Anatomy & Physiology: The Unity of Form and Function, 7th Edition

Published by McGraw-Hill Education
ISBN 10: 0073403717
ISBN 13: 978-0-07340-371-7

Chapter 12 - Section 12.6 - Study Guide - Assess Your Learning Outcomes - Page 471: 5

Answer

Temporal and spatial summation are fundamental mechanisms by which neurons integrate postsynaptic potentials (both Excitatory Postsynaptic Potentials or EPSPs and Inhibitory Postsynaptic Potentials or IPSPs) to determine whether they will fire an action potential. These mechanisms take place at the axon hillock or initial segment of the neuron, where the decision to fire an action potential is made. 1. **Temporal Summation:** - **Definition:** Temporal summation involves the integration of postsynaptic potentials that occur at the same synapse in rapid succession. - **Mechanism:** When a presynaptic neuron repeatedly fires and releases neurotransmitter at a synapse within a short time frame, the postsynaptic potentials generated by each release can add up. If the individual EPSPs or IPSPs are close enough in time and accumulate to reach the neuron's threshold for firing, they can trigger an action potential. - **Importance:** Temporal summation allows a single synapse to have a more significant impact on the neuron's firing decision. It is particularly relevant when the synaptic input is not strong enough with a single release but becomes sufficient through repeated stimulation. 2. **Spatial Summation:** - **Definition:** Spatial summation involves the integration of postsynaptic potentials from multiple synapses occurring at different locations on the neuron's dendrites and cell body. - **Mechanism:** Postsynaptic potentials generated at different synapses on the same neuron can summate spatially. If the collective effect of EPSPs from various synapses is sufficient to depolarize the neuron's membrane potential past the threshold, it can lead to the initiation of an action potential. - **Importance:** Spatial summation allows for the integration of information from different sources, such as sensory inputs or inputs from multiple neurons. It enables complex information processing by taking into account the combined effects of multiple synaptic inputs. The axon hillock or initial segment is a critical location for these summation processes. This region is particularly sensitive to changes in membrane potential and serves as the trigger zone for action potential initiation. When the net effect of temporal and spatial summation leads to the membrane potential reaching or surpassing the action potential threshold (typically around -55 to -50 millivolts), the neuron fires an action potential. If the threshold is not reached, the neuron remains in a resting state. In summary, temporal summation involves the accumulation of postsynaptic potentials over time at a single synapse, while spatial summation involves the integration of potentials from multiple synapses on the neuron's dendrites and cell body. These summation mechanisms allow neurons to make complex decisions about firing based on the combined effects of their synaptic inputs, contributing to the versatility and adaptability of neural information processing.

Work Step by Step

Temporal and spatial summation are fundamental mechanisms by which neurons integrate postsynaptic potentials (both Excitatory Postsynaptic Potentials or EPSPs and Inhibitory Postsynaptic Potentials or IPSPs) to determine whether they will fire an action potential. These mechanisms take place at the axon hillock or initial segment of the neuron, where the decision to fire an action potential is made. 1. **Temporal Summation:** - **Definition:** Temporal summation involves the integration of postsynaptic potentials that occur at the same synapse in rapid succession. - **Mechanism:** When a presynaptic neuron repeatedly fires and releases neurotransmitter at a synapse within a short time frame, the postsynaptic potentials generated by each release can add up. If the individual EPSPs or IPSPs are close enough in time and accumulate to reach the neuron's threshold for firing, they can trigger an action potential. - **Importance:** Temporal summation allows a single synapse to have a more significant impact on the neuron's firing decision. It is particularly relevant when the synaptic input is not strong enough with a single release but becomes sufficient through repeated stimulation. 2. **Spatial Summation:** - **Definition:** Spatial summation involves the integration of postsynaptic potentials from multiple synapses occurring at different locations on the neuron's dendrites and cell body. - **Mechanism:** Postsynaptic potentials generated at different synapses on the same neuron can summate spatially. If the collective effect of EPSPs from various synapses is sufficient to depolarize the neuron's membrane potential past the threshold, it can lead to the initiation of an action potential. - **Importance:** Spatial summation allows for the integration of information from different sources, such as sensory inputs or inputs from multiple neurons. It enables complex information processing by taking into account the combined effects of multiple synaptic inputs. The axon hillock or initial segment is a critical location for these summation processes. This region is particularly sensitive to changes in membrane potential and serves as the trigger zone for action potential initiation. When the net effect of temporal and spatial summation leads to the membrane potential reaching or surpassing the action potential threshold (typically around -55 to -50 millivolts), the neuron fires an action potential. If the threshold is not reached, the neuron remains in a resting state. In summary, temporal summation involves the accumulation of postsynaptic potentials over time at a single synapse, while spatial summation involves the integration of potentials from multiple synapses on the neuron's dendrites and cell body. These summation mechanisms allow neurons to make complex decisions about firing based on the combined effects of their synaptic inputs, contributing to the versatility and adaptability of neural information processing.
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