Chapter 12 - Section 12.5 - Synapses - Before You Go On - Page 461: 20

The termination of synaptic transmission is a crucial process that ensures precise and controlled signaling in the nervous system. Here are three mechanisms that stop synaptic transmission: 1. **Reuptake by Transporter Proteins:** - In many synapses, neurotransmitters are cleared from the synaptic cleft by transporter proteins located on the presynaptic neuron's membrane or nearby glial cells. - These transporter proteins actively pump neurotransmitters back into the presynaptic neuron or adjacent glial cells, effectively removing them from the synaptic cleft. - For example, serotonin is reuptaken by serotonin transporters, dopamine by dopamine transporters, and norepinephrine by norepinephrine transporters. 2. **Enzymatic Degradation:** - Some neurotransmitters are broken down by enzymes present in the synaptic cleft. Enzymatic degradation rapidly inactivates neurotransmitters. - Acetylcholinesterase, for instance, is an enzyme that breaks down acetylcholine into acetate and choline at cholinergic synapses, effectively terminating the action of acetylcholine. 3. **Diffusion Away from Receptors:** - Neurotransmitters can diffuse away from their receptors in the synaptic cleft. - As neurotransmitters are released into the synaptic cleft, they disperse in the extracellular fluid and may move away from the postsynaptic receptors. - As the concentration of neurotransmitter molecules decreases in the synaptic cleft, the binding of neurotransmitters to receptors becomes less frequent, reducing the postsynaptic response. These mechanisms work in concert to ensure that the postsynaptic neuron's response is brief and precisely controlled. By removing neurotransmitters from the synaptic cleft or inactivating them, these mechanisms prevent continuous signaling and allow for the termination of one synaptic event before another can occur. This fine-tuned regulation is essential for the accuracy and specificity of neuronal communication in the nervous system.

The termination of synaptic transmission is a crucial process that ensures precise and controlled signaling in the nervous system. Here are three mechanisms that stop synaptic transmission: 1. **Reuptake by Transporter Proteins:** - In many synapses, neurotransmitters are cleared from the synaptic cleft by transporter proteins located on the presynaptic neuron's membrane or nearby glial cells. - These transporter proteins actively pump neurotransmitters back into the presynaptic neuron or adjacent glial cells, effectively removing them from the synaptic cleft. - For example, serotonin is reuptaken by serotonin transporters, dopamine by dopamine transporters, and norepinephrine by norepinephrine transporters. 2. **Enzymatic Degradation:** - Some neurotransmitters are broken down by enzymes present in the synaptic cleft. Enzymatic degradation rapidly inactivates neurotransmitters. - Acetylcholinesterase, for instance, is an enzyme that breaks down acetylcholine into acetate and choline at cholinergic synapses, effectively terminating the action of acetylcholine. 3. **Diffusion Away from Receptors:** - Neurotransmitters can diffuse away from their receptors in the synaptic cleft. - As neurotransmitters are released into the synaptic cleft, they disperse in the extracellular fluid and may move away from the postsynaptic receptors. - As the concentration of neurotransmitter molecules decreases in the synaptic cleft, the binding of neurotransmitters to receptors becomes less frequent, reducing the postsynaptic response. These mechanisms work in concert to ensure that the postsynaptic neuron's response is brief and precisely controlled. By removing neurotransmitters from the synaptic cleft or inactivating them, these mechanisms prevent continuous signaling and allow for the termination of one synaptic event before another can occur. This fine-tuned regulation is essential for the accuracy and specificity of neuronal communication in the nervous system.