Synaptic vesicles are a. at the ends of dendrites and axons. b. at the ends of axons only. c. along the length of all long fibers. d. All of these are correct.

Neurons are composed of three main parts: the cell body (soma), dendrites, and axon. Dendrites, which project from the soma, receive incoming signals from other neurons, while the axon is responsible for transmitting electrical signals to other neurons. At the end of the axon, we find the axon terminals, which contain synaptic vesicles.

Synaptic vesicles are small, membrane-bound organelles filled with neurotransmitters, which are chemicals that facilitate communication between neurons. When an electrical impulse (action potential) reaches the axon terminal, it triggers the release of neurotransmitters from the vesicles. These neurotransmitters cross the synaptic cleft between the neurons and bind to specific receptors on the dendrites of the receiving neuron.

Now that we understand the structure of neurons and the role of synaptic vesicles, let's evaluate each statement provided in the exercise: a. at the ends of dendrites and axons. - This statement is partially correct, as synaptic vesicles are found at the ends of axons. However, they are not found at the ends of dendrites. b. at the ends of axons only. - This statement is correct, as synaptic vesicles are located within the axon terminals at the ends of axons, where they release neurotransmitters to communicate with other neurons. c. along the length of all long fibers. - This statement is incorrect, as synaptic vesicles are not distributed along the entire length of axons or other fibers within neurons. d. All of these are correct. - Since only statement (b) is correct, this statement is incorrect. As a conclusion, only statement (b) is correct regarding the location of synaptic vesicles within a neuron.