Nervous tissue has a soft, jelly-like consistency and ranges in color from pinkish-gray to creamy white, depending on the region. To the naked eye, it looks unremarkable compared to muscle or bone. But under a microscope, it reveals one of the most complex and visually striking architectures in the human body, with sprawling cells that branch like trees and long fibers wrapped in layers of insulation.
What It Looks Like to the Naked Eye
Fresh brain tissue is extremely soft, roughly the consistency of soft tofu or gelatin. It’s delicate enough that handling it without careful support can distort its shape. Once preserved with chemicals (a process called fixation), it firms up considerably, which is why the brains you see in jars or anatomy labs look more solid than they actually are in life.
The most obvious visual feature is the contrast between gray matter and white matter. Gray matter, found on the brain’s outer surface and in the interior of the spinal cord, has a pinkish-gray tone. It gets its color from the densely packed cell bodies of neurons, along with their branching extensions and the tiny blood vessels that feed them. White matter sits beneath the brain’s surface and around the outside of the spinal cord. Its pale, almost creamy appearance comes from myelin, a fatty substance that wraps around nerve fibers like insulation around a wire. Myelin is rich in lipids, and those fats give white matter its characteristic color.
If you were to slice through the spinal cord crosswise, you’d see a butterfly or H-shaped core of gray matter surrounded by a rim of white matter, with a tiny central canal at the very center. In the brain, the arrangement flips: gray matter forms the outer cortex, with white matter filling the interior.
How Peripheral Nerves Appear
Outside the brain and spinal cord, nervous tissue takes a different form. Peripheral nerves, the cables that run to your limbs and organs, look like thin, whitish cords or threads. Larger nerves, like the sciatic nerve in the thigh, can be several millimeters thick and are visible during surgery as glistening, rope-like structures.
Cut one crosswise and you’ll see it isn’t a single wire. Instead, it’s a bundle of smaller bundles called fascicles, each containing hundreds or thousands of individual nerve fibers. These fascicles are wrapped in layers of connective tissue that give the nerve its structural strength. The outermost layer, the epineurium, is a tough sheath that protects the whole nerve. Inside, each fascicle has its own protective wrapping. This layered, cable-within-a-cable design is one reason peripheral nerves are somewhat resilient to stretching and compression.
Neurons Under the Microscope
The defining cell of nervous tissue is the neuron, and it has one of the most distinctive shapes of any cell in the body. A typical neuron has a rounded or pyramid-shaped cell body with a large, pale nucleus containing a single prominent dark spot (the nucleolus). Branching out from the cell body are dendrites, tree-like extensions that receive signals from other cells. A single long projection called an axon carries signals away from the cell body, sometimes over distances of a meter or more.
Different staining techniques reveal different features. A standard stain used in pathology labs turns the gray matter pink and the white matter blue (due to myelin absorbing the blue dye). A closer look at neurons in gray matter reveals clumps of dark, bluish-purple material in the cytoplasm, historically called Nissl substance, which is actually concentrated RNA involved in protein production. The classic Golgi stain, developed in the 1800s, fills entire neurons with dark silver deposits, making their full branching shape visible against a clear background. It’s the technique that first revealed just how elaborate a single neuron’s shape can be.
The Support Cells: Glia
Neurons get most of the attention, but they’re actually outnumbered by glial cells, the support cells of nervous tissue. These have their own distinctive appearances.
Astrocytes are the largest, ranging from 10 to 40 micrometers across. They have a star-like shape with many radiating branches. In gray matter, they tend to have thicker, bushier processes and relatively clear cytoplasm. In white matter, the same cell type takes on a more twig-like appearance, with straighter, more fibrous branches packed with structural filaments. Their nucleus is oval-shaped with a fairly uniform interior and a thin dark rim around the edge.
Oligodendrocytes are smaller and denser, roughly 10 to 20 micrometers, with a globular cell body and far fewer visible branches. Their nucleus stains dark, with clumps of dense material inside, sometimes making it hard to distinguish from the surrounding cytoplasm. In white matter, these are the cells responsible for producing myelin. In gray matter, a smaller variety called satellite oligodendrocytes sit pressed right up against the surface of neurons, almost like attendants.
Microglia are the smallest and hardest to spot. They have narrow, spindle-shaped bodies with a thin rim of dark cytoplasm that’s difficult to tell apart from the nucleus. When they become activated (during injury or infection), they change shape dramatically, extending arm-like projections to engulf damaged cells and debris.
What Myelin Looks Like Up Close
Myelin is one of the most visually recognizable structures in nervous tissue. Under an electron microscope, a myelinated nerve fiber in cross-section looks like a series of concentric dark and light rings surrounding a central pale circle (the axon itself). Each ring represents a layer of cell membrane wrapped tightly around the fiber. The whole sheath is typically less than one micrometer thick, too thin to see clearly with a standard light microscope, which is why electron microscopy is used to study it in detail.
Researchers measure myelin thickness using something called the g-ratio: the diameter of the inner axon divided by the outer diameter of the whole myelinated fiber. A healthy nerve fiber has a g-ratio around 0.6 to 0.8. Lower values mean thicker myelin relative to the axon. This measurement shows up consistently in studies of neurological diseases where myelin is damaged or thinning.
What Synapses Look Like
At the highest magnifications, electron microscopy reveals the synapse, the junction where one neuron communicates with another. A synapse is only about 20 to 40 nanometers wide, far too small for any light microscope. In electron micrographs, it appears as a narrow gap between two membranes, filled with a thin line of dense material that anchors the two sides together.
On the sending side, you can see clusters of tiny round vesicles, each loaded with chemical messengers, docked against the membrane and ready to release their contents. The receiving side has its own band of dense material, thicker at excitatory synapses (where signals are amplified) and thinner but more spread out at inhibitory synapses (where signals are dampened). These structural differences are consistent enough that researchers can identify the type of synapse just from its appearance in an electron micrograph.
Color in Stained Preparations
Most of the images you’ll encounter online are stained tissue, not the natural color of living nervous tissue. The specific colors depend entirely on which stain was used. In a common protocol combining standard dyes with a myelin-specific stain, gray matter appears pink while white matter turns blue because of its high myelin content. Lipofuscin, a yellowish pigment that accumulates in aging neurons, stains yellow. Nissl staining turns the RNA-rich regions of neuron cell bodies a deep violet or blue, making it easy to map where neuron cell bodies are concentrated.
These staining differences are why images of the same brain region can look completely different depending on the technique. A Nissl-stained section emphasizes cell body locations. A myelin stain highlights the fiber pathways. A Golgi preparation reveals the full branching architecture of individual cells while leaving most of the tissue transparent. Each method is essentially a different way of asking the tissue to show you one specific aspect of its structure.