Chapter 12 - Section 12.6 - Study Guide - Assess Your Learning Outcomes - Page 471: 6

Facilitation and presynaptic inhibition are mechanisms that modulate the strength of synaptic communication between neurons. These mechanisms can influence the communication between two neurons when a third neuron employs them. Here's an explanation of these mechanisms and how they affect neural communication: 1. **Facilitation:** - **Definition:** Facilitation is a presynaptic mechanism that enhances the release of neurotransmitters from the presynaptic neuron when it is repeatedly stimulated. - **Mechanism:** When a presynaptic neuron is stimulated repeatedly, calcium ions accumulate in the presynaptic terminal. This increased calcium concentration can lead to the facilitation of neurotransmitter release. It means that subsequent action potentials in the presynaptic neuron result in larger amounts of neurotransmitter being released into the synaptic cleft. This can lead to stronger postsynaptic responses (EPSPs) in the target neuron. - **Role in Communication:** When a third neuron employs facilitation at a synapse, it can enhance the synaptic strength between the third neuron and the postsynaptic neuron. This can be important in situations where increased synaptic strength is required for effective communication. For example, during prolonged or high-frequency signaling, facilitation can ensure that the postsynaptic neuron receives a more substantial signal. 2. **Presynaptic Inhibition:** - **Definition:** Presynaptic inhibition is a mechanism that reduces the release of neurotransmitters from the presynaptic neuron. - **Mechanism:** In presynaptic inhibition, a third neuron releases inhibitory neurotransmitters (e.g., GABA or glycine) onto the presynaptic terminal of the neuron whose communication is to be inhibited. These inhibitory signals hyperpolarize the presynaptic terminal, making it less likely to release neurotransmitters in response to action potentials. This results in a decrease in the postsynaptic response (IPSPs) in the target neuron. - **Role in Communication:** When a third neuron employs presynaptic inhibition at a synapse, it reduces the synaptic strength between the third neuron and the postsynaptic neuron. This can be crucial for controlling or limiting the flow of information between neurons in a neural circuit. It acts as a "gatekeeper" to prevent excessive or unwanted signaling. **Influence on Communication:** - **Enhancement:** Facilitation can enhance communication by increasing the strength of synaptic transmission between neurons. It is often employed when a more robust signal is needed. - **Inhibition:** Presynaptic inhibition can limit or dampen communication by reducing synaptic transmission. It is typically used when the flow of information needs to be controlled or modulated. The involvement of a third neuron employing these mechanisms allows for dynamic and precise control over the communication between two neurons in a neural circuit. It enables the nervous system to adapt to changing demands and regulate the strength and timing of signals, contributing to the complexity and flexibility of neural information processing.

Facilitation and presynaptic inhibition are mechanisms that modulate the strength of synaptic communication between neurons. These mechanisms can influence the communication between two neurons when a third neuron employs them. Here's an explanation of these mechanisms and how they affect neural communication: 1. **Facilitation:** - **Definition:** Facilitation is a presynaptic mechanism that enhances the release of neurotransmitters from the presynaptic neuron when it is repeatedly stimulated. - **Mechanism:** When a presynaptic neuron is stimulated repeatedly, calcium ions accumulate in the presynaptic terminal. This increased calcium concentration can lead to the facilitation of neurotransmitter release. It means that subsequent action potentials in the presynaptic neuron result in larger amounts of neurotransmitter being released into the synaptic cleft. This can lead to stronger postsynaptic responses (EPSPs) in the target neuron. - **Role in Communication:** When a third neuron employs facilitation at a synapse, it can enhance the synaptic strength between the third neuron and the postsynaptic neuron. This can be important in situations where increased synaptic strength is required for effective communication. For example, during prolonged or high-frequency signaling, facilitation can ensure that the postsynaptic neuron receives a more substantial signal. 2. **Presynaptic Inhibition:** - **Definition:** Presynaptic inhibition is a mechanism that reduces the release of neurotransmitters from the presynaptic neuron. - **Mechanism:** In presynaptic inhibition, a third neuron releases inhibitory neurotransmitters (e.g., GABA or glycine) onto the presynaptic terminal of the neuron whose communication is to be inhibited. These inhibitory signals hyperpolarize the presynaptic terminal, making it less likely to release neurotransmitters in response to action potentials. This results in a decrease in the postsynaptic response (IPSPs) in the target neuron. - **Role in Communication:** When a third neuron employs presynaptic inhibition at a synapse, it reduces the synaptic strength between the third neuron and the postsynaptic neuron. This can be crucial for controlling or limiting the flow of information between neurons in a neural circuit. It acts as a "gatekeeper" to prevent excessive or unwanted signaling. **Influence on Communication:** - **Enhancement:** Facilitation can enhance communication by increasing the strength of synaptic transmission between neurons. It is often employed when a more robust signal is needed. - **Inhibition:** Presynaptic inhibition can limit or dampen communication by reducing synaptic transmission. It is typically used when the flow of information needs to be controlled or modulated. The involvement of a third neuron employing these mechanisms allows for dynamic and precise control over the communication between two neurons in a neural circuit. It enables the nervous system to adapt to changing demands and regulate the strength and timing of signals, contributing to the complexity and flexibility of neural information processing.