Final answer:
Long-term depression (LTD) is a long-term weakening of a synaptic connection, resulting in a decrease in excitability of a neuron.
Step-by-step explanation:
Long-term depression (LTD) in the context of neuron excitability refers to a long-term weakening of a synaptic connection, resulting in a decrease in the excitability of a neuron.
One mechanism that causes LTD involves the removal of AMPA receptors from the postsynaptic membrane through a signaling cascade initiated by calcium entering through NMDA receptors. This decrease in AMPA receptors makes the postsynaptic neuron less responsive to glutamate released from the presynaptic neuron.
In summary, LTD decreases the excitability of a neuron by weakening the synaptic connection and reducing the responsiveness of the postsynaptic neuron to neurotransmitter release.