Temporal Summation: What, Why, Where, When, and How Does It Happen

Temporal Summation

We come across the term ‘Temporal Summation’ while studying Neurophysiology. It can be defined as the summation of postsynaptic potentials (PSPs) that occurs when two or more action potentials (APs) arrive at a postsynaptic neuron within a short interval of time. The concept of temporal summation helps us to understand how the nervous system processes information.

What is a temporal summation?

The phenomenon of temporal summation was first described by German physiologist Hermann von Helmholtz in the year 1852. He observed that when two or more stimuli are applied to a nerve at close intervals of time, the resultant response is greater than what would be expected from the simple summation of the individual responses.

It is important to note that temporal summation is different from spatial summation. Spatial summation refers to the summation of PSPs that occurs when two or more inputs (action potentials or synaptic potentials) arrive at different points on a postsynaptic neuron.

Why does temporal summation happen?

The phenomenon of temporal summation happens because the voltage-gated ion channels in the postsynaptic cell take some time to close after an action potential has passed through them. This means that if a second action potential arrives while the channels are still open, it will cause a greater influx of ions into the cell and produce a larger PSP.

There are two types of temporal summation:

• Linear summation: This occurs when the size of the PSP produced by each successive action potential is proportional to the number of action potentials that have arrived.
• Non-linear summation: This occurs when the size of the PSP produced by each successive action potential is greater than what would be predicted from linear summation. This type of summation is thought to occur because of the presence of other voltage-gated ion channels in the postsynaptic cell, which are activated by the PSP.

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Where does temporal summation happen?

Temporal summation is thought to play an important role in information processing by the nervous system. It has been shown to occur at various points in the nervous system, including the thalamus, hippocampus, and cortex.

In the thalamus, the temporal summation is thought to play a role in the detection of moving objects. This is because the thalamus receives input from both the ipsilateral and contralateral sides of the body, and temporal summation allows it to compare the inputs from these two sides.

In the hippocampus, the temporal summation is thought to be important for the encoding of memories. This is because when a person experiences a particular event, the hippocampus receives input from various parts of the brain, and temporal summation allows it to integrate this information.

In the cortex, the temporal summation is thought to be important for the perception of stimuli. This is because the cortex receives input from all of the senses, and temporal summation allows it to integrate this information.

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When does temporal summation happen?

Temporal summation is thought to occur when the nervous system is processing information that is important for the survival of the organism. For example, it has been shown to occur when an animal is confronted with a predator. In this situation, the animal’s brain receives input from all of its senses, and temporal summation allows it to integrate this information and respond appropriately.

How does temporal summation happen?

The temporal summation process can be broken down into four steps:

1. The arrival of an action potential at the presynaptic terminal.
2. The release of neurotransmitters from the presynaptic terminal.
3. The binding of neurotransmitters to receptors on the postsynaptic cell.
4. The opening of ion channels in the postsynaptic cell.

These steps result in the influx of ions into the postsynaptic cell and the generation of a PSP. If another action potential arrives while the ion channels are still open, it will cause a greater influx of ions and produce a larger PSP.

Temporal summation is thought to play an important role in information processing by the nervous system. It has been shown to occur at various points in the nervous system, including the thalamus, hippocampus, and cortex. In each of these regions, the temporal summation is thought to be important for different aspects of information processing. Hence, a better understanding of temporal summation may provide insights into how the nervous system processes information.

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