Research suggests that learning may involve: Ca^2+ influx into a postsynaptic cell, causing biochemical changes and enhanced response to stimulation. strengthening the sodium-potassium pump. changes in action potential duration caused by blocking voltage-gated K^+ channels. synaptic changes caused by decreasing the size of the synaptic cleft and increasing the effectiveness of neurotransmitter diffusion. synaptic changes causing slower reuptake of neurotransmitter from the synaptic cleft. This question can be used to confirm that students understand that changes in ion flow are important for signal transduction in all parts of the nervous system.