Muscle contraction

Question 1

first step

Answer 1

there is no impulse arriving at neuromuscular junction so the muscle is relaxed

Question 2

second step

Answer 2

impulse arrives at neuromuscular junction depolarising sarcoplasmic reticulum membrane so the calcium ion channel proteins open causing calcium ions to bind to troponin

Question 3

third step

Answer 3

troponin changes shape so tropomyosin is moved exposing the myosin-actin binding site. a cross bridge is then formed with requires ATP

Question 4

fourth step

Answer 4

actin pulled past the myosin by myosin head changing shape and pulls the actin causing muscle fibre to shorten. the pulling of actin requires ATP

Question 5

fifth step

Answer 5

myosin head released from actin, requires ATP, and binds to the next attachment site

Question 6

sixth step

Answer 6

nerve impulses stop arriving and calcium ions are actively transported back into sarcoplasmic reticulum
tropomyosin covers binding site and muscle contraction stops