Nervous Tissue

Nervous tissues have a wide distribution throughout the body, innervating most visceral and peripheral tissues. Nervous tissue is what forms the communicative pathways, allowing the integrated control of all parts of the body, including those parts not directly connected to one another. In terms of anatomy, the nervous system is divided into the central nervous system (CNS), which is comprised of the brain and spinal cord, and the peripheral nervous system (PNS) which is comprised of all the other nervous tissue in the body. The PNS serves to gather signals from all parts of the body and send them to the CNS, and also to return signals from the CNS to the body. The CNS serves to integrate and relay these signals for passage through the PNS to the appropriate targets in the body. In terms of function, the nervous system is divided into the somatic (voluntary) and autonomic (involuntary) parts. The somatic nervous system is responsible for sending and relaying signals which we can consciously control to achieve an effect (i.e. you can contract your biceps when you choose to). The autonomic nervous system functions below conscious awareness to control the smooth muscle of the viscera, glands, cardiac muscle, etc.

Within the nervous system, there are two basic varieties of cells: neurons and supportive cells. Neurons are highly specialized cells that easily conduct electrical impulses and are easily excited to produce them (a property of a cell known as irritability). Typical neurons show a large cell body with large central nucleus and many cytoplasmic extensions, of which there are two types. One type are dendrites, which are numerous and serve to collect incoming signals, either from the periphery or other neurons, and send them to the cell body. The other type is the single axon, which is where the electrical impulse is sent away from the neuronal cell body to stimulate other neurons or tissues. This occurs when the neuron has been sufficiently excited by the incoming signals received through its dendrites. The supportive cells are found in conjunction with neurons and, as the name implies, assist the neuron with its functioning. If the supportive cells are in the CNS, they are called neuroglia, if the supportive cells are in the PNS, they are known as Schwann cells.

Nervous Tissue
Neuron and surrounding neuroglia

This slide is a smear from a mammalian spinal cord showing an isolated neuron (large arrow) and the nuclei of the surrounding neuroglial cells (small arrows). Note the numerous cytoplasmic extensions emanating from the neuronal cell body and the size of the neuron compared with the neuroglial cells.

Nervous Tissue

This slide is a smear from a mammalian spinal cord showing an isolated neuron (large arrow) and the nuclei of the surrounding neuroglial cells (small arrows). Note the numerous cytoplasmic extensions emanating from the neuronal cell body and the size of the neuron compared with the neuroglial cells.

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Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1.