Electrical Activity of the Heart Flashcards
What is excitation-contraction coupling?
The physiological process of converting an electrical stimulus to a mechanical response
Transduction between the action potential generated in the sarcolemma and the start of a muscle contraction
What depolarises the myocyte?
Action potential
When and how do calcium ions enter the cells?
During phase 2 of the action potential through L-type calcium channels located on the sarcolemma
What does calcium entry trigger?
Subsequent release of calcium, that is stored in the sarcoplasmic reticulum and released through calcium-release channels
What does calcium released by the sarcoplasmic reticulum increase?
Intracellular calcium concentration
What does free calcium bind to?
Troponin
What does the binding of calcium and troponin cause?
Conformational change in the regulatory complex so troponin exposes the binding sites of the actin molecule
What does exposure of the binding sites of the actin molecule allow?
Myosin to bind
What does actin-myosin binding result in?
ATP-hydrolysis that supplies energy for a conformational change to occur in the actin-myosin complex
What does the conformational change occurring in the actin-myosin complex result in?
Shortening of sarcomere length
How is initial sarcomere length restored?
ATP binds to the myosin head and displaces ADP, initial sarcomere length is restored
Of myosin and actin, which is the thin filament and which is the thick filament?
Myosin is the thick filament, actin is the thin filament
How does actin-myosin binding cause changes in sarcomere length?
Binding forms cross bridges in the sarcoplasmic reticulum to shorten the muscle
Why can the regulation of calcium release be used to vary the strength of contraction?
Calcium release does not saturate the troponin
What is needed in order for the whole heart to shorten on contraction?
Physical connections and electrical connections between the two membranes
What are the electrical and physical connections?
Gap junctions are the electrical connections
Desmosomes form the physical connections
How are the physical and electrical connections arranged?
Intercalated discs;
Desmosome-gap junction-desmosome-gap junction etc. etc.
What is the action potential in skeletal muscle compared to cardiac muscle?
2ms in skeletal muscle vs 250ms in cardiac muscle