A GABA receptor is a neuron (brain cell) shaped to receive the neurotransmitter gamma-aminobutyric acid (GABA). GABA functions as the major chemical messenger that slows and stops chemical reactions throughout the central nervous system. The receptor also reacts to other chemicals, including alcohol, that increase the inhibition of the neuron. When certain muscles are not inhibited and told when to stop moving, they can spasm painfully.
This is the most famous symptom of tetanus, which starts with the nickname of 'lockjaw' because the muscle in the face are spasming and the mouth cannot open properly.