ganglion

A ganglion is usually a small lump filled with fluid that forms under the skin, often on the wrist, hand, or foot. It is usually harmless, though it can feel sore or get in the way if it presses on a nerve. You can think of it as a little sac that grows near a joint or tendon. Doctors do not fully agree on why it forms, but it may appear after repeated strain or irritation. In another medical sense, it can also mean a cluster of nerve cells.

The word "ganglion" has a fascinatingly diverse history. Originally, in ancient Greek medicine, it referred to a knot-like swelling or a nerve center—essentially a cluster of nerve cells. Today, while that original meaning remains central to the field of neurology (referring to autonomic ganglia involved in regulating bodily functions), we most commonly encounter "ganglion" describing a different kind of lump: a benign, fluid-filled cyst that develops near joints or tendons.

These cysts are typically found on the wrists, hands, and feet, appearing as noticeable bumps under the skin. They are not usually dangerous, but they can sometimes cause discomfort, pain if they press on nerves, or limited movement. Doctors believe they form when tissue around a joint or tendon bulges out, creating a sac filled with synovial fluid, the slippery liquid that helps joints move smoothly.

The neurological meaning of "ganglion" is equally important. In this context, it refers to a cluster of nerve cell bodies outside the central nervous system, playing a crucial role in transmitting signals throughout the body. For example, sympathetic ganglia are part of the autonomic nervous system and help regulate vital functions like heart rate and digestion.

So, whether you're talking about a visible lump under your skin or a vital component of your nervous system, "ganglion" describes a cluster—either of fluid-filled tissue or nerve cells—playing a distinct role in the body's structure and function.