Problem 9 - Biological Psychology

Question

When the action potential reaches the presynaptic terminal, which ion must enter the presynaptic terminal to evoke release of the neurotransmitter?

Step-by-Step Solution

Answer

Calcium ions (Ca²⁺) must enter the presynaptic terminal.

Step 1: Understanding the Action Potential

An action potential is an electrical signal that is propagated along a neuron's axon, reaching the presynaptic terminal at the neuron’s end. It's crucial because it triggers the next necessary events for communication between neurons.

Step 2: Identify Ion Involvement in Neurotransmitter Release

When the action potential arrives at the presynaptic terminal, it causes the opening of voltage-gated calcium channels. Calcium ions (Ca²⁺) are particularly essential at this juncture.

Step 3: Role of Calcium Ions

The entry of calcium ions into the presynaptic terminal through these channels is fundamental. Calcium ions facilitate the fusion of synaptic vesicles (which contain neurotransmitters) with the presynaptic membrane, thereby triggering the release of neurotransmitters into the synaptic cleft.

Step 4: Conclusion of Ion Function

The influx of calcium ions following an action potential is a critical factor that enables the subsequent step of neurotransmitter release. Without calcium entry, the vesicles would not release their neurotransmitter contents.

Key Concepts

Action Potential

The action potential is a powerful electrical signal crucial for nerve cell communication. It travels along the axon, from the neuron's body to the presynaptic terminal. Imagine it as a wave traveling down a stadium wave. Each spectator (or nerve cell component) passes on the wave in sequence. This wave-like signal ensures that neurons can quickly convey messages over long distances.

• Spreads rapidly along the axon
• Triggered by a change in voltage across the neuron's membrane
• Essential for synaptic transmission leading to neurotransmitter release

Calcium Ions

Calcium ions (Ca²⁺) play a fundamental role in neuronal communication. When an action potential reaches the presynaptic terminal, it doesn't work alone. It cues calcium ions to swing into action. This entry of calcium ions is paramount, almost like a key unlocking a door.

• Highly concentrated outside the neuron compared to inside
• Rush into the neuron when channels open, helping in signaling
• Facilitate neurotransmitter release by aiding vesicle fusion

Voltage-Gated Calcium Channels

Imagine voltage-gated calcium channels as the gateway guardians of the neuron. They open in response to an action potential, allowing calcium ions to flow into the neuron. These channels are sensitive to changes in electrical voltage, which makes them open or close.

• Located on the presynaptic membrane
• Open when the membrane potential is altered by an action potential
• Vital for the precise timing of neurotransmitter release

Calcium's entry through these channels ensures the neuron reacts exactly when it needs to, maintaining efficient communication.

Synaptic Vesicles

In the neurotransmitter release process, synaptic vesicles are the vital transport vehicles. Think of them like tiny delivery trucks. Each synaptic vesicle is filled with neurotransmitters, ready for delivery into the synaptic cleft upon receiving the go signal from calcium ions.

• Present in the presynaptic terminal
• Store neurotransmitters essential for neuron signaling
• Fuse with the membrane to release their contents upon calcium entry

This fusion and release are critical, as they enable the transmission of signals to the next neuron, ensuring the brain's seamless communication network.