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Nervous Tissue: Mediates Perception and Response

Author: Sophia

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In this lesson, you will explore the structure and function of the fourth of the four primary tissue categories, nervous tissue. Specifically, this lesson will cover:

1. Characteristics of Nervous Tissue
2. Nervous Tissue

1. Characteristics of Nervous Tissue

Nervous tissue is characterized as being excitable and capable of sending and receiving electrochemical signals that provide the body with information. Two main classes of cells make up nervous tissue: the neuron and neuroglia. Neurons propagate information via electrochemical impulses, called action potentials, which are biochemically linked to the release of chemical signals. Neuroglia (glia, glue), or glial cells, are a group of six different cells that play an essential role in supporting neurons and modulating their information propagation. You will learn more about neuroglia (glial cells) in future lessons on the nervous system.

terms to know

Neuron

A nervous tissue cell that is capable of generating and propagating information via electrochemical impulses.

Neuroglia

A group of nervous tissue cells that play an essential role in supporting neurons and modulating their information; also known as glial cells.

2. Nervous Tissue

The first class of nervous tissue cells are neurons. Neurons function to provide communication between different parts of the body, whether close to or far away from one another. This communication is done by the propagation of an electrochemical (electrical and chemical) signal. Neurons display a unique three-part morphology which suits this role. They are required to monitor a given area for electrochemical signals, generate electrochemical signals, and propagate electrochemical signals onto the next cell.

This figure shows a diagram of a neuron and a micrograph showing two neuron cells. The body of the neuron contains a single, purple nucleus. The cell is irregularly shaped, having many projections emerging from its surface. Six sets of dendrites project from the top, right, and bottom edges of the cell. The dendrites are yellow and branch many times after leaving the cell, taking on the appearance of tiny trees. The axon projects from the left edge of the cell. The axon is a long cable like structure that branches into several finger like projections at its end. This is where the neuron makes contact with other cells. A label also notes that the area where the axon emerges from the cell body contains microfibrils and microtubules. The micrograph is considerably less magnified than the diagram. The neurons stain darkly and their nuclei are clearly visible. Their irregular cell body is also visible, along with the beginning of the axons. — The Neuron - The cell body of a neuron, also called the soma, contains the nucleus and mitochondria. The dendrites transfer the nerve impulse to the soma. The axon carries the action potential away to another excitable cell.

Neurons are formed by a cell body and two types of cell processes or extensions, dendrites and the axon, which most often form what resembles a tree. The branches of the tree are dendrites. These processes branch off of the cell body and monitor the electrochemical activity in their surrounding area. The cell body, also called the soma, includes most of the cytoplasm, the organelles, and the nucleus. This part of the cell receives incoming electrochemical input from the dendrites and is able to determine if a signal will be generated and sent forward. The trunk of the tree is the axon, the long “tail” (sometimes multiple) that extends away from the cell body and propagates an electrochemical signal onto the next cell.

Image shows neurons with tree-like shapes. — Neuron Anatomy - The structure of neurons resembles a tree where the dendrites extend out from the cell body like branches and the axon extends out like a tree trunk and roots

Some neurons have a protective wrapping around the axon called myelin which protects the axon and speeds up the propagation of the electrochemical signal. Myelin is produced by neuroglial cells as you will see later in this lesson. At the end of the axon are axon terminals (terminus, ending) which function to transfer the electrochemical signal onto the next cell, a cell-to-cell connection called a synapse.

The second class of nervous tissue cells is the neuroglia or glial cells, which have been characterized as having a simple support role. There are six types of neuroglia in the body. Four of these are located in the central nervous system, the brain and spinal cord—astrocytes, microglia, ependymal cells, and oligodendrocytes. Two of these are located in the peripheral nervous system, outside of the brain and spinal cord—satellite cells and Schwann cells.

Neuroglia	Description
Astrocytes (astro, star)	Named for their distinctive star shape and are abundant in the brain and spinal cord. The astrocytes have many functions, including regulation of ion concentration in the intercellular space, uptake and/or breakdown of some chemical signal molecules, and formation of the blood-brain barrier, the membrane that separates the circulatory system from the brain.
Microglia (micro, small)	Protect the nervous system against infection.
Ependymal cells	Produces a fluid that circulates around the brain and spinal cord to provide nutrients, remove waste, and provide cushion.
Oligodendrocytes	Produce myelin in the brain and spinal cord. This covering of the axon allows electrochemical signals to propagate faster and protects the neuron from damage.
Satellite cells	These work like astrocytes but in the peripheral nervous system, regulating ion concentration and the uptake/breakdown of some chemical signal molecules.
Schwann cells	Produce myelin in the peripheral parts of the nervous system (not the brain and spinal cord).

Part A of this diagram shows various types of nerve cells. The largest cell is a neuron. The central body of the neuron contains a single nucleus. Six sets of dendrites project from the top, left and right, edges of the neuron. The dendrites are yellow and branch many times after leaving the cell, taking on the appearance of tiny trees. The axon projects from the bottom edge of the cell and is covered with purple sheaths labeled the myelin sheath. The sheath is not continuous, but instead is a series of equally spaced segments along the axon. Another cell, called an oligodendrocyte, is spider-like in appearance, with its leg-like projections each connecting to a segment of the neuron’s myelin sheath. Above the neuron are three astrocytes. They are much smaller than the neuron and have no axons and are also irregularly shaped cells with many dendrites projecting from the central body. Finally, a microglial cell is shown above the neuron. It is the smallest of the cells in this figure and is an elongated cell with many fine, tentacle-like projections. The projections are concentrated at the two ends of the cell, with the middle area lacking any projections. The micrograph of the neural tissue shows that this tissue is very heterogenous, with both large and small cells embedded in the matrix. Much of the space between the cells is occupied by threadlike nerve fibers. — Nervous Tissue - Nervous tissue is made up of neurons and neuroglia. The cells of nervous tissue are specialized to transmit and receive impulses.

terms to know

Dendrites

Neuronal cell processes that monitor electrochemical signals and propagate them towards the cell body.

Soma

The neuronal cell body.

Axon

A neuronal cell process that propagates an electrochemical signal away from the cell body.

Myelin

A wrapping found around certain axons which provides protection and speeds up the propagation of the electrochemical signal.

Axon Terminal

The end of an axon that participates in a neuronal synapse.

Astrocyte

A glial cell of the central nervous system that regulates ion concentration, uptake and breakdown of chemical signal molecules, and regulation of the blood-brain barrier.

Microglia

A glial cell of the central nervous system that protects against infection.

Ependymal Cell

A glial cell of the central nervous system that produces a fluid that circulates around the brain and spinal cord to provide nutrients, remove waste, and provide cushion.

Oligodendrocyte

A glial cell of the central nervous system that creates myelin.

Satellite Cell

A glial cell of the peripheral nervous system that regulates ion concentration and the uptake and breakdown of chemical signal molecules.

Schwann Cell

A glial cell of the peripheral nervous system that creates myelin.

summary

In this lesson, you learned the common characteristics of nervous tissue. You also learned the individual cells present and their function in nervous tissue.

Source: THIS TUTORIAL HAS BEEN ADAPTED FROM OPENSTAX “ANATOMY AND PHYSIOLOGY 2E.” ACCESS FOR FREE AT HTTPS://OPENSTAX.ORG/DETAILS/BOOKS/ANATOMY-AND-PHYSIOLOGY-2E. LICENSE: CC ATTRIBUTION 4.0 INTERNATIONAL.

Terms to Know

Astrocyte: A glial cell of the central nervous system that regulates ion concentration, uptake and breakdown of chemical signal molecules, and regulation of the blood-brain barrier.
Axon: A neuronal cell process that propagates an electrochemical signal away from the cell body.
Dendrites: Neuronal cell processes that monitor electrochemical signals and propagate them towards the cell body.
Ependymal Cell: A glial cell of the central nervous system that produces a fluid that circulates around the brain and spinal cord to provide nutrients, remove waste, and provide cushion.
Microglia: A glial cell of the central nervous system that protects against infection.
Myelin: A wrapping found around certain axons which provides protection and speeds up the propagation of the electrochemical signal.
Neuroglia: A group of nervous tissue cells that play an essential role in supporting neurons and modulating their information; also known as glial cells.
Neuron: A nervous tissue cell that is capable of generating and propagating information via electrochemical impulses.
Oligodendrocyte: A glial cell of the central nervous system that creates myelin.
Satellite Cell: A glial cell of the peripheral nervous system that regulates ion concentration and the uptake and breakdown of chemical signal molecules.
Schwann Cell: A glial cell of the peripheral nervous system that creates myelin.
Soma: The neuronal cell body.

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Nervous Tissue: Mediates Perception and Response

Table of Contents

1. Characteristics of Nervous Tissue

2. Nervous Tissue