Describe the process of synaptic transmission in the central nervous system, including the steps involved in neurotransmitter release, synaptic signaling, and postsynaptic responses. How do action potentials in the presynaptic neuron trigger the opening of voltage-gated calcium channels, leading to calcium influx and neurotransmitter release into the synaptic cleft? Furthermore, how do neurotransmitters bind to specific receptors on the postsynaptic neuron, eliciting excitatory or inhibitory responses through depolarization or hyperpolarization? Additionally, how do factors like neurotransmitter reuptake, enzymatic degradation, and modulation by neuromodulators regulate synaptic transmission and neuronal communication?