Every movement, smell, taste, touch, sound, thought, and dream has its origin in the nervous system.
Every function of your body, both voluntarily and involuntarily is controlled, at least in part, by your nervous system.
To better understand how the nervous system works, it is necessary to discuss what makes up the nervous system.
The Nervous system is made up of two primary systems – the central nervous system and the peripheral nervous system.
The central nervous system (CNS) is made of the brain and spinal cord, while the peripheral nervous system (PNS) is comprised of nerves such as those in our arms, legs, and torso that deliver information back to the CNS for processing.
Many of the functions of the PNS are voluntary – that is, we can control actons like reaching for plate, swinging a golf club, or swimming.
Other actions are involuntary like the beating of the heart, breathing rates during exercise, digesting food, regulating our blood sugar, metabolism, and so on.
Many of the automatic involuntary functions are controlled by a subcategory of the PNS called the autonomic nervous system (ANS) which has two components: the sympathetic and parasympathetic nervous systems.
There is always activity in the sympathetic nervous system operating at a basal level called "sympathetic tone" and its activity increases at times of stress (producing a "fight-or-flight" response).
The parasympathetic nervous system basically does the opposite of the sympathetic nervous system.
When the heart rate increases (sympathetic response), the parasympathetic nervous system slows it down. Just as the "fight-or-flight" response relates to the sympathetic NS, a "rest and digest" function describes the parasympathetic NS.
Hence, the autonomic nervous system (ANS) is made up of nerves that innervate cardiac muscle, smooth muscle, and glandular tissue.
From a functional perspective, think of the nervous system as a highway with information being transmitted to and from different locations.
The roads or pathways bring information to the CNS (brain/spinal cord) and are called sensory nerves (afferent).
Consider what happens when you touch a hot stove…
In this example, your hand is quickly pulled away from the stove. To accomplish this, there are nerve fibers that connect or bridge between the afferent (sensory) and efferent (motor) nerves called interneurons.
To break this down even further, under a microscope, the space or junction between two neurons/nerves is called a synapse, which is a very narrow gap where chemicals called neurotransmitters allow an impulse to pass through the gap so an impulse can travel onto another "road" (nerve) to bring information to and from the CNS. Therefore, each synapse is like a ferry boat (chemicals) carrying a car (the impulse) across the gap to the next road in route to the brain and/or spinal cord. This gets further complicated as there are many different chemicals ("ferry boats") called neurotransmitters that result in different types of responses. These responses are broadly classified into either those that excite or inhibit and result in an action that is incredibly fast, which is often needed to avoid injury or death. The example of touching the stove clearly describes the quick reaction that results from the combined chemical and electrical signaling that takes place. If these chemicals get out of balance, different reactions can occur and many of the medications used in treating depression, bipolar disorder, schizophrenia and other psychological conditions exert their effects directly on these neurotransmitters (such as serotonin).
So as you can see, the nervous system is very complex and yet, very balanced allowing us to function and perform in an automatic, coordinated way, so most of the time, we don't have to think about what we are doing to a point of exhaustion.
Many things can negatively affect the functions of the nervous system such as trauma/injury, lack of sleep, stress, chemical abuse (alcohol, cocaine, heroin, etc.), and diet.
Chiropractic focuses much attention on balancing these functions through manipulation of the spine, which has both local and more distant effects through "somatovisceral" and "somatic" responses, thus affecting both voluntary and involuntary functions.
Management of sleep, stress, diet, exercise, and other aspects of life are important in maintaining a healthy lifestyle and quality of life.
Much of this information was obtained from the following URL (check it out!): http://en.wikipedia.org/wiki/Nervous_system#Nervous_system_in_humans. This site includes many pictures of the CNS and PNS as well as a description of all the components that make up the nervous system.