The nervous system processes information and coordinates actions across the organism. It is composed of two distinct populations of cells: neurons and glial cells. Differentiating these two cell types is key to understanding nervous system function. Neurons are associated with brain function, while glial cells provide the necessary environment for that function to occur.
Core Functional Roles
Neurons are the principal cells for information processing and rapid communication within the nervous system. Their primary function involves generating and transmitting electrochemical signals, known as action potentials, over long distances throughout the body. Neurons communicate with other cells at specialized junctions called synapses, releasing chemical messengers called neurotransmitters to pass information. This specialization for signal transmission underlies all cognitive functions, motor control, and sensory perception.
Glial cells, or glia, perform the support functions that maintain the delicate environment required for neuronal activity. Their roles include regulating the ionic milieu surrounding neurons to ensure proper electrical signaling. Glia also provide metabolic support by supplying nutrients and removing cellular waste products. This work ensures the stability and homeostasis of the nervous tissue.
Distinct Structural Organization
The structure of a neuron is highly polarized, meaning it is specialized for directional signal flow. A typical neuron features a central cell body, or soma, from which two types of extensions project: dendrites and a single axon. Dendrites are highly branched structures that receive incoming signals, while the axon is a long, slender projection that transmits the signal away from the cell body toward synaptic terminals. This unique morphology is designed for the rapid, long-distance relay of information.
In contrast, glial cells lack the distinct, polarized structure of an axon and dendrites. Instead, their shapes are varied and often diffuse or star-like, such as the processes extending from astrocytes. Glia are designed to wrap around, fill spaces, and interface with multiple other cells, including blood vessels and neuronal processes. Unlike neurons, glial cells do not form chemical synapses, reflecting their role in maintenance rather than direct signal transmission.
Major Subtypes and Locations
Both cell types exist in a variety of forms that are specialized according to their location. These locations include the Central Nervous System (CNS—brain and spinal cord) or the Peripheral Nervous System (PNS—nerves outside the CNS). Neurons can be functionally classified as sensory neurons, which carry information from the body to the CNS. They can also be motor neurons, which carry signals from the CNS to muscles and glands. Interneurons, the most numerous type, are found entirely within the CNS and link other neurons together for complex processing.
Glial cells comprise several distinct subtypes, each performing a unique service. In the CNS, Astrocytes are star-shaped cells that provide physical and metabolic support and help form the blood-brain barrier. Oligodendrocytes wrap the axons of CNS neurons with myelin, a fatty sheath that speeds up signal conduction.
In the PNS, Schwann Cells perform the same myelination function. A key difference is that a single Schwann cell covers only one section of one axon, while one oligodendrocyte can myelinate segments of multiple axons. Other CNS glia include Microglia, which act as the resident immune cells, and Ependymal cells, which line the brain’s fluid-filled ventricles and produce cerebrospinal fluid.
Electrical Activity and Proliferation
A fundamental difference between the two cell types lies in their ability to generate electrical signals. Neurons are electrically excitable cells that use voltage-gated ion channels to fire rapid, self-propagating electrical impulses called action potentials. While glia possess a resting membrane potential, they are generally not electrically excitable and do not generate action potentials. They communicate via slower, passive changes in membrane potential or through the release of chemical signals.
Another significant distinction is their capacity for cell division, or proliferation, in the adult nervous system. Mature neurons are typically post-mitotic, meaning they lose the ability to divide and regenerate themselves after development. Glial cells, however, retain the capacity for mitosis throughout life. This ability allows glia to proliferate in response to injury or disease, a process called gliosis, which often results in scar tissue that can impede neuronal regeneration.