Final answer:
Long-term potentiation (LTP) is a persistent strengthening of a synaptic connection, while long-term depression (LTD) is a long-term weakening of a synaptic connection. LTP involves the insertion of AMPA receptors into the postsynaptic membrane, making the synapse stronger. LTD removes AMPA receptors from the membrane, leading to a weaker response to neurotransmitter release.
Step-by-step explanation:
Long-term potentiation (LTP) is a persistent strengthening of a synaptic connection, based on the Hebbian principle. When a postsynaptic neuron is depolarized by multiple presynaptic inputs in quick succession, calcium ions enter the cell and initiate a signaling cascade. This cascade causes AMPA receptors to be inserted into the postsynaptic membrane, making the synapse stronger. The insertion of additional AMPA receptors allows for a larger excitatory effect on the postsynaptic cell, increasing the likelihood of firing in response to neurotransmitter release from the presynaptic neuron.
On the other hand, long-term depression (LTD) is a long-term weakening of a synaptic connection. Calcium entry through NMDA receptors initiates a different signaling cascade, resulting in the removal of AMPA receptors from the postsynaptic membrane. This makes the postsynaptic neuron less responsive to glutamate released from the presynaptic neuron. LTD plays an important role in pruning unused synapses and strengthening the synapses that have undergone LTP.