Human Nervous System: An Overview

The human nervous system is well developed and complex, and is broadly organised into three interlocking parts: the central nervous system (CNS -- the brain and spinal cord, lying along the mid-dorsal body axis and enclosed respectively by the cranium and the vertebral canal), the peripheral nervous system (PNS -- the network of cranial and spinal nerves connecting the CNS to the rest of the body), and the autonomic nervous system (ANS -- the specialised set of nerves governing involuntary organs, itself made of sympathetic and parasympathetic divisions). Inner to their bony coverings, the brain and spinal cord are further wrapped in three protective connective-tissue membranes, the meninges, and cushioned by cerebrospinal fluid, both covered in the next section, before the chapter works through the brain, the spinal cord, the cranial and spinal nerves, reflex action, and the autonomic nervous system in turn.