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: Ca2+ 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 = Ca2+ release 2. Ca2+ binds troponin 3. troponin moves tropomyosin off active sites C. Contraction 1. myosin heads bind actin active sites 2. cross bridges 3. power stroke 4. myosin ATPase resets myosin 5. repeat

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D. Relaxation 1. Ca2+ absorbed 2. Ca2+ 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. Ca2+ released 2. Ca2+ 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

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Sarcomere-resting length 1.6-2.6 µm-composed of:

1. thick filaments - myosin2. thin filaments - actin3. stabilizing proteins: hold thick and thin filaments in place4. 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 microscopically2. M-line = center of each thick filament, middle of A-band: attaches neighboring thick filaments3. H-zone = light region either side of M line, contains thick filaments only4. 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

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Thin filaments (5-6nm diameter)made of four proteins:

1. actin 2. nebulinF-actin (filamentous) consists of rows of G-actin (globular), held together with nebulin. Each G-

actin has an active site that can bind to myosin3. tropomyosin: covers the active sites on G actin to prevent myosin binding4. troponin: holds tropomyosin on the actin.

Also has receptor for Ca2+: when Ca2+ binds the troponin-tropomyosin complex it releases actin allowing it to bind to myosin

Actin + Myosin binding = crossbridge → crossbridge formation = contractionThe 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 moleculeseach myosin has three parts:1. tail: tails bundled together to make length of thick filament, all point toward M-line2. hinge: flexible region, allows movement for contraction3. 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

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The Neuromuscular Junction

Neuromuscular junction = where a nerve terminal interfaces with a muscle fiber at the motor end plate, onejunction 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

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Excitation

Vesicles containing Ach fuse with theneuronal membrane and exocytosetheir contents into the synaptic cleft through sodium channels triggering

a change in the transmembrane potentialand the sodium

channels close.

resting transmembrane potential restored

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Excitation-Contraction CouplingAction 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 thesarcomeres.

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.

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Contraction

1. Actin, free oftropomyosin, binds tomyosin via its active sites.

2. Cross bridges are formed (actin activesites bound to myosin heads)

3. Myosin heads have been pre-primed for movement via ATPenergy prior to cross bridge formation and are pointed awayfrom the M line. Upon actin binding, the myosin heads pivottoward the M line in an event called the power stroke, whichpulls the thick filament along the thin filament

4. Myosin ATPase uses ATP to break the crossbridges releasing the myosin head from the actinactive site, and resets the myosin head pointed awayfrom the M-line

5. The myosin head is now primed to interact with anew active site on actin. Myosin can carry out 5power strokes per second while calcium and ATPare available. Each power stroke shortens thesarcomere by 1%

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