A ganglion is a cluster or bundle of nerve cells grouped together in one spot. Your nervous system contains many ganglia (that's the plural form) scattered throughout your body, like relay stations that help transmit signals between your brain and different body parts.

Think of a ganglion as a junction box where electrical wires meet and connect. When you touch something hot, nerve signals travel from your hand through ganglia on their way to your spinal cord and brain, which process the information and send back the command to pull your hand away. Some ganglia handle automatic functions you don't think about, like digesting food or controlling your heartbeat.

The word also has a completely different medical meaning: a ganglion can be a harmless, fluid-filled lump that forms near a joint or tendon, usually on the wrist or hand. These bumps feel squishy and sometimes appear or disappear on their own. Doctors can drain or remove them if they cause discomfort, though they're generally not dangerous.

In biology class, you'll most often encounter the nerve-related meaning when studying how your nervous system works. Scientists have discovered that even simple animals like insects have ganglia that act like tiny brains, helping them respond quickly to their environment.