nervous system

• Threshold: the minimum stimulation required to send a message along a neuron
• Synapse: the region where two neurons meet
• Synaptic cleft: the gap between two neurons
• Neurotransmitter: a chemical that carries a nerve message across a synapse
• Grey matter: the part of the CNS that contains cell bodies and has a darker colour
• White matter: the part of the CNS that contains the axons and has a lighter colour
• Reflex action: the automatic, unthinkin, unconscious or involuntary response to a stimulus
• Reflex arc: the nerve pathway of a reflex action