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More than any other organ, the nervous system makes human beings special. The human central nervous system (CNS), smaller and weighing less than most desktop computers, is the most complex and elegant computing device that exists. It receives and interprets an immense array of sensory information, controls a variety of simple and complex motor behaviors, and engages in deductive and inductive logic. The brain can make complex decisions, think creatively, and feel emotions. It can generalize and possesses an elegant ability to recognize that cannot be reproduced by even advanced computers. The human nervous system, for example, can immediately identify a familiar face regardless of the angle at which it is presented. It can carry out many of these demanding tasks in a nearly simultaneous manner.

Given the complexity of the nervous system and the richness of its actions, one might ask whether it can ever be understood. Indeed, neuroscience has begun to provide an understanding, in elegant detail, of the organization and physiology of the nervous system and the alterations in nervous system function that occur in various diseases. This understanding is firmly based on an appreciation of the structure of the nervous system and the interrelation between structure and function.

The complexity of the nervous system's actions is reflected by a rich and complex structure—in a sense, the nervous system can be viewed as a complex and dynamic network of interlinked computers. Nevertheless, the anatomy of the nervous system can be readily understood. Since different parts of the brain and spinal cord subserve different functions, the astute clinician can often make relatively accurate predictions about the site(s) of dysfunction on the basis of the clinical history and careful neurological examination. An understanding of neuroanatomy is immediately relevant to both basic neuroscience and clinical medicine. Clinical neuroanatomy (i.e., the structure of the nervous system, considered in the context of disorders of the nervous system) can teach us important lessons about the structure and organization of the normal nervous system, and is essential for an understanding of disorders of the nervous system.

Main Divisions


Anatomically, the human nervous system is a complex of two subdivisions.


The CNS, comprising the brain and spinal cord, is enclosed in bone and wrapped in protective coverings (meninges) and fluid-filled spaces.

Peripheral nervous system (PNS)

The PNS is formed by the cranial and spinal nerves (Fig 1–1).

Figure 1–1

The structure of the central nervous system and the peripheral nervous system, showing the relationship between the central nervous system and its bony coverings.


Functionally, the nervous system is divided into two systems.

Somatic nervous system

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