The nervous system in humans can be divided into (1) the Central Nervous System (CNS) and (2) the Peripheral Nervous System (PNS).

The human nervous system can be divided into two major divisions: the central nervous system (CNS) and the peripheral nervous system (PNS).

Central Nervous System (CNS)

• The CNS consists of the brain and spinal cord, and it serves as the main control center for the entire nervous system. The brain is responsible for processing and integrating sensory information, initiating voluntary movements, and regulating various physiological functions. The spinal cord acts as a pathway for transmitting signals between the brain and the rest of the body, and it also controls some reflex actions independently of the brain.

Peripheral Nervous System (PNS)

• The PNS includes all the nerve cells and fibers outside of the CNS. It is further divided into two sub-divisions: Somatic Nervous System (SNS) and Autonomic Nervous System (ANS).

a. Somatic Nervous System (SNS)

• The SNS is responsible for transmitting sensory information from the sensory organs (such as skin, eyes, ears, etc.) to the CNS and for carrying motor signals from the CNS to the voluntary muscles. It controls conscious and voluntary movements, allowing us to interact with our environment.

b. Autonomic Nervous System (ANS)

• The ANS regulates involuntary functions and maintains internal homeostasis. It controls various internal organs and glands, regulating processes such as heart rate, digestion, respiratory rate, and glandular secretions. The ANS itself is further divided into two branches:

• Sympathetic Nervous System: Responsible for the "fight or flight" response, which prepares the body for stress or emergencies by increasing heart rate, dilating pupils, and redirecting blood flow to essential organs.

• Parasympathetic Nervous System: Responsible for the "rest and digest" response, which promotes relaxation and recovery by slowing down heart rate, constricting pupils, and enhancing digestion.

The central nervous system (CNS) and the peripheral nervous system (PNS) work in coordination to allow the human body to function, respond to stimuli, and maintain internal balance (homeostasis).

Key Points

• The Central Nervous System (CNS) contains the brain and spinal cord.

• The Peripheral Nervous System (PNS) contains everything outside, or "peripheral" to, the brain and spinal cord such as cranial nerves, spinal nerves, and the autonomic nervous system.