The white color of myelinated nerve fibers is primarily due to the presence of what substance?

The white color of myelinated nerve fibers is primarily due to the presence of the myelin sheath. Myelin is a fatty substance that wraps around the axons of neurons, creating a protective and insulating layer that facilitates faster transmission of electrical signals along the nerve fibers. This fatty composition contributes to the overall white appearance of the myelinated regions in the nervous system.

The myelin sheath is crucial for the efficient conduction of impulses through a process known as saltatory conduction, where nerve impulses jump from one node of Ranvier (gaps in the myelin sheath) to another, rather than traveling continuously along the axon membrane. This not only speeds up the transmission but also conserves energy for the neuron.

Other options refer to components of the nervous system that do not directly correlate with the white coloration of myelinated fibers. Neurotransmitters are chemical messengers involved in signal transmission at synapses but do not contribute to the physical color of nerve fibers. Axons are the long projections of neurons that transmit signals but are not inherently white without the myelin sheath. Dendrites are branching extensions of neurons that receive signals from other neurons and are typically not associated with the myelin sheath or the coloration of nerve fibers.