Neurotransmitter release | Nervous system physiology | NCLEX-RN | Khan Academy

Summary

This video explains how neurotransmitters are released at the synapse. It covers the role of voltage-gated calcium channels in facilitating neurotransmitter release when an action potential reaches the axon terminal. Calcium influx triggers the fusion of synaptic vesicles with the presynaptic membrane, allowing neurotransmitters to diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane. The video also explores how the frequency and duration of action potentials influence neurotransmitter release, ultimately transmitting information to the target cell.

Takeaways

• 😀 Neurotransmitters are released at the synapse when synaptic vesicles in the axon terminal fuse with the presynaptic membrane.
• 😀 The process of neurotransmitter release is triggered by the opening of voltage-gated calcium channels at the axon terminal.
• 😀 Action potentials cause a change in membrane potential at the axon terminal, which opens voltage-gated calcium channels, allowing calcium to flow in.
• 😀 Calcium concentration is much higher outside the neuron than inside, so calcium flows into the axon terminal, triggering a series of events.
• 😀 The influx of calcium causes proteins on synaptic vesicles and the presynaptic membrane to interact and fuse, allowing neurotransmitters to be released.
• 😀 Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane of the target cell.
• 😀 Information from action potentials is encoded in the frequency and duration of their firing, which influences the amount and duration of neurotransmitter release.
• 😀 Higher frequencies of action potentials open more calcium channels, leading to greater calcium influx and more neurotransmitter release.
• 😀 The duration of action potentials also affects how long neurotransmitter release lasts, influencing the overall signaling time.
• 😀 The process of neurotransmitter release ends when the action potential stops firing, causing calcium channels to close and calcium to be pumped out, halting neurotransmitter release.

Q & A

What is the primary focus of the video?

The primary focus of the video is explaining how neurotransmitters are released at the synapse, including the role of voltage-gated calcium channels in this process.

What did the previous video cover?

The previous video covered the structure of a typical chemical synapse, including the axon terminal with synaptic vesicles and receptors on the postsynaptic membrane.

How do neurotransmitter molecules leave the synaptic vesicles and reach the target cell?

Neurotransmitter molecules exit the synaptic vesicles when voltage-gated calcium channels open, causing calcium ions to flow into the axon terminal. This leads to the fusion of synaptic vesicles with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft.

What is the function of the voltage-gated calcium channels?

The voltage-gated calcium channels open when the action potential reaches the axon terminal. This allows calcium ions to flow into the terminal, increasing the intracellular calcium concentration, which then triggers the release of neurotransmitters.

How does calcium concentration affect neurotransmitter release?

An increase in calcium concentration inside the axon terminal triggers the fusion of synaptic vesicles with the presynaptic membrane, which results in the release of neurotransmitters into the synaptic cleft.

What happens when the action potential reaches the axon terminal?

When the action potential reaches the axon terminal, it changes the membrane potential, opening the voltage-gated calcium channels and allowing calcium to flow into the terminal, starting the process of neurotransmitter release.

How is the information in action potentials transferred to the target cell?

The information in action potentials is transferred by converting the frequency and duration of the action potentials into the amount and duration of neurotransmitter release, which then binds to receptors on the postsynaptic membrane.

What role does the frequency of action potentials play in neurotransmitter release?

An increase in the frequency of action potentials causes more frequent openings of the voltage-gated calcium channels, leading to a greater influx of calcium and a larger release of neurotransmitters into the synaptic cleft.

What happens when the train of action potentials stops firing?

When the action potentials stop, the voltage-gated calcium channels close, calcium stops flowing into the axon terminal, and the calcium concentration is reduced. This halts the release of neurotransmitters as synaptic vesicles stop fusing with the presynaptic membrane.

What is the relationship between neurotransmitter duration in the synaptic cleft and action potential firing?

The duration of neurotransmitter presence in the synaptic cleft is linked to the duration of action potential firing. A longer train of action potentials results in neurotransmitter release over a longer period of time, increasing the duration of neurotransmitter binding to receptors.