Nervous System
The nervous system is a very complex and delicate component of the body. It is the central command
center that allows us to gather information about our internal and external environments, process
and interpret it, and then respond. The main, and most important, component of the nervous
system is the central nervous system, which is composed of the brain, brainstem and spinal
cord. The second component is the peripheral nervous system, which is composed of cranial
nerves that arise from the brainstem, and the spinal nerves that arise from the spinal cord. The third
component is the autonomic nervous system, which can be broken down into the sympathetic
and parasympathetic nervous systems. These three major components work together to transmit
signals, or messages, controlling all aspects of bodily function.
The Central Nervous System
The central nervous system (CNS) represents the largest part of the nervous system, including
the brain and the spinal cord. These serve as the main processing center for the whole nervous
system, thus controlling all the workings of the body. It is one of two major divisions of the nervous
system. Together with the peripheral nervous system (PNS), it has a fundamental role in the control
of behavior.
The PNS is outside the brain and spinal cord. It consists of the nerves and neurons that reside or
extend outside the CNS – to serve the limbs and organs. Unlike the CNS, however, the PNS is not
protected by bone or the blood-brain barrier, leaving it exposed to toxins and mechanical injuries.
The Brain
The brain is the command center of the nervous system. It processes and sends messages
throughout the entire nervous system. The brain receives sensory input from the spinal cord, and
the spinal and cranial nerves. It then processes these inputs and coordinates appropriate responses
and motor outputs. Weighing about three pounds, the brain consists of three main structures: the
cerebrum, cerebellum and brainstem. It can be further divided into the lower or mid-brain, and the
cerebral cortex. Figure 1 shows a detailed diagram of all the areas of the brain.