Neuromuscular

Question 1

Resting phase of muscle contraction

Answer 1

Muscle is relaxed as there are no calcium ions in myofibril/ sarcoplasm therefore myosin doesnt bind to actin

Question 2

Excitation phase of muscle contraction

Answer 2

1) Impulse/ AP is sent from the CNS to the spinal chord
2) Travels down motor neurone (Dendrite —> axon —> axon terminal) to the neuromuscular junction
3) impulse cause ACH to be released from synaptic vesicles
4) ACH diffuses across synaptic cleft
5) ACH binds to sodium channel which depolarises the motor end plate
6) triggers caclium ions to be released from the sarcoplasmic reticulum into the sarcoplasm of the muscle

Question 3

Contraction phase of muscle contraction

Answer 3

SFT

1) Calcium binds to troponin causing it to change shape
2) causes tropomyosin to move and uncover binding site of actin
3) myosin filament binds to actin creating cross bridge
4) Breakdown in ATP in myosin head provides energy for myosin to pull on actin
5) filament slide therefore contraction

Question 4

Recharge phase of muscle contraction

Answer 4

If there is sufficient ATP and calcium, power stroke will continuously occur, causing a ratchet like mechanism until either ATP or Calcium has depleted

Question 5

Relaxation phase of muscle contraction

Answer 5

1) The nerve impulse ends
2) Ca2+ re-enters into the sarcoplasmic reticulum
3) tropomyosin covers the active site to prevent cross bridge formation