Pretend you are a teacher preparing a quiz for the text I will provide. 
            Each quiz question should follow the format below. 
            Ensure that you carefully recheck the questions and answers for accuracy. 
            The output should be a ready-to-use list of dictionaries for the Python eval function:

            [

                    "question": "WRITE THE QUESTION HERE",
                    "options": ["A) OPTION_1", "B) OPTION_2", "C) OPTION_3", "D) OPTION_4"],
                    "answer": INDEX_OF_CORRECT_ANSWER_IN_OPTIONS_LIST,
                    "explanation": "EXPLAIN WHY THE ANSWER IS CORRECT"

            ]

            Text:
            ac muscle membrane, the action potential 
spreads to the interior of the cardiac muscle fiber along the 
membranes of the transverse (T) tubules. The T tubule action 
potentials then act on the membranes of the longitudinal
sarcoplasmic tubules to cause release of calcium ions into the 
muscle sarcoplasm from the sarcoplasmic reticulum. In another few 
thousandths of a second, these calcium ions diffuse into the 
myofibrils and catalyze the chemical reactions that promote sliding
of the actin and myosin filaments along one another, which
produces the muscle contraction.
Steps of ECC
1. Depolarization: The action potential travels along the sarcolemma 
and T-tubules, leading to depolarization.
2. Calcium Influx: Calcium channels in the T-tubules open, allowing 
calcium to enter the cell from the extracellular space.
3. Calcium-Induced Calcium Release:
The influx of calcium activates ryanodine receptors on the SR.
This triggers the release of a larger amount of calcium from the 
SR into the cytoplasm.
4. Contraction:
The increase in intracellular calcium concentration binds to troponin, 
causing a conformational change in tropomyosin, which exposes binding 
sites on actin.
Myosin heads attach to actin, initiating cross-bridge cycling and muscle 
contraction.
5. Relaxation:
Is actively pumped back into the SR by the SERCA (sarcoplasmic 
reticulum calcium ATPase) pump and extruded from the cell via the 
sodium-calcium exchanger (NCX) and plasma membrane calcium ATPase 
(PMCA).
 As calcium levels decrease, troponin and tropomyosin return to their 
resting states, leading to muscle relaxation.
Duration of Contraction. 
Cardiac muscle begins to contract a few milliseconds 
after the action potential begins and continues to 
contract until a few milliseconds after the action 
potential ends. Therefore, the duration of contraction of 
cardiac muscle is mainly a function of the duration of 
the action potential, including the plateau— about 0.2 
second in atrial muscle and 0.3 second in ventricular 
muscle.
Importance of ECC
ECC is crucial for maintaining the heart's rhythmic and coordinated 
contractions. Dysregulation of calcium handling can lead to various 
cardiac pathologies, including heart failure and arrhythmias.
The strength of contraction of cardiac muscle depends to a great extent 
on the concentration of calcium ions in the extracellular fluids. In fact, a 
heart placed in a calcium-free solution will quickly stop beating. The 
reason for this response is that the openings of the T tubules pass 
directly through the cardiac muscle cell membrane into the extracellular 
spaces surrounding the cells, allowing the same extracellular fluid that 
is in the cardiac muscle interstitium to percolate through the T tubules.
Clinical Relevance
Understanding contractile cardiomyocytes and ECC is vital in 
the context of various cardiovascular diseases:
1. Heart Failure: Altered calcium handling can lead to impaired 
contractility.
2. Arrhythmias: Abnormalit

            Quiz: