What structural component of white matter gives it a whitish appearance?

The correct answer is myelin, which is a fatty substance that surrounds and insulates the axons of many neurons in the central nervous system. This coating, known as myelin sheath, enhances the speed of electrical impulses along the nerve cells, facilitating rapid communication between different parts of the nervous system.

The whitish appearance of white matter is primarily due to the high lipid content in myelin. Since lipids scatter light differently than other cellular components, this leads to the characteristic color of white matter in the brain and spinal cord. White matter contrasts with gray matter, which consists largely of neuronal cell bodies, dendrites, and unmyelinated axons, resulting in a darker coloration.

The other options are not responsible for the coloration of white matter. Neurotransmitters, while vital for neural communication, are small molecules that play a role in synaptic transmission but do not contribute to the structural appearance of white matter. Glial cells, which support and protect neurons, are mostly found in both gray and white matter but do not impart the characteristic whitish hue. Nerve endings represent the terminals of neurons where transmission of signals occurs but are not involved in the structural makeup that defines the color of white matter.