Final answer:
Presynaptic modulation can occur at any type of synapse, not just at axosomatic synapses. Hence, the statement that it occurs only at axosomatic synapses is false. Synaptic modulation is influenced by many factors, and synapses exist both within the central nervous system and at neuromuscular junctions.
Step-by-step explanation:
Presynaptic modulation typically occurs at all types of synapses, not exclusively at axosomatic synapses. There are various types of synapses, including axodendritic (axon to dendrite), axosomatic (axon to soma), and axoaxonic (axon to axon) synapses.
The statement 'Presynaptic modulation occurs at axosomatic synapses' is not entirely accurate as it implies exclusivity, which is not the case. Therefore, the correct answer to the question is b) False. Synaptic modulation can indeed occur at axosomatic synapses, but also at other types of synapses.
Presynaptic modulation involves mechanisms that alter the release of neurotransmitters from the presynaptic neuron.
Factors such as the number of synaptic vesicles and the presence of modulatory neurotransmitters can affect neurotransmitter release, hence modulating the signal transmitted to the postsynaptic neuron regardless of the type of synapse.
Moreover, synapses are not solely between neurons; they also exist between neurons and muscle cells, for example, at the neuromuscular junction where acetylcholine is released to initiate muscle contraction.
Synapses are also found in different parts of the central nervous system, in both gray and white matter, not just the gray matter as some might incorrectly believe.