Chemical synapses are characterized by all of the following

Chemical synapses are characterized by all of the following, except

(a) the release of neurotransmitter by the presynaptic membranes,

(b) postsynaptic membranes bearing receptors that bind neurotransmitter,

(c) ions flowing through protein channels from the presynaptic to the postsynaptic neuron,

(d) a fluid-filled gap separating the neurons.

The correct answer and explanation is:

The correct answer is (c) ions flowing through protein channels from the presynaptic to the postsynaptic neuron.

Chemical synapses are specialized junctions between two neurons, where communication occurs through the release of neurotransmitters. Here’s why the other options are correct, and option (c) is not:

1. Release of neurotransmitter by the presynaptic membranes (a):
   This is a key feature of chemical synapses. When an action potential reaches the presynaptic terminal, it triggers the opening of voltage-gated calcium channels. Calcium ions flow into the presynaptic terminal, causing vesicles filled with neurotransmitters to fuse with the presynaptic membrane. This fusion releases neurotransmitters into the synaptic cleft.
2. Postsynaptic membranes bearing receptors that bind neurotransmitter (b):
   After neurotransmitters are released into the synaptic cleft, they travel across the gap and bind to specific receptors located on the postsynaptic membrane. These receptors are specialized proteins that detect the neurotransmitters and initiate a response in the postsynaptic neuron.
3. A fluid-filled gap separating the neurons (d):
   The gap between the presynaptic and postsynaptic membranes is called the synaptic cleft, and it is indeed fluid-filled. This space is essential for the transmission of chemical signals, as it allows neurotransmitters to diffuse from one neuron to the other.
4. Ions flowing through protein channels from the presynaptic to the postsynaptic neuron (c):
   This statement is incorrect in the context of a chemical synapse. While ions do flow through ion channels, this occurs in the postsynaptic neuron, not from the presynaptic to the postsynaptic neuron. The action potential is propagated along the axon of the presynaptic neuron, and neurotransmitters are released into the synaptic cleft. The neurotransmitters bind to receptors on the postsynaptic membrane, which then leads to ion channels opening on the postsynaptic neuron. This influx of ions may create a new electrical signal (postsynaptic potential) in the postsynaptic neuron.

In summary, the flow of ions from the presynaptic to the postsynaptic neuron is not the mechanism of signal transmission in a chemical synapse. Instead, neurotransmitters are released and bind to receptors on the postsynaptic membrane, and this binding opens ion channels in the postsynaptic neuron.