The human nervous system can be compared to a college computer network with a central processing unit made of layers of servers and storage, as well as wiring to multiple input devices and output displays. Analogously, the nervous system controls all bodily functions and is responsible for perceiving and reacting to stimuli, whether automatically or by conscious thought/command of the person. The two major branches of the nervous system are the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).
The Central Nervous System is the more important of the two as it controls all bodily functions, deliberate movement, homeostasis, the constant activity of the heart, and breathing, just to name a few. The CNS is made up of the brain and the spinal cord. Pursuing the computer analogy, the brain is the central Processing Unit of the entire nervous system. All information must first travel to the brain via an electric current before the body can trigger a response. The spinal cord is the main pathway where all electrical signals from stimuli pass and it is this part of the CNS that makes contact with the Peripheral Nervous System.
As powerful as it sounds, the Central Nervous system is very delicate and is protected by a variety of bony structures to prevent damage. External damage can be devastating to the human condition. Damage to the spinal cord may result in paralysis, while damage to the brain can incur amnesia or serious impairment of bodily functions. For this reason, the brain and the spinal cord are protected by the skull and the vertebral column respectively.
The Peripheral Nervous System is, as the term implies, scattered throughout the body. The PNS can be likened to a collection of input and output devices serving the brain. In organic terms, the PNS consists of all nerve cells external to the CNS. While the essential element of a nerve cell is the neuron, many of these form longer processes called axons. Axons are responsible for conveying electric impulses to and from the CNS. They thus form one long intricate connection of nerves throughout the body.
The PNS is made up of two types of neurons, the afferent and efferent types. Afferent neurons are responsible for carrying the electrical signal produced by stimuli towards the Central Nervous System for processing, while efferent neurons are responsible for delivering these electric currents from the CNS towards the Peripheral Nervous System and thence, the organs of motion, speech, and locomotion; the muscles that direct posture and “body language”; even the instinctual reactions that require no conscious thought such as sneezing, curling up one’s toes at the sight of an attractive person, jumping with surprise, and the well-known “fight or flight” stance that pumped-up adrenalin provokes.
In sum, the Human Nervous system can be compared to a mainframe computer, with the CNS playing the role of the Central Processing Unit and the PNS that of the monitor and keyboard as the output and input devices, respectively. The Nervous system plays a vital role in the human condition, controlling both deliberate and instinctual processes. Autonomous organs like the heart, lungs, and indeed, the entire digestive system are all under the control of the nervous system. As fragile as it seems the nervous system is as fast as it is powerful.