Human Neural System

In humans, the neural system is organised into two connected divisions: the central neural system (CNS), made up of the brain and spinal cord, and the peripheral neural system (PNS), made up of all the nerves and ganglia that lie outside the CNS. Both divisions depend on neurons as their working units, but neurons are outnumbered by a second, non-nervous cell type called neuroglia (or glial cells), which forms the supporting tissue of the nervous system and fills the spaces between neurons since the CNS itself lacks ordinary connective tissue.

Neurons are not all the same — functionally, they fall into three classes. Afferent (sensory) neurons carry impulses from sense organs into the CNS. Efferent (motor) neurons carry commands from the CNS out to muscles and glands (the effector organs). Interneurons never leave the CNS at all; they sit between afferent and efferent neurons and do the work of relaying, comparing and integrating signals. Glial cells, meanwhile, do much more than just fill space: they nourish neurons, are thought to help with memory, and — because they retain the ability to divide (unlike mature neurons) — they can repair injured tissue and act as scaven …