To some extent, the nervous system is able to alter its structure and function as a result of experience, and in response to injury. This may involve the formation of new synapses, as well as the loss of some old ones. The ability of the nervous system to adapt to the environment by changing the number and location of synapses present is known as synaptic plasticity. Experiments with rats, for example, have shown that the number of synapses per neurone can increase by up to 20% in those exposed to a stimulating environment compared with those that weren't. It has also been shown that the area of the sensory cortex devoted to the fingertips increases in size in people who use braille.
It is this process which contributes to the neurological development of children, the acquisition of new skills and rehabilitation after injury.
References and further reading:
Johansson, B (2000) Brain Plasticity and Stroke Rehabilitation: The Willis Lecture Stroke 31(1), 223
Kolb, B and Whishaw, I (1998) Brain Plasticity and Behaviour Annual Review of Psychology 49, 43-64