The human body maintains homeostasis (maintenance of constant internal environment ), effective function, and coordination of trillions of cells by using the endocrine system and nervous system. The Nervous System employs electrical and chemical means to send messages very quickly from cell to cell.
Nervous system has two major anatomical subdivisions:
1. The Central Nervous System (CNS) consists of the brain and spinal cord, which are enclosed and protected by the cranium and vertebral column.
2. The Peripheral Nervous System (PNS) consists of the remainder of the nervous system such as nerves, ganglia, and sensory organs.
The peripheral nervous system is divided into sensory and motor divisions, and each of these is further divided into somatic division (pertaining to the body as a whole, e.g., skin, bones, and muscle)
and visceral division (pertaining to the inner or deeper layer) divisions.
Sensory neurons are nerve cells (neurons) that respond to a stimulus and conduct signals to the central nervous system.
Motor neurons are neurons that transmit signals from the CNS to any muscle or gland cells.
SUBDIVISIONS OF NERVOUS SYSTEM
The Autonomic Nervous System
The visceral motor division, also known as autonomic nervous system, carries signals to glands, cardiac muscle, and smooth muscle. The autonomic system has two divisions:
1. The sympathetic division tends to arouse the body for action by accelerating the heart beat and increasing respiratory airflow and inhibiting digestion.
2. The parasympathetic division is responsible for energy intake and conservation by stimulating digestion and slowing down the heartbeat and reducing respiratory airflow.