Muscles

Question 1

Types of muscle

Answer 1

• Smooth muscle (contracts without conscious control, found in walls of internal organs)
• Cardiac muscle (contracts without conscious control, found in heart)
• Skeletal muscle (voluntary movement)

Question 2

What are antagonistic pairs?

Answer 2

Muscles that work together to move a bone. The contracting muscle is the agonist and the relaxing muscle is the antagonist

Question 3

Skeletal muscle structure

Answer 3

• Long cylindrical cells called muscle fibres contain many mitochondria
• Muscle fibres are multinucleate
• Muscle fibres contain long organelles called myofibrils
• Myofibrils contain myofilaments (actin & myosin)

Question 4

Myofibril structure

Answer 4

• Made of short units called sarcomeres
• A-band (thick myofilaments of myosin, darker)
• I-band (thin myofilaments of actin only, lighter)
• M-line (middle of myosin filaments)
• H-zone (unoverlapped myosin)
• Z-line (ends of each sarcomere)

Question 5

Sliding filament theory

Answer 5

• Action potential depolarises sarcolemma, causing sarcoplasmic reticulum to release Ca2+ into sarcoplasm
• Ca2+ causes tropomysoin to move out of the binding site, allowing an actomyosin bridge to be formed
• Ca2+ activates ATPase (ATP —> ADP + Pi)
• ATP is used to change shape of myosin head (power stroke), detach the myosin head, return myosin head to resting position (recovery stroke) and re-absorb Ca2+ into sarcoplasmic reticulum by active transport

Question 6

What happens when a sarcomere contracts?

Answer 6

Sarcomere, I-band and H-zone get shorter and A-band stays the same

Question 7

How is energy released for muscle contraction?

Answer 7

1) Phosphocreatine (short, high intensity exercise as PO4^3- added to ADP from PCr stores in cells)
2) Anaerobic respiration (short, high intensity exercise as 2ATP and lactate produced by glycolysis)
3) Aerobic respiration (long, low intensity exercise as many ATP by oxidative phosphorylation)

Question 8

Slow twitch muscle fibres

Answer 8

• Contract and relax slowly
• Low force of contraction
• Resistant to fatigue
• Respire aerobically (many mitochondria, blood vessels, myoglobin)

Question 9

Fast twitch muscle fibres

Answer 9

• Contract and relax quickly
• High force of contraction
• Fatigue quickly
• Respire anaerobically (few mitochondria, blood vessels, myoglobin)