Neurons communicate with each other at intersections called synapse function. In the synapse, one neuron sends a message to the target neuron – another cell. Most synapses are chemical; these synapses communicate using chemical transmitters. Other synapses are electric; in these synapses, ions flow directly between the cells.
In a chemical synapse, action potential triggers a presynaptic neuron to release neurotransmitters. These molecules bind to the receptors on the postsynaptic cell and make the triggering of the action potential more or less likely.
Introduction synapse function
A single neuron, or a nerve cell, can do a lot! It can maintain the potential of resting voltage on the diaphragm. It can trigger nerve impulses or action potentials. And it can carry out the metabolic processes necessary to stay alive.
However, the neuron signaling is much more exciting – it does not make sense! – when we consider its interaction with other neurons. Individual neurons connect to target neurons and stimulate or inhibit their activity, creating circuits that can process incoming information and perform a reaction.
How do neurons “talk” with each other? The action happens in the synapse, the point of communication between two neurons or between the neuron and the target cell, like the muscle or gland. In the synapse, triggering the action potential in one neuron – presynaptic or sending.
Electrical or chemical transmission synapse function?
At the end of the 19th and the beginning of the 20th century, there were many controversies as to whether the synaptic transmission was electric or chemical.
Some thought that synapse signals are related to the flow of ions directly from one neuron to another electrical transmission.
Other people thought it depends on the release of a chemical substance from one neuron, causing a reaction in the receiving neuron-chemical transmission.
We now know that synaptic transmission can be either electric or chemical – in some cases both in the same synapse function!
Chemical transmission is more common and more complicated than electrical transmission. First, let’s look at the chemical transmission.
Review of transmission in chemical synapse function
Chemical transfer includes the release of chemical messengers called neurotransmitters. The neurotransmitters carry information from the neuron sending pre-synaptically to the postsynaptic receiving cell.
As you can remember from the article about the synapse function of the neuron, synapses are usually created between the nerve endings – the axon tips – on the sending neuron and the cell body or dendrites that receive the neuron.
Barrier and inhibitory postsynaptic potentials
When the neurotransmitter binds to the receptor in the recipient cell, it causes the ion channels to open or close. This can cause a localized change in the potential of the membrane on the membrane of the receiving cell.
In some cases, the change causes the target cell to be more inclined to trigger its own action potential. The membrane potential shift is called excitatory post-synaptic potential or EPSP.
In other cases, the change causes the target cell to have less potential to trigger a functional potential and is called post-synaptic inhibitory potential or IPSP.
The EPSP depressivity causes the inside of the cell to be more positive, bringing the potential of the membrane closer to its threshold to trigger the action potential. Sometimes a single EPSP is not big enough to bring the neuron to the threshold. It can add up with other EPSPs to trigger the action potential.
IPSP have the opposite effect. This means that they have a tendency to maintain the potential of the postsynaptic neuron membrane. IPSPs are important because they can counteract or neutralize the exciting effect of EPSP.
Spatial and temporal summation
How do EPSP and IPSP interact?
Essentially, the postsynaptic neuron adds together or integrates all the stimulant and inhibitory inputs. It receives and “decides” whether to trigger the action potential.
The integration of postsynaptic potentials that occur in different places – but more or less at the same time – is called spatial summation. The integration of postsynaptic potentials, which occur in the same place, but at a slightly different time, is called time summation.