**Core Concept**
The vasomotor center of the medulla oblongata plays a crucial role in regulating blood pressure (BP) through the autonomic nervous system. It acts in conjunction with the cardiovagal center, also located in the medulla, to maintain homeostatic balance.

**Why the Correct Answer is Right**
The vasomotor center and the cardiovagal center work synergistically to regulate blood pressure. The vasomotor center controls the sympathetic outflow to the vascular smooth muscle, causing vasoconstriction and increased peripheral resistance, thereby elevating blood pressure. On the other hand, the cardiovagal center controls the parasympathetic outflow to the heart, promoting vagal tone and reducing heart rate, which also contributes to the maintenance of blood pressure. This coordinated effort helps to maintain blood pressure stability, especially during changes in posture, stress, or physical activity.

**Why Each Wrong Option is Incorrect**
**Option B:** The vasomotor center is actually influenced by corticohypothalamic inputs, which provide it with information about the body's overall physiological state, allowing it to adjust its output accordingly.

**Option C:** The vasomotor center is influenced by both baroreceptors and chemoreceptors. Baroreceptors, located in the walls of the carotid sinus and aortic arch, detect changes in blood pressure and send signals to the vasomotor center to adjust its output. Chemoreceptors, located in the carotid bodies and aortic bodies, detect changes in the levels of oxygen, carbon dioxide, and pH in the blood and also send signals to the vasomotor center.

**Option D:** The vasomotor center is actually more active during sleep, particularly during the rapid eye movement (REM) stage, when blood pressure is typically higher due to increased sympathetic tone.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the autonomic nervous system, particularly the vasomotor and cardiovagal centers, plays a vital role in regulating blood pressure. Understanding their interactions and influences is crucial for managing hypertension and other cardiovascular disorders.

**✓ Correct Answer: A. Acts with the cardiovagal centre to maintain BP**