Compare and contrast the EPSP, IPSP, and action potential as to ions involved, a

EPSPs and IPSPs are graded potentials in postsynaptic cells resulting from the action of neurotransmitters at synapses, which are usually on dendrites of multipolar neurons, but could also be on the synaptic region of any target cell. EPSPs increase the probability that a postsynaptic action potential will result, because they involve an influx of sodium, which depolarizes the membrane potential, bringing it closer to threshold. IPSPs decrease the probability that a postsynaptic action potential will result, because they involve either an influx of chloride or an efflux of potassium, either of which hyperpolarizes the membrane potential, moving it farther from threshold.

Action potentials occur in axons of neurons, or in muscle cell membranes. They may result from PSPs or in the case of sensory neurons, specific stimuli such as sound or odor, which cause a type of graded potential called a receptor potential. Action potentials begin when graded potentials depolarize the membrane potential to threshold. The rising phase of an action potential results from sodium influx, and the falling phase from potassium efflux. Action potentials, but not graded potentials, are an all-or-none phenomenon.