In horse racing, these definitions may differ: For example, in the British Isles, Thoroughbred horse racing defines colts and fillies as less than five years old. However, Australian Thoroughbred racing defines colts and fillies as less than four years old.
For the general concept of brain plasticity, see neuroplasticity. In neuroscience, synaptic plasticity is the ability of synapses to strengthen or weaken over time, in response to increases or decreases in their activity. Plastic change also results from the alteration of the number of neurotransmitter receptors located on a synapse.
Synapses on somas are termed axosomatic synapses; those on dendrites are termed axodendritic; and those on other axons or boutons are axoaxonic. The fiber's bouton is called the presynaptic element and the structure it contacts is the postsynaptic element. A schematic diagram of a synapse is shown in Figure 13-1A. The pre- and postsynaptic elements are separated by a space 15-200 nm wide, known as the synaptic cleft.