Final answer:
Unused synaptic connections are replaced or pruned as part of neuroplasticity, optimizing the brain's efficiency in transmitting neuronal signals and supporting cognitive functions like learning and memory,the correct option is D).
Step-by-step explanation:
Synaptic connections that are unused are replaced or pruned. This process is part of neuroplasticity, which allows the nervous system to adapt by changing the strength and number of synaptic connections. Unused synapses are pruned to increase the efficiency of neuronal transmissions.
The brain continues to go through these changes throughout life, although it is most plastic during the early years. This adaptation process is also a critical aspect of learning and memory, with mechanisms such as long-term potentiation (LTP) and long-term depression (LTD) playing essential roles in the modification of synaptic strength.
Synaptic plasticity is facilitated by the creation of new synaptic connections and the elimination of those that are no longer needed. This is evident in the hippocampus, which is involved in storing memories and where neurogenesis, the birth of new neurons, occurs. The formation of myelin sheath by Schwann cells and its role in the Nodes of Ranvier also enhances signal transmission in the nervous system, further explaining the complexity of neuronal communication and synaptic plasticity.