3.6.3 Skeletal muscles

Question 1

What are the features of slow muscle fibres?

Answer 1

• endurance: contract slowly, contract for longer - sustained muscle contraction
• High resistance to fatigue
• muscle contraction not as powerful
• adapted for aerobic respiration- many mitochondria present for the production of lots of ATP
• Small amounts of glycogen present
• a rich blood supply: deliver oxygen and glucose
• lots of Myoglobin
• not as many enzymes regulating glycolysis
• found in muscles for posture (eg calf muscle)

Question 2

What are features of fast muscle fibres?

Answer 2

• contract quickly: immediate, rapid muscle contractions but for short lengths of time
• low resistance to fatigue - fatigue easily
• powerful muscle contractions
• depend mainly on glycolysis for the anaerobic production of ATP
• more enzymes regulating glycolysis
• few mitochondria present
• Large amounts of glycogen present
• not as many blood vessels or Myoglobin
• thicker and more myosin present
• lots of phosphocreatine present
• eg sprinting, weight lifting

Question 3

All of muscle contraction

Answer 3

• nerve impulse arrives at the neuromuscular junction
• acetylcholine is released into the synaptic cleft
• an action potential is produced in the sacrolemma of the muscle fibre
• the action potential is transmitted down T-tubules
• causing the sarcplasmic reticulum to release calcium ions
• calcium ions bind to tropomyosin which moves tropomyosin away from the actin
• exposing it’s myosin binding sites
• myosin heads bind to the exposed sites on the actin filaments
• myosin heads change position (powerstroke) and slides actin over the myosin
• ATP binds and breaks crossbridge
• ATP hydrolysis provides the energy to reposition the myosin head, so it can bind again
• process repeats

Question 4

What does phosphocreatine do? Where is it stored?

Answer 4

• provides the phosphate needed for condensation of ADP to ATP in order to regenerate ATP
• stored in muscles

Question 5

What is temporal summation?

Answer 5

one neurone releases neurotransmitter repeatedly over a short time to add up to exceed threshold

Question 6

What is spatial summation?

Answer 6

Many different neurones collectively trigger an action potential by combining neurotransmitter they release to exceed threshold

Question 7

What are the roles of phosphocreatine?

Answer 7

• used to regeneate ATP in aerobic conditions
• provides energy and Pi to make ATP from ADP in substrate level phosphorylation