11: Nervous System and Nervous Tissue
The nervous system is responsible for controlling much of the body, both through voluntary and involuntary functions. The focus of this chapter is on nervous (neural) tissue composed of neurons and glial cells. Within this chapter, you will look at the functions of the nervous system, its divisions, the characteristics of the cells found in it and how they communicate. Lastly, you will learn how the nervous system develops.
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- 11.1: Introduction to the Nervous System
- The nervous system is a very complex organ system. The anatomy of the nervous system was first studied by Egyptians in the 300 BC. However, the electrical properties were discovered much later in the 18th century. The progress made in neuroscience in the past decades highlighted how much we still do not know about the nervous system.
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- 11.2: Organization and Functions of the Nervous System
- Neurons and glial cells are cells found in the nervous tissue. The nervous tissue can be visibly differentiated between white and gray matter. This difference is due to a substance called myelin, that insulates neurons. The nervous system (NS) can be divided anatomically in central nervous system (CNS) which includes brain and spinal cord, and peripheral nervous system (PNS) which includes nerves and ganglia. Functionally the NS can be divided in somatic, autonomic and enteric divisions.
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- 11.3: Anatomy of Nervous Tissue
- Neurons are responsible for the computation and communication that the nervous system provides and they can be classified by structure (unipolar, bipolar, multipolar) or function (sensory, motor, interneuron). In the CNS, glial cells, or glia, are astrocytes (support and contribution to BBB barrier), oligodendrocyte (myelination), microglia (defense), and ependymal cells (production of CSF). In the PNS, glial cells are Schwann cells (myelination) and satellite cells (support).
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- 11.4: Neuronal Communication
- Neurons communicate with each other and with muscles and glands through electrical changes in their cell membrane. The electrical change that is carried down the axon is called an action potential. In electrical synapses, the action potential can be carried from one neuron to another through gap junctions. In chemical synapses, the action potential can be converted into chemical signals called neurotransmitters.
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- 11.5: Development of the Nervous System
- The embryonic nervous system begins as a very simple structure called a neural tube, that is essentially just a hollow tube. During embryonic development, the neural tube enlarges into primary vesicles (prosencephalon, mesencephalon and rhombencephalon) and secondary vesicles (telencephalon, diencephalon, mesencephalon, metencephalon and myelencephalon), which will give rise to the regions of the brain and the spinal cord.