Muscle Lecture Slides PDF 2020

Muscle I Patel 2020 Learning Objectives Overview: Mechanism of muscle contraction and relaxation Discuss and compare the following: Muscle twitch Treppe Wave summation Tetanus...

Muscle I Patel 2020 Learning Objectives Overview: Mechanism of muscle contraction and relaxation Discuss and compare the following: Muscle twitch Treppe Wave summation Tetanus Isotonic and isometric contractions Muscle relaxation  Skeletal Muscle Surrounded by: Epimysium Epimysium Contains: Muscle fascicles 3  The picture can't be display ed. Muscle Fascicle Surrounded by: Perimysium Perimysium Contains: Muscle fibers The picture can't be display ed. 4  The picture can't be display ed. Muscle Fiber Surrounded by: Endomysium Endomysium Contains: Myofibrils The picture can't be display ed. 5  The picture can't be display ed. Myofibril Surrounded by: Sarcoplasmic reticulum Consists of: Sarcomeres (Z line to Z line) The picture can't be display ed. 6  The picture can't be display ed. Sarcomere I band A band Contains: Thick filaments Thin filaments Z line M line Titin Z line H band The picture can't be display ed. 7 Events at the Neuromuscular Junction 8  The picture can't be display ed. Events at the Neuromuscular junction 1) Impulse (action potential) arrives at a nerve terminal Sequence of events at a neuromuscular junction 2) Ca moves into the nerve terminal 2+ 3) Vesicles containing acetylcholine fuses with presynaptic membrane 4) Acetylcholine (Ach) is released into synaptic cleft 5) Acetylcholine binds to the postsynaptic membrane 6) Sudden influx of Na+ into sarcolemma (motor end plate) while K+ moves out 7) Impulse (action potential) spreads into the muscle cells The picture can't be display ed. 8) ACh is broken down to acetyl CoA and choline by acetylcholinesterase 9 Excitation-Contraction Coupling 10  The picture can't be display ed. Excitation-Contraction Coupling Excitation-contraction coupling = link between generation of action potential in sarcolemma & start of muscle contraction Action potential conducted via T-tubules causes release of calcium from terminal cisternae of SR Calcium binding changes the shape of troponin causing the troponin to roll the tropomyosin strand away from the actin Causing the contraction cycle to begin The picture can't be display ed. 11  The picture can't be display ed. The picture can't be display ed. 12 The Cross Bridge Cycle 13  The Sliding Filament Theory: The picture can't be display ed. Muscle Contraction  Activation by nerve causes myosin heads (crossbridges) to attach to binding sites on the thin filament  Myosin heads then bind to the next site of the thin filament  This continued action causes a sliding of the myosin along the actin  The result is that the muscle is shortened (contracted) The picture can't be display ed. 14  The picture can't be display ed. The Sliding Filament Theory The picture can't be display ed. 15  The picture can't be display ed. Muscle Relaxation Duration of contraction depends on: Duration of stimulation at neuromuscular junction Presence of free calcium ions in sarcoplasm Availability of ATP Single stimulus only has brief effect on muscle fibre since ACh is broken down by acetylcholinesterase Therefore contraction will continue only if additional action potentials arrive at synaptic terminal Calcium ions are removed from sarcoplasm via 2 mechanisms: 1. active calcium transport across plasma membrane into ECF 2. active calcium transport back into SR Contraction is an active process while relaxation is entirely The picture can't be display ed. passive 16  The picture can't be display ed. Contraction of a Skeletal Muscle  Muscle fiber contraction is “all or none”  Within a skeletal muscle, not all fibers may be stimulated during the same interval  Different combinations of muscle fiber contractions may give differing responses  Graded responses – different degrees of skeletal muscle shortening The picture can't be display ed. 17  The picture can't be display ed. Frequency of stimulation A Single stimulation produces a muscle twitch Twitches vary in duration depending on type of muscle, its location and internal & external conditions A twitch contains: Latent period: action potential sweeps across sarcolemma & SR releases calcium ions Contraction phase: crossbridge interactions are occurring, tension rises to a peak Relaxation phase: calcium levels fall, active sites covered by tropomyosin, number of active cross-bridges declines The picture can't be display ed. 18  The picture can't be display ed. Tension Production and Contraction Types Tension Production by Muscle Fibers Treppe A stair-step increase in twitch tension Repeated stimulations immediately after relaxation phase Stimulus frequency 50/second Causes a series of contractions with increasing tension The picture can't be display ed. 19  The picture can't be display ed. Tension Production by Muscle Fibers Wave summation Increasing tension or summation of twitches Repeated stimulations before the end of relaxation phase Stimulus frequency 50/second Causes increasing tension or summation of twitches The picture can't be display ed. 20  The picture can't be display ed. Tension Production by Muscle Fibers Incomplete tetanus Twitches reach maximum tension If rapid stimulation continues and muscle is not allowed to relax, twitches reach maximum level of tension The picture can't be display ed. 21  The picture can't be display ed. Tension Production by Muscle Fibers Complete tetanus If stimulation frequency is high enough, muscle never begins to relax, and is in continuous contraction The picture can't be display ed. 22  The picture can't be display ed. Tension Production by Muscles Fibers As a whole, a muscle fiber is either contracted or relaxed Depends on: The number of pivoting cross-bridges The fiber’s resting length at the time of stimulation The frequency of stimulation The picture can't be display ed. 23  The picture can't be display ed. Tension Production by Muscles Fibers Length–Tension Relationships Number of pivoting cross-bridges depends on: Amount of overlap between thick and thin fibers Optimum overlap produces greatest amount of tension Too much or too little reduces efficiency Normal resting sarcomere length Is 75 to 130 percent of optimal length The picture can't be display ed. 24  The picture can't be display ed. Maximum tension is produced when the zone of overlap is large but the thin filaments do not extend At short resting lengths, thin across the sarcomere’s center. filaments extending across the center of the sarcomere interfere If the sarcomeres are stretched too far, the with the normal orientation of thick zone of overlap is reduced or disappears, and thin filaments, decreasing and cross-bridge interactions are reduced tension production. or cannot occur. 100 Tension (percent of maximum) 80 60 When the thick When the zone of overlap is reduced to filaments contact the 40 zero, thin and thick filaments cannot Z lines, the sarcomere interact at all. The muscle fiber cannot cannot shorten—the produce any active tension, and a 20 Normal myosin heads cannot contraction cannot occur. Such extreme range pivot and tension stretching of a muscle fiber is normally cannot be produced. prevented by titin filaments (which tie the 0 thick filaments to the Z lines) and by the 1.2 μm 1.6 μm 2.6 μm 3.6 μm surrounding connective tissues. Sarcomere length Sarcomere length decreases increases Optimal resting length: The normal range of sarcomere The picture can't be display ed. lengths in the body is 75 to 130 percent of the optimal length. 25  The picture can't be display ed. Types of Muscle Contractions  Isotonic contractions  Myofilaments are able to slide past each other during contractions  The muscle shortens  Isometric contractions  Tension in the muscles increases  The muscle is unable to shorten The picture can't be display ed. 26  The picture can't be display ed. Isotonic Contraction Skeletal muscle changes length Resulting in motion If muscle tension  load (resistance): Muscle shortens (concentric contraction) If muscle tension  load (resistance): Muscle lengthens (eccentric contraction) The picture can't be display ed. 27  The picture can't be display ed. Tendon Amount of Muscle Muscle 4 load relaxes tension Peak tension (kg) 2 production Muscle contracts 0 (concentric Contraction contraction) begins Resting length 100 Muscle 2 kg 90 length (percent 2 kg 80 of resting length) 70 Time a muscle is attached to a weight one-half its peak tension potential On stimulation, muscle develops enough tension to lift the weight Tension remains constant for the duration of the contraction even though the length of the muscle changes This is an example of isotonic contraction. The picture can't be display ed. 28  The picture can't be display ed. When the eccentric contraction ends, the unopposed load stretches the muscle until either the muscle tears, a tendon breaks, or the elastic recoil of the skeletal muscle is sufficient to oppose the load. Support removed 4 140 when contraction Muscle begins Peak tension 130 tension 2 (eccentric contraction) (kg) production 120 Muscle 0 length 110 (percent Support removed, contraction begins of resting 100 length) 6 kg Resting length 90 80 6 kg 70 Time Eccentric contraction, the muscle elongates as it generates tension. The picture can't be display ed. 29  The picture can't be display ed. Isometric Contraction Skeletal muscle develops tension, but is prevented from changing length iso-  same, metric  measure Amount of load 6 Muscle Muscle relaxes 4 tension (kg) Peak tension Muscle 2 contracts production (isometric 0 contraction) Contraction begins Length unchanged 100 90 6 kg 6 kg Muscle 80 length (percent 70 Time of resting length) Muscle is attached to a weight that exceeds its peak tension On stimulation, tension will rise to a peak, but the muscle as a whole cannot shorten This is an isometric contraction. The picture can't be display ed. 30  The picture can't be display ed. Load and Speed of Contraction Are inversely related The heavier the load (resistance) on a muscle: The longer it takes for shortening to begin And the less the muscle will shorten The picture can't be display ed. 31  The picture can't be display ed. Muscle Tone  Some fibers are contracted even in a relaxed muscle  Different fibers contract at different times to provide muscle tone  The process of stimulating various fibers is under involuntary control  Increasing muscle tone increases metabolic energy used, even at rest The picture can't be display ed. 32 Learning Objectives Describe the mechanism by which muscle fibres obtain energy Distinguish between energy production in: A resting muscle A moderately active muscle A muscle at peak levels of activity Explain muscle fatigue and recovery from fatigue Describe the role of different hormones on muscle activity  The picture can't be display ed. Energy to Power Contractions ATP Provides Energy for Muscle Contraction Sustained muscle contraction uses a lot of ATP energy Muscles store enough energy to start contraction Muscle fibers must manufacture more ATP as needed The picture can't be display ed. 34  The picture can't be display ed. The picture can't be display ed. 35  The picture can't be display ed. ATP and CP Reserves Adenosine triphosphate (ATP) The active energy molecule Creatine phosphate (CP) The storage molecule for excess ATP energy in resting muscle Energy recharges ADP to ATP Using the enzyme creatine kinase (CK) When CP is used up, other mechanisms generate ATP The picture can't be display ed. 36  The picture can't be display ed. The picture can't be display ed. The picture can't be display ed. 37  The picture can't be display ed. ATP Generation Cells produce ATP in two ways 1. Aerobic metabolism of fatty acids in the mitochondria 2. Anaerobic glycolysis in the cytoplasm The picture can't be display ed. 38  The picture can't be display ed. ATP Generation Aerobic Metabolism Is the primary energy source of resting muscles Breaks down fatty acids Produces 34 ATP molecules per glucose molecule Glycolysis Is the primary energy source for peak muscular activity Produces two ATP molecules per molecule of glucose Breaks down glucose from glycogen stored in skeletal muscles The picture can't be display ed. 39  The picture can't be display ed. Thepicture The picturecan't can'tbe bedisplay displayed. ed. The picture can't be display ed. 40  The picture can't be display ed. The picture can't be display ed. 41  The picture can't be display ed. The picture can't be display ed. The picture can't be display ed. 42  The picture can't be display ed. The picture can't be display ed. 43  The picture can't be display ed. Energy Use and the Level of Muscular Activity Skeletal muscles at rest metabolize fatty acids and store glycogen During light activity, muscles generate ATP through anaerobic breakdown of carbohydrates, lipids, or amino acids At peak activity, energy is provided by anaerobic reactions that generate lactic acid as a by-product The picture can't be display ed. 44  The picture can't be display ed. Resting Muscle Metabolism in a Resting Muscle Fiber In a resting skeletal muscle, the demand for ATP is low, Fatty acids O2 G Blood vessels and there is more than enough oxygen available for mitochondria to meet that demand. Resting muscle fibers absorb fatty acids, which are broken down in the mitochondria creating a surplus of ATP. Glucose Glycogen Some mitochondrial ATP is used to convert absorbed glucose to glycogen. ADP ADP CP Mitochondrial ATP is also used to convert creatine to Mitochondria ATP creatine phosphate (CP). This results in the buildup of energy reserves (glycogen CO2 Creatine and CP) in the muscle. The picture can't be display ed. 45  The picture can't be display ed. Moderate Activity Muscle Metabolism during Moderate Activity During moderate levels of activity, the demand for ATP Fatty acids O2 increases. There is still enough oxygen for the mitochondria to meet that demand, but no excess ATP is produced. Glucose Glycogen The muscle fiber now relies primarily on the aerobic 2 ADP metabolism of glucose from stored glycogen to generate ATP. 2 ATP If the glycogen reserves are low, the muscle fiber can also Pyruvate break down other substrates, such as fatty acids. 34 ADP All of the ATP now produced is used to power muscle 34 ATP contraction. CO2 To myofibrils to support muscle contraction The picture can't be display ed. 46  The picture can't be display ed. Peak Activity Muscle Metabolism during Peak Activity During peak levels of activity, the demand for ATP is enormous. Oxygen cannot diffuse into the fiber fast Lactate enough for the mitochondria to meet that demand. Only a third of the cell’s ATP needs can be met by the mitochondria (not shown). Glucose Glycogen The rest of the ATP comes from glycolysis, and when this 2 ADP produces pyruvate faster than the mitochondria can utilize ADP CP 2 ATP it, the pyruvate builds up in the cytosol. This process is called anaerobic metabolism because no oxygen is used. Pyruvate ATP Creatine Under these conditions, pyruvate is converted to lactic Lactate acid, which dissociates into a lactate ion and a hydrogen ion. To myofibrils to support H+ muscle contraction The buildup of hydrogen ions increases fiber acidity, which inhibits muscle contraction, leading to rapid fatigue. The picture can't be display ed. 47  The picture can't be display ed. Muscle Fatigue When muscles can no longer perform a required activity, they are fatigued Results of Muscle Fatigue Depletion of metabolic reserves Damage to sarcolemma and sarcoplasmic reticulum Low pH (lactic acid) Muscle exhaustion and pain The picture can't be display ed. 48  The picture can't be display ed. The Recovery Period The time required after exertion for muscles to return to normal Oxygen becomes available Mitochondrial activity resumes The picture can't be display ed. 49  The picture can't be display ed. Lactic Acid Removal and Recycling The Cori Cycle The removal and recycling of lactic acid by the liver Liver converts lactate to pyruvate Glucose is released to recharge muscle glycogen reserves The picture can't be display ed. 50  The picture can't be display ed. Oxygen Debt After exercise or other exertion: The body needs more oxygen than usual to normalize metabolic activities Resulting in heavy breathing Also called excess postexercise oxygen consumption (EPOC) The picture can't be display ed. 51  The picture can't be display ed. Hormones and Muscle Metabolism Growth hormone Testosterone Thyroid hormones Epinephrine The picture can't be display ed. 52 Learning Objectives Relate muscle fibre types to muscle performance Distinguish between aerobic and anaerobic endurance Explain implications for muscle performance Describe the effect of exercise and aging on the muscular system  The picture can't be display ed. Types of Muscle Fibers and Endurance Muscle Performance Force The maximum amount of tension produced Endurance The amount of time an activity can be sustained The picture can't be display ed. 54  The picture can't be display ed. Factors affecting muscle performance: 1. Diet that promotes glycogen storage 2. Type of muscle fibres 3. Distribution of muscle fibres 4. Physical conditioning The picture can't be display ed. 55  The picture can't be display ed. 1. Diet that promotes glycogen storage: Stored glycogen Running at typical (gm/kg muscle) marathon pace (min) High CHO diet 40 240 Mixed diet 20 120 High fat diet 6 85 The picture can't be display ed. 56  The picture can't be display ed. Muscle Performance The picture can't be display ed. 57  The picture can't be display ed. 2 - Types of Muscle Fibers Three Major Types of Skeletal Muscle Fibers 1. Fast fibers 2. Slow fibers 3. Intermediate fibers The picture can't be display ed. 58  The picture can't be display ed. 2 - Types of Muscle Fibers Fast Fibers Contract very quickly Have large diameter large glycogen reserves few mitochondria Have strong contractions fatigue quickly The picture can't be display ed. 59  The picture can't be display ed. 2 - Types of Muscle Fibers Slow Fibers Are slow to contract slow to fatigue Have small diameter more mitochondria Have high oxygen supply Contain myoglobin red pigment, binds oxygen The picture can't be display ed. 60  The picture can't be display ed. 2 - Types of Muscle Fibers Intermediate Fibers Are mid-sized Have low myoglobin Have more capillaries than fast fibers slower to fatigue The picture can't be display ed. 61  The picture can't be display ed. The picture can't be display ed. 62  The picture can't be display ed. The picture can't be display ed. 63  The picture can't be display ed. The picture can't be display ed. 64  The picture can't be display ed. The picture can't be display ed. 65  The picture can't be display ed. The picture can't be display ed. 66  The picture can't be display ed. 3. Distribution of types of fibres in muscle % fibre type in quadriceps Fast Twitch Slow Twitch Marathoners 18 82 Swimmers 26 74 Weight lifters 55 45 Sprinters 63 37 The picture can't be display ed. 67  The picture can't be display ed. 4. Physical conditioning May cause muscle hypertrophy associated with cellular changes: ↑ number of mitochondria and mitochondrial enzymes ↑ [glycolytic enzymes] 50% ↑ in glycogen reserves ↑ number of myofilaments and myofibrils 60-80% ↑ in phosphagen components 75-100% ↑ in stored triglycerides The picture can't be display ed. 68  The picture can't be display ed. 4. Physical conditioning Improving power - frequent, brief, intensive activity causes: ↑ number of mitochondria ↑ levels of glycolytic enzymes ↑ glycogen reserves ↑ number of myofibrils ↑ number of myofilaments The picture can't be display ed. 69  The picture can't be display ed. 4. Physical conditioning Improving endurance - sustained, low, intensity activity causes: ↑ muscle capillarity ↑number of mitochondria ↑ levels of intracellular myoglobin ↑ muscle glycogen ↑ activity of ß-oxidation enzymes Fast fibres adopt characteristics of intermediate fibres The picture can't be display ed. 70  The picture can't be display ed. The effect of exercise on muscles Training elicits: a proliferation of muscle capillaries an increase in oxidative enzyme activity a significant improvement in VO2max muscular hypertrophy increased strength and endurance, if the stimulus is of a sufficient intensity and duration Muscle becomes fatigue resistant All of the above increase muscle performance The picture can't be display ed. 71  The picture can't be display ed. The effect of age on muscles Impaired motor performance characterized by slow movements A decrease in muscular strength or maximal force production A decrease in skeletal muscle mass ( Muscular atrophy) A loss of fine co-ordination Symptoms usually result from poor perfusion as a result of vascular alterations (arterial stiffness, varicose veins, etc) The picture can't be display ed. 72 Learning Objectives Describe the cause and pathophysiology related to the muscular system for the following disorders Polio Botulism Tetanus Myasthenia gravis Duchenne’s muscular dystrophy  The picture can't be display ed. Poliomyelitus A viral infectious disease caused by an Enterovirus (poliovirus) results in inflammation of the grey matter in the spinal cord and destroys motor neurons leads to muscle weakness and acute flaccid paralysis. Symptoms include : fever, headache, stiffness in the back and neck, asymmetrical weakness of various muscles, sensitivity to touch, difficulty swallowing, muscle pain, loss of superficial and deep reflexes, paresthesia (pins and needles), irritability, constipation, difficulty urinating and paralysis The virus is communicable and may be spread via the oral-oral (oropharyngeal source) and fecal-oral (intestinal source) routes. There is no cure for the virus, however vaccines are available. The picture can't be display ed. 74  The picture can't be display ed. Poliomyelitus The picture can't be display ed. 75  The picture can't be display ed. Botulism Caused by a bacterial toxin – Clostridium botulinum Botulinum toxin acts by binding presynaptically to recognition sites on the cholinergic nerve terminals decreasing the release of acetylcholine Results in a severe, potentially fatal paralysis of skeletal muscles Infant botulism - Bacterial colonization in the digestive tract. Foodborne botulism – ingestion of toxin from foods (adult intestinal toxemia) Wound botulism - contamination of a wound by the bacterium All forms lead to paralysis - starts with the muscles of the face and then spreads towards the limbs. In severe forms, it leads to paralysis of the breathing muscles and causes respiratory failure. The picture can't be display ed. 76  The picture can't be display ed. Botulism The picture can't be display ed. 77  The picture can't be display ed. Tetanus The primary symptoms are caused by tetanospasmin, a neurotoxin produced by the bacterium Clostridium tetani. Tetanospasmin inhibits the enzyme acetylcholinesterase (therefore it cannot inhibit motor neuron activity) A disease characterized by a prolonged contraction of skeletal muscle fibers. Infection generally occurs through wound contamination and often involves a deep cut or puncture wound. As the infection progresses, muscle spasms develop in the jaw (thus the name "lockjaw") and elsewhere in the body. Infection can be prevented by proper immunization (human tetanus immune globulin) and by post-exposure prophylaxis (2 to 3 injections of tetanus vaccine) The picture can't be display ed. 78  The picture can't be display ed. Tetanus The picture can't be display ed. 79  The picture can't be display ed. Myasthenia Gravis Muscle weakness is caused by circulating antibodies that block acetylcholine receptors at the postsynaptic neuromuscular junction. Muscles become progressively weaker during periods of activity and improve after periods of rest. An autoimmune neuromuscular disease leading to fluctuating muscle weakness and fatigue Fatigue of muscles that control eye and eyelid movement, facial expressions, chewing, talking, and swallowing, breathing and neck and limb movements. Myasthenia is treated with acetylcholinesterase inhibitors or immunosuppressants, and, in selected cases, thymectomy. The picture can't be display ed. 80  The picture can't be display ed. Myasthenia Gravis The picture can't be display ed. 81  The picture can't be display ed. Duchenne’s muscular dystrophy A progressive neuromuscular disorder that is a recessive X-linked form of muscular dystrophy, affecting males, resulting in muscle degeneration and eventual death. It is caused by a mutation in the dystrophin gene, located on the human X chromosome, which codes for the protein dystrophin, an important structural component within muscle tissue. Progressive proximal muscle weakness associated with muscle wasting of the legs and pelvis. Eventually this weakness spreads to the arms, neck, and other areas. There is no current cure for DMD and treatment is generally aimed at controlling the onset of symptoms to maximize the quality of life such as corticosteroids and B2 agonist which help improve muscle strength and orthopaedic appliances (wheelchairs and braces) The picture can't be display ed. 82  The picture can't be display ed. Duchenne’s muscular dystrophy The picture can't be display ed. 83