Final answer:
LTP and LTD are types of synaptic plasticity responsible for strengthening or weakening synaptic connections, respectively. These changes occur in response to the frequency of synaptic activity and are crucial for learning, memory, and adaptability of the nervous system. At chemical synapses, neurotransmitters facilitate neuronal communication by binding to receptor proteins on postsynaptic neurons.
Step-by-step explanation:
Long-term potentiation (LTP) and long-term depression (LTD) are two forms of synaptic plasticity, which is essential for the functioning of the nervous system and is a basis for learning and memory. LTP is the process through which synaptic connections become stronger with frequent activation, enhancing the synaptic transmission over time. This phenomenon occurs in the synapses within the hippocampus and is instrumental in storing memories. On the other side, LTD involves the weakening of synaptic connections resulting from less frequent activation, leading to reduced synaptic transmission. This too plays a crucial role in the erasure or modification of old memories and allows for adaptability in the network of synaptic connections.
At a chemical synapse, neurotransmitter molecules are released from the presynaptic neuron and cross the synaptic cleft to bind to receptor proteins on the postsynaptic neuron, creating a postsynaptic potential (PSP). When neurotransmitters bind to ligand-gated ion channels, they cause a change that may result in neuronal activation or inhibition, depending on the type of neurotransmitter and the receptors it engages with. After the neurotransmitter has had its effect, it must be inactivated or removed to ensure the signal is brief and precise, thereby terminating the PSP.