**Core Concept**

The spinal cord is a part of the central nervous system (CNS) that connects the brain to the rest of the body, transmitting sensory and motor information. Nerve roots are the nerve fibers that branch out from the spinal cord and form the peripheral nervous system (PNS). Both the spinal cord and nerve roots require a constant supply of nutrients and oxygen to maintain their functions.

**Why the Correct Answer is Right:**

The correct answer is **D**: The spinal cord and nerve roots are supplied by the intercostal arteries, which are branches of the thoracic aorta. The thoracic aorta is the largest artery in the body and carries oxygenated blood from the heart to the rest of the body. These arteries supply the blood to the spinal cord and nerve roots, ensuring their viability and proper functioning.

**Why Each Wrong Option is Incorrect:**

**Option A:** The vertebral arteries arise from the subclavian arteries, which are branches of the aortic arch. While the subclavian arteries supply blood to the neck and upper limbs, they do not supply blood to the spinal cord and nerve roots directly.

**Option B:** The brachial arteries supply blood to the upper limbs and are not responsible for supplying blood to the spinal cord and nerve roots.

**Option C:** The lumbar arteries originate from the lumbar arteries, which supply blood to the lower limbs and abdominal organs, not the spinal cord and nerve roots.

**Clinical Pearl / High-Yield Fact:**

Understanding the correct arterial supply to the spinal cord and nerve roots is essential for understanding spinal surgery, trauma, and neurological disorders. A disruption in the blood supply can lead to spinal cord ischemia and neurological deficits.

**Correct Answer:** D. Intercostal arteries (branches of the thoracic aorta) supply the blood to the spinal cord and nerve roots.