Chapter 10 Muscle Tissue Lecture Outline Muscle tissue types 1. Skeletal muscle = voluntary striated 2. Cardiac muscle = involuntary striated 3. Smooth muscle = involuntary nonstriated Characteristics 1. cells 2. excitability 3. contractility 4. extensibility 5. elasticity Skeletal Muscle Tissue Functions 1. movement 2. posture 3. stability 4. support 5. guard 6. heat Anatomy Connective tissue sheaths 1. Epimysium Collagen 2. Perimysium Fascicles Collagen & Elastin 3. Endomysium Reticular fibers Satellite cells Tendon Aponeurosis Muscle fiber (cell) Myoblasts Satellite cells Sarcolemma Transmembrane potential Resting potential = -85mV Transverse tubules Sarcoplasm Glycosomes Myoglobin Myofibrils Myofilaments Actin = thin filaments Myosin = thick filaments Sarcoplasmic reticulum: Ca 2+ Terminal cisternae Triad Sarcomere Compostion 1. thick filaments 2. thin filaments 3. stabilizing proteins 4. regulatory proteins Regions 1. A-band 2. M-line 3. H-zone 4. Zone of overlap 5. I-band 6. Z-disc/line Actinins Titin Thin filaments 1. Actin F actin Active site G actin 2. Nebulin 3. Tropomyosin 4. Troponin Cross bridge = contraction Thick filaments 1. Myosin a. tail b. hinge c. head 2. Titin Sliding Filament Theory 1. H-zones and I-bands width 2. Zones of overlap width 3. Z-lines closer 4. A-band constant Events of Muscle Contraction Neuromuscular junction Synaptic terminal Acetylcholine (Ach) Synaptic cleft Motor end plate Ach receptors Acetylcholinesterase (AchE) A. Excitation 1. action potential at terminal 2. Ach released 3. Ach binds receptors Na + channels open 4. action potential down transverse tubules 5. AchE breaks down Ach B. Excitation-Contraction coupling 1. action potential at triad = Ca 2+ release 2. Ca 2+ binds troponin 3. troponin frees active sites C. Contraction 1. actin binds myosin 2. cross bridges 3. power stroke 4. ATP resets myosin 5. repeat Amy Warenda Czura, Ph.D. 1 SCCC BIO130 Chapter 10 Handout
D. Relaxation 1. Ca 2+ absorbed 2. Ca 2+ detaches from troponin 3. tropomyosin covers active sites 4. sarcomeres stretch out Rigor Mortis Necrosis Diseases Botulism Flaccid paralysis Tetanus Spastic paralysis Myasthenia gravis Tension Production Muscle tension Load Cell tension 1. Resting length 2. Frequency of stimulation Twitch a. Latent period b. Contraction phase c. Relaxation phase Treppe Wave summation Incomplete tetanus Complete tetanus Muscle tension 1. Internal tension vs. External tension 2. Number of fibers Motor unit Recruitment Muscle tone Isotonic contractions Isometric contractions Muscle Metabolism Creatine phosphate Creatine phosphokinase Activity 1. Rest Aerobic respiration 2. Moderate activity Aerobic respiration 3. High activity Anaerobic fermentation Glycolysis Lactic acid Muscle fatigue 1. depletion of reserves 2. acid ph Lactic acid disposal Liver Glucose Muscle performance Fiber types 1. Fast glycolytic fibers Fast Myosin ATPase Fermentation: glucose Glycogen 2. Slow oxidative fibers Slow Myosin ATPase Aerobic respiration: glucose, lipid, aa s Mitochondria Myoglobin 3. Intermediate fibers / Fast oxidative fibers Physical conditioning 1. Aerobic exercise 2. Resistance exercise Hypertrophy Growth Hormone Epinephrine Atrophy Cardiac Muscle Tissue Heart Cardiocytes Few nuclei Amitotic Aerobic respiration Mitochondria Myoglobin Glycogen & lipid reserves Intercalated discs Features 1. automaticity 2. nervous adjustment 3. longer contraction 4. twitch only Smooth Muscle Tissue Hollow organs & Arrector pili Circular layer Longitudinal layer Cell Uninuclear Dense bodies Desmin Excitation-Contraction: 1. Ca 2+ released 2. Ca 2+ binds calmodulin 3. Calmodulin activates MLC kinase 4. ATP ADP: cock myosin head 5. Cross bridges contraction Aging myofibrils reserves cardiovascular performance fibrosis satellite cells Amy Warenda Czura, Ph.D. 2 SCCC BIO130 Chapter 10 Handout
Amy Warenda Czura, Ph.D. 3 SCCC BIO130 Chapter 10 Handout
Sarcomere -resting length 1.6-2.6 µm -composed of: 1. thick filaments - myosin 2. thin filaments - actin 3. stabilizing proteins: hold thick and thin filaments in place 4. regulatory proteins: control interactions of thick and thin filaments -organization of the proteins in sarcomere causes striated appearance of the muscle fiber Regions of the sarcomere: 1. A-band = whole width of thick filaments, looks dark microscopically 2. M-line = center of each thick filament, middle of A-band: attaches neighboring thick filaments 3. H-zone = light region either side of M line, contains thick filaments only 4. Zone of overlap = ends of A-bands, place where thin filaments intercalate between thick filaments (triads encircle zones of overlap) 5. I-band = area that contains thin filaments outside zone of overlap (not whole width of thin filaments) 6. Z-line/disc = center of I band, constructed of actinins, function to anchor thin filaments and bind neighboring sarcomeres, titin proteins bind thick filaments to Z-line, Z-lines mark ends of each sarcomere Amy Warenda Czura, Ph.D. 4 SCCC BIO130 Chapter 10 Handout
Thin filaments (5-6nm diameter) made of four proteins: 1. actin 2. nebulin F-actin (filamentous) consists of rows of G-actin (globular), held together with nebulin. Each G- actin has an active site that can bind to myosin 3. tropomyosin: covers the active sites on G actin to prevent myosin binding 4. troponin: holds tropomyosin on the actin. Also has receptor for Ca 2+ : when Ca 2+ binds the troponin-tropomyosin complex it releases actin allowing it to bind to myosin Actin + Myosin binding = crossbridge crossbridge formation = contraction The end of each thin filament is bound to thin filaments in neighboring sarcomeres by actinin in the Z-line Thick Filaments (10-12nm diameter) -composed of bundled myosin molecules each myosin has three parts: 1. tail: tails bundled together to make length of thick filament, all point toward M-line 2. hinge: flexible region, allows movement for contraction 3. head: hangs off tail by hinge, will bind actin at active site. No heads in H-zone -also contains core of titin: elastic protein that attaches thick filament to Z-line -titin holds thick filament in place and aid elastic recoil of muscle after stretching -each thick filament is surrounded by a hexagonal arrangement of thin filaments with which it will interact Amy Warenda Czura, Ph.D. 5 SCCC BIO130 Chapter 10 Handout
The Neuromuscular Junction Neuromuscular junction = where a nerve terminal interfaces with a muscle fiber at the motor end plate, one junction per fiber (control of fiber from one neuron) Synaptic terminal = expanded end of axon, contains vesicles of neurotransmitter Acetylcholine (Ach) Motor end plate = specialized sarcolemma that contains Ach receptors and the enzyme acetylcholinesterase (AchE) Synaptic cleft = space between synaptic terminal and motor end plate where neurotransmitter is released Amy Warenda Czura, Ph.D. 6 SCCC BIO130 Chapter 10 Handout
Excitation resting transmembrane potential restored Vesicles containing Ach fuse with the neuronal membrane and exocytose their contents into the synaptic cleft through sodium channels triggering a change in the transmembrane potential channels close. and the sodium Amy Warenda Czura, Ph.D. 7 SCCC BIO130 Chapter 10 Handout
Excitation-Contraction Coupling Action potential on the sarcolemma is coupled to contraction events via the triads 1. The action potential on the transverse tubules reaches a triad and causes release of calcium ions from the cisternae of the sarcoplasmic reticulum into the sarcoplasm around the zones of overlap of the sarcomeres. 2. Calcium binds to troponin on the thin filaments. 3. Troponin pulls tropomyosin off the active sites of the actin so that cross bridges can form. Amy Warenda Czura, Ph.D. 8 SCCC BIO130 Chapter 10 Handout
Contraction 1. Actin, free of tropomyosin, binds to myosin via its active sites. 2. Cross bridges are formed (actin active sites bound to myosin heads) 3. Myosin heads have been pre-primed for movement via ATP energy prior to cross bridge formation and are pointed away from the M line. Upon actin binding, the myosin heads pivot toward the M line in an event called the power stroke, which pulls the thick filament along the thin filament 4. Myosin ATPase uses ATP to break the cross bridges releasing the myosin head from the actin active site, and resets the myosin head pointed away from the M-line 5. The myosin head is now primed to interact with a new active site on actin. Myosin can carry out 5 power strokes per second while calcium and ATP are available. Each power stroke shortens the sarcomere by 1% Amy Warenda Czura, Ph.D. 9 SCCC BIO130 Chapter 10 Handout