Muscle Tissue PDF

Chapter 10 Introduction to Skeletal Muscle Copyright © McGraw-Hill Education. Permission required for reproduction or display. 1  Muscle Tissue Muscles tissue distributed almost everywhere Three types of muscle tissue: – Compose...

Chapter 10 Introduction to Skeletal Muscle Copyright © McGraw-Hill Education. Permission required for reproduction or display. 1  Muscle Tissue Muscles tissue distributed almost everywhere Three types of muscle tissue: – Composes 40-50% of weight of the adult Some functions of muscular tissue – Allows you to bend your joints – Pumps the blood to body tissues – Propels food we eat along gastrointestinal tract – Changes amount of air that enters the lung 700 skeletal muscles in the muscular system 1. Body movement 2. Maintenance of posture 3. Protection and support 4. Storage and movement of materials - Sphincters 5. Heat production 1  Characteristics of Skeletal Muscle Tissue 1. Excitability – due to resting membrane potential (RMP) – responsive to nervous system stimulation 2. Conductivity – electrical change traveling along plasma membrane – due to the voltage gated channels 3. Contractility – due to contractile proteins within muscle cells – tension used to pull on bones of skeleton 4. Extensibility – e.g., extension of the triceps brachii when flexing elbow joint – Due to partial overlap of the actin and myosin filaments 5. Elasticity – due to protein fibers acting like compressed coils – when contraction ended, tension in proteins 2 released Structural Organization of Skeletal Muscle Tendon Muscle composed of fibers, connective tissue, blood vessels, nerves Deep fascia Epimysium – Three concentric layers of connective Skeletal muscle tissue: epimysium, perimysium, endomysium Dense irregular connective tissue or areolar tissue Artery Vein Perimysium – Provide Nerve protection Fascicle sites for blood vessel and nerve distribution means of attachment to skeleton or Endomysium other structures Electrical insulation Muscle fiber Tendon and aponeurosis https://www.youtube.com/watch?v=SCznFaTwTPE 4 4  Microscopic Anatomy of Skeletal Muscle Myoblasts Multinucleated cell – Elongated cells extending length of Muscle fiber muscle Myoblasts fuse to form a skeletal – Myoblasts are embryonic cells muscle fiber. – Satellite cells Satellite cell – Stem cells Muscle fiber – Contribute nuclei – Proliferate – Differentiate into myoblasts Nuclei Satellite cell 3 Microscopic Anatomy 5  Test your knowledge. Match the following. 1. Sacs of sarcoplasm reticulum surrounding A. _____ T – tubules each myofibril. B. _____ Voltage gated Na+ channels 2. Rings of sarcolemma surrounding myofibril C. _____ Na+/K+ pumps 3. Channels found in the sarcolemma. 4. Channels found in the sarcoplasm reticulum D. _____ Terminal cisternae membrane E. _____ Ca+2 pumps 5. Pumps found the sarcolemma F. _____ Voltage gated Ca+2 Channels 6. Pumps found in the sarcoplasm reticulum membrane G. _____Voltage gated K+ channels  Test your knowledge. Match the following. 1. Sacs of sarcoplasm reticulum surrounding 2 A. _____ T – tubules each myofibril. 3 B. _____ Voltage gated Na+ channels 2. Rings of sarcolemma surrounding myofibril 5 Na+/K+ pumps C. _____ 3. Channels found in the sarcolemma. 1 D. _____ Terminal cisternae 4. Channels found in the sarcoplasm reticulum membrane 6 Ca+2 pumps E. _____ 5. Pumps found the sarcolemma F. 4 Voltage gated Ca+2 Channels _____ 6. Pumps found in the sarcoplasm reticulum membrane 3 G. _____Voltage gated K+ channels  Structure and Organization of a Skeletal Muscle Fiber Myofibrils long cylindrical structures extend length of muscle fiber compose 80% of volume of muscle fiber each fiber with hundreds to thousands Myofilaments bundles of protein filaments takes many to extend length of myofibril two types: thick and thin 6  Thick Filaments Assembled from bundles of protein molecules, myosin – each myosin protein with two intertwined strands – each strand with a globular head and elongated tail – tails pointing toward center of thick filaments – heads pointing toward edges of thick filaments – head with a binding site for actin (thin filaments) – head with site where ATP attaches and is split Thin filaments – 5-6nm in thickness Primarily composed of two strands of protein, actin Two strands twisted around each other Many small spherical molecules, globular actin Connected to form a fibrous strand, filamentous actin Globular actin with myosin binding site where myosin head attaches during contraction Tropomyosin twisted “stringlike” protein cover small bands of the actin strands covers myosin binding sites in a noncontracting muscle Troponin globular protein attached to tropomyosin binding site for Ca2+ together form troponin-tropomyosin complex 6  Organization of Myofilaments: Sarcomere Striations Other structural and functional proteins – Connectin spring like to produce passive tension during contraction during relaxation, passive tension released – Nebulin – Dystrophin Light dark 7  Organization of Myofilaments: Sarcomere Organization of a sarcomere – Myofilaments arranged in repeating units, sarcomeres – Number varies with length of myofibril – Composed of overlapping thick and thin filaments – Delineated at both ends by Z discs specialized proteins perpendicular to myofilaments anchors for thin filaments Light dark 7  Organization of Myofilaments: Sarcomere Overlapping filaments – I bands region containing only thin filaments extend from both directions of Z disc bisected by Z disc appear light under a microscope disappear at maximal muscle contraction – A band central region of sarcomere contains entire thick filament contains partially overlapping thin filaments appears dark under a microscope Light dark 7  Organization of Myofilaments: Sarcomere H zone – central portion of A band – thick filaments only present; no thin filament overlap – disappears during maximal muscle contraction M line – protein meshwork structure at center of H zone – attachment site for thick filaments Form alternating patterns of light and dark regions Appears striated under a microscope – due to size and density differences between thick and thin filaments – Each thin filament with three thick filaments Light dark 7  Sarcomere: Contractility, Extensibility, Elasticity Sliding filament theory Relaxed sarcomere Relaxed sarcomere Z disc Thick filament Z disc Connectin Thin filament Thin filament M line Z disc Z disc M line H zone H zone I band A band I band I band A band I band (a) Relaxed skeletal muscle Contraction Contraction M line Z disc Z disc Z disc Z disc M line A band A band Fully contracted Fully contracted sarcomere sarcomere (b) Fully contracted skeletal muscle 9  Sarcomere: Contractility, Extensibility, Elasticity Sliding filament theory Relaxed sarcomere Relaxed sarcomere Z disc Thick filament Z disc Connectin Thin filament Thin filament M line Z disc Z disc M line H zone H zone I band A band I band I band A band I band (a) Relaxed skeletal muscle Contraction Contraction M line Z disc Z disc Z disc Z disc M line A band A band Fully contracted Fully contracted sarcomere sarcomere (b) Fully contracted skeletal muscle 9  Test your knowledge. Match the following. 1. Myosin proteins are found in A. ______ connectin 2. Actin proteins are found in B. ______ thin filaments 3. Coil like proteins are attached to thick C. ______ troponin filaments 4. These have myosin binding sites D. ______ I bands 5. These cover the myosing binding sites E. ______ tropomyosin 6. Bead like protein found in association with the F. ______ Myosin heads thin filaments which bind Ca+2 G. ______ A bands 7. These have ATPase activity.  Test your knowledge. Match the following. 1. Myosin proteins are found in 3 A. ______ connectin 2. Actin proteins are found in 2 B. ______ thin filaments 3. Coil like proteins are attached to thick 6 C. ______ troponin filaments 2 D. ______ I bands 4. These have myosin binding sites 5. These cover the myosing binding sites E. ______ 4 tropomyosin 6. Bead like protein found in association with the F. ______ 7 Myosin heads thin filaments which bind Ca+2 1 G. ______ A bands 7. These have ATPase activity. 1  Excitability Depends on Resting Membrane Potential Plasma membrane establishes and maintains electrochemical gradient —resting membrane potential Membrane potential—potential energy of charge difference Resting membrane potential (RMP)— potential when a cell is at rest Essential for muscle and nerve cell function 10 Electro-Chemical gradients Na+ Na+ Na+ K+ K+ K+ Na+ K+ K+ K+ Na+ Na+ Electro-Chemical gradients Na+ Na+ Na+ K+ K+ K+ Na+ K+ K+ K+ Na+ Na+ K+ leak channels  Electro-Chemical gradients The role of K+ – Most important determinant in specific value of RMP Na+ Na+ – K moves down steep concentration + gradient through leak channels from Na+ K+ cytosol to interstitial fluid – K+ Negatively charged proteins remain inside cell K+ K+ – Electrochemical gradient Na+ o Positive charge outside repels movement of K+ out K+ Na+ o Negative charge on inside attracts K+ inward o Equilibrium reached when two forces Na+ K+ leak channels become equal K+  Electro-Chemical gradients The role of Na+ – Na+ diffuses into cells from Na+ leak channels interstitial fluid to cytosol simultaneous to the loss of K+ – Enters through Na+ leak Na+ channels Na+ K+ – Down concentration gradient Na+ K+ K+ K+ – Pulled by electrical gradient Na+ – Fewer leak channels prevent as much Na+ into the cytosol Na+ K+ a K+ out – Inside becomes relatively more positive Na+ K+ leak channels K+  Electro-Chemical gradients Na+ leak channels – Na /K pumps significant + + o Maintains K+ and Na + gradients following their K+ K+ Na+/K+ pumps diffusion K+ o Na + pumped out Na+ K+ Na+ o K + pumped in K+ Na+ o Opposite directions Na+ o Against concentration gradient Na+ Na+ K+ leak channels K+  Electro-Chemical gradients Cells maintain an Na+ leak channels electrochemical gradient Na+ electrical charge difference Na+ across plasma membrane Na+ Na+/K+ pumps K+ due to unequal distribution of positive and negative K+ substances across membrane K K + + K + voltage differences termed Na+ membrane potential at rest, termed resting Na+ membrane potential Na+ K+ leak channels K+  Innervation of Skeletal Muscle Fibers Motor Unit – single motor neuron + fibers it controls Varied number of fibers a neuron innervates – small motor units – large motor units – inverse relationship between size of motor unit and degree of control – Fibers dispersed throughout most of a muscle produce a weak contraction over a wide area Muscle tone – Resting tension in a muscle – Generated by involuntary nervous stimulation of muscle – Some motor units stimulated randomly at any time – Doesn’t produce strong enough contraction for movement but helps to stabilize the tendons and joints. 11  Test your knowledge. Match the following. 1. Space between the neuron and the muscle cell A. _______ leak channels 2. Part of muscle cell membrane in contact with B. _______ Synaptic cleft the neuron C. _______ Inside the cell 3. Greater Na+ concentration 4. Greater K+ concentration D. _______ Na+/K+ pumps 5. Role in generating the RMP E. _______ Motor end plate 6. Role is maintaining the RMP F. _______ outside the cell  Test your knowledge. Match the following. 1. Space between the neuron and the muscle cell 5 A. _______ leak channels 2. Part of muscle cell membrane in contact with 1 B. _______ Synaptic cleft the neuron 4 C. _______ Inside the cell 3. Greater Na+ concentration 4. Greater K+ concentration 6 D. _______ Na+/K+ pumps 5. Role in generating the RMP 2 E. _______ Motor end plate 6. Role is maintaining the RMP F. _______ 3 outside the cell Microscopic Anatomy: Neuromuscular Junction 14 12 Overview of Events in Skeletal Muscle Contraction 13  Excitation of Skeletal Muscle Fiber Polio Botulism Tetanus Acetylcholinesterase Myasthenia Gravis https://www.youtube.com/watch?v=8Hu5W_tFXLs 20 14 Excitation-Contraction Coupling 15 16  Sarcomere: https://www.youtube Crossbridge Cycling.com/watch?v=p8iK zWqUU2s Third physiological event Binding of Ca2+ and cross bridge cycling Results in muscle contraction Sliding filament model Results in sarcomere shortening into a contracted state Disappearance of H zone Narrowing or disappearance of I band Z discs closer together 17  Test your knowledge. Match the following. 1. Helps breakdown the neurotransmitter A. _____ Voltage gated Na+ channels 2. Ach gated channels are found here B. _____ Motor end plate 3. Responsible for depolarization C. _____ Ca+2 ions 4. Responsible for repolarization D. _____ ATP 5. Released from terminal cisternae E. _____ Ca+2 ions 6. Binds to troponin F. _____ Voltage gated K+ channels 7. Binds to myosin G. _____ I band 8. When myosin pulls on thin filaments H. _____ Acetylcholinestrase 9. Disappears from a contracted sarcomere I. _____ Power stroke  Test your knowledge. Match the following. 1. Helps breakdown the neurotransmitter 3 Voltage gated Na+ channels A. _____ 2. Ach gated channels are found here 2 Motor end plate B. _____ 3. Responsible for depolarization C. _____ 5 Ca+2 ions 4. Responsible for repolarization 7 ATP D. _____ 5. Released from terminal cisternae 6 Ca+2 ions E. _____ 6. Binds to troponin F. 4 Voltage gated K+ channels _____ 7. Binds to myosin 9 I band G. _____ 8. When myosin pulls on thin filaments H. _____ 1 Acetylcholinestrase 9. Disappears from a contracted sarcomere I. _____ 8 Power stroke  Action Potential the change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell. 18  Skeletal Muscle Relaxation Events in muscle relaxation 1. Termination of the nerve signal in the motor neuron Ceasing of end plate potential Break down the Ach and no further release No further end – plate potential and depolarization 2. Closure of voltage-gated calcium channels in SR Calcium transported back into storage via calcium pumps 3. Return of troponin to its original shape – Tropomyosin moves back – Prevents cross bridge formation – Returns to original relaxed position through natural elasticity of muscle fiber – connectin 19 Skeletal Muscle Metabolism Glycogen and fat reserves Creatine Kinase and Myokinase Three ways to generate ATP in skeletal muscle fiber: Immediate supply via the kinase systems – few seconds only Short-term supply via lactic acid fermentation or anaerobic respiration – glycogen only triglycerides Long-term supply via aerobic cellular respiration – Mitochondria needed 20 Supplying Energy for Skeletal Muscle Contraction Oxygen debt – Amount of additional oxygen that must be inhaled following exercise – Needed to restore pre-exercise conditions – Additional oxygen required to 1. replenish glycogen 2. replace oxygen on hemoglobin and myoglobin 3. replenish ATP and creatine phosphate in 4. convert lactic acid back to glucose (in the liver) 21  Measurement of Skeletal Muscle Tension Muscle tension Force generated when a skeletal muscle stimulated to contract Measured in several laboratory experiments used to produce myogram, graphic recording of changes in muscle tension latent period, all of the events are occurring that lead up to the generation of tension. contraction period, power strokes pull the thin filaments past the thick. During the relaxation period, calcium is returned back to the sarcoplasmic reticulum and crossbridges are released. 46  Measurement of Skeletal Muscle Tension—Changes in Stimulus Intensity: Motor Unit Recruitment Experiments to demonstrate recruitment (Motor unit summation) Each increase in voltage Maximum contractions – increase in tension with increased stimulus Muscle tension – greater number of motor unit contract – tension increases until all motor units stimulated – Helps explain how muscles can exert varying levels of force – Difference in force and precision varied by changing number of motor units 0 1 2 3 4 5 6 7 8 9 Voltage increments (mV) 47 Measurement of Muscle Tension—Temporal/Wave Summation Normal stimulation < 25 stimuli per second Sustained Contraction?  Muscle Fatigue Muscle fatigue – Reduced ability to produce muscle tension due to repetitive stimulation – Decrease in glycogen stores Other causes of muscle fatigue – Problems of excitation at the neuromuscular junction – Problems of excitation-contraction coupling – Problems with crossbridge cycling  Skeletal Muscle Tension : Isometric and Isotonic Contractions Isometric contraction – Muscle tension insufficient to overcome resistance – Contraction of muscle and increased tension – Muscle length the same Isotonic contraction – Muscle tension able to overcome resistance – Results in movement – Tone same but length changes – Concentric contraction muscle shortens as it contracts – Eccentric contraction muscle lengthens as it contracts  Skeletal Muscle Tension: Length-Tension Relationship length-tension curve Influence of muscle length on tension (b) Resting length – tension dependent on length at Muscle tension (% of maximum) 100 (a) Contracted stimulation – Fiber at resting length generates 75 (c) Stretched maximum contractile force 50 – Fiber already contracted weaker contraction when stimulated 25 – Fiber already contracted or 0 overly stretched weaker 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 contraction when stimulated Sarcomere length (µm) Skeletal Muscle Fiber Types Muscle fibers categorized by: 1. type of contraction generated 2. the primary means used for supplying ATP 1. Characteristic of contractions – Differ in power, speed, and duration – Speed based on slow or fast genetic variant of myosin ATPase Slow-twitch fibers FO Fast-twitch fibers SO FO FO greater speed than slow-twitch fibers FG FG a. initiate contraction more quickly following FO SO FG stimulation SO FO b. produce a strong contraction c. produce contraction of shorter duration LM SO 40 x FG 2. Means for supplying ATP – Oxidative fibers – Glycolytic fibers © Gladden Willis/ Visuals Unlimited 22  Effects of Exercise Changes in muscle from a sustained exercise program Hypertrophy – increase in skeletal muscle size – results from repetitive stimulation of fibers – Endurance exercise results in more mitochondria and increased ATP production larger glycogen reserves – Resistance exercise results in more myofibrils that contain larger number of myofilaments Hyperplasia – increase in the number of muscle fibers – may occur in a limited way with exercise Atrophy – decreasing muscle fiber size – results from lack of exercise – can arise from temporary reduction in muscle use (Cast) – causes decrease in muscle tone and power – initially reversible, but dead fibers not replaced – with extreme atrophy, loss of muscle function permanent Location of Smooth Muscle Smooth muscle is found in a variety of organ systems with a variety of roles – In blood vessels of cardiovascular system o Helps regulate blood pressure and flow – In bronchioles of respiratory system o Controls airflow to alveoli – In intestines of digestive system o Mixes and propels materials – In ureters of urinary system o Propels urine from kidneys to bladder – In uterus of female reproductive system o Delivers baby – Several other locations and functions 52  Microscopic Anatomy of Smooth Muscle 1. Smooth muscle cells have fusiform shape 2. Smaller than skeletal muscle fibers 3. Sarcolemma has varied types of Ca2+ channels (gated by chemicals, voltage, etc.) 4. Transverse tubules absent 5. Sarcoplasmic reticulum sparse 6. Arrangement of anchoring proteins and contractile proteins of smooth muscle – Intermediate filaments – Dense bodies – Dense plaques – Lack Z disks and sarcomere arrangement 53  Smooth Muscle Contraction Relaxation of smooth muscle 1. Cessation of stimulation 2. Removal of Ca2+ from sarcoplasm 3. Dephosphorylation of myosin by myosin light-chain phosphatase 4. Can be slow to relax due to latch bridge mechanism 54  Controlling Smooth Muscle Control of smooth muscle – Autonomic (involuntary) nervous system secretes transmitters o Muscle’s response depends on neurotransmitter present and muscle’s receptor for it o E.g., smooth muscle of bronchioles contracts in response to ACh and relaxes in response to norepinephrine – Response to stretch o Myogenic response is contraction in reaction to stretch o Stress-relaxation response is relaxation after prolonged stretch – Other stimulating factors include: o Various hormones, low pH, low O2, high CO2, certain drugs 55  Functional Categories Multiunit smooth muscle – Arranged in units that receive stimulation to contract individually – Found in o Iris and ciliary muscles of the eye o Arrector pili muscles in skin o Larger air passageways in respiratory system o Walls of larger arteries – Degree of contraction depends on number of motor units activated Single-unit (visceral) smooth muscle – Stimulated to contract in unison as cells linked by gap junctions – Form two or three sheets in wall of hollow organ – More common type; locations include o Walls of digestive, urinary, and reproductive tracts o Portions of respiratory tract o Most blood vessels 56