Describe the events at a synapse: (a) an impulse stimulates the release of neurotransmitter molecules from vesicles into the synaptic gap (b) the neurotransmitter molecules diffuse across the gap and bind with receptor proteins (c) an impulse is stimulated in the next neurone
Describe the events at a synapse: (a) an impulse stimulates the release of neurotransmitter molecules from vesicles into the synaptic gap (b) the neurotransmitter molecules diffuse across the gap and bind with receptor proteins (c) an impulse is stimulated in the next neurone
Answer
The events at a synapse involve a series of well-coordinated steps that facilitate communication between neurons. Here’s a detailed description of the process:
(a) Impulse Stimulates the Release of Neurotransmitter Molecules
When an electrical impulse, known as an action potential, reaches the presynaptic terminal of a neuron, it triggers the opening of voltage-gated calcium channels. Calcium ions (Ca²⁺) then flow into the neuron, prompting synaptic vesicles filled with neurotransmitter molecules to move toward and fuse with the presynaptic membrane. This fusion results in the release of neurotransmitters into the synaptic cleft, the small gap between the presynaptic neuron and the postsynaptic neuron. This process is essential for transmitting signals across synapses and is often referred to as exocytosis.
(b) Neurotransmitter Molecules Diffuse Across the Gap and Bind with Receptor Proteins
Once released, neurotransmitter molecules diffuse across the synaptic cleft, which is typically about 20-40 nanometers wide. They then bind to specific receptor proteins located on the membrane of the postsynaptic neuron. This binding is highly selective; each type of neurotransmitter fits into its corresponding receptor like a key in a lock. The interaction between neurotransmitters and receptors can lead to various effects, such as opening ion channels or activating intracellular signaling pathways, depending on the type of receptor involved.
(c) An Impulse is Stimulated in the Next Neuron
The binding of neurotransmitters to receptors on the postsynaptic membrane generates a change in the postsynaptic neuron’s membrane potential. If this change is sufficient to reach a threshold level, it triggers an action potential in the postsynaptic neuron, propagating the signal further along the neural pathway. This process allows for rapid communication between neurons and is fundamental to all nervous system functions, including reflexes, sensory processing, and motor control.
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