Nervous tissue

You don't need to be Editor-In-Chief to add or edit content to WikiDoc. You can begin to add to or edit text on this WikiDoc page by clicking on the edit button at the top of this page. Next enter or edit the information that you would like to appear here. Once you are done editing, scroll down and click the Save page button at the bottom of the page.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Phone:617-525-6884

Please Take Over This Page and Apply to be Editor-In-Chief for this topic: There can be one or more than one Editor-In-Chief. You may also apply to be an Associate Editor-In-Chief of one of the subtopics below. Please mail us [2] to indicate your interest in serving either as an Editor-In-Chief of the entire topic or as an Associate Editor-In-Chief for a subtopic. Please be sure to attach your CV and or biographical sketch.

Overview

Nervous tissue is the fourth major class of vertebrate tissue. The function of the nervous tissue is in communication between parts of the body. It is composed of neurons, which transmit impulses, and the neuroglia, which assist propagation of the nerve impulse as well as provide nutrients to the neuron.

All nervous tissue of an organism makes up its nervous system, which may include the brain, spinal cord, and nerves throughout the organism.

Nervous tissue is made of nerve cells that come in many varieties, all of which are distinctly characteristic by the axon or long stem like part of the cell that sends action potential signals to the next cell.

All living cells have the ability to react to stimuli. Nervous tissue is specialized to react to stimuli and to conduct impulses to various organs in the body which bring about a response to the stimulus. Nerve tissue (as in the brain, spinal cord and peripheral nerves that branch throughout the body) are all made up of specialized nerve cells called neurons. Neurons are easily stimulated and transmit impulses very rapidly. A nerve is made up of many nerve cell fibers (neurons) bound together by connective tissue. A sheath of dense connective tissue, the epineurium surrounds the nerve. This sheath penetrates the nerve to form the perineurium which surrounds bundles of nerve fibers. blood vessels of various sizes can be seen in the epineurium. The endoneurium, which consists of a thin layer of loose connective tissue, surrounds the individual nerve fibers.

Organizational Structure

There are three main types of neurons, which are classified according their function:

• Those that conduct impulses from the sensory organs to the central nervous system (brain and spinal cord) are called sensory (or afferent) neurons.
• Those that conduct impulses from the central nervous system to the effector organs (such as muscles and glands) are called motor (or efferent) neurons.
• Those that connect sensory neurons to motor neurons are called interneurons (also known as connector neurons or association neurons)

Structure of a Motor Neuron

A motor neuron has many processes (cytoplasmic extensions), called dendrites, which enter a large, grey cell body at one end. A single process, the axon, leaves at the other end, extending towards the dendrites of the next neuron or to form a motor endplate in a muscle. Dendrites are usually short and divided while the axons are very long and does not branched freely. The impulses are transmitted through the motor neuron in one direction, i.e. into the cell body by the dendrites and away from the cell body by the axon . The cell body is enclosed by a cell (plasma) membrane and has a central nucleus. Granules called Nissl bodies are found in the cytoplasm of the cell body. Within the cell body, extremely fine neurofibrils extend from the dendrites into the axon. The axon is surrounded by the myelin sheath, which forms a whitish, non-cellular, fatty layer around the axon. Outside the myelin sheath is a cellular layer called the neurilemma or sheath of Schwann cells. The myelin sheath together with the neurilemma is also known as the medullary sheath. This medullary sheath is interrupted at intervals by the nodes of Ranvier.

Neuronal Communication

Nerve cells are functionally connected to each other at a junction known as a synapse, where the terminal branches of an axon and the dendrites of another neuron lie in close proximity to each other but normally without direct contact. Information is transmitted across the gap by chemical secretions called neurotransmitters. It causes activation in the post-synaptic cell.

Classification of Neurons

On the basis of their structure, neurons can also be classified into three main types:

• Unipolar Neurons

Sensory neurons have only a single process or fibre which divides close to the cell body into two main branches (axon and dendrite). Because of their structure they are often referred to as unipolar neurons.

• Multipolar Neurons

Motor neurons, which have numerous cell processes (an axon and many dendrites) are often referred to as multipolar neurons. Interneurons are also multipolar.

• Bipolar Neurons

Bipolar neurons are spindle-shaped, with a dendrite at one end and an axon at the other . An example can be found in the light-sensitive retina of the eye.

bg:Нервна тъкан ca:Teixit nerviós de:Nervengewebe et:Närvikudefr:Tissu nerveux hr:Živčano tkivo it:Tessuto nervoso lt:Nervinis audinys hu:Idegszövetsr:Нервно ткиво fi:Hermokudos sv:Nervvävnad th:เนื้อเยื่อประสาท vi:Mô thần kinh

WikiDoc Help Menu Quick Start.. Get Started Here! How to Login How to Search Pages How to Start a New Page How to Edit a Page Cheat Sheet Editing basics Learning Basic Formatting How to make Links in WikiDoc & to External Sites How to Make Lists How to Ignoring Formatting Adding References or Footnotes to Articles Tracking Changes You Have Made How to Put an Article Into a Category When Multiple Topics Should Go To The Same Page (MI, Acute MI, AMI) Using Redirection Advanced editing How to Make Tables How to Insert Images and Other Media How to Add Video Help:How to Make Columns Web Colors How To Make Templates How to Move Pages Inserting Dynamic Dates and Times Inserting WikiDoc Statistics Editing the Table of Contents Communicating your edits Let others know what you changed: The importance of Edit Summaries Minor Edits Edit Conflicts Help Videos You Can Watch Getting Started Video

Acknowledgement and Attribution Regarding Sources of Content

Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .