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Functions of skeletal muscles
Movement Maintain posture and body position Support soft tissues, ex abdominal wall
supports ventral body organs Guards entrances and exits- openings of
digestive tract are encircled w/ muscle Maintain body temperature
Anatomy of Skeletal Muscle
Epimysium- dense layer of collagen that surrounds the entire muscle
Perimysium- divide muscle into smaller compartments called fascicles, which contain blood vessels and nerves
Endomysium- surrounds individual muscle fibers These 3 fibers join together at the end of muscles
to form tendons
Microanatomy of muscle tissue
Skeletal muscle cells are multinucleated, so that they can more quickly produce proteins and enzymes necessary for proper muscle contractions
Myoblasts fuse together to make muscle fibers
The Sarcolemma
Sarcolemma- cell membrane of muscle fiber Sarcoplasm- cytoplasm of muscle fiber Transverse Tubules “T tubules”-
passageways through the muscle Electrical impulses, also called action
potentials, travel through T tubules to begin muscle contraction
Myofibrils
Unit of muscle fibers Contains myofilaments, thin “actin, and
thick “myosin” Myofilaments are organized into repeating
units called sarcomeres
Sarcomere Organization
A bands (thick filaments)- dark– M line- stabilizes positions of thick filaments– H zone- only thick filaments, appears lighter on
each side of the m line– Zone of overlap- thin filaments are situate
between thick filaments
I band- between A bands– Z line marks boundary of one sarcomere
Sliding Filament Theory
H and I bands get smaller Zones of overlap get larger Z lines get closer A band width remains constant
Neuromuscular Junction
A neuron controls each muscle fiber using acetylcholine, which makes the muscle fibers more permeable to sodium causing an action potential to begin
The action potential triggers muscle fibers to allow Ca to pass into cells (quick .03s)
Ca binding to the active site of the thin filaments starts the contraction cycle
Contraction cycle
Cross bridges from between thick and thin filaments
Myosin heads of thick filaments pivot, shortening muscle fiber
Relaxation
Acetylcholinesterase breaks down acetylcholine to stop action potential
Ca is pumped out of muscle fibers into the extracellular fluid
Ca is transported back into the sarcoplasmic reticulum
Active site is covered up again
Types of contractions
Isotonic- tension increases, and muscle shortens, walking and running
Isometric- tension produces, but muscle size stays the same, pushing on a door
Aerobic Metabolism
Energy produced in muscle tissue in the presence of oxygen
Muscle cells only keep small reserves of ATP
Cellular respiration allows muscle cells to produce more ATP using glycogen and glucose reserves
Anaerobic Metabolism Demands on muscle exceed bodies
ability to supply oxygen Lactic acid is produced and builds up in
the muscle tissue Muscle Fatigue- muscles can’t contract
despite neural stimulation– Short peak levels (spinting)– Prolonged excertion, Ca can’t be
regulated (marathon)
Recovery Period
Conditions in muscle fibers return to normal Oxygen converts lactic acid into pyruvate
which can then become ATP or glycogen Oxygen debt occures after exercise until your
cells use new incoming oxygen to generate ATP
85% of heat needed to thermoregulate comes from skeletal muscles
Muscle Performance
Fast twitch fibers “white muscle”- anaerobic, high intensity and short duration, low myoglobin, fewer mitochondria
Slow twitch fibers “red muscle”- opposite of above
Intermediate fibers- characteristics between fast and slow
% of fast to slow muscle fibers is genetically determined
Cardiac Muscle Tissue
Found only in the heart Contracts with out neural stimulation Longer contractions Intercalated discs ensure cells contract
in unison
Smooth Muscle Tissue
Oval shaped cells with a central nucleus
Found in almost every organ Doesn’t have myofibrils or sarcomeres,
so no striations Involuntary control