Which type of cells are filled with myelin and aid in speeding up signals?

Schwann cells are specialized cells in the nervous system that produce myelin, a fatty substance that wraps around the axons of neurons. This myelination serves an essential role in increasing the speed of electrical signals along the nerve fibers. By insulating the axons, myelin prevents the loss of electrical signals and facilitates more rapid transmission through a process known as saltatory conduction, where the action potential jumps from one node of Ranvier (gaps in the myelin sheath) to the next.

In contrast to Schwann cells, dendrites are branches of neurons that receive signals but do not myelinate fibers. Bipolar neurons, which are involved in sensory processing (like vision and smell), do not have a unique role in myelination, nor do they typically produce myelin. Neurotransmitters are chemical messengers that facilitate communication between neurons at synapses, rather than being involved in the structure of neurons themselves or the myelination process. Therefore, Schwann cells are essential for enhancing the efficiency of signals within the nervous system through their myelin-producing capability.