What happens in the synaptic cleft during summation?

During summation in the synaptic cleft, a neuron is stimulated by two or more other neurons, which results in the integration of multiple signals. This process occurs when neurotransmitters released from presynaptic neurons bind to receptors on the postsynaptic neuron's membrane. If multiple signals arrive in quick succession or simultaneously from different neurons, their combined effect can lead to a significant change in the postsynaptic neuron’s membrane potential, potentially triggering an action potential if the threshold is reached.

This summation can happen through two mechanisms: temporal summation, where multiple impulses from the same neuron occur in rapid succession, and spatial summation, where impulses from multiple neurons arrive at the same time. The ability to integrate these signals allows the nervous system to process complex information and respond appropriately. Thus, the correct answer highlights the importance of simultaneous stimulation in summation, distinguishing it from scenarios where a neuron would only receive a signal from one source or where neurotransmitter activity is inhibited or reabsorbed.