What is the Difference Between Temporal and Spatial Summation

The main difference between temporal and spatial summation is that temporal summation occurs when one presynaptic neuron releases neurotransmitters over a period of time to fire an action potential whereas spatial summation occurs when multiple presynaptic neurons release neurotransmitters together to fire an action potential in the postsynaptic neuron. Furthermore, the temporal summation is a type of high–frequency stimulation while spatial summation is a type of simultaneous stimulation.

Temporal and spatial summation are two types of summation processes in the nervous system. Moreover, multiple stimuli are involved in firing an action potential.

Key Areas Covered

1. What is Temporal Summation
     – Definition, Mechanism, Importance
2. What is Spatial Summation
     – Definition, Mechanism, Importance
3. What are the Similarities Between Temporal and Spatial Summation
     – Outline of Common Features
4. What is the Difference Between Temporal and Spatial Summation
     – Comparison of Key Differences

Key Terms

Action Potential, Multiple Stimuli, Postsynaptic Neuron, Presynaptic Neuron, Spatial Summation, Temporal Summation

What is Temporal Summation

Temporal summation is the summation in the nervous system in which a single presynaptic neuron involves in the production of multiple subthresholds over a period of time. At a certain point, the sum of these subthreshold become sufficient for the generation or firing of an action potential on the postsynaptic neuron. Here, each subthreshold is generated by the released neurotransmitters to the synaptic gap by the presynaptic neuron. Also, each of the subthreshold can be considered as an excitatory postsynaptic potential (EPSPs). However, an action potential is generated only if the sum of the subthresholds becomes equal to the suprathreshold.

What is Spatial Summation

Spatial summation is another type of summation in the nervous system; here, the subthresholds produced by multiple presynaptic neurons are responsible for the generation of an action potential on the postsynaptic neuron. Therefore, this is a type of simultaneous summation in which multiple ESPSs are responsible for the generation of an action potential.

Figure 1: Spatial and Temporal Summation

However, during spatial summation, both excitatory and inhibitory postsynaptic potentials can be summed up together, preventing the generation of an action potential on the postsynaptic neuron as well. This process is known as postsynaptic inhibition.

Similarities Between Temporal and Spatial Summation

• Temporal and spatial summation are two types of summation mechanisms which occur in the nervous system.
• Multiple stimuli are involved in generating an action potential in the postsynaptic neuron.
• Here, each of the stimulus is subthreshold, which together form a suprathreshold through summation.

Difference Between Temporal and Spatial Summation

Definition

Temporal summation refers to the sensory summation that involves the addition of single stimuli over a short period of time while spatial summation refers to the sensory summation that involves stimulation of several spatially separated neurons at the same time. Thus, this is the main difference between temporal and spatial summation.

Presynaptic Neurons

Furthermore, a single presynaptic neuron is responsible for generating the action potential in temporal summation while multiple presynaptic neurons are responsible for generating the action potential in spatial summation.

Mechanism

One presynaptic neuron generates subthresholds over a certain period of time in temporal summation while multiple presynaptic neurons generate subthresholds in spatial summation. Hence, this is another difference between temporal and spatial summation.

Efficiency

Efficiency is another difference between temporal and spatial summation. Temporal summation is a less efficient process as it takes time to generate an action potential while spatial summation is an efficient mechanism.

Conclusion

Temporal summation is a summation process in the nervous system in which subthresholds generated by a single presynaptic neuron over a period of time are responsible for the generation of an action potential on the postsynaptic neuron. In comparison, the spatial summation is another type of summation process in which the subthresholds generated by multiple presynaptic neurons are responsible for the generation of an action potential on the postsynaptic neuron. Therefore, the main difference between temporal and spatial summation is the type of multiple stimuli involved in each type of summation.

References:

1. “Summation.” The School of Biomedical Sciences Wiki, Available Here

Image Courtesy:

1. “Types of summation” (CC BY-NC-SA 3.0) via The School of Biomedical Sciences Wiki