Final answer:
During presynaptic inhibition, a metabotropic response reduces the amount of calcium entering the nerve terminus, leading to a decrease in neurotransmitter release and synaptic transmission strength. The correct option is 2) A metabotropic response reduces the amount of calcium entering the nerve terminus.
Step-by-step explanation:
During presynaptic inhibition, a metabotropic response reduces the amount of calcium entering the nerve terminus. This occurs because metabotropic receptors, when activated by neurotransmitters, can initiate a cascade of intracellular events that lead to the closing of voltage-gated calcium channels.
As a result, less calcium enters the presynaptic neuron, which means that fewer neurotransmitter vesicles are released into the synaptic cleft. This mechanism serves to decrease the neurotransmission strength and thus inhibits synaptic transmission. While ionotropic receptors directly affect ion channels and can influence membrane potential, they do not directly control the action potentials arriving at a presynapse and do not regulate calcium entry related to neurotransmitter release in the context of presynaptic inhibition. The correct option is 2) A metabotropic response reduces the amount of calcium entering the nerve terminus.