A nerve cell, or neuron, looks like a tiny star or spider with a rounded central body and long, thin branches extending outward. It’s one of the most distinctive-looking cells in the human body, immediately recognizable under a microscope by its unusual shape: a compact center with thread-like projections stretching far from it. Some of those projections are short and bushy, while one is typically much longer than the rest.
The Three Main Parts
A typical neuron has three visible structures: the cell body, dendrites, and an axon. The cell body (also called the soma) is the rounded central hub. It contains the nucleus, which looks like a dark circle inside the cell, and all the machinery the cell needs to stay alive. Depending on the type of neuron, the cell body can be globe-shaped, pear-shaped, or star-shaped.
Branching out from the cell body are dendrites, which look like the bare branches of a winter tree. A single neuron can have one dendrite or dozens, depending on its job and location in the body. These branch-like extensions receive incoming signals from other nerve cells.
The axon is the single long projection that carries signals away from the cell body. It looks like a thin cable or fiber, and it can be dramatically longer than the rest of the cell. While the cell body might be only a few millionths of a meter wide, the axon of a motor neuron running from your spinal cord to your foot can stretch over three feet. At its far end, the axon splits into fine branches tipped with tiny bulb-shaped swellings called terminal boutons. These little bulbs are packed with chemical messengers and energy-producing structures, ready to pass a signal to the next cell across a microscopic gap.
Size and Scale
Nerve cell bodies range considerably in size. The smallest, like the granule cells in the cerebellum, measure roughly 6 to 8 micrometers across, about the size of a red blood cell. The largest, like the Purkinje cells of the cerebellum or the motor neurons in the spinal cord, can reach 60 to 80 micrometers in diameter. That’s still far too small to see with the naked eye, but under a basic light microscope, the larger neurons are easy to spot.
What makes neurons remarkable isn’t just their width but their length. The axon of a single cell can be thousands of times longer than the cell body is wide, giving the whole neuron an extremely elongated, asymmetric look that no other cell type in the body shares.
The Insulating Coating
Many axons are wrapped in a fatty insulating layer called the myelin sheath, which changes their appearance significantly. Under a microscope, a myelinated axon looks segmented, like a string of sausages or beads. Each segment of insulation is separated by a tiny exposed gap about one micrometer long, called a node of Ranvier. The insulated sections between the gaps are much longer. This wrapping gives the axon a distinctive banded pattern and serves a practical purpose: it speeds up electrical signal transmission dramatically, the same way rubber insulation on a wire prevents energy from leaking out.
When you look at bulk nerve tissue with the naked eye, myelin is what gives “white matter” in the brain and spinal cord its pale, glossy appearance. Regions where cell bodies cluster together without much myelin look darker and are called “gray matter.”
Not All Neurons Look the Same
The textbook image of a neuron, with a central body, several dendrites on one side, and a single long axon on the other, describes a multipolar neuron. This is the most common type, found throughout the brain and spinal cord. But neurons come in several structural varieties.
Bipolar neurons have just two projections extending from opposite ends of the cell body, one dendrite and one axon, giving them a simpler, more elongated shape. These are found in sensory organs like the retina and inner ear. Unipolar (sometimes called pseudounipolar) neurons have a single projection that splits into two branches shortly after leaving the cell body, creating a T-shaped or Y-shaped appearance. These carry sensory information like pain and touch from the body to the spinal cord.
Some neurons are visually spectacular. Purkinje cells in the cerebellum have an enormous, flat, fan-shaped dendritic tree that looks almost like a coral or a fern frond. Covered in thousands of tiny spines, a single Purkinje cell can receive signals from hundreds of thousands of other neurons. Pyramidal cells in the cerebral cortex, by contrast, have a more triangular cell body with a prominent main dendrite extending straight upward and several shorter ones fanning out from the base, giving them a roughly cone-shaped profile.
What Neurons Look Like Under a Microscope
Without special preparation, neurons are nearly transparent and very difficult to see. Most of the classic images of neurons rely on staining techniques that highlight different parts of the cell. A traditional stain using silver (developed in the late 1800s by Camillo Golgi) fills random individual neurons with dark pigment, making them stand out against a clear background. This is what produces the dramatic, tree-like silhouettes most people picture when they think of a nerve cell.
Other stains highlight the cell body specifically. One common approach reveals clumps of protein-making machinery inside the soma called Nissl substance, which appear as dark, grainy spots clustered throughout the cell body. These granular masses are dense enough to be visible even under a standard light microscope and help pathologists distinguish neurons from other cell types.
Under an electron microscope, which magnifies structures thousands of times more than a light microscope, neurons reveal far more internal detail: layered membranes, tiny energy-producing compartments, and the fine texture of the myelin wrapping. At this scale, identifying different cell types becomes challenging even for experts, because the characteristic overall shape of the neuron is no longer visible. Instead, specialists rely on the pattern of internal structures, the darkness of the nucleus, and the cell’s relationships with surrounding cells to tell neurons apart from other brain cells.
The Sending End Up Close
At the far end of the axon, where one neuron communicates with the next, the structure gets intricate. The axon splits into a spray of fine branches called the terminal arbor. Each branch ends in a small, rounded swelling, the terminal bouton. Inside each bouton, tiny bubble-like sacs called synaptic vesicles are loaded with chemical messengers, visible under an electron microscope as small, dark circles clustered near the cell membrane. Between the bouton and the next cell is a narrow gap, the synaptic cleft, only about 20 nanometers wide.
Some neurons don’t confine their signaling to the very tip. Certain axons have swellings spaced along their length, like knots on a rope. These “passing” boutons can release chemical signals at multiple points along the axon, not just at the end, giving these neurons a beaded or varicose appearance.