Synaptic plasticity is associated with structural and morphological changes in spines. The change in synaptic weight is provided mainly by the insertion/removal of AMPA-type glutamate receptors in the post-synaptic membrane and by a change in their conductance. At the same time, it is believed that a change in the size of the spine on which the synapse is located does not directly affect the magnitude of the change in the input signal. In this article, a physical model based on analysis of published works is proposed to demonstrate that structural changes in spines are an important factor in synaptic plasticity. These changes can determine more than half of the long-term value of synaptic weight. The molecular mechanisms of both functional and morphological changes in spines are also analysed.