Concept: This question tests your understanding of the structural organization of the brain, specifically distinguishing between grey and white matter.

Why (A) is correct: The cerebral cortex is the outermost layer of the cerebrum and is primarily composed of neuron cell bodies, dendrites, unmyelinated axons, and glial cells. This high concentration of cell bodies gives it a grayish appearance, hence it is referred to as grey matter. It is the site of higher cognitive functions like thought, memory, and voluntary movement.

Why other options are wrong:

• (B) white matter: White matter is located beneath the grey matter and consists mainly of myelinated axons, which appear white due to the fatty myelin sheath.
• (C) Both (a) and (b): While the cerebrum contains both grey and white matter, the cerebral cortex specifically refers to the grey matter on the surface.
• (D) non-myelinated nerve fibres: While non-myelinated nerve fibres are present in grey matter, the term 'grey matter' encompasses more than just these fibres; it primarily refers to the cell bodies.

Common Mistake: Students sometimes confuse the location and composition of grey and white matter within the brain and spinal cord.

NEET Tip: Remember that the cortex (outer layer) of the brain is grey matter, while the medulla (inner part) is white matter. In the spinal cord, this arrangement is reversed: grey matter is internal, and white matter is external.

Correct Answer: (A)