So nervous tissue, comprised of neurons and neuroglia, forms our nervous organs (e.g. the brain, nerves). These organs unite according to their common function, forming the evolutionary perfection that is our nervous system.
The nervous system (NS) is structurally broken down into two divisions;
- Central nervous system (CNS) – consists of the brain and spinal cord
- Peripheral nervous system (PNS) – gathers all neural tissue outside the CNS
Functionally, the PNS is further subdivided into two functional divisions;
- Somatic nervous system (SNS) – informally described as the voluntary system
- Autonomic nervous system (ANS) – described as the involuntary system.
Although divided structurally into central and peripheral parts, the nervous system divisions are actually interconnected with each other. Axon bundles pass impulses between the brain and spinal cord. These bundles within the CNS are called afferent and efferent neural pathways or tracts. Axons that extend from the CNS to connect with peripheral tissues belong to the PNS. Axons bundles within the PNS are called afferent and efferent peripheral nerves.