Compare and contrast spatial and temporal summation. What are these processes us
ID: 12129 • Letter: C
Question
Compare and contrast spatial and temporal summation. What are these processes used for in sensory processing? Please use a different example than the one described below in quotes.
"Spatial summation occurs when excitatory potentials from many different presynaptic neurons cause the postsynaptic neuron to reach its threshold and fire.
Temporal summation occurs when a single presynaptic neuron fires many times in succession, causing the postsynaptic neuron to reach its threshold and fire.
As an analogy, spatial summation is like using many shovels to fill up a hole all at once. Temporal summation is like using a single shovel to fill up a hole over time. Both methods work to fill up the whole (the postsynaptic neuron reaches its action potential threshold)."
Explanation / Answer
Temporal summation is the addition of stimuli occurring in rapid successions. It occurs at a single synapse that is active repeatedly. The greater number of action potentials elicited in a single sensory neuron and the greater number of excitatory postsynaptic potential (EPSPs) produced in the motor neuron from an action potential in the sensory neuron, leads to a change in the potential of the motor neuron. For example: - Consider that you want to fill a bathtub with single bucket of water but cannot fill it at once but you keep using the bucket over and over to fill it fully. The water in each bucketful corresponds to the Na+ ions that enter the cytoplasm during and EPSP. If a second EPSP arrives before the effects of the first have disappeared. Each time when an action potential arrives, a group of vesicles discharges acetylcholine (ACh) into the synaptic cleft. Then each time, ACh molecules arrive at the postsynaptic membrane, more chemically regulated channels open and the degree of depolarization increases. In this way, a series of small steps can eventually bring the intial segment to threshold. Spatial summation occurs when simultaneous or multiple stimuli at different locations have a cumulative effect on the transmembrane potential. It involves muliple synapses that are active simultaneously. For example: - In terms of our bucket example given in temporal summation, you can fill a bathtub immediately if your 10 friends emptied their buckets into the bathtub at the same time. The activity of one synapse produces a graded potential with localized effects. If multiple synapses are acitvated at the same time, all will pour Na+ ions across the postsynaptic membrane. The effects on the initial segment are cumulative. As in temporal summation, an action potential appears when the transmembrane potential at the initial segment reaches threshold.Related Questions
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