Dendritic spines may change morpholgoically (changing size) depending on synaptic input.

Question

BlackTom AI · Accepted Answer

Dendritic spines are small, actin-rich protrusions on dendrites that serve as the primary postsynaptic sites for excitatory synapses, so their shape and size are tightly coupled to synaptic strength and activity. Key concepts: structural plasticity (spine morphology changes), synaptic plasticity mechanisms (LTP/LTD), calcium-dependent signaling (NMDA receptor Ca2+ influx), actin cytoskeleton remodeling, and AMPA receptor trafficking.

Step-by-step reasoning:
1. Synaptic input (e.g., high-frequency stimulation) activates postsynaptic glutamate receptors, including NMDA receptors. NMDA receptor opening allows Ca2+ to enter the spine.
2. Elevated intracellular Ca2+ activates signaling cascades (for example, CaMKII and other kinases) that regulate actin-binding proteins.
3. Actin polymerization and reorganization within the spine cause enlargement of the spine head and sometimes shortening of the neck. Concurrently, AMPA receptors are trafficked into the postsynaptic membrane, increasing synaptic efficacy. These morphological and molecular changes are characteristic of long-term potentiation (LTP).
4. Conversely, low or depressed synaptic activity triggers processes (phosphatases, actin depolymerization) that lead to spine shrinkage or elimination and removal of AMPA receptors, as seen in long-term depression (LTD).
5. Empirical evidence from two-photon imaging and electron microscopy shows that spine size changes occur over minutes to hours during plasticity and that spine formation/elimination correlates with learning.

Why the correct answer is correct: The mechanistic link between synaptic activity, calcium signaling, cytoskeletal remodeling, and receptor trafficking directly explains activity-dependent enlargement or shrinkage of dendritic spines. Many studies have observed these morphological changes in vitro and in vivo.

Why the other option (False) is incorrect: Saying spines do not change size contradicts extensive experimental evidence demonstrating dynamic, activity-dependent spine morphology.

Conclusion: True — dendritic spines change morphology (size) depending on synaptic input, matching the provided answer.

Dendritic spines may change morpholgoically (changing size) depending on synaptic input.Single choice

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