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:
            ion
Sodium channels close, and potassium (K+) channels open, allowing 
K+ to exit the cell. This results in a brief decrease in membrane 
potential.
3. Phase 2: Plateau Phase
Calcium (Ca2+) channels open, allowing Ca2+ to enter the cell 
while K+ continues to exit. This phase maintains depolarization 
and is crucial for muscle contraction.
4. Phase 3: Repolarization
Calcium channels close, and potassium continues to exit, 
returning the membrane potential to its resting state.
5. Phase 4: Resting Membrane Potential
The cell returns to its resting state, ready to respond to the next 
electrical impulse.
Heart Rate Regulation
Heart rate is influenced by both intrinsic and extrinsic factors:
1. Intrinsic Regulation
The SA node sets the basic rhythm of the heart. If it fails, other pacemakers, 
like the AV node or Purkinje fibers, can take over, but at a slower rate.
2. Extrinsic Regulation
The autonomic nervous system plays a crucial role in regulating heart rate.
The sympathetic nervous system through norepinephrine release will
increases heart rate and contractility in response to stress or exercise, while
the parasympathetic system by acetylcholine release will decreases heart rate
during rest and relaxation through the vagus nerve.
3. Hormonal Influences
Hormones such as adrenaline (epinephrine) can also affect heart rate, 
particularly during stress or physical activity.
Clinical Implications
Understanding the electrical activity of the heart is essential for diagnosing 
and treating various cardiac conditions:
1. Arrhythmias
Arrhythmias are irregular heartbeats caused by abnormalities in the 
conduction system. They can range from benign to life-threatening.
2. Electrocardiogram (ECG)
An ECG is a diagnostic tool that records the electrical activity of the heart. It 
helps identify arrhythmias, heart attacks, and other cardiac conditions.
3. Pacemakers and Defibrillators
In cases of significant conduction abnormalities, medical devices like
pacemakers or implantable cardioverter-defibrillators (ICDs) may be used to 
restore normal rhythm.
4. Importance of Lifestyle
Factors such as diet, exercise, and stress management play a critical 
role in maintaining a healthy heart and preventing electrical 
dysfunction.
5. Coordination of Heart Activity
The electrical conduction system not only initiates heartbeats but also 
coordinates the timing of contractions. The sequential contraction of 
the atria followed by the ventricles ensures efficient blood flow. The 
normal rhythm, or sinus rhythm, is regulated by the autonomic 
nervous system, which can adjust heart rate based on the body’s 
needs.
Conclusion
The electrical components of the heart are vital for its function as the body’s 
pump. From the pacemaking activity of the SA node to the intricate pathways 
of the conduction system, these electrical processes ensure that the heart 
beats in a coordinated and efficient manner. Understanding these mechanisms 
not only deepens our appreciation for card

            Quiz: