In the Central Nervous System (CNS)
The Central Nervous System (CNS) is made up of the brain and the spinal chord, it receives information from the nervous system, where neurons are the building blocks of the CNS. Many inputs from hundreds of other neurons are received by a single neuron which then can form synapses with many thousands of other cells. This type of neuronal transmission is known as convergence, where a small number of presynaptic neurons can affect a large number of postsynaptic neurons, forming branches called collateral axons. The following are examples of convergence where some will create an action potential and some won't.
Type of Potentials
Among these synapses on a single neuron, some get excited when others get inhibited. In the excitatory synapse, neurotransmitter is released which then causes a small depolarisation within the postsynaptic membrane, naming: excitatory postsynaptic potential (EPSP).
Process: When there is an electrical impules and the neurotransmitter binds the to the channel on the postsynaptic membrane, the channel opens.If sodium channels open, then Na+ enter the cell→ EPSP (positive), but if K+ or chloro channels open, then they will leave the cell→ IPSP (negative).
- Temporal Summation: Occur from one presynaptic neuron. This is when the graded potential occur at a time that is so close to each other but from the same presynaptic neuron, therefore the summed potential hits threshold potential and triggers an action potential. 
- Spaital Summation: Neurons fire EPSP, which is positive due to sodium ions, each EPSP is subthreshold, meaning there is no action potential, but if subthreshold reaches the trigger zone at the same time, together, they will createa suprathreshold, which will create an action potential.
- Postsynaptic Inhibition: There is no action potential because the graded potential do not reach threshold potential when they reach the trigger zone.
1. Cherry K. Structure and Function of the Central Nervous System [Internet]. Verywell Mind. 2018 [cited 6 December 2018]. Available from: https://www.verywellmind.com/what-is-the-central-nervous-system-2794981
2. Dharani K. Molecular-Grid Model. The Biology of Thought [Internet]. 2015 [cited 6 December 2018];:123-142. Available from: https://www.sciencedirect.com/science/article/pii/B9780128009000000075
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