Chapter 10: Muscle Tissue

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Chapter 10Muscle Tissue
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Muscle Tissue

• A primary tissue type, divided into
• Cardiac muscle
• Smooth muscle
• Skeletal muscle
• Attached to bones
• Allows us to move
• Contains CT, nerves and blood vessels

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Functions of Skeletal Muscles

• 1.
• 2.
• 3.
• 4.
• 5.

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CT Organization 3 layers
1. Epimysium

• Surrounds entire muscle
• Separates muscle from surrounding tissues
• Connected to deep fascia

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1. Perimysium

• Divides the skeletal muscle into a series of
  compartments
• Each compartment contains a bundle of muscle
  fibers

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1. Endomysium

• Surrounds individual skeletal muscle fibers
• Interconnects adjacent muscle fibers
• Satellite Cells -

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At the end of a muscle

• All 3 layers come together to form a
• Both attach skeletal muscles to bones
• Tendon fibers extend into the bone matrix
  

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Microanatomy of Skeletal Muscle Fibers

• Skeletal muscle cells are called fibers
• Enormous
• Multinucleate
• Myoblasts fuse during development to form
  individual skeletal muscle fibers

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Microanatomy of Skeletal Muscle Fibers

• Sarcolemma cell membrane of muscle fiber
• Surround sarcoplasm
• Change in the transmembrane potential is the
  start of a contraction
• Transverse Tubules continuous with sarcolemma
  and extends into the sarcoplasm
• form passageways through muscle fibers
• Filled with extracellular fluid
• Action potentials

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Microanatomy of Skeletal Muscle Fibers

• Myofibrils cylindrical structures encircled by
  T tubules
• As long as the cell
• Made of myofilaments
• Thin filaments - actin
• Thick filaments myosin
• Responsible for muscle fiber contraction
• Mitochondria and glycogen

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Microanatomy of Skeletal Muscle Fibers

• Sarcoplasmic Reticulum similar to ER of other
  cells
• Forms network around each myofibril
• Terminal cisternae expanded chambers of SR on
  either side of a T tubule
• Ca2 ions storage
• Triad pair of terminal cisternae plus a T
  tubule
• Separate fluids

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Microanatomy of Skeletal Muscle Fibers

• Sarcomere repeating contractile units that make
  up myofibrils
• Smallest functional unit in muscle fibers
• Muscle contraction
• Made up of thick and thin filaments,
  stabilizing proteins and regulating proteins
• Striated

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Microanatomy of Skeletal Muscle Fibers

• A bands dark bands at center of sarcomere
• Thick filaments (myosin)
• Contains
• M line center of A band, connects each thick
  filament together
• H zone lighter region on either side of M line,
  contains thick filaments
• Zone of overlap thick and thin filaments
  overlap one another

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Microanatomy of Skeletal Muscle Fibers

• I bands light bands on both sides of A band
• Thin filaments (actin)
• Contains
• Z lines boundary between adjacent sarcomeres
• Titin protein that aligns thick and thin
  filaments
• Extends from thick filaments

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Level 1 Skeletal Muscle
Level 4 Myofibril
Level 2 Muscle Fascicle
Level 5 Sarcomere
Level 3 Muscle Fiber
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Muscle Contraction

• Sliding Filament Theory
• Caused by interactions of thick and thin
  filaments
• Triggered by free Ca2 in sarcoplasm

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Muscle Contraction

• Thin Filaments made of 4 proteins
• F actin 2 twisted strands of G actin, contain
  active sites for the binding of myosin
• Nebulin holds 2 strands of G actin together
• Tropomyosin covers G actin active sites to
  prevent actin/myosin interactions
• Troponin holds tropomyosin to G actin AND
  contains a site for the binding of Ca2
• Holds until Ca2 binds to the active site
• Contraction can only occur if position changes

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Muscle Contraction

• Thick Filaments consist of a pair of myosin
  subunits wrapped around each other
• Tail binds to other myosin molecules
• Head 2 subunits, project towards nearest thin
  filament
• During muscle contractions myosin heads pivot
  towards thin filaments, forming cross-bridges
  with G actin active sites

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Muscle Contraction

• Sliding Filament Theory
• Thin filaments slide towards M line shortening
• A band remains the same, but the Z lines move
  closer together

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Muscle Contraction

• Neuromuscular Junction - NMJ
• Where the action potential starts
• Each branch ends at a synaptic terminal, which
  contains mitochondria and Acetylcholine
• Neurotransmitter that alters the permeability of
  the sarcolemma

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Muscle Contraction

• Synaptic cleft
• Motor end plate
• Both contain AChE breaks down Ach
• Action potential travels along the nerve axon and
  ends at the synaptic terminal, which changes the
  permeability
• ACh is released

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Muscle Contraction

• ACh diffuses across the synaptic cleft and binds
  to ACh receptors on motor end plate
• Increase in membrane permeability to sodium ions
  that rush into the sarcoplasm
• Keeps going until AChE removes all ACh
• Travels along sarcolemma to T tubules and leads
  to excitation-contraction coupling -
• Action potential leads to contraction
• Triads release Ca2
• Triggers muscle contractions

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Muscle Contraction at Sarcomere

• 1. Exposure of active sites
• Calcium ions bind to troponin, changing its
  position and shifting tropomyosin away from
  active sites
• 2. Attachment of cross-bridges
• Myosin heads bind to active sites

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Muscle Contraction at Sarcomere

• 3. Pivoting
• Power stroke
• 4. Detachment of cross-bridges
• ATP binds to myosin head, link is broken
• Attach to another active site

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Muscle Contraction at Sarcomere

• 5. Reactivation of myosin
• ATP to ADP and phosphate
• Cycle is repeated
• All sarcomeres contract at the same time
• Contraction duration depends on
• Duration of neural stimulus
• Amount of free Ca2 ions in sarcoplasm
• Availability of ATP

• Muscle Contraction at Sarcomere

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Muscle Contraction

• 1. At NMJ, ACh is released and binds to
  receptors on sarcolemma
• 2. Change in transmembrane potential results in
  action potential that spreads across entire
  surface of cell and T tubules
• 3. SR releases stored calcium ions, increasing
  Ca2 around sarcomeres
• 4. Calcium ions bind to troponin, which exposes
  active sites on thin filaments and cross-bridges
  form
• 5. Contraction begins as repeated cycles of
  cross-bridge formation and detachment happen

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Muscle Contraction

• 6. ACh is broken down by AChE and action
  potential ends
• 7. SR reabsorbs calcium ions and concentration
  in sarcoplasm decreases
• 8. Active sites are re-covered
• 9. Contraction ends
• 10. Muscle relaxation sarcomeres remain
  uncontracted

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Rigor Mortis

• Stop in blood circulation causes skeletal muscles
  to be deprived of oxygen and nutrients
• SR becomes unable to pump calcium ions out of
  sarcoplasm
• Extra calcium ions trigger a sustained
  contraction
• Cross-bridges form, but cannot detach
• Lasts 15-25 hours after death

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2 Types of Muscle Tension

• Isotonic Contraction
• Skeletal muscle changes length resulting in
  motion
• If muscle tension gt resistance muscle shortens
  (concentric contraction)
• If muscle tension lt resistance muscle lengthens
  (eccentric contraction)

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2 Types of Muscle Contraction

• Isometric Contraction
• Muscle develops tension, but does not shorten

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Resistance and Speed of Contraction

• Inversely related
• The heavier the resistance on a muscle
• the longer it takes for shortening to begin
• the less the muscle will shorten

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Muscle Relaxation

• After contraction, a muscle fiber returns to
  resting length by
• Elastic forces
• The pull of elastic elements (tendons and
  ligaments)
• Expands the sarcomeres to resting length
• Opposing muscle contractions
• Reverse the direction of the original motion
• The work of opposing skeletal muscle pairs
• Gravity
• Can take the place of opposing muscle contraction
  to return a muscle to its resting state

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ATP and Muscle Contraction

• Muscle contraction uses a lot of ATP
• Muscles store enough energy to start contraction,
  but must manufacture more ATP
• Generates ATP at the same rate that it is used
• ATP and CP
• ATP active energy model (aerobic and anaerobic)
• Creatine Phosphate (CP) storage molecule for
  excess ATP in resting muscle
• ATP 2 seconds
• CP 15 seconds
• Glycogen 130 seconds (anaerobic) and 40 mins
  (aerobic)
• Fats

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ATP and Muscle Contraction

• At rest
• Cells use fatty acids to create CP, ATP and
  glycogen rebuilding their storages (beta
  oxidation)
• Moderate Activity
• Cells use fatty acids or glucose and oxygen to
  produce ATP (aerobic respiration)
• Muscle wont fatigue until all energy is used up
• Marathon runners
• Peak Activity
• Cells use oxygen faster than it is supplied
• Aerobic resp only provides 1/3 of needed ATP
• Anaerobic resp provides the rest lactic acid

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Muscle Metabolism
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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 SR
• Low pH (lactic acid)
• Muscle exhaustion and pain
• The Recovery Period
• The time required after exertion for muscles to
  return to normal
• Oxygen becomes available
• Mitochondrial activity resumes

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Muscle Fatigue

• The Cori Cycle
• The removal and recycling of lactic acid by the
  liver
• Liver converts lactic acid to pyruvic acid
• Glucose is released to recharge muscle glycogen
  reserves
• Oxygen Debt after exercise
• Body needs more oxygen than usual to normalize
  metabolic activity
• Heavy breathing

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3 Types of Skeletal Fibers

• Fast Fibers
• Contract quickly
• High CP
• Large diameter, huge glycogen reserves and few
  mitochondria
• Strong contractions, but fatigue quickly
• White meat chicken breast
• Slow Fibers
• Slow to contract and slow to fatigue
• Low CP
• Small diameter, but a lot of mitochondria
• High oxygen supply
• Contain myoglobin (red pigment, binds to oxygen)
• Dark meat chicken legs

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3 Types of Muscle Fibers

• Intermediate Fibers
• Mid-sized
• Low myoglobin
• More capillaries than fast fibers, slower to
  fatigue
• Table 10-3, page 298
• Human Muscles

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• Muscle Hypertrophy - muscle Growth from heavy
  training
• increases diameter of muscle fibers
• increases number of myofibrils
• increases mitochondria, glycogen reserves
• Muscle Atrophy lack of muscle activity
• Reduced in muscle size, tone and power

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Physical Conditioning

• Anaerobic Endurance
• Uses fast fibers, fatigues quickly with strenuous
  activities
• 50 m dash, weightlifting
• Improved by frequent, brief, intensive workouts
  interval training
• Aerobic Endurance supported by mitochondria
• Prolonged activity uses a lot of oxygen and
  nutrients
• Marathon running
• Improved by repetitive and cardiovascular
  training

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Cardiac Muscle Tissue

• Striated tissue
• Smaller cells with single nucleus
• Short T-tubules and sarcoplasm
• No triads or terminal cisternae
• All aerobic
• High in myoglobin and mitochondria
• Intercalated discs

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Smooth Muscle

• Blood vessels, reproductive and digestive
  systems, etc
• Different arrangement of actin and myosin
• Non-striated

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Characteristics of Skeletal, Cardiac, and Smooth
Muscle