Which of the following statements about myelination are correct? A. It…

Concept

Myelination is the formation of an insulating myelin sheath around axons. It supports saltatory conduction, which makes neural signalling faster and more efficient, and the added white matter contributes to growth in brain volume during development. Myelination proceeds at different rates across brain regions and continues well beyond early childhood.

Application

• The conduction-speed statement agrees with the mechanism of saltatory conduction, so it is true.

• The brain-size statement is also true because increasing myelinated white matter contributes to developmental growth in brain volume.

• The all-areas-by-age-four statement is false: some regions continue myelinating through later childhood, adolescence, and beyond.

• The no-benefit statement is false because knowledge of myelination helps explain learning, attention, neural development, and demyelinating disorders.

Contrast

• The combination ‘C and D only’ depends on two claims that are not supported.

• The combination ‘B, C and D only’ includes the unsupported age-four and no-benefit claims.

• The combination ‘A, C and D only’ likewise includes those two unsupported claims.

Cross-check

The supported set contains exactly the conduction-speed and brain-size claims; the regional developmental timeline and practical importance exclude the other two claims.

Therefore, the correct combination is ‘A and B only’.