ABSTRACT
A basic problem of cell physiology is the nature of the communication between excitable cells that is mediated by a chemical transmitter substance. The functional contact between nerve cells or nerve and muscle cells that mediates the cell-to-cell communication is termed a synapse. The vast majority of synapses in vertebrates operate by means of a chemical synaptic transmitter, but a few synapses have been reported to operate electrically, without a neurotransmitter. Chemical synapses are of two types: excitatory (E-) synapses and inhibitory (1-) synapses. The excitatory synapses tend to depolarize the postsynaptic cell to threshold and cause it to frre an action potential, whereas inhibitory synapses tend to hyperpolarize the postsynaptic cell and so tend to keep it from firing an action potential. At synapses in the CNS (e.g., on the anterior hom cell of the spinal cord), the excitatory and inhibitory synaptic currents add and subtract (i.e., these are integrating synapses), and the postsynaptic cell frres only when the net depolarizing synaptic current is sufficient to bring the postsynaptic cell to its threshold (Eccles, 1964).
