1. Classification of Nervous System
The nervous system is classified into the Central Nervous System (CNS) (brain and spinal cord) and the Peripheral Nervous System (PNS) (nerves outside the CNS). Functionally, the PNS further divides into the Somatic Nervous System (voluntary control of muscles) and the Autonomic Nervous System (ANS), which regulates involuntary functions and splits into the Sympathetic (fight-or-flight) and Parasympathetic (rest-and-digest) systems.