Catalyst
A substance that starts or speeds up a change or action.
Enzyme
A protein that acts as a catalyst by speeding up chemical reactions. The human body uses more than 1,000 different enzymes.
Nervous system
One of the nine major systems in the human body. The nervous system consists of the brain, spinal cord, and nerve network.
Neuron
The major cell type of the nervous system. Neurons can communicate with each other in two ways: by passing along electrical signals, or by passing along chemicals called neurotransmitters.
Neurotoxin
A poison that acts on the nervous system.
Neurotransmitters
Chemical "messages" that are passed between neurons.
Proteins
Naturally occurring substances made up of amino acids. The human body needs many types of proteins, including hormones, enzymes, and antibodies.
Synapse
The fluid-filled space between neurons where neurotransmitters travel back and forth.
Tissue
A group of cells with similar functions and structures. For example, muscle tissue is made up of many muscle cells.
Toxin
A poison created by an animal or plant.