Download Thin filaments - Jordan High School

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Each muscle cell is a fiber
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Functions of skeletal muscle:
◦ Produce movement
◦ Maintain posture & position
◦ Support tissues
◦ Guard entrances/exits
◦ Maintain body temp
◦ Store nutrients
Organization of Connective Tissues
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Epimysium vs. perimysium vs.
endomysium
Blood vessels & enter perimysium;
arterioles supply endomysium
Nerve fibers penetrate through to
endomysium
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Muscle fibers are large &
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Sarcolemma surrounds sarcoplasm
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multinucleate
Transverse tubules extend into
sarcoplasm to conduct impulses
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Myofibril vs. myofilament
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Myofilaments:
◦ Thin filaments (actin)
◦ Thick filaments (myosin)
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Myofibrils contract to shorten muscle
fiber
Sarcomeres
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Myofibrils arrange in sarcomeres
A bands (dark) contain thick & thin
filaments
◦ M line connects thick filaments
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I bands (light) contain thin filaments
◦ Z line marks boundary of sarcomere
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Thin filament contains twisted actin
strands
◦ Active sites bind to myosin
◦ Tropomyosin blocks active site at rest
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Thick filament contains myosin
molecules
◦ Myosin heads form cross-bridges when
join thin filaments
Sliding Filament & Contraction

Sliding filament theory of contraction:
◦ I band gets smaller
◦ Zone of overlap gets larger
◦ Z lines move closer together
◦ A band width remains constant
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Muscle fiber shortens & contracts,
pulling muscle
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Nervous system & muscle fiber
connect at neuromuscular junction
◦ Examine Figure 10-11 (pg 292-293)
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Excitation-contraction coupling
◦ Release of Ca+ causes troponin to open
active sites on actin
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Contraction cycle
◦ Examine Figure 10-12 (pg 294-295)
◦ Formation & detachment of cross-bridges
Relaxation


Contraction continues until action
potential, Ca+, and/or ATP reserves
are gone
Muscle fiber returns to original length
Tension & Muscle Fibers

Max tension

No tension

More cross-bridges = more tension
◦ Large zone of overlap, thin filaments don’t
contact center of sarcomere
◦ Thick filaments contact Z lines, OR no
zone of overlap
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Twitch = stimulus-contractionrelaxation sequence
◦ Latent period vs. contraction period vs.
relaxation period
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Repeated stimulations: treppe, wave
summation, incomplete tetanus,
complete tetanus
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Motor unit—all fibers controlled by a
motor neuron
◦ Recruitment adds more muscle fibers
Muscle Tone

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Some motor units remain active &
provide muscle tone
Requires energy even at rest

Muscles use creatine phosphate & ATP
for energy
Aerobic Metabolism

Mitochondria use citric acid cycle &
electron transport chain to provide
95% of needed ATP
Anaerobic Metabolism

Glycolysis breaks down glucose from
glycogen stores
◦ Provides ATP during periods of high
muscle activity
◦ Lactic acid produced

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Muscle fatigue: low oxygen, blood pH
Recovery—muscle fibers return to
pre-exertion condition
Types of Skeletal Muscle Fibers

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Fast fibers vs. slow fibers vs.
intermediate fibers
Hypertrophy vs. atrophy
Anaerobic endurance vs. aerobic
endurance
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Single nucleus, typically branched,
intercalated discs
Completely dependent on aerobic
metabolism
Have automaticity through pacemaker
cells
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Found in sheets in many body systems
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Cells spindle-shaped & nonstriated
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Contract over wide range of lengths
(plasticity)
Multiunit vs. visceral smooth muscle