chemical synaptic transmission

Definition

Target type: biologicalprocess

The vesicular release of classical neurotransmitter molecules from a presynapse, across a chemical synapse, the subsequent activation of neurotransmitter receptors at the postsynapse of a target cell (neuron, muscle, or secretory cell) and the effects of this activation on the postsynaptic membrane potential and ionic composition of the postsynaptic cytosol. This process encompasses both spontaneous and evoked release of neurotransmitter and all parts of synaptic vesicle exocytosis. Evoked transmission starts with the arrival of an action potential at the presynapse. [GOC:jl, MeSH:D009435]

Chemical synaptic transmission is a fundamental process in neuronal communication, enabling the transfer of information between nerve cells. It involves a complex sequence of events that occur at specialized junctions called synapses. Here's a detailed breakdown:

1. **Presynaptic Events:**
a. **Action Potential Arrival:** An electrical signal, known as an action potential, travels down the axon of a presynaptic neuron.
b. **Calcium Influx:** When the action potential reaches the presynaptic terminal, it triggers the opening of voltage-gated calcium channels. Calcium ions (Ca2+) rush into the terminal, increasing their concentration.
c. **Vesicle Fusion and Neurotransmitter Release:** The influx of Ca2+ initiates a cascade of events that lead to the fusion of synaptic vesicles with the presynaptic membrane. These vesicles contain neurotransmitters, chemical messengers that carry the signal across the synapse. Fusion releases the neurotransmitters into the synaptic cleft, the narrow space between the presynaptic and postsynaptic neurons.

2. **Synaptic Cleft:**
a. **Diffusion:** Neurotransmitters released into the synaptic cleft rapidly diffuse across the space.
b. **Binding to Receptors:** The neurotransmitters bind to specific receptors on the postsynaptic membrane, initiating a signal transduction cascade.

3. **Postsynaptic Events:**
a. **Ligand-gated Ion Channels:** Many neurotransmitter receptors are ligand-gated ion channels. When a neurotransmitter binds, it causes the channel to open, allowing specific ions to flow across the postsynaptic membrane. This ion flow generates a postsynaptic potential (PSP).
b. **Signal Amplification:** The binding of neurotransmitters can also activate intracellular signaling pathways, amplifying the signal and leading to various cellular responses, including changes in gene expression.
c. **Excitatory vs. Inhibitory:** Neurotransmitters can have either excitatory or inhibitory effects on the postsynaptic neuron. Excitatory neurotransmitters, like glutamate, depolarize the postsynaptic membrane, making it more likely to fire an action potential. Inhibitory neurotransmitters, like GABA, hyperpolarize the membrane, making it less likely to fire.

4. **Termination of Transmission:**
a. **Reuptake:** Neurotransmitters are removed from the synaptic cleft by various mechanisms, including reuptake by presynaptic transporters.
b. **Enzymatic Degradation:** Some neurotransmitters are broken down by enzymes in the synaptic cleft.
c. **Diffusion:** Neurotransmitters can also diffuse away from the synapse.

5. **Integration:**
a. **Spatial Summation:** Multiple presynaptic neurons can release neurotransmitters at the same time, causing their postsynaptic potentials to summate.
b. **Temporal Summation:** If neurotransmitters are released in rapid succession, their postsynaptic potentials can summate over time.

The precise mechanisms of chemical synaptic transmission can vary depending on the type of synapse, the neurotransmitters involved, and the postsynaptic neuron. However, the fundamental principles outlined above are common to all chemical synapses. This intricate process underlies a vast array of cognitive, sensory, and motor functions, playing a crucial role in our ability to perceive, learn, and interact with the world.'
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Proteins (118)

Compounds (2,717)