Myelinated and unmyelinated axons differ primarily in their structure and functionality, which significantly affects the speed of nerve signal transmission.
Myelinated Axons: These axons are coated with a fatty substance called myelin, which is produced by glial cells. The presence of myelin creates segments along the axon known as nodes of Ranvier, which facilitate the rapid transmission of electrical impulses via a process called saltatory conduction. In this process, the electric signal jumps from node to node, allowing it to travel much faster than in unmyelinated axons. Myelinated axons are typically found in parts of the central and peripheral nervous systems where speed is crucial, such as in motor and sensory pathways.
Unmyelinated Axons: In contrast, unmyelinated axons lack this myelin sheath and do not have nodes of Ranvier. As a result, the nerve impulse must travel continuously along the entire length of the axon, leading to slower signal conduction. Unmyelinated axons are often found in autonomic nervous system pathways and in regions where rapid response is less critical.
Summary: In summary, the key differences lie in the presence of myelin, the conduction speed, and the specific functions each type of axon serves within the nervous system. Myelinated axons enable faster communication between neurons, while unmyelinated axons are associated with slower, more general signals.