Which of the following statements is CORRECT regarding the chemical synapse? A. After an excitatory neurotransmitter binds to its receptor on the postsynaptic neuron, a rush of K+ inside the cell depolarizes the postsynaptic neuron. B. When an action potential arrives at the synaptic terminal of the presynaptic neuron, neurotransmitters are released into the synaptic cleft. C. Neurotransmitters are stored in the dendrites of the postsynaptic neuron. D. Once released, a neurotransmitter will bind to receptors on the presynaptic neuron E. The synaptic terminal of the presynaptic neuron is fused to the cell body of the postsynaptic neuron.
The Correct Answer and Explanation is:
The correct statement regarding the chemical synapse is B. When an action potential arrives at the synaptic terminal of the presynaptic neuron, neurotransmitters are released into the synaptic cleft.
Explanation:
Chemical synapses are junctions where one neuron communicates with another. The process involves several key steps:
- Action Potential Arrival: The process begins when an action potential (an electrical signal) travels down the axon of the presynaptic neuron. This electrical signal reaches the synaptic terminal (also known as the axon terminal) of the presynaptic neuron.
- Release of Neurotransmitters: When the action potential reaches the synaptic terminal, it triggers the opening of voltage-gated calcium (Ca²⁺) channels. The influx of calcium ions causes synaptic vesicles containing neurotransmitters to fuse with the membrane of the presynaptic neuron. These vesicles then release their contents (neurotransmitters) into the synaptic cleft, the tiny gap between the two neurons.
- Neurotransmitter Binding: The released neurotransmitters cross the synaptic cleft and bind to receptors on the postsynaptic neuron, typically on the dendrites or cell body. This binding causes changes in the postsynaptic neuron, which may lead to a new action potential if the depolarization is sufficient.
- Clearing of Neurotransmitters: After the neurotransmitters bind to receptors, they are quickly cleared from the synaptic cleft by various mechanisms, such as reuptake into the presynaptic neuron or enzymatic breakdown.
Why the other choices are incorrect:
- A is incorrect because a rush of K⁺ ions inside the cell would cause hyperpolarization, not depolarization. Depolarization typically involves a rush of Na⁺ ions into the cell.
- C is incorrect because neurotransmitters are stored in synaptic vesicles within the presynaptic neuron, not in the postsynaptic neuron.
- D is incorrect because neurotransmitters bind to receptors on the postsynaptic neuron, not the presynaptic neuron.
- E is incorrect because the synaptic terminal of the presynaptic neuron does not physically fuse with the cell body of the postsynaptic neuron. There is always a synaptic cleft between the two.
Thus, the correct process involves the release of neurotransmitters from the presynaptic neuron into the synaptic cleft, which then bind to receptors on the postsynaptic neuron.
