Ventricular contraction is in command of `:-`

Options

A. SA node
B. AV node
C. Purkinje fibers
D. Papillary muscles

Answer

### Step-by-Step Solution:

1. **Understanding the Heart's Conduction System**: The heart has a specialized conduction system that controls the rhythm and timing of contractions. The main components include the Sinoatrial (SA) node, Atrioventricular (AV) node, Bundle of His, and Purkinje fibers.

2. **Role of the SA Node**: The SA node, located in the right atrium, is known as the natural pacemaker of the heart. It generates electrical impulses that initiate the contraction of the atria.

3. **Transmission to the AV Node**: After the SA node fires, the electrical signal travels to the AV node, which is located in the inter-atrial septum. The AV node serves as a gatekeeper that delays the impulse slightly to ensure that the atria have time to contract and fill the ventricles with blood.

4. **Conduction through the Bundle of His**: Following the delay at the AV node, the impulse travels down the Bundle of His, which splits into the left and right bundle branches that extend into the ventricles.

5. **Activation of Purkinje Fibers**: The electrical signal is then conducted to the Purkinje fibers, which spread throughout the ventricles. This is crucial as the Purkinje fibers ensure that the contraction of the ventricles is synchronized and occurs effectively.

6. **Conclusion**: The Purkinje fibers are responsible for commanding the ventricular contraction, making them the correct answer to the question. Other options, such as the SA node, AV node, and papillary muscles, do not directly control ventricular contraction.

### Final Answer:
Ventricular contraction is in command of **Purkinje fibers**.

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