes skeletal muscle fibers Reverses charge of membrane Impulse travels through transverse tubules to reach all of the muscle fibers Muscle depolarization causes release of calcium from the sarcoplasmic reticulum into the sarcoplasm
Slide 36-

Relationship of the sarcoplasmic reticulum and T tubules to myofibrils of skeletal muscle Myofibril Myofibrils Triad Tubules of sarcoplasmic reticulum Sarcolemma Sarcolemma Mitochondrion I band I band A band H zone Z disc Z disc Part of a skeletal muscle fiber (cell) T tubule Terminal cisterna of the sarcoplasmic reticulum M line
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Physiology of Skeletal Muscle Contraction: Power Stroke Calcium binds troponin (which is attached to tropomyosin Moves tropomyosin from the myosin binding sites on actin Myosin crossbridges (heads) bind to actin ATP hydrolysis supplies energy Actin is pulled inward towards the center of the sarcomere = POWER STROKE Sarcomeres shorten as muscle contracts
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The Sliding-Filament Mechanism With exposure of the myosin binding sites on actin (the thin filaments)—in the presence of Ca2+ and ATP—the thick and thin filaments “slide” on one another and the sarcomere is shortened
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Step 1: ATP hydrolysis Step 2: Attachment
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Step 3: Power Stroke Step 4: Detachment
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The Cross Bridge Cycle ATP ADP ADP ATP hydrolysis ADP ATP Pi Pi Myosin head (high-energy configuration) Myosin head attaches to the actin myofilament, forming a cross bridge. Thin filament As ATP is split into ADP and Pi, the myosin head is energized (cocked into the high-energy conformation). Inorganic phosphate (Pi) generated in the previous contraction cycle is released, initiating the power (working) stroke. The myosin head pivots and bends as it pulls on the actin filament, sliding it toward the M line. Then ADP is released. Myosin head (low-energy configuration) Thick filament As new ATP attaches to the myosin head, the link between Myosin and actin weakens, and the cross bridge detaches. 1 2 3 4
Slide 42-

The Sliding-Filament Mechanism
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Excitation-Contraction Coupling ADP Pi Net entry of Na+ initiates an action potential which is propagated along the sarcolemma and down the T tubules. T tubule Sarcolemma SR tubules (cut) Synaptic cleft Synapticvesicle Axon terminal ACh ACh ACh Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh Action potential in T tubule activates voltage-sensitive receptors, which in turn trigger Ca2+ release from terminal cisternae of SR into cytosol. Calcium ions bind to troponin; troponin changes shape, removing the blocking action of tropomyosin; actin active sites exposed. Contraction; myosin heads alternately attach to actin and detach, pulling the actin filaments toward the center of the sarcomere; release of energy by ATP hydrolysis powers the cycling process. Removal of Ca2+ by active transport into the SR after the action potential ends. SR Tropomyosin blockage restored, blocking myosin binding sites on actin; contraction ends and muscle fiber relaxes. Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ 1 2 6 5 4 3
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Muscle Relaxation Mechanism 1. Acetylcholinesterase present in the NMJ destroys ACh (preventing continual stimulation) 2. Calcium ions are transported from the sarcoplasm back into the SR 3. Linkages between myosin and actin are broken Requires ATP binding THEN: The muscle fiber relaxes
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Contraction in the Sarcomere A band stays the same I band gets smaller H zone gets smaller Sarcomere shortens
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Sliding filament model of contraction A Z Z I I A Z Z A Z Z H 1 2 3
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Energy for Contraction Muscle cells require huge amounts of ATP energy to power contraction The cells have only a very small store of ATP Three pathways supply ATP to power muscle contraction
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ATP Supply for Contraction Pathway 1 DEPHOSPHORYLATION CREATINE PHOSPHATE Pathway 2 AEROBIC RESPIRATION Pathway 3 GLYCOLYSIS ALONE creatine oxygen glucose from bloodstream and from glycogen breakdown in cells ADP + Pi Relaxation Contraction
Slide 49-

Energy for Contraction ATP initially supplied from cellular respiration If ATP is abundant, is converted to creatine phosphate and stored in skeletal muscles When ATP is low, creatine phosphate supplies phosphate to ADP making ATP CP & ATP stores only good for about a 10 second maximal contraction ATP must then come from cellular respiration or glycolysis
Slide 50-

Methods of regenerating ATP during muscle activity Creatine Energy source: CP Oxygen use: None Products: 1 ATP per CP, creatine Duration of energy provision: 15s (a) Direct phosphorylation [coupled reaction of creatine phosphate (CP) and ADP] (b) Anaerobic mechanism (glycolysis and lactic acid formation) (c) Aerobic mechanism (aerobic cellular respiration) Energy source: glucose Oxygen use: None Products: 2 ATP per glucose, lactic acid Duration of energy provision: 30–60 s. Energy source: glucose; pyruvic acid; free fatty acids from adipose tissue; amino acids from protein catabolism Oxygen use: Required Products: 38 ATP per glucose, CO2, H2O Duration of energy provision: Hours O2 O2 ATP ATP net gain Glucose (from glycogen breakdown or delivered from blood) Pyruvic acid Glycolysis in cytosol Glucose (from glycogen breakdown or delivered from blood) Pyruvic acid 2 ATP net gain per glucose 38 Lactic acid Released to blood O2 H2O O2 Fatty acids Amino acids CP ADP Aerobic respiration in mitochondria CO2
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Oxygen & Muscle Contraction Myoglobin of muscle (similar to hemoglobin) binds to and stores oxygen Supplies O2 needed to make ATP for contraction
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Exercise and Skeletal Muscles Prolonged, moderate exercise ATP supplied through cellular respiration Once glycogen stores are depleted in muscle, glucose and fatty acid deliveries from blood are used as fuel source
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Exercise and Contraction In intense strenuous activity, oxygen can be depleted Why? Contraction of skeletal muscles decreases blood delivery to muscles Nutrient and O2 levels in contracting muscles decrease
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Exercise and Skeletal Muscles Intense, strenuous exercise Muscles exceed capacity of respiratory and cardiovascular systems to deliver oxygen for contraction ATP supplied anaerobically through glycolysis Pyruvate is converted to lactic acid Lactic acid builds up in muscles Causes muscles to fatigue
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Oxygen Debt 56 Oxygen not available Glycolysis continues Pyruvic acid converted to lactic acid Liver converts lactic acid to glucose Also the amount of oxygen needed to replace O2 levels in skeletal muscle to pre-exercise levels Amount of oxygen needed by liver cells to use the accumulated lactic acid to produce glucose Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ATP Glucose Glycogen Lactic acid Pyruvic acid Energy to synthesize Energy from Glycolysis and lactic acid formation (in muscle) Synthesis of glucose from lactic acid (in liver) ATP
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Heat Production Cellular respiration is only about 40% efficient About 60% of the energy found in a glucose is lost as heat during cellular respiration Muscle contraction generates heat because muscles use large amounts of nutrients to make ATP, generating large amounts of heat Heat is used to maintain body temperature
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Glycogenolysis Do you remember what glycogen is?????? Glycogenolysis is the breakdown of glycogen into glucose molecules Epinephrine can trigger this pathyway too Depends upon the presence of an enzyme – glycogen phosphorylase
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McArdle’s Disease Absence of the muscle glycogen phosphorylase enzyme Individuals must rely on blood-transported fuels Fatty acids, protein, glucose from the liver These reserves take 5-10 minutes to arrive to the mitochondria Muscles stop functioning until these fuels arrive Autosomal Recessive Disorder
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Symptoms of McArdle’s Disease Premature muscle fatigue and weakness and pain during exercise Muscles can become injured during exercise
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McArdle’s Disease What should an individual with McArdle’s eat? Can they participate in intense strenuous activity? Can they participate in Prolonged, moderate exercise? Where does their supply of ATP come from?