Fifteen different presynaptic neurons synapse on a single po

Fifteen different presynaptic neurons synapse on a single postsynaptic neuron. The postsynaptic neuron has a RMP of -70 mV. At the trigger zone, 14 of the presynaptic neurons produce excitatory postsynaptic potentials of 2 mV each, and the other one produces an inhibitory postsynaptic potential of 9 mV. The threshold for the postsynaptic neuron is -50 mV. Will action potentials be produced in the postsynaptic neuron? Is this an example of temporal summation or spatial summation? Explain your answers.

Solution

The excitatory postsynaptic potential produced by 14 neurons is = 14* 2 = 28 mV

The inhibitory postsynaptic potential produced by one neurone is = -9 mV

The resting membrane potential is = -70 mV

Threshold potential is = -50 mV

The potential difference contributed by the synapses is = 28-9 = 19 mV

The resting membrane potential changes to -70+19 = -51 mV (does not reach threshold potential difference). Thus, no action potential will be produced. This is an example of spatial summation because different neurones are involved in this.