Chemical synapses are specialised junctions through which cells of the nervous system signal to one another and to non-neuronal cells such as muscles or glands. A chemical synapse between a motor neuron and a muscle cell is called a neuromuscular junction. Chemical synapses allow the neurons of the central nervous system to form interconnected neural circuits. They are thus crucial to the biological computations that underlie perception and thought. They also provide the means through which the nervous system connects to and controls the other systems of the body. The human brain contains a huge number of chemical synapses, with young children having about 1016 synapses (10,000 trillion[1].). This number declines with age, stabilising by adulthood. Estimates for an adult vary from 1015 to 5 × 1015 synapses (1,000 to 5,000 trillion).