Thin filaments - Jordan High School
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Transcript Thin filaments - Jordan High School
Each muscle cell is a fiber
Functions of skeletal muscle:
◦ Produce movement
◦ Maintain posture & position
◦ Support tissues
◦ Guard entrances/exits
◦ Maintain body temp
◦ Store nutrients
Organization of Connective Tissues
Epimysium vs. perimysium vs.
endomysium
Blood vessels & enter perimysium;
arterioles supply endomysium
Nerve fibers penetrate through to
endomysium
Muscle fibers are large &
Sarcolemma surrounds sarcoplasm
multinucleate
Transverse tubules extend into
sarcoplasm to conduct impulses
Myofibril vs. myofilament
Myofilaments:
◦ Thin filaments (actin)
◦ Thick filaments (myosin)
Myofibrils contract to shorten muscle
fiber
Sarcomeres
Myofibrils arrange in sarcomeres
A bands (dark) contain thick & thin
filaments
◦ M line connects thick filaments
I bands (light) contain thin filaments
◦ Z line marks boundary of sarcomere
Thin filament contains twisted actin
strands
◦ Active sites bind to myosin
◦ Tropomyosin blocks active site at rest
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
Muscle fiber shortens & contracts,
pulling muscle
Nervous system & muscle fiber
connect at neuromuscular junction
◦ Examine Figure 10-11 (pg 292-293)
Excitation-contraction coupling
◦ Release of Ca+ causes troponin to open
active sites on actin
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
Twitch = stimulus-contractionrelaxation sequence
◦ Latent period vs. contraction period vs.
relaxation period
Repeated stimulations: treppe, wave
summation, incomplete tetanus,
complete tetanus
Motor unit—all fibers controlled by a
motor neuron
◦ Recruitment adds more muscle fibers
Muscle Tone
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
Muscle fatigue: low oxygen, blood pH
Recovery—muscle fibers return to
pre-exertion condition
Types of Skeletal Muscle Fibers
Fast fibers vs. slow fibers vs.
intermediate fibers
Hypertrophy vs. atrophy
Anaerobic endurance vs. aerobic
endurance
Single nucleus, typically branched,
intercalated discs
Completely dependent on aerobic
metabolism
Have automaticity through pacemaker
cells
Found in sheets in many body systems
Cells spindle-shaped & nonstriated
Contract over wide range of lengths
(plasticity)
Multiunit vs. visceral smooth muscle