Inputs or information are received by thousands of neurons from other neurons surrounding or around them. However, Summation is the process that makes sure whether the inputs received have the potential to elicit an action or not. Inhibitory and excitatory signals are capable enough in generating an action potential. However, this process is defined as Summation.
The process of Summation can be grouped into two types, temporal Summation and spatial Summation. Temporal Summation is generated from repeated inputs, and the spatial Summation is calculated from simultaneously occurring multiple inputs. A threshold voltage is generally achieved to get an action potential. The determination of the threshold voltage is done by the addition of the individual inputs coming from spatial Summation and temporal Summation.
Temporal vs Spatial Summation
The main difference between temporal Summation and spatial Summation is that temporal Summation involves a single presynaptic neuron, whereas spatial Summation involves multiple presynaptic neurons. In temporal Summation, the generation of the action potential is done by a single presynaptic neuron, whereas in spatial Summation, the generation of the action potential is done by multiple presynaptic neurons.
Temporal Summation refers to Summation in which postsynaptic action potentials are triggered by action potentials of a large number of the presynaptic neuron. In the case of temporal Summation, the duration of the postsynaptic action potential is higher than the interval between the action potentials.
Spatial Summation comes into existence when an action potential is triggered by inputs and information from multiple neurons. The action potential comes mainly from the dendrites, and the addition of the information and the inputs gives the spatial Summation. The mechanism or process in which the action potentials are drawn out from multiple presynaptic cells inside a neuron is called spatial Summation.
Comparison Table Between Temporal and Spatial Summation
| Parameters of Comparison | Temporal Summation | Spatial Summation |
| Definition | Temporal summation is a kind of sensory summary that involves incorporating single stimuli over a short period. | Spatial Summation is a kind of sensory summation, which at the same time, involves several neurons separated spatially during stimulation. |
| Presynaptic Neuron | Involves single presynaptic neuron. | Involves multiple presynaptic neurons. |
| Mechanism | The generation of the subthreshold is done by only one presynaptic neuron. | The generation of the subthreshold is done by multiple presynaptic neurons. |
| Efficiency | Temporal summation is less efficient. | Spatial Summation is more efficient. |
| Frequency | Temporal summation occurs at high frequency. | Spatial summation occurs as simultaneous stimulation. |
What is Temporal Summation?
Temporal Summation is a kind of sensory summary that over a short period involves the incorporation of single stimuli. This process occurs when the action potentials that summate in a high frequency elicits postsynaptic potentials. The process of temporal Summation occurs inside the nervous system. If the time constant of the cell membrane is long enough, the span of the Summation can be increased.
To reach the threshold potential, the previous postsynaptic potential summates with the next postsynaptic potential, which produces an increasing greater potential. Here, over a period, there occurs production of multiple subthreshold done by a single presynaptic neuron. The addition of the subthreshold is sufficient for the postsynaptic neuron to fire an action potential or for generating the action potential.
By the presynaptic neuron, the neurotransmitters are released into the synaptic gap, and the generation of each subthreshold occurs. EPSPs or excitatory postsynaptic potential is another way of considering subthreshold. If the addition of the subthreshold and the suprathreshold becomes equal, the generation of action potential takes place.
What is Spatial Summation?
Spatial Summation is a kind of sensory Summation, which at the same time involves several neurons separated spatially during stimulation. This process of spatial Summation occurs in the nervous system, in which on the postsynaptic neuron, the action potential generation is done by multiple presynaptic neurons. Spatial Summation is also a variety of simultaneous Summation. In spatial Summation, the responsibility of the action potential generation is on multiple EPSPs.
When the chances of achieving the threshold potential increases, the amount of excitatory postsynaptic potentials also increases quantitatively to elicit an action potential. However, the chance of reaching the threshold potential is less when the amount of inhibitory postsynaptic potentials is high, in order of generation of the action potential.
In the process of algebraic addition of potentials, it is carried from various areas of fetching information or inputs, specifically on the dendrites. Inhibitory postsynaptic potentials and excitatory postsynaptic potentials can be added together during spatial Summation. On the postsynaptic neuron, this process prevents the action potential from generating. Postsynaptic inhibition is the name of the above process.
Main Differences Between Temporal and Spatial Summation
- Temporal Summation is a kind of sensory summary that over a short period involves the incorporation of single stimuli, whereas Spatial Summation is a kind of sensory Summation, which at the same time involves several neurons separated spatially during stimulation.
- In temporal Summation, the generation of the action potential is done by a single presynaptic neuron, whereas in spatial Summation, the generation of the action potential is done by multiple presynaptic neurons.
- In temporal Summation, the generation of the subthreshold is done by only one presynaptic neuron. Whereas in spatial Summation, the generation of the subthreshold is done by multiple presynaptic neurons.
- Temporal Summation requires more time in the generation of an action potential and thus is less efficient. In contrast, spatial Summation is a more efficient mechanism.
- The occurrence of temporal Summation is high. That is, in temporal Summation, the stimulation occurs at a high frequency. Whereas spatial Summation is a type and consequence of simultaneous stimulation.
Conclusion
Temporal Summation differs from spatial Summation in the involvement of multiple stimuli in the type and process of Summation. In temporal Summation, one presynaptic neuron generates the subthreshold over some time. Therefore, the presynaptic neuron is responsible for an action potential generation. In spatial Summation, multiple presynaptic neurons generate subthreshold, and they are solely responsible for action potential generation.
References
- https://journals.physiology.org/doi/pdf/10.1152/ajplegacy.1933.106.2.365
- https://physoc.onlinelibrary.wiley.com/doi/abs/10.1113/jphysiol.1993.sp019597