Muscular contractions

Question 1

Latent period

Answer 1

• Motor end-plate depolarisation
• Depolarisation (AP) transmitted down T tubules
• Ca2+ channels open in SR
• [Ca2+] in the sarcoplasm
• Ca2+ binds to troponin revealing myosin binding site on actin

Question 2

Contraction

Answer 2

• Myosin binds to actin, moves (powerstroke, ADP ejected), releases (new ATP binds) and reforms many times causing sarcomeres to shorten.

Question 3

Relaxation

Answer 3

• Ca2+ actively transported back into SR
• Troponin-tropomyosin complex blocks myosin binding
• Muscle fibre lengthens passively (relaxation)

Question 4

Motor unit

Answer 4

1 motor neuron & its muscle fibres
- One nerve with one nerve impulse
- Small contractions over whole muscle

Question 5

Multiple motor units

Answer 5

• Activation of more motor neurones
• More muscle fibres
• more contractile strength

Force dependant on number of motor units

Question 6

Threshold

Answer 6

If the threshold stimulus for a nerve is reached and the threshold for muscle contraction is reached, the muscle fibre will contract, otherwise it will not.

Question 7

Recruitment

Answer 7

• The greater the force of contraction needed, the more motor units are required
• Each motor unit operates in an all or none fashion

Question 8

Increase stimulus sensitvity

Answer 8

• Controls the force of contraction (in absence of internal changes, such as fatigue, fibres will contract ‘fully’ each time).
• The more motor units the bigger the twitch

Question 9

Order of tension

Answer 9

• Subthreashold
• Threshold
• Submaximal
• Maximal
• Supamaximal

Question 10

Lower frequency

Answer 10

Muscle fibres relax fully before next AP arrives

Question 11

Low frequency and contractile force

Answer 11

• Muscle fibres relax fully before next AP arrives
• Twitches (tension returns to baseline – not shown)
• Before next AP can occour fibres must fully relax

Question 12

High frequency contractile force

Answer 12

• No time for the muscle fibres to relax before the next AP arrives
• Continual exposure to Ca2+ maximal contraction Tetanus

Question 13

ATP need in contraction

Answer 13

• Contraction (crossbridge forming and release),
• Relaxation ( pump Ca2+)
• Restore Na+ and K+ levels afer AP

Question 14

Sorces of ATP for muscles

Answer 14

• Phosphocreatine - A source of ATP
• Carbohydrates
• Aerobic metabolism : producing about 30
  ATP for each molecule of glucose
• Anaerobic glycolysis : glucose is metabolized to lactate/lactic acid with a yield of only 2 ATP per glucose

Question 15

Slow twitch oxidative red muscle

Answer 15

• Smallest with slow contraction and ATP breakdown
• Fatigue resistant and high aerobic metabolism
• High myoglobin and mitochondria

Question 16

Fast-twitch oxidative red muscle

Answer 16

• Medium size fast contraction time and breakdown of ATP
• Fatigue resistant and high anaeobic respiration

Question 17

Fast-twitch white muscle

Answer 17

• Large very fast muscle contraction with fast breakdown of ATP
• Easily fatigued and highest anaerobic respiration rate

Question 18

Slow-twitch muscle activation

Answer 18

• Only neurones with low threshold minimal force one neurone so lasts longer