Final answer:
Glutamate is the amino acid that helps relay messages in the nervous system by causing depolarization of the postsynaptic cell.
Step-by-step explanation:
The amino acid that helps relay messages in the nervous system is glutamate. Glutamate is an excitatory amino acid and acts as a neurotransmitter by causing depolarization of the postsynaptic cell. It is part of the glutamatergic system and has its own specific receptors in the nervous system.