Blood supply of brain-
**Core Concept**
The blood supply of the brain is a complex network of arteries and veins that provide oxygen and nutrients to the brain tissue. The cerebral circulation is characterized by a high metabolic demand, high blood flow, and a low tolerance for ischemia.
**Why the Correct Answer is Right**
The correct answer is based on the fact that the brain receives its blood supply through two main sets of arteries: the internal carotid arteries and the vertebral arteries. The internal carotid arteries supply the anterior circulation of the brain, including the frontal, parietal, and temporal lobes, while the vertebral arteries merge to form the basilar artery, which supplies the posterior circulation, including the occipital lobe and the brainstem. The blood then drains into the venous sinuses and ultimately into the jugular veins.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the middle cerebral artery is a branch of the internal carotid artery, but it is not the primary supplier of blood to the brain.
**Option B:** This option is incorrect because the external carotid artery primarily supplies blood to the face and neck, not the brain.
**Option C:** This option is incorrect because the subclavian artery supplies blood to the arm, not the brain.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the brain is highly vulnerable to ischemia, and any significant reduction in blood flow can lead to serious neurological deficits, including stroke.
**Correct Answer: D. Both internal carotid and vertebral arteries supply blood to the brain.**