Excitation contraction coupling

Question 1

What is the mechanism for excitation contraction coupling?

Answer 1

Action potential triggers depolarisation of the sarcolemma and T-tubules.
Calcium is released from the sarcoplasmic reticulum via ryanodine receptors.
Calcium binds troponin, initiating contraction.

Question 2

What is the architecture of cardiac muscle?

Answer 2

Branched fibres with intercalated discs for electrical coupling.
Contains sarcomeres as the functional unit.

Question 3

What is the myofilament structure?

Answer 3

Thin Filament: Actin, troponin, and tropomyosin.
Thick Filament: Myosin.

Question 4

What are the actin-myosin interactions?

Answer 4

Calcium binding to troponin shifts tropomyosin, exposing myosin-binding sites on actin.
Myosin heads bind actin, forming cross-bridges.

Question 5

What are the steps of the cross bridge cycle?

Answer 5

ATP binds myosin, causing detachment from actin.
ATP hydrolysis energises myosin.
Myosin binds actin, and the power stroke pulls actin filaments inward.
ADP is released, and the cycle repeats