The outer membrane that covers the brain is

Step 1: Analyze the question The question asks which membrane forms the outermost covering of the brain. The brain and spinal cord are protected by three membranes called the meninges.

Step 2: Explain the concept The meninges, from outside to inside, are:

1. Dura mater: the tough, thick outer layer, just beneath the skull.
2. Arachnoid membrane: the middle, web-like layer. Cerebrospinal fluid circulates in the space beneath it.
3. Pia mater: the thin inner layer that sticks closely to the surface of the brain.

The myelin sheath is not a covering of the brain. It is a fatty insulating layer around the axons of nerve fibres, and it speeds up the transmission of nerve impulses.

Step 3: Solve

• A. Myelin sheath: wrong, it surrounds nerve fibres, not the whole brain.
• B. Dura mater: correct, it is the outermost meninx.
• C. Arachnoid membrane: wrong, it is the middle layer.
• D. Pia mater: wrong, it is the innermost layer, directly on the brain.

Step 4: Answer The outer membrane covering the brain is the dura mater, which is option B.

Tip: Remember the order D-A-P, from outside to inside: Dura, Arachnoid, Pia. You can also remember that "dura" means "tough" (like the word "durable"), so the toughest layer is the outermost, protecting everything beneath it.