When a neurotransmitter molecule binds briefly with a receptor site, changes occur in the receiving neuron's charge. If there is a voltage shift in a negative direction, then the effect is ________

a. inhibitory, and so the probability that the receiving neuron will fire decreases.
b. excitatory, and so the probability that the receiving neuron will fire increases.
c. inhibitory, and so the probability that the receiving neuron will fire increases.
d. excitatory, and so the probability that the receiving neuron will fire decreases.

Answer: a