Nervous tissue

Example of nervous tissue.

Nervous tissue is one of four major classes of vertebrate tissue.

Nervous tissue is the main component of the nervous system - the brain, spinal cord, and nerves-which regulates and controls body functions. It is composed of neurons, which transmit impulses, and the neuroglia cells, which assist propagation of the nerve impulse as well as provide nutrients to the neuron.

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.

Functions of the nervous system are sensory input, integration, controls of muscles and glands, homeostasis, and mental activity.

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.

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.

Contents

Neuronal Communication

Nerve cells are functionally made to each other at a junction known as a synapse, where the terminal branches of an axon and the dendrites of another neuron lie close 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. All cells possess the ability to respond to stimuli. The messages carried by the nervous system are electrical signals called impulses.

Classification of Neurons

Neurons are classified both structurally and functionally.

Structural Classification Neurons are grouped structurally according to the number of processes extending from their cell body. Three major neuron groups make up this classification: multipolar (polar = end, pole), bipolar and unipolar neurons.

Multipolar Neurons (3+ processes) 
These are the most common neuron type in humans (more than 99% of neurons belong to this class) and the major neuron type in the CNS
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.
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.

Cancer

Tumors in nervous tissue include:

Gliomatosis cerebri, Oligoastrocytoma, Choroid plexus papilloma, Ependymoma, Astrocytoma (Pilocytic astrocytoma, Glioblastoma multiforme), Dysembryoplastic neuroepithelial tumour, Oligodendroglioma, Medulloblastoma, Primitive neuroectodermal tumor
  • Neuroepitheliomatous tumors
Ganglioneuroma, Neuroblastoma, Atypical teratoid rhabdoid tumor, Retinoblastoma, Esthesioneuroblastoma
Neurofibroma (Neurofibrosarcoma, Neurofibromatosis), Schwannoma, Neurinoma, Acoustic neuroma, Neuroma

See also


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • nervous tissue — noun tissue composed of neurons • Syn: ↑nerve tissue • Hypernyms: ↑animal tissue • Hyponyms: ↑fiber bundle, ↑fibre bundle, ↑fascicle, ↑fasciculus …   Useful english dictionary

  • Nervous system neoplasm — Classification and external resources ICD 10 C69 C72 D31 D …   Wikipedia

  • nervous system disease — Introduction       any of the diseases or disorders that affect the functioning of the human nervous system (nervous system, human). Everything that humans sense, consider, and effect and all the unlearned reflexes of the body depend on the… …   Universalium

  • Nervous system — Nerve redirects here. For other uses, see Nerve (disambiguation). This article is about the nervous system. For parts of the nervous system commonly called nerves, see Peripheral nerve. Nervous system The Human N …   Wikipedia

  • Tissue (biology) — This article is about biological tissue. For other uses, see Tissue. Cross section of sclerenchyma fibers in plant ground tissue …   Wikipedia

  • tissue — tissual, adj. tissuey, adj. /tish ooh/ or, esp. Brit., /tis yooh/, n., v., tissued, tissuing. n. 1. Biol. an aggregate of similar cells and cell products forming a definite kind of structural material with a specific function, in a multicellular… …   Universalium

  • Nervous system — The nervous system is the body tissue that records and distributes information in the body using electrical and chemical transmission. It has two parts. The "central" nervous system is comprised of the brain and spinal cord. The… …   Medical dictionary

  • nervous system — noun the sensory and control apparatus consisting of a network of nerve cells (Freq. 2) • Syn: ↑systema nervosum • Hypernyms: ↑system • Hyponyms: ↑sympathetic nervous system, ↑parasympathetic nervous system …   Useful english dictionary

  • Tissue — A tissue in medicine is not like a piece of tissue paper. It is a broad term that is applied to any group of cells that perform specific functions. A tissue in medicine need not form a layer. Thus, The bone marrow is a tissue; Connective tissue… …   Medical dictionary

  • tissue — I (New American Roget s College Thesaurus) n. gauze, fabric, web, net, mesh; membrane, cartilage, muscle; tissue or crepe paper; structure. See crossing, texture. II (Roget s IV) n. 1. [A network] Syn. web, mesh, filigree, crossing, parcel,… …   English dictionary for students


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.