Which of the following is true of spatial summation? Simultaneous stimulation of more than one postsynaptic neuron occurs. Impulses are fired in rapid succession by the same neuron. Neurotransmitters released simultaneously from several presynaptic knobs converge on the same region of one postsynaptic cell. Speed of impulse transmission is increased when several neurotransmitters are released.
The Correct Answer and Explanation is:
The correct statement about spatial summation is:
Neurotransmitters released simultaneously from several presynaptic knobs converge on the same region of one postsynaptic cell.
Explanation:
Spatial summation refers to the process by which multiple presynaptic neurons release neurotransmitters simultaneously onto a single postsynaptic neuron, leading to a stronger postsynaptic potential. This is in contrast to temporal summation, where a single presynaptic neuron fires multiple times in rapid succession to generate a stronger signal.
In spatial summation, the combined effect of neurotransmitter release from several presynaptic terminals, often at different locations on the dendrites or soma of the postsynaptic neuron, results in the depolarization or hyperpolarization of the postsynaptic membrane. If the combined excitatory postsynaptic potentials (EPSPs) or inhibitory postsynaptic potentials (IPSPs) are strong enough to reach the threshold, an action potential will be initiated in the postsynaptic neuron.
Here’s how the other options differ:
- Simultaneous stimulation of more than one postsynaptic neuron occurs: This refers to a situation involving multiple postsynaptic neurons, not spatial summation in the traditional sense. In spatial summation, several presynaptic neurons act on the same postsynaptic neuron.
- Impulses are fired in rapid succession by the same neuron: This is characteristic of temporal summation, where a single presynaptic neuron fires many impulses in a short period of time to generate a stronger response.
- Speed of impulse transmission is increased when several neurotransmitters are released: This is not an accurate description of spatial summation. The release of neurotransmitters in spatial summation helps to generate a stronger postsynaptic potential, but it doesn’t directly increase the speed of impulse transmission. Speed is more influenced by factors like axon diameter and myelination.
Thus, the correct statement aligns with the concept of spatial summation, where multiple inputs converge on a single postsynaptic neuron to influence its membrane potential.
