nervous system

Central Nervous System

The central nervous system is divided into two parts: the brain and the spinal cord. The average adult human brain weighs 1.3 to 1.4 kg approximately 3 pounds. The brain contains about 100 billion nerve cells neurons and trillions of support cells called glia. The spinal cord is about 43 cm long in adult women and 45 cm long in adult men and weighs about 35-40 grams.The vertebral column, the collection of bones back bone that houses the spinal cord, is about 70 cm long. Therefore, the spinal cord is much shorter than the vertebral column.

Peripheral Nervous System
The peripheral nervous system is divided into two major parts: the somatic nervous system and the autonomic nervous system.

Somatic Nervous System
The somatic nervous system consists of peripheral nerve fibers that send sensory information to the central nervous system AND motor nerve fibers that project to skeletal muscle.

Autonomic Nervous System
The autonomic nervous system is divided into three parts the sympathetic nervous system, the parasympathetic nervous system and the enteric nervous system. The autonomic nervous system controls smooth muscle of the viscera internal organs and glands.