3. Figure 9.2: Connective tissue sheaths of skeletal muscle, an organ (b) (a) Bone Perimysium Endomysium Blood vessel Muscle fiber (cell) Fascicle (wrapped by perimysium) Endomysium (between fibers) Epimysium Tendon Epimysium Muscle fiber in middle of a fascicle Perimysium Blood vessel Endomysium
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7. Patterns of Arrangements of Fascicles in skeletal Muscles Circular arrangement – the orbicularis oris and orbicularis oculi - muscles around the mouth and eyes, respectively
8. Attachment sites for each skeletal muscle Skeletal muscles span joints and they have at least 2 attachment sites – the ORIGIN and the INSERTION The bone that moves (the movable bone) when the skeletal muscle contracts is known as the INSERTION; and the bone that does not move ( the immovable bone) is the ORIGIN . Hence, when the skeletal muscle contracts, the insertion moves toward the origin. Example: Brachioradialis Origin (O) - lateral supracondylar ridge at distal end of the humerus Insertion(I) – base of styloid process of radius Refer to tables in the lab manual and in the textbook ( pages 329-379)
9. Direct Skeletal Muscle Attachments DIRECT ATTACMENTS - the epimysium of the skeletal Muscle is fused directly to the periosteum
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11. Figure 9.2a: Connective tissue sheaths of skeletal muscle, p. 283. (a) Bone Perimysium Endomysium Blood vessel Muscle fiber (cell) Fascicle (wrapped by perimysium) Endomysium (between fibers) Epimysium Tendon INDIRECT ATTACHMENT- the Connective tissue wrappings of the skeletal muscle extends as a tendon or an aponeurosis to anchor the muscle to bone, cartilage or fascia
12. Figure 9.3a-c : Microscopic anatomy of a skeletal muscle fiber , p. 285. Nuclei Fiber Nucleus Light I band Dark A band Sarcolemma Mitochondrion H zone (b) Myofibril (a) (c) Thin (actin) filament Thick (myosin) filament Z disc Z disc
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15. Figure 9.5: Relationship of the sarcoplasmic reticulum and T tubules to myofibrils of skeletal muscle, p. 288. 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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17. Figure 9.4: Composition of thick and thin filaments, p. 286. (b) (c) (d) (e) (a) Heads Flexible hinge region Tail Myosin head Troponin complex Tropomyosin Actin Thin filament Thick filament Thin filament (actin) Thick filament (myosin) Myosin heads Myosin molecule Portion of a thick filament Portion of a thin filament Longitudinal section of filaments within one sarcomere of a myofibril Transmission electron micrograph of part of a sarcomere
18. Figure 9.11: Role of ionic calcium in the contraction mechanism, p. 294. (a) (b) (c) (d) Actin Actin Tnl TnT Tropomyosin Myosin binding sites Troponin complex TnC Myosin head Myosin binding site Additional calcium ions bind Additional calcium ions bind to TnC Myosin head Actin Overview Troponin Tropomyosin Myosin head Plane of (a) Plane of (d) + Ca 2+
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20. Figure 9.3c-e: Microscopic anatomy of a skeletal muscle fiber, p. 285. 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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22. Figure 9.6: Sliding filament model of contraction , p. 289. A Z Z I I A Z Z A Z Z H 1 2 3
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24. Figure 9.7a: The neuromuscular junction, p. 290. (a) Action potential Axon terminal at neuromuscular junction Sarcolemma of the muscle fiber Nucleus Myelinated axon of motor neuron
25. Figure 9.7: The neuromuscular junction, p. 290. (a) (b) (c) Axon terminal of a motor neuron Junctional folds of the sarcolemma at motor end plate Part of a myofibril Mitochondrion Synaptic cleft T tubule Binding of Ach to receptor opens Na + /K + channel Acetylcholinesterase Synaptic cleft ACh molecules Fusing synaptic vesicle Synaptic vesicle Acetic acid Choline Axon terminal Action potential Axon terminal at neuromuscular junction Sarcolemma of the muscle fiber Nucleus Na + K + Myelinated axon of motor neuron Ca 2+
26. Figure 9.7b : The neuromuscular junction, p. 290. (b) Axon terminal of a motor neuron Junctional folds of the sarcolemma at motor end plate Part of a myofibril Mitochondrion Synaptic cleft T tubule Synaptic vesicle Ca 2+
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28. Figure 9.13: A motor unit consists of a motor neuron and all the muscle fibers it innervates , p. 296. (b) (a) Spinal cord Motor neuron cell body Muscle Branching axon to motor unit Muscle fibers Nerve Motor unit 1 Motor unit 2 Muscle fibers Motor neuron axon Axon terminals at neuromuscular junctions
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30. Figure 9.10: Excitation-contraction coupling, p. 292. ADP P i 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 Synaptic vesicle 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 Ca 2+ 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 Ca 2+ by active transport into the SR after the action potential ends. SR Tropomyosin blockage restored, blocking myosin binding sites onactin; contraction ends and muscle fiber relaxes. Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ Ca 2+ 1 2 6 5 4 3
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32. Figure 9.12: The cross bridge cycle, p. 295. ATP ADP ADP ATP hydrolysis ADP ATP P i P i 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 P i , the myosin head is energized (cocked into the high-energy conformation). Inorganic phosphate (P i ) generated in theprevious 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 A s new ATP attaches to the myosin head, the link between Myosin and actin weakens, and the cross bridge detaches. 1 2 3 4
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34. Figure 9.21: Factors influencing force, velocity, and duration of skeletal muscle contraction, p. 304. (a) (b) (c) Increased contractile force Large number of muscle fibers activated Large muscle fibers Asynchronous tetanic contractions Muscle and sarcomere length slightly over 100% of resting length Predominance of fast glycolytic (fatigable) fibers Predominance of slow oxidative (fatigue-resistant) fibers Small load Increased contractile velocity Increased contractile duration
37. Figure 9.20 : Methods of regenerating ATP during muscle activity , p. 303. 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, CO 2 , H 2 O Duration of energy provision: Hours O 2 O 2 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 O 2 H 2 O O 2 Fatty acids Amino acids CP ADP Aerobic respiration in mitochondria CO 2
45. Figure 9.27: Sequence of events in excitation-contraction coupling of smooth muscle, p. 313. ATP P i P i P i P i ADP Calcium ions (Ca 2+ ) enter the cytosol from the ECF or from the scant SR. Ca 2+ binds to and activates calmodulin. Ca 2+ Ca 2+ Ca 2+ Sarcoplasmic reticulum Plasma membrane Activated calmodulin activates the myosin light chain kinase enzymes. Inactive calmodulin Activated calmodulin Inactive kinase Activated kinase Extracellular fluid Cytoplasm The activated kinase enzyme catalyzes transfer of phosphate to myosin heads, activating the myosin head ATPases. Phosphorylated myosin heads form cross bridges with actin of the thin filaments and shortening occurs. Inactive myosin molecule Activated (phosphorylated) myosin molecule Thin myofilament Thick filament Cross bridge activity ends when phosphate is removed from the myosin heads by phosphorylase enzymes and intracellular Ca 2+ levels fall. 1 2 3 4 5 6
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Notes de l'éditeur
Muscle as a tissue
Muscle fibers = skeletal muscle The last bullet was something she mentioned in the lecture Talked about slide 5, 6 SLIDE 4
3 rd organ system muscular system Composed mainly of muscles (organs) Skeletal muscle (organ) Composed of a) skeletal muscle tissue – main component b) connective tissue c) blood vessels d) lymphatic vessels e) nerve fibers Arrangement of skeletal muscle fibers inside the skeletal muscle tissue (which are inside the skeletal muscle) Each skeletal muscle fiber (cell) is wrapped in a delicate connective tissue membrane called the ENDOMYSIUM A group of endomysium-covered skeletal muscle fibers forms a FASCICLE wrapped by CT membrane called the Perimysium A bundle of perimysium-covered fascicles forms skeletal muscle wrapped in a coarse CT membrane called epimysium Went to slide 9
Blood vessels, nerve fibers, etc to form the organ, Then wrote down bullets on slide 3
Went back to slide 2
Attachment sites for skeletal muscles attachment may be DIRECT OR INDIRECT via tendons Most of the skeletal muscle in the body are attached to bones (or cartilage) indirectly 2 advantages to indirect attachment of skeletal muscles: The rope-like tendons can fit into small spaces to reach the bones Skeletal muscles that course over joints will be protected if tendons run directly over the joint sites skeletal muscles will be damaged at the joint sites as the joints move
Microscopic arrangement of the skeletal muscle fiber because this explains the mechanism of skeletal muscle contraction Each skeletal muscle (the organ) consists of skeletal muscle fibers that run the entire length of the skeletal muscle Each skeletal muscle fiber 80% of volume occupied by rod-like structures called MYOFIBRILS (run the entire length of skeletal muscle fibers) MYOFIBRILS are composed of smaller filaments called MYOFILAMENTS 2 types of myofilaments thick filament – thicker than the thin filament thin
2 types of myofilaments thick filament – thicker than the thin filament; composed of structural proteins called myosin structure of a myosin molecule a rod-like tail that ends in 2 globular heads MYOSIN HEADS myosin heads have a binding site for ACTIN; also has binding site for enzyme ATPase that hydrolyzes ATP ADP + Pi; myosin head itself can act as an ATPase THICK FILAMENTS consists of 300 molecules of myosin molecules arranged such that the tails form the core with the heads exposed thin - composed of 3 types of proteins (actin, tropomyosin, troponin) actin – double helical structure that forms the core of the thin filament; contains binding sites for MYOSIN (binding sites on actin bind to the actin binding sites on myosin) tropomyosin – in a relaxed skeletal muscle (not contracted), tropomyosin spirals about the actin blocking myosin binding sites on actin troponin – a three-complex protein that consists of: 1) troponin C binds calcium ions 2) troponin subunit that binds to tropomosin (TnT) 3) troponin subunit that binds to actin and inhibits actin inhibitory troponin (TnI)
In a skeletal muscle fiber, the thick and the thin filaments are arranged in an alternating pattern THICK, THIN, THICK, THIN and so on Which explains the straited appearance of skeletal muscles The thin filaments are anchored/stabilized by proteins called the Z disc or Z lines The distance between 2 successive Z lines is referred to as a SARCOMERE structural unit of skeletal muscle Shortening of sarcomeres results in skeletal muscle contraction ======================== Components of a sarcomere distance between two z-lines z lines anchor the thin filaments in a sarcomere we know the thin and thick filaments alternate in a sarcomere thick filament is referred to as the “A BAND” in a sarcomere the regions of the thin filaments not overlapping with the A band are called the I bands the region of the A band not overlapping with the thin filaments is called the H zone the line bisecting the H zone is called M line anchors the A band in a sarcomere I band are located toward the Z lines The H zone is located in the central region of the A band
Sliding fillament mechanism of the skeletal muscle contraction Sliding of the thin filament in sarcomeres toward the M line in the H zones causes shortening of sarcomeres as the Z lines are pulled inward Since sarcomeres run the entire length of the myofibrils, the myofibrils also shorten Since the myofibrils run the entire length of skeletal muscle fibers, the fibers also shorten Since skeletal muscle fibers run the entire length of the skeletal muscle, the organ (skeletal muscle) ALSO SHORTENS.
10-18 started here
Factors that affect the strength of skeletal muscle contraction force developed by the skeletal muscle Size of the motor units activated Number of motor units activated when we’re looking at recruitment FREQUENCY of skeletal muscle activation If action potentials are developed at a higher rate such that the skeletal muscle fibers do not have time to sequester calcium ions into the SR more and more calcium ions remain in the sarcoplasm resulting in stronger and stronger skeletal muscle contraction this effect is referred to as TEMPORAL (time) or WAVE SUMMATION Slide 35 after slide 34
Drew a graph of strength of skeletal muscle contraction vs. frequency of activation where both increase until a plateau is reached When the skeletal muscle contraction levels off it is called TETANY The response in contraction of a motor unit to a single action potential is what is referred to as a TWITCH
4) (from slide 33) Length of the sarcomere before contraction begins… The optimum length of sarcomeres = 2.0 microns – 2.25 microns At these lengths MAXIMUM contraction of the skeletal muscle because H zone is present and the activated myosin heads can reach/bind to their sites on actin to initiate sliding of the thin filament into the H zone that is available Sarcomere lengths below the optimum (less than 2.0 micron)… The H zone present is decreased hence, sliding of thin filaments is reduced (impeded) = less sliding of the thin filaments less shortening of the sarcomeres less contraction of the skeletal muscle less force generated Sarcomere lengths above the optimum (more than 2.25 micron) Ample space in the H zone; however there is little or NO overlap between the A band and the thin filaments. Hence, the activated myosin heads can NOT reach and bind to their sites on actin NO SLIDING of the thin filaments NO SHORTENING OF SARCOMERES WILL OCCUR NO CONTRACTION of skeletal muscle no force generated
Sources of ATP to support skeletal muscle contraction Stored ATP in skeletal muscle fibers stored ATP can support ONLY 5 seconds of skeletal muscle activity Creatin phosphate (CP) = unique in muscle cells (especially in skeletal muscle fibers) CP phosphorylates ADP to give ATP (ADP + CP ATP + Creatine **where creatine kinase is over the arrow as an enzyme) 3) Catabolism (break down) of glucose in the absence of oxygen is referred to as ANAEROBIC CATABOLISM of glucose (Glycolysis) The anaerobic catabolism of glucose (anaerobic respiration) yields 2 molecules of ATP and pyruvic acid (when O2 absent, pyruvic acid Lactic acid contributes to MUSCLE FATIGUE halts skeletal muscle contraction 4) AEROBIC CATABOLISM OF GLUCOSE (with O2) 36 – 38 molecules of ATP; more efficient in generating ATP to support muscle contraction, BUT it involves MORE steps then anaerobic catabolism of glucose
Based on the table in the book s SLOW oxidative fibers also called RED fibers Fast glycolytic fibers are also called WHITE FIBERS Activities the 3 types of skeletal muscle fibers are suited for Slow oxidative fibers use aerobic respiration to generate ATP hence, they are fatigue-resistant and suited for endurance-type activities A successful marathon runner possesses more of the slow oxidative fibers Fast oxidative fibers are intermediate fibers that are more efficient and fatigue-resistant compared to glycolytic fibers however, they are less efficient when compared to the slow oxidative fibers Hence, you use fast oxidative fibers in medium length activities such as walking, standing Fast glycolytic fibers largest, use anaerobic respiration. Hence, lactic acid builds up, causing muscle fatigue fatigable so they are suited for intense but short-lived activities such as weight lifting
Matured skeletal muscle grows by HYPERTROPHY increase in the size of the skeletal muscle fibers (which are actually cells) in the skeletal muscle Skeletal muscle fibers are MULTINUCLEATE cells and therefore, they lose the ability to undergo mitosis which would have resulted in hyperplasia As skeletal muscle grows by hypertrophy, the larger skeletal muscle generates MORE FORCE = “the bigger the skeletal muscle, the greater the force it generates” Skeletal muscle NOT activated or used will undergo muscle atrophy (DECREASE in skeletal muscle size) decrease the force generated by the skeletal muscle
Usually found lining tracts in the body (tracts = opening to the exterior) No striations
No troponin, z discs absent, no sarcomeres Skeletal muscle fiber (drew T tubule and terminal cisternae) Smooth Muscle cell (shallow dips called caveolae instead of T tubules)
Excitation-contraction coupling of smooth muscle cells Smooth muscle cells may be activated to contract or inhibited from contracting resulting in RELAXATION Smooth muscle cells are innervated by the AUTONOMIC NERVOUS SYSTEM Sympathetic Nervous System Parasympathetic Nervous system Typically, activation of the sympathetic nervous system will result in smooth muscle contraction (exception: in the bronchioles in the lungs, activation of the sympathetic nervous system actually results in relaxation of the smooth muscle BRONCHODILATION) The autonomic fibers innervating the smooth muscle cells form DIFFUSE JUNCTIONS wide spaces between the smooth muscle cells and the ends of the autonomic fibers the ends of the autonomic fibers appear bulbous referred to as VARICOSITIES. HENCE a diffuse junction forms between the sarcolemma of the smooth muscle cell and a varicosity of an autonomic fiber Activation of the parasympathetic nervous system will result in RELAXATION of the smooth muscle. 3) Unlike skeletal muscle, smooth muscle can be activated to contract or relax by blood-borne chemicals such as hormones 4) Some smooth muscle cells have intrinsic cells that depolarize spontaneously to stimulate smooth muscle contraction these cells are called PACEMAKER cells Hence, the smooth muscle has the INTRINSIC ability to contract = pacemaker activity THREE WAYS TO CONTRACT SMOOTH MUSCLE (she went to 45)
SEQUENCE OF EVENTS When smooth muscle is activated to contract by the sympathetic nervous system/chemical/pacemaker activity, depolarization of the sarcolemma causes calcium channels in the sarcolemma to open up and these channels will allow calcium ions in the fluid inside the caveolae to enter into the sarcoplasm of the smooth muscle cell. Entry of calcium ions into the sarcolemma triggers more calcium ions to be released from the poorly developed SR in the smooth muscle cells (TRIADS ARE ABSENT) ** because calcium ions must enter from the extracellular fluid, calcium channel blockers reduce or abolish smooth muscle contraction Since troponin is absent in smooth muscle cells, the increased calcium ions bind to a regulatory protein in the sarcoplasm called CALMODULIN ============== 10/27/10 Excitation-Contraction Coupling in smooth muscle cell step 1: Sarcolemma is depolarized by the pacemaker activity or autonomic fiber activation or by chemicals in blood. step 2: Calcium channels open up in the sarcolemma and Ca+ ions enter the cell from the extracellular fluid in the caveolae. Hence, calcium channel blockers can inhibit smooth muscle contraction Ca+ ions are also released from the SR in the smooth muscle cell **calcium ions to support or initiate smooth muscle contraction come from 2 sources a) extracellular fluid b) from the SR step 3: Calcium ions bind to calmodulin to form Calcium-calmodulin complex step 4: calcium calmodulin complex activates a kinase called MYOSIN LIGHT CHAIN kinase (MLCK) step 5: activated MLCK attaches phosphate to the myosin heads results in activation of the myosin heads step 6: activated myosin heads bind to their sites on actin (in a smooth muscle cell the myosin binding sites on actin are ALWAYS accessible; although tropomysoin is present, it does NOT block myosin binding sites on actin) step 7: the attached activated myosin heads form CROSSBRIDGES and as the phosphate dissociate from the crossbridge, the crossbridge undergoes a change in orientation termed the POWER STROKE which causes the thin filaments to slide downward along the axis of the smooth muscle results in contraction of the smooth muscle step 8: cross bridge detachment is caused by the enzyme PHOSPHORYLASE To cause complete relaxion of the smooth muscle Phosphorylase to cause crossbridge detachment Calcium ions are pumped (active transport) into the SR and out into the extracellular fluid Turn off the pacemaker activity or turn off the hormone released or stop activation of the autonomic nervous system sympathetic nervous system **Activation of the autonomic nervous system may cause smooth muscle relaxation or smooth muscle contraction. In contrast, activation of the motor nuerons ALWAYS cause skeletal muscle contraction
202 material - Cardiac Muscle Striated have sarcomeres Highly branchedwith lateral contacts called INTERCALATED DISCS 2 parts Desmosomes and Gap Junctions Cardiac muscle is located in the wall of the heart in the middle layer of the heart wall called the myocardium If you look at the excitation-contraction coupling of cardiac muscle, it is similar to smooth muscle 1) Pacemaker activity 2) Autonomic Nervous system 3) Chemicals In addition, calcium ions enter the cardiac cells to trigger release of more Ca+ from the SR in the cardiac muscle cells Cardiac muscle similar to skeletal muscle structurally, but similar to smooth muscle in terms of FUNCTION
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