The brain and spinal cord constitute the central nervous system (CNS). The CNS is an immensely complex and integrated processing system that simultaneously and constantly processes vast amount of information. The CNS can be considered as one of the most complex structures in the known universe and its function extent from sensory, motor, memory, perception, cognition, emotion, speech, and homeostasis etc. All these sophisticated functions are controlled and coordinated by the inter-connected circuitry formed by morphologically complex and highly excitable post-mitotic cells called the neurons. Glial cells support neurons by providing insulation (oligodendrocytes in CNS and Schwann cells in peripheral nervous system (PNS)), nourishment (astrocytes) and by destroying pathogens (microglia) that invade the CNS. Over and above that it is becoming lucid that glia also participates in the modulation of neuronal signaling. It is estimated that there are equal number of neurons to glia. However, at some regions of the brain, glia outnumbers neurons.
The architecture of a typical mature neuron includes a soma (cell body), an axon and dendrites . The soma contains most of the organelles and cytosol. The soma often serves as a hub for integrating the information received by a neuron. The axon is portrayed as a long tubular projection beginning at axon hillock and extending outward along with varying protein composition compared to the soma. Axons can carry electrical signals over very long distances from the soma, for e.g. axons in the spinal cord extend more than 1m . The electrical signals conveyed through the axon and dendrites is termed as an Action potential.
Generally, dendrites are the shorter branching structures that extend out of soma and functions to convey information to the soma from external stimuli or a neuron . The size and shape of dendrites vary depending on the type of neurons and hence this is often regarded as a method for neuronal classification Dendrites encompasses mushroom-like projections called dendritic spines that serves as the ‘antennae’ of neurons.Dendritic spines form specialized junctions with adjacent neurons known as ‘synapse’ the fundamental anatomical structure for information transfer in the CNS .
In the adult brain, there are millions of neurons and trillions of synapses.