Figure 1.

Plasticity in the central nervous system. (A) Axons from two different pathways synapse onto spines on the same dendrites. Each synapse is surrounded by astrocytes (red), microglia (green), and extracellular matrix. (B) Increases in activity, such as occur during learning, can strengthen connections by axonal sprouting (blue) as well as formation of new filopodia and dendritic spines (^*). Adjacent afferents, surrounding glia, and extracellular matrix are relatively unaffected. (C) Disruption of afferents, such as following injury, leads to degeneration of damaged axons (dotted lines), activation of astrocytes, microglia, and extracellular matrix, as well as retraction of dendritic spines (^*). Compensatory sprouting of undamaged afferents from another brain region (orange) can form new synapses, including contacts with denervated spines (^#).