Describe the events at a synapse as: (a) an impulse stimulates the release of neurotransmitter molecules from vesicles into the synaptic gap (b) the neurotransmitter molecules diffuse across the gap (c) neurotransmitter molecules bind with receptor proteins on the next neurone (d) an impulse is then stimulated in the next neurone
Describe the events at a synapse as: (a) an impulse stimulates the release of neurotransmitter molecules from vesicles into the synaptic gap (b) the neurotransmitter molecules diffuse across the gap (c) neurotransmitter molecules bind with receptor proteins on the next neurone (d) an impulse is then stimulated in the next neurone
Answer
The events at a synapse involve a series of coordinated actions that facilitate communication between neurons. Here’s a detailed description of these events:
(a) An Impulse Stimulates the Release of Neurotransmitter Molecules from Vesicles into the Synaptic Gap
When an action potential (electrical impulse) reaches the presynaptic terminal of a neuron, it causes the membrane to depolarize. This depolarization opens voltage-gated calcium channels, allowing calcium ions (Ca2+) to flow into the presynaptic neuron. The influx of calcium ions triggers synaptic vesicles, which contain neurotransmitter molecules, to move toward and fuse with the presynaptic membrane. This process is mediated by proteins known as SNARE proteins. Once fused, the vesicles release their contents (neurotransmitters) into the synaptic cleft through a process called exocytosis.
(b) The Neurotransmitter Molecules Diffuse Across the Gap
After their release, the neurotransmitter molecules diffuse across the synaptic cleft, which is a small gap (approximately 20-40 nanometers wide) between the presynaptic and postsynaptic neurons. This diffusion occurs rapidly, allowing neurotransmitters to reach the postsynaptic membrane almost instantaneously.
(c) Neurotransmitter Molecules Bind with Receptor Proteins on the Next Neuron
Upon reaching the postsynaptic neuron, neurotransmitter molecules bind to specific receptor proteins located on the postsynaptic membrane. These receptors can be classified into two main types:
- Ionotropic Receptors: These are directly linked to ion channels; when a neurotransmitter binds, it causes the channel to open, allowing ions to flow in or out of the neuron.
- Metabotropic Receptors: These are linked to G-proteins and initiate intracellular signaling cascades when activated by neurotransmitters, leading to longer-lasting effects .
The binding of neurotransmitters to their receptors alters the postsynaptic neuron’s membrane potential, which can either excite or inhibit it, depending on the type of neurotransmitter and receptor involved .
(d) An Impulse is Then Stimulated in the Next Neuron
If the binding of neurotransmitters leads to sufficient depolarization of the postsynaptic membrane (i.e., if it reaches a certain threshold), an action potential is generated in the postsynaptic neuron. This new impulse then propagates along its axon, continuing the signal transmission process. If the signal is inhibitory instead, it may prevent an action potential from occurring.
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