Which of the following is the most direct result of depolarizing the presynaptic membrane of an axon terminal? a. Voltage-gated calcium channels in the membrane open. b. Synaptic vesicles fuse with the membrane. c. Ligand-gated channels open, allowing neurotransmitters to enter the synaptic cleft. d. An EPSP or IPSP is generated in the postsynaptic cell.

Verified step by step guidance

1. Step 1: Understand the question. The question is asking about the immediate result of depolarizing the presynaptic membrane of an axon terminal. Depolarization is the process by which the membrane potential of a cell becomes less negative or more positive.
2. Step 2: Review the options. Each option represents a different event that can occur in a neuron during signal transmission.
3. Step 3: Recall that depolarization of the presynaptic membrane leads to the opening of voltage-gated calcium channels. This is because the change in membrane potential triggers these specific channels to open.
4. Step 4: Compare this information with the options. Option a states 'Voltage-gated calcium channels in the membrane open.' This is the most direct result of depolarizing the presynaptic membrane.
5. Step 5: Therefore, the correct answer is option a.

Key Concepts

Depolarization of the Presynaptic Membrane

Depolarization refers to the change in membrane potential that makes the inside of the neuron less negative compared to the outside. In the context of an axon terminal, this change is crucial for initiating the release of neurotransmitters. When the presynaptic membrane depolarizes, it triggers a series of events that lead to the opening of voltage-gated channels.

Voltage-Gated Calcium Channels

Voltage-gated calcium channels are specialized proteins in the presynaptic membrane that open in response to depolarization. When these channels open, calcium ions (Ca²+) flow into the neuron, which is essential for the process of neurotransmitter release. The influx of calcium ions is a key trigger for synaptic vesicles to fuse with the membrane and release their contents into the synaptic cleft.

Synaptic Transmission

Synaptic transmission is the process by which signaling molecules, or neurotransmitters, are released from the presynaptic neuron and bind to receptors on the postsynaptic neuron. This process is initiated by the fusion of synaptic vesicles with the presynaptic membrane, which occurs after calcium influx. The binding of neurotransmitters can lead to excitatory or inhibitory postsynaptic potentials (EPSPs or IPSPs), influencing the likelihood of the postsynaptic neuron firing an action potential.