Figure 1. Human Nervous System. The ability to balance like an acrobat combines functions throughout the nervous system. The central and peripheral divisions coordinate control of the body using the senses of balance, body position, and touch on the soles of the feet. (credit: Rhett Sutphin)

The nervous system is responsible for controlling much of the body, both through somatic (voluntary) and autonomic (involuntary) functions. The structures of the nervous system must be described in detail to understand how many of these functions are possible. There is a physiological concept known as localization of function that states that certain structures are specifically responsible for prescribed functions. It is an underlying concept in all of anatomy and physiology, but the nervous system illustrates the concept very well.

Fresh, unstained nervous tissue can be described as gray or white matter, and within those two types of tissue it can be very hard to see any detail. However, as specific regions and structures have been described, they were related to specific functions. Understanding these structures and the functions they perform requires a detailed description of the anatomy of the nervous system, delving deep into what the central and peripheral structures are.

The place to start this study of the nervous system is the beginning of the individual human life, within the womb. The embryonic development of the nervous system allows for a simple framework on which progressively more complicated structures can be built. With this framework in place, a thorough investigation of the nervous system is possible.

The nervous system is often referred to as the master controller of the human body. Like the endocrine system, the other internal control system of the human body, the nervous system is specialized for communication of information from one part of the body to another. The nervous system communicates quickly using neurons, the specialized cells of the nervous system. Neurons can convey and process information using electrical and chemical signals. Ultimately, neural communication helps coordinate body activities and ensures we maintain homeostasis.

The Components of the Nervous System

Imagine that you decide to bake a cake for your Anatomy and Physiology professor’s birthday. You find a recipe, locate the ingredients and then one by one, measure and add each to the mixing bowl. You stir the mixture and before you know it, the cake is in the oven and you can return to your homework. You start to salivate as a yummy chocolate aroma wafts through the room. The timer goes off, but unfortunately, when removing the pan from the oven you burn your hand through a hole in the hot pad. Rather than dropping the cake, you make a split second decision to hold on, enduring the pain so that you can set the cake pan down safely even though the consequences of a burnt hand will be with you for a few days. All aspects of baking a cake from your decision to bake a cake, to reading the recipe, measuring and mixing ingredients, smelling a delicious chocolate aroma and automatically starting to salivate in case you decide to sneak a piece of cake, and withdrawing your hand to prevent a burn are functions of the nervous system. Although quite different behaviors, they all include the general functions of the nervous system listed below:

1. The nervous system detects changes in our internal and external environment (stimuli) using specific neurons or specialized cells communicating with neurons called sensory receptors.Sensory receptors can detect a variety of different external and internal stimuli such as: skin temperature, light (for vision), sound, chemicals in food (taste) and air (smells), pressure, pain, blood pH, core body temperature, bladder distension as well as many other stimuli.
2. Sensory receptors transform stimuli into electric signals that our nervous system can understand. The nervous system cannot directly interpret stimuli like light, heat or sound. The information has to be transformed into an electrical signal for the nervous system to receive and process the information.
3. Sensory neurons transmit the electrical signals from the periphery to the central nervous system (brain and spinal cord). This information travels from the sensory receptor (the site of transformation) along neural processes called axons towards the central nervous system (CNS).
4. The central nervous system (brain and spinal cord) processes incoming sensory information to generate “appropriate” responses and also to give us the perception of the stimulus. The signal can be compared to a normal value (set point) or related to past experiences to determine if the stimulus requires a response. Processing of the signal is called integration. In order to perceive a stimulus, the sensory information must be transmitted to specific areas of the brain.
5. The central nervous system sends commands (electrical signals passed along neurons) out to the target tissues to produce the response. The target tissues of the nervous system are muscles and glands.