Unit 4: Muscular System Notes

Naming of muscles

direction, size, location, shape, action, number of origins

Function of muscle

• Movement

• Maintain posture

• Stabilize joints

• Generate heat

Muscle terminology

Myo; muscle

Mys; muscle

Sarco: flesh

Connective tissue of SKELETAL muscle

Fascia: outermost layer

Epimysium: covers entire muscle

Perimysium: around a fascicle(bundle of fibers)

Endomysium: around a single muscle fiber(cell)

Muscle attachment

Tendon: cord-like structure

Aponeuroses: sheet-like structure

Sites of muscle attachment

Bone, cartilages, connect tissue coverings

Sarcolemma

cell membrane

Sarcoplasm

cytoplasm

Thick filament

Myosin(mayo)

Thin filament

Actin

SKELETAL muscle fibers are made up of

Myofibrils

Sarcoplasmic reticulum

where we get calcium

Sarcomeres

striated patterns formed by filaments

I band

thin filament

A band

thick and thin filament

H zone

thick filament

Z line

sarcomere boundary line

M line

center of A band

Muscle contraction

Results from actin and myosin filaments sliding past one another, shortening of sarcomeres.

Neuromuscular Junction

A type of synapse, motor neuron and muscle cell interact

Motor neuron

nerve cell that carries a signal to the muscle cell

Motor end plate

cell membrane of muscle cell

Synaptic cleft

the gap between the neuron and muscle cell

Synaptic vesicles

carry neurotransmitters

Neurotransmitter

THE signal

Stimulus for contraction

Acetylcholine releases and binds to muscle receptors. Sarcolemmas permeability increase to let Na+(sodium) and K+(potassium) ions create action potential. Impulse causes the SR to release calcium, which leads to muscle contraction.

Acetylcholine

the signal

Muscle relaxation

• Ca+2 ions are stored in SR

• Troponin-tropomyosin cover actin bind sites

Cross-Bridging Cycle

• Myosin attached to actin, forming the cross-bridges

• Myosin cross-bridge pulls actin

• ADP and P are released from myosin

• New ATP binds to myosin

• Actin and myosin cross-bridge breaks

• ATP spilts into ADP and phosphate

Energy sources for Contraction

• ATP reserves

• Creatine phosphate: initial source of energy to regenerate ATP from ADP and P.

• Cellular respiration: creates large amounts of ATP(36-38)

Cellular Respiration

creates lactic acid

Anaerobic(lactic acid) threshold

shift from aerobic, during strenuous muscle activity. When not enough oxygen is supplied, lactic acid is produced.

Oxygen debt

amount of oxygen needed to convert lactic acid to glucose and restore muscle ATP and creatine concentrations.

Muscle fatigue

inability to contract muscle

Common causes of muscle fatigue

• decreased blood flow

• Ion imbalances across the sarcolemma

• Loss of desire to continue exercise

• Accumulation of lactic acid

Muscle cramp

sustained, involuntary muscle contraction.

• may be caused by changes in electrolyte concentration in extraceullular fluids in the area

Smooth Muscle

• Lack striations

• Slow and tireless

• Short

Cardiac muscle

• Branched cells

• Cells joined by intercalated discs

• Self-exciting and rythmic

Skeletal muscle

• voluntary

• Multi-nucleated

• cylindrical shapes

Muscle Characteristics

Contractibility: shorten and thicken

Extensibility: ability to stretch

Elasticity: return to og length

Irritability: respond to stimuli

Muscle tone: tension/resistance, even at rest