Question

A chemical signal is transmitted across a synapse from
a. Dendrite end of one neuron to axon end of next neuron
b. Axon end of one neuron to dendrite end of next neuron
c. Dendrite to cell body of the same neuron
d. Cell body to axon of the same neuron

Answer 1

Hint: When a nerve impulse is generated, it originates from the cell body and often results in several smaller branches before ending up at nerve terminals.

Complete answer:
> Option A is incorrect. Dendrites stretch from the cell body of the neuron and accept signals from other neurons. Chemical signal transmission only takes place from the end of the axon to the end of the dendrite.

> Option B is correct. A nerve impulse passes from the neuronal axon end to the synapse in a process of electric charge. In the synaptic cleft, the electrical impulse is transformed here to the chemical impulse. Typically synapses grow between axon terminals and dendritic ends.

> Option C is incorrect. As the neurons receive or send messages, electrical impulses are emitted through their axons. Thus, it is not possible to transfer the nerve impulse from dendrite to the same neuron's cell body.

> Option D is incorrect. A potential action activates the release of neurotransmitters to the presynaptic neuron and these molecules bind to postsynaptic cell receptors.

So, the correct answer is Option B.

Additional information: When an action potential enters the axon terminal the membrane is depolarized and the Na+ channels are opened with voltage-gated. Na+ ions enter the cell and depolarize the presynaptic membrane further. This depolarization allows the channels to be opened by voltage-gated Ca2 +. Calcium ions invading the cell induce signal transduction containing neurotransmitter molecules, which causes the presynaptic membrane to fuse with small membrane-bound vesicles, called synaptic vesicles. The fusion of a vesicle with the presynaptic membrane induces the release of neurotransmitter into the synaptic cleft, the extracellular space between the presynaptic membranes and the postsynaptic ones. The neurotransmitter diffuses across the synaptic cleft and binds on the postsynaptic membrane to the receptor proteins.

Note: A mammalian neuron consists of a cell, dendrites, and an axon. The body of cells includes both the nucleus and the cytoplasm. The axon spreads from the cell body and sometimes occurs in several smaller branches until ending up at the terminals of the nerves. Dendrites spread from the cell body of the neuron and accept signals from other neurons.