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:
            ialized cells responsible for 
the contractile function of the heart. They exhibit unique properties that enable 
the heart to pump blood effectively, including automaticity, rhythmicity, and 
contractility. This lecture will focus on the structure and function of contractile 
cardiomyocytes and the intricate process of excitation-contraction coupling
(ECC).
Structure of Contractile Cardiomyocytes
Cardiomyocytes are striated muscle cells characterized by a cylindrical shape. 
They typically measure 10-25 micrometers in diameter and can be up to 100 
micrometers in length. Unlike skeletal muscle cells, cardiomyocytes are 
connected end-to-end, forming a functional syncytium, which is crucial for 
coordinated heart contractions.
Organelles and Components
1. Nucleus: Cardiomyocytes usually contain one or two centrally located nuclei.
2. Sarcoplasmic Reticulum (SR): The SR in cardiomyocytes plays a critical role 
in calcium storage and release.
3. Mitochondria: Cardiomyocytes are rich in mitochondria, providing the energy 
required for continuous contractions.
4. Myofibrils: These are the contractile units composed of actin and myosin 
filaments, organized into sarcomeres.
5. Intercalated Discs
Intercalated discs are unique to cardiac muscle and contain gap junctions and 
desmosomes. Gap junctions allow for electrical coupling between cells, facilitating 
the rapid propagation of action potentials, while desmosomes provide structural 
integrity.
Physiology of Contractile Cardiomyocytes
Resting Membrane Potential
The resting membrane potential of cardiomyocytes is 
approximately -85 to -90 mV, primarily determined by 
potassium ion permeability. This negative charge is 
essential for the cells' excitability and responsiveness 
to stimuli.
Action Potential
The action potential in cardiomyocytes consists of five phases (0-4):
1. Phase 0: Rapid depolarization due to the influx of sodium ions 
(Na+).
2. Phase 1: Partial repolarization as sodium channels inactivate and 
potassium channels open.
3. Phase 2: Plateau phase, where calcium ions (Ca2+) enter the cell 
through calcium channels, counteracting potassium efflux.
4. Phase 3: Repolarization, where potassium efflux dominates as 
calcium channels close.
5. Phase 4: Resting potential is restored.
Calcium Handling
Calcium plays a central role in the contraction of cardiomyocytes. The 
influx of calcium during the action potential triggers further calcium 
release from the sarcoplasmic reticulum (SR) through a process called
calcium-induced calcium release (CICR).
Excitation-Contraction Coupling (ECC)
Excitation-contraction coupling is the physiological process that links 
electrical excitation of the cardiomyocyte to muscle contraction. This 
process ensures that an action potential leads to an increase in 
intracellular calcium, resulting in contraction.
(ECC) refers to the mechanism whereby the action potential causes 
the myofibrils of muscle to contract. When an action potential 
passes over the cardi

            Quiz: