Ventricular contraction in command of `:-`

Options

A. S.A. Node
B. A.V. Node
C. Purkinje fibres
D. Papillary muscles

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about which structure is responsible for commanding ventricular contraction in the heart.

2. **Identifying the Structures**: The options given are:
- SC node (Sinoatrial node)
- AV node (Atrioventricular node)
- Purkinje fibers
- Papillary muscles

3. **Role of the SC Node**: The SC node, also known as the pacemaker of the heart, initiates the electrical impulse that triggers the heartbeat. It primarily controls the rhythm of the heart but does not directly command ventricular contraction.

4. **Role of the AV Node**: The AV node acts as a relay station between the atria and ventricles. It delays the electrical signal before it passes to the ventricles, allowing them to fill with blood. However, it does not directly command the contraction of the ventricles.

5. **Role of Purkinje Fibers**: The Purkinje fibers are specialized conductive fibers that spread the electrical impulse throughout the ventricles. They ensure that the ventricles contract in a coordinated manner, effectively commanding the contraction of the ventricular myocardium.

6. **Role of Papillary Muscles**: Papillary muscles are attached to the heart valves and help in their functioning during ventricular contraction. However, they do not command the contraction itself.

7. **Conclusion**: Based on the roles of each structure, the Purkinje fibers are the ones that command the contraction of the ventricles.

**Final Answer**: Ventricular contraction is commanded by **Purkinje fibers**.

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