CNS stands for Central Nervous System. The CNS consist of the brain and the spinal cord. The Central nervous system receives and processes sensory information. The brain is encased in the skull; the average human brain weighs between 1.3 to 1.4 kg.
The spinal cord is protected by the vertebral column. It is about 43cm long. PNS stands for Peripheral Nervous System. It consists of cranial nerves from the brain and spinal nerves from the spinal cord. The PNS is divided into the somatic nervous system and autonomic nervous system.
The somatic nervous system contains nerve fibers that send motor nerve fiber to the skeletal muscles and sensory information to the CNS. The autonomic nervous system is further divided into the sympathetic and parasympathetic nervous systems.