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After studying this chapter, the student should be able to:

  • Outline the major anatomic components of the central nervous system (CNS) and peripheral nervous system (PNS).

  • Diagram the functional areas of the brain and spinal cord.

  • Describe the types of nerves and ganglia in the PNS and their structure.

  • Distinguish the different categories of neurons.

  • Identify the neuronal organelles and their biochemical functions.

  • Diagram the specialized neuronal processes and their functions.

  • Describe the main CNS and PNS glial cells and their functions.


The nervous system mediates a wide range of functions, from detection of environmental stimuli, to control of muscle contraction, to problem solving, language, and memory. The nervous system is divided into 2 main parts, the central nervous system (CNS) and the peripheral nervous system (PNS) (Figures 1–1 and 1–2). Anatomically, the CNS is divided into the brain and spinal cord, whereas the PNS is composed of ganglia and nerves, including cranial and spinal nerves and their branches. Functionally, the PNS can be divided into the somatic, autonomic (visceral), and enteric nervous systems. In the overall flow of information, the PNS detects and relays sensory information about the external and internal environments to the CNS. The CNS receives, integrates, and stores information and controls the output to the PNS to generate responses and behavior.


Anatomic divisions of the nervous system and their structures: CNS and PNS. Forming the CNS, the brain (encased in the skull) is continuous with the spinal cord (encased in the spinal column). Forming the PNS, cranial nerves emerge from the brainstem, while spinal nerves emerge from the spinal cord. In the PNS, nerves are associated with spinal, cranial or autonomic ganglia, which are not shown.


Functional divisions of the nervous system: CNS and PNS.

At the cellular level, the nervous system is composed of neurons and glial cells (Figure 1–3). Neurons (also called nerve cells or neuronal cells) are the main signaling cells that communicate with other neurons, muscles, or glands. Neurons can be categorized by their function as sensory neurons, motor neurons, or interneurons or by their morphology or neurotransmitter. Glial cells (also called neuroglia or glia) are the support cells in the nervous system. Astrocytes and satellite cells provide structural and metabolic support, oligodendrocytes and Schwann cells furnish myelination of axons, pericytes regulate capillaries, ependymal cells synthesize cerebrospinal fluid (CSF), microglia are immune cells, and enteric glia are part of the gastrointestinal (GI) tract. Neurons have a cell body where the nucleus and majority of cellular organelles are located and many biochemical activities occur. Neurons also contain specialized processes and regions that allow them to send and receive signals rapidly and precisely. The axon ...

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