Central nervous system subdivisions

Anatomically, the human nervous system may be divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The major subdivision of the central nervous system is into the brain and spinal cord. The peripheral nervous system is divided into the motor or efferent system (efferent = away from ), and the sensory or afferent (afferent = toward ) nervous systems (Figure 2.1). 

Anatomically, the nervous system is divided into the central nervous system (CNS) consisting of the brain and the spinal cord and the peripheral nervous system comprised of neural cells forming a network throughout the body. The peripheral system is itself subdivided into two sections the somatic system, where control of skeletal muscles allows movement and breathing, and the autonomic system which controls the actions of smooth muscle, cardiac muscle and glandular tissues. Further subdivision of the autonomic system based on anatomical and biochemical factors creates the sympathetic and parasympathetic nervous systems. 

The term central nervous system is sometimes used as a synonym for the brain, but it also includes the spinal cord. Indeed, the word system implies the entirety of the tissues working together to achieve a single function. Usage, however, has validated its division into the central and peripheral nervous systems, and even the subdivision of the latter into the autonomic nervous system and the voluntary nervous system. 

The nervous system is conventionally divided into the central nervous system (CNS the brain and spinal cord) and the peripheral nervous system (PNS neuronal tissues outside the CNS). The motor (efferent) portion of the nervous system can be divided into two major subdivisions autonomic and somatic. The autonomic nervous system (ANS) is largely independent (autonomous) in that its activities are not under direct conscious control. It is concerned primarily with visceral functions such as cardiac output, blood flow to various organs, and digestion, which are necessary for life. The somatic subdivision is largely concerned with consciously controlled functions such as movement, respiration, and posture. Both systems have important afferent (sensory) inputs that provide information regarding the internal and external environments and modify motor output through reflex arcs of varying size and complexity. 

Redies, C. and Takeichi, M. 1996. Cadherine in the developing central nervous system an adhesive code for segmental and functional subdivisions. Developmental Biology, 180,413-423. 

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