chapter 10 - part 1rnrausch.com/25x/pdf/251/chapter_10a_2x.pdf · 2017-10-25 · chapter 10, part 1...
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Chapter 10, Part 1 - Muscle!
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Chapter 10 - Part 1!Muscle Tissue pp. 289 - 308!
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SECTION 10-1 !Skeletal muscle performs six major functions!
Major focus is on skeletal muscle tissue
Chapter 10, Part 1 - Muscle!
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Cardiac!• Found in walls of heart!• Pumps blood!
Smooth!• Walls of hollow organs!• Moves eggs, sperm, urine, food, hairs!
Skeletal!• Attached to bone or fascia!• Many functions - next slide!
Three Types of Muscle!
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1. Produce skeletal movement!2. Maintain posture and body position!3. Support soft tissues!
• e.g. floor of pelvic cavity!4. Guard entrances and exits!
• e.g. esophagus, external anal sphincter!5. Produce heat - maintain body temperature!6. Store nutrient!
• Breakdown releases amino acids!
Skeletal Muscle Functions!
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SECTION 10-2 !A skeletal muscle contains muscle tissue, connective tissues, blood vessels and nerves!
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Organization of Skeletal Muscles Figure 10-1a !
More details later, but CT
layers are named for where they are relative to a
fascicle.!
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Muscle Fascicle Figure 10-1b!
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Muscle Fiber (Cell) Figure 10-1c!
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SECTION 10-3 !Skeletal muscle fibers have distinctive features!!On a prepared slide:!• Stain darkly (why?) !• Long and thin!• Striated (why?)!• Peripheral nuclei (useful?)!• Multinucleated (why?)!• Do not branch!
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Development of Muscle Fibers Figure 10-2!
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Myoblasts, Myosatellite Cells!
Are stem cells• Live in endomysium!• Function in muscle
development, repair (and hypertrophy/hyperplasia?)!
• Myoblasts proliferate, differentiate, fuse into multinucleate muscle cells!
• Some remain as myosatellite (satellite) cells in skeletal muscle!
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Epimysium surrounds entire muscle!• Dense irregular CT!
Perimysium defines bundles of muscle fibers (fascicles)!• Dense irregular CT!
Endomysium surrounds individual muscle fibers!• Areolar CT!• Myosatellite cells (stem cells)!
All three CT layers contribute to tendons and aponeuroses
Organization of Connective Tissues Layers!
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Muscle CT and Organization Figure 10-6!
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Muscle cell = muscle fiber = myofiber!• Sarcolemma (cell membrane)!
Sarco = “flesh”; lemma = “husk”!• Sarcoplasm (muscle cell cytoplasm)!• Sarcoplasmic reticulum (modified ER)!• T-tubules = invaginations of cell membrane!• Myofibrils = contain contractile proteins
wrapped by SR!• Sarcomeres = regular arrangement of
myofilaments within myofibril!
Skeletal Muscle Fibers (Cells)!
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Structure of a Skeletal Muscle Fiber (Cell) !
Figure 10-3
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Sarcoplasmic Reticulum (SR)!
Specialized smooth endoplasmic reticulum!Wraps around many myofilaments (contractile
proteins) to form myofibrils!Stores Ca2+ in cisternae!• Swellings called terminal cisternae!• Ca2+ is continuously pumped into SR from
cytoplasm!• SR membrane not very leaky (permeable) to
Ca2+ in resting muscle cell!
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Calcium and Muscle Cells!
SR contains calcium-binding protein, calsequestrin!As a result of pumping Ca2+ into the SR:!• [Ca2+] in SR about 40,000X higher than in
sarcoplasm!• Total [Ca2+] = free Ca2+ + Ca2+ bound to
calsequestrin!About 40X more Ca2+ is bound to calsequestrin than is in the form of free Ca2+!
During contraction process, SR membrane becomes leaky, Ca2+ rapidly enters sarcoplasm !
Flux = P • ΔC
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Transverse Tubules Figure 10-3!
Transverse tubules (a.k.a. T-tubules)!• Invaginations of sarcolemma (cell membrane)!• Carry action potential deep into cell!• Contain extracellular fluid!
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SR wraps around myofilaments.!Organizes them into myofibrils.!
Myofibrils Figure 10-3!
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Myofilaments!
Myofilaments = proteins!
Types:!• Thin filament - actin and other proteins!• Thick filament - myosin and titin!
Arranged within myofibril into sarcomeres!
WATCH VIDEOS labeled with a “ ⋅ “ on the Links page. * These are gone. Try Martini’s website or some of the other links on my page.!
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Sarcomeres Figure 10-2!
Sarcomere = smallest functional unit of muscle contraction!• Repeating units along the length of a muscle
fiber!• Regular arrangement causes striated
appearance!
Dark = A bands!Light = I bands!
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Sarcomere Structure, Part 1 Figure 10-4!
Longitudinal section!
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Two Sarcomeres in Series !
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Multiple Sarcomeres at 20,000X!
http://163.178.103.176/Tema1G/Grupos1/GermanT1/GATP18/b3.htm!
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Sarcomere Structure, Part 2 Figure 10-5!• Cross-section!• Note that titin is
missing in this longitudinal section!
Actin!
Myomesin!
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Sarcomere - Filament Arrangement (1 of 2)!
Z line!• Actinin filaments - anchors thin filaments
between sarcomeres!• Titin - attaches here to anchor myosin!
(largest known protein: 27,000 amino acids)!!I band = isotropic = light in color!• Thin filament and titin!• Shrinks when muscle contracts!
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Sarcomere - Filament Arrangement (2 of 2)!
A band = anisotropic = dArk colored!• Where thick filament is present• Does not shrink when muscle contracts!
Contains:!1. M line!• Myomesin - stabilizes thick filaments!
2. H band (zone)!• Thick filament only!
3. Zone of overlap!• Both thin and thick filaments!
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Thin and Thick Filaments Figure 10-7!
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1. F actin• Composed of 2 strands of G actin subunits!• Has active sites (myosin-binding sites)!
2. Nebulin• Helps hold G actin subunits together into F
actin molecule!
Thin Filament (1 of 2) Figure 10-7b!
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Thin Filament - the T-T Complex (2 of 2)!
3. Tropomyosin• Covers myosin-binding sites on actin in
resting muscle!4. Troponin
• Binds tropomyosin!• Binds to G-actin and holds tropomyosin in
place!• Has Ca2+-binding site
5. Dystrophin - links actin to sarcolemma proteins!• Transmits force to membrane → tendons!
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Are bundles of myosin filaments around a titin core• Myosin molecules have elongated tail, globular
head, and hinge region!ü Heads have ATP-binding site!ü Heads form cross-bridges with actin during
contraction!
Thick Filaments Figure 10-7c,d!
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Thick and Thin Filaments Figure 10-7!
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Sliding Filament Theory Figure 10-8!
I band and H zone shrink, A band does not.!Think about why this is the case.!
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SECTION 10-4 !The nervous system communicates with skeletal muscles at the neuromuscular junction!!See “Events at the Neuromuscular Junction” Spotlight on pages 300 and 301.!!See “Excitation-contraction Coupling” Spotlight on page 303.!!See “The Contraction Cycle” Spotlight on pages 304 and 305.!
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Contraction Events – Big Picture!
a. Neural stimulus arrives at muscle cell causing…!b. Ca2+ release from SR into cytoplasm causing…!c. Interaction between thick and thin filaments
causing… !d. Muscle fiber contraction (shortening) causing…!e. Tension produced on tendons!!
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The Neuromuscular Junction Spotlight Figure 10-9!
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Neuromuscular Junction Figure 10-9.1, .2!
Synapse!
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Neuromuscular Junction Figure 10-9.3, .4!
Ca2+ influx ! causes ACh
release!
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Skeletal Muscle Innervation Figure 10-9.5!
Graded potential travels along membrane of synapse.!!Action potential spreads across entire muscle cell membrane.!!(The difference will be discussed in Ch. 12.)!
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In a resting muscle fiber:!
1. [Ca2+] in cytoplasm is relatively low vs. SR!2. [Ca2+] in sarcoplasmic reticulum (SR) is
relatively high (40,000X higher than cytoplasm)!a. Ca2+ is continually pumped into SR!b. Calsequestrin binds Ca2+ within SR!
3. Myosin heads are already “cocked” with ATP!4. Myosin-binding sites on actin are blocked by
troponin-tropomyosin complex!
Conditions in a Resting Muscle Fiber!
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Events Leading to Contraction (1 of 3)!
1. Electrical signal (action potential) travels along axon of motor neuron to motor end plate (a.k.a. neuromuscular junction).!
2. Ca2+ enters the bouton!3. Neurotransmitter (acetylcholine - ACh) is
released into synapse between nerve and muscle cells.!
4. ACh diffuses across synapse and binds to ACh receptors on muscle cell surface.!
5. Receptor changes shape and allows Na+ to move down its concentration gradient into muscle cell.!
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Events Leading to Contraction (2 of 3)!
5. Action potential spreads over muscle cell surface (sarcolemma), including transverse tubules (Excitation).!
6. Sarcoplasmic reticulum releases Ca2+ into cytoplasm (Excitation/Contraction coupling).!
7. Ca2+ interacts with troponin.!8. Troponin pulls tropomyosin.!9. Myosin-binding sites are uncovered.!
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Events Leading to Contraction (3 of 3)!
10. Myosin heads grab and pull on actin. (“power stroke” of contraction)!
11. Myosin heads bind and split new ATP.!12. Myosin heads release actin and “recock” for
another power stroke.!Repeat steps 10–12 as long as [Ca2+] and [ATP]
are high enough.!• Cross-bridges are formed at different times by
individual myosin heads causing a smooth sliding of filaments.!
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Excitation-Contraction Coupling!
Spotlight Figure 10-10!Make certain you understand this before moving on to the details on the next slides.!
E-C coupling is the link between an action potential on the muscle cell membrane and the beginning of contraction.!
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The Contraction Cycle Figure 10-12!
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The Contraction Cycle Figure 10-12.1, .2, .3!
Ca2+ released from SR, then…!
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The Contraction Cycle Figure 10-12.4, .5, .6!
See Links Page – Muscle contraction video 1 !
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1. Motor neuron quits firing → no new ACh release!2. Acetylcholinesterase (AChE) in synapse is
continually breaking down ACh!Result:!• No new action potential on muscle cell!
Ø No new Ca2+ release from SR!Ø Ca2+ continuously pumped into SR!Ø [Ca2+] in cytoplasm drops!
• T-T complex covers up myosin-binding sites!Ø No interaction between actin and myosin!Ø Muscle relaxes passively!
Relaxation!
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Rigor Mortis = “Stiffness of Death”!
• Myosin heads already “cocked” with ATP!• Ca2+ leaks out of SR (ATP required to pump it back in)!
• Intracellular [Ca2+] rises!• T-T complex binds Ca2+ and uncovers myosin-
binding sites!• Contraction occurs!• ATP stores depleted over time !• No ATP available to release myosin from actin
and recock heads!• Rigor mortis!
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Steps Leading to Contraction Figure 10.13 top!
Nice summary!
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Steps Ending a Contraction Figure 10-13 bottom!
Nice summary!
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Some Drug and Toxin Effects on Contraction!
Inhibitory effects!• Block ACh release - Botulinum toxin!• Block binding of ACh to receptor - Atropine
(belladonna), curare!!Excitatory effects!• Block acetylcholinesterase - Neostigmine,
DFP (nerve gas)!• Increase ACh release - some spider venoms!• Mimic ACh - Nicotine!