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