Muscular System Flashcards
Major Organs
Skeletal muscle and tendons
Functions
- Produces movements
- Maintains posture and body position
- Support soft tissue
- Guard body entrances and exits
- Maintains body temperature
Skeletal Muscle
- Contains skeletal muscle fibre
- Endomysium: surrounds muscle fibre
- Perimysium: surrounds muscles fascicle
- Epimysium: surrounds entire muscle
Level of organisation within skeletal muscle
Skeletal Muscle Muscle Fascicle Muscle Fibre Myofibril Myofilament Thick/Thin Filament Sarcomere
Sarcolemma
Physical barrier between intracellular and extracellular environment, structural support and generation and propagation of action potentials
Sarcomere
Smallest functional units of the muscle fibre (cell) interaction between thin and thick filaments within sarcomeres are responsible for muscle contraction
Transverse (T) Tubules
Conduct an electrical signal (action potential) inside the muscle fibre (cell) enables all regions of muscle fibre (cell) to contract at the same
Sarcoplasmic Reticulum
Forms tubular network around each myofibril and stores/releases Ca2+ into cytosol
Myofibril
Active shortening of myofibrils produces muscle contraction
Thin Filament
- Strands of proteins that consist of actin, troponin, tropomyosin
- They are separated from thick filaments at rest, but when cross bridges form between thin and thick filaments, contraction occurs
Thick Filament
- contain protein myosin
- separated from thin filaments at rest
- when cross bridges form between thin and thick filaments, contraction occurs
Initiating muscle contraction
Action potential on sarcolemma
Spreads to t-tubule
Ca2+ release from sarcoplasmic reticulum
Ca2+ binds to troponin
Causes Tropomyosin to roll off active site on actin
Enables actin and myosin binding (cross-bridge formation)
Myosin head pivot (power stroke)
Thin filament slides towards sarcomere centre
Muscle contraction
Cross-bridge breaks
Recock myosin head with ATP
Ending Muscle Contraction
Ach broke down
Sarcoplasmic reticulum reabsorbs ca2+
Active site covered, cross bridge formation ends
Contraction ends
Muscle relaxation occurs
What would happen to resting skeletal muscle is sarcolemma became permeable to ca2+
- Ca2+ would leak into muscle cell, resulting in an increase in intracellular ca2+ concentration
- This would lead to muscle contraction that would persist for as long as the concentration of Ca2+ remained elevated
Factors that determine tension (single muscle fibre cell )
1) Sarcomere length
(length tension relationship)
-optimal: zone of overlap large, thin filaments don’t extend across sarcomere
-small: too much overlap
-large: too little overlap
2) Stimulation frequency
- high frequency of action potential= high tension
