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Nervous tissue, also called neural tissue, is the main tissue component of the
nervous system In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes t ...
. The nervous system regulates and controls body functions and activity. It consists of two parts: the
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...
(CNS) comprising the brain and
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spin ...
, and the peripheral nervous system (PNS) comprising the branching peripheral
nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the ...
s. It is composed of
neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. ...
s, also known as nerve cells, which receive and transmit impulses, and
neuroglia Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system ( brain and spinal cord) and the peripheral nervous system that do not produce electrical impulses. They maintain homeostasis, form ...
, also known as glial cells or glia, which assist the propagation of the
nerve impulse An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, c ...
as well as provide
nutrients A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
to the neurons. Nervous tissue is made up of different types of neurons, all of which have an
axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action p ...
. An axon is the long stem-like part of the
cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
that sends
action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...
s to the next cell. Bundles of axons make up the
nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the ...
s in the PNS and tracts in the CNS. Functions of the nervous system are sensory input, integration, control of
muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscle ...
s and
gland In animals, a gland is a group of cells in an animal's body that synthesizes substances (such as hormones) for release into the bloodstream ( endocrine gland) or into cavities inside the body or its outer surface ( exocrine gland). Structure ...
s,
homeostasis In biology, homeostasis (British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and i ...
, and mental activity.


Structure

Nervous tissue is composed of
neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. ...
s, also called nerve cells, and neuroglial cells. Four types of neuroglia found in the CNS are astrocytes, microglial cells, ependymal cells, and oligodendrocytes. Two types of neuroglia found in the PNS are satellite cells and Schwann cells. In the
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...
(CNS), the tissue types found are
grey matter Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil ( dendrites and unmyelinated axons), glial cells ( astrocytes and oligodendrocytes), synapses, and capillaries. Grey matter is distin ...
and
white matter White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distributio ...
. The tissue is categorized by its neuronal and neuroglial components.


Components

Neurons are cells with specialized features that allow them to receive and facilitate nerve impulses, or
action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...
s, across their membrane to the next neuron. They possess a large cell body (
soma Soma may refer to: Businesses and brands * SOMA (architects), a New York–based firm of architects * Soma (company), a company that designs eco-friendly water filtration systems * SOMA Fabrications, a builder of bicycle frames and other bicyc ...
), with cell projections called
dendrite Dendrites (from Greek δένδρον ''déndron'', "tree"), also dendrons, are branched protoplasmic extensions of a nerve cell that propagate the electrochemical stimulation received from other neural cells to the cell body, or soma, of the n ...
s and an
axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action p ...
. Dendrites are thin, branching projections that receive
electrochemical Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outco ...
signaling (
neurotransmitters A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell. Neurotr ...
) to create a change in voltage in the cell. Axons are long projections that carry the action potential away from the cell body toward the next neuron. The bulb-like end of the axon, called the
axon terminal Axon terminals (also called synaptic boutons, terminal boutons, or end-feet) are distal terminations of the telodendria (branches) of an axon. An axon, also called a nerve fiber, is a long, slender projection of a nerve cell, or neuron, that condu ...
, is separated from the dendrite of the following neuron by a small gap called a
synaptic cleft Chemical synapses are biological junctions through which neurons' signals can be sent to each other and to non-neuronal cells such as those in muscles or glands. Chemical synapses allow neurons to form circuits within the central nervous syste ...
. When the action potential travels to the axon terminal, neurotransmitters are released across the synapse and bind to the post-synaptic receptors, continuing the nerve impulse. Neurons are classified both functionally and structurally. Functional classification: *
Sensory neuron Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded potentials. This process is called sensory transduction. The ...
s ( afferent): Relay sensory information in the form of an
action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...
(nerve impulse) from the PNS to the CNS *
Motor neuron A motor neuron (or motoneuron or efferent neuron) is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectly ...
s ( efferent): Relay an action potential out of the CNS to the proper effector (muscles, glands) *
Interneuron Interneurons (also called internuncial neurons, relay neurons, association neurons, connector neurons, intermediate neurons or local circuit neurons) are neurons that connect two brain regions, i.e. not direct motor neurons or sensory neurons. In ...
s: Cells that form connections between neurons and whose processes are limited to a single local area in the brain or spinal cord Structural classification: *
Multipolar neuron A multipolar neuron is a type of neuron that possesses a single axon and many dendrites (and dendritic branches), allowing for the integration of a great deal of information from other neurons. These processes are projections from the neuron cell ...
s: Have 3 or more processes coming off the
soma Soma may refer to: Businesses and brands * SOMA (architects), a New York–based firm of architects * Soma (company), a company that designs eco-friendly water filtration systems * SOMA Fabrications, a builder of bicycle frames and other bicyc ...
(cell body). They are the major neuron type in the CNS and include interneurons and motor neurons. *
Bipolar neuron A bipolar neuron, or bipolar cell, is a type of neuron that has two extensions (one axon and one dendrite). Many bipolar cells are specialized sensory neurons for the transmission of sense. As such, they are part of the sensory pathways for smell ...
s: Sensory neurons that have two processes coming off the soma, one dendrite and one axon *
Pseudounipolar neuron A pseudounipolar neuron is a type of neuron which has one extension from its cell body. This type of neuron contains an axon that has split into two branches. A single process arises from the cell body and then divides into an axon and a dendrite. ...
s: Sensory neurons that have one process that splits into two branches, forming the axon and dendrite *
Unipolar brush cell Unipolar brush cells (UBCs) are a class of excitatory glutamatergic interneuron found in the granular layer of the cerebellar cortex and also in the granule cell domain of the cochlear nucleus. Structure The UBC has a round or oval cell body ...
s: Are
excitatory In neuroscience, an excitatory postsynaptic potential (EPSP) is a postsynaptic potential that makes the postsynaptic neuron more likely to fire an action potential. This temporary depolarization of postsynaptic membrane potential, caused by the ...
glutamatergic Glutamatergic means "related to glutamate". A glutamatergic agent (or drug) is a chemical that directly modulates the excitatory amino acid (glutamate/aspartate) system in the body or brain. Examples include excitatory amino acid receptor agonis ...
interneuron Interneurons (also called internuncial neurons, relay neurons, association neurons, connector neurons, intermediate neurons or local circuit neurons) are neurons that connect two brain regions, i.e. not direct motor neurons or sensory neurons. In ...
s that have a single short dendrite terminating in a brush-like tuft of dendrioles. These are found in the granular layer of the
cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebe ...
. Neuroglia encompasses the non-neural cells in nervous tissue that provide various crucial supportive functions for neurons. They are smaller than neurons, and vary in structure according to their function. Neuroglial cells are classified as follows: * Microglial cells: Microglia are
macrophage Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer cell ...
cells that make up the primary immune system for the CNS. They are the smallest neuroglial cell. *
Astrocyte Astrocytes (from Ancient Greek , , "star" + , , "cavity", "cell"), also known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord. They perform many functions, including biochemical control of endo ...
s: Star-shaped
macroglia Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system that do not produce electrical impulses. They maintain homeostasis, form myel ...
l cells with many processes found in the CNS. They are the most abundant cell type in the brain, and are intrinsic to a healthy CNS. *
Oligodendrocyte Oligodendrocytes (), or oligodendroglia, are a type of neuroglia whose main functions are to provide support and insulation to axons in the central nervous system of jawed vertebrates, equivalent to the function performed by Schwann cells in the ...
s: CNS cells with very few processes. They form
myelin sheaths Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can be ...
on the axons of a neuron, which are lipid-based insulation that increases the speed at which the action potential, can travel down the axon. * NG2 glia: CNS cells that are distinct from astrocytes, oligodendrocytes, and microglia, and serve as the developmental precursors of oligodendrocytes *
Schwann cells Schwann cells or neurolemmocytes (named after German physiologist Theodor Schwann) are the principal glia of the peripheral nervous system (PNS). Glial cells function to support neurons and in the PNS, also include satellite cells, olfactory ens ...
: The PNS equivalent of oligodendrocytes, they help maintain axons and form myelin sheaths in the PNS. *
Satellite glial cell Satellite glial cells, formerly called amphicytes, are glial cells that cover the surface of neuron cell bodies in ganglia of the peripheral nervous system. Thus, they are found in sensory, sympathetic, and parasympathetic ganglia. Both sat ...
: Line the surface of neuron cell bodies in
ganglia A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympathe ...
(groups of nerve body cells bundled or connected together in the PNS) *Enteric glia: Found in the
enteric nervous system The enteric nervous system (ENS) or intrinsic nervous system is one of the main divisions of the autonomic nervous system (ANS) and consists of a mesh-like system of neurons that governs the function of the gastrointestinal tract. It is capable of ...
, within the gastrointestinal tract.


Classification of tissue

In the central nervous system: *
Grey matter Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil ( dendrites and unmyelinated axons), glial cells ( astrocytes and oligodendrocytes), synapses, and capillaries. Grey matter is distin ...
is composed of cell bodies, dendrites, unmyelinated axons, protoplasmic astrocytes (astrocyte subtype), satellite oligodendrocytes (non-myelinating oligodendrocyte subtype), microglia, and very few myelinated axons. *
White matter White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distributio ...
is composed of myelinated axons, fibrous astrocytes, myelinating oligodendrocytes, and microglia. In the peripheral nervous system: *
Ganglion A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympathe ...
tissue is composed of cell bodies, dendrites, and satellite glial cells. *
Nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the ...
s are composed of myelinated and unmyelinated axons, Schwann cells surrounded by connective tissue. The three layers of connective tissue surrounding each nerve are: *
Endoneurium The endoneurium (also called endoneurial channel, endoneurial sheath, endoneurial tube, or Henle's sheath) is a layer of delicate connective tissue around the myelin sheath of each myelinated nerve fiber in the peripheral nervous system. Its co ...
. Each nerve axon, or fiber is surrounded by the
endoneurium The endoneurium (also called endoneurial channel, endoneurial sheath, endoneurial tube, or Henle's sheath) is a layer of delicate connective tissue around the myelin sheath of each myelinated nerve fiber in the peripheral nervous system. Its co ...
, which is also called the endoneurial tube, channel or sheath. This is a thin, delicate, protective layer of connective tissue. *
Perineurium The perineurium is a protective sheath that surrounds a nerve fascicle. This bundles together axons targeting the same anatomical location. The perineurium is composed from fibroblasts. In the peripheral nervous system, the myelin sheath of e ...
. Each
nerve fascicle A nerve fascicle, is a bundle of nerve fibers belonging to a nerve in the peripheral nervous system. A nerve fascicle is also called a fasciculus. A nerve fascicle is enclosed by perineurium, a layer of fascial connective tissue. Each enclosed ...
containing one or more axons, is enclosed by the perineurium, a connective tissue having a lamellar arrangement in seven or eight concentric layers. This plays a very important role in the protection and support of the nerve fibers and also serves to prevent the passage of large molecules from the epineurium into a fascicle. *
Epineurium The epineurium is the outermost layer of dense irregular connective tissue surrounding a peripheral nerve. It usually surrounds multiple nerve fascicles as well as blood vessels which supply the nerve. Smaller branches of these blood vessels penet ...
. The epineurium is the outermost layer of dense connective tissue enclosing the (peripheral) nerve.


Function

The function of nervous tissue is to form the communication network of the
nervous system In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes t ...
by conducting electric signals across tissue. In the CNS, grey matter, which contains the
synapses In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell. Synapses are essential to the transmission of nervous impulses from ...
, is important for information processing. White matter, containing myelinated axons, connects and facilitates nerve impulse between grey matter areas in the CNS. In the PNS, the ganglion tissue, containing the cell bodies and dendrites, contain relay points for
nerve tissue Nervous tissue, also called neural tissue, is the main tissue component of the nervous system. The nervous system regulates and controls body functions and activity. It consists of two parts: the central nervous system (CNS) comprising the brain ...
impulses. The nerve tissue, containing myelinated axons bundles, carry action potential nerve impulses.


Clinical significance


Tumours

Neoplasm A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
s (tumours) in nervous tissue include: *
Glioma A glioma is a type of tumor that starts in the glial cells of the brain or the spine. Gliomas comprise about 30 percent of all brain tumors and central nervous system tumours, and 80 percent of all malignant brain tumours. Signs and symptoms ...
s (
glial cell Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system that do not produce electrical impulses. They maintain homeostasis, form mye ...
tumors) :
Gliomatosis cerebri Gliomatosis cerebri is a rare primary diffuse brain tumor that has a poor prognosis. It is defined by the World Health Organization as a diffusely infiltrating glial tumor impacting at least three cerebral lobes, mostly with bilateral involvement ...
,
Oligoastrocytoma Oligoastrocytomas are a subset of brain tumors that present with an appearance of mixed glial cell origin, astrocytoma and oligodendroglioma. However, the term "Oligoastrocytoma" is now considered obsolete by the National Comprehensive Cancer Ne ...
,
Choroid plexus papilloma Choroid plexus papilloma, also known as papilloma of the choroid plexus, is a rare benign neuroepithelial intraventricular WHO grade I lesion found in the choroid plexus. It leads to increased cerebrospinal fluid production, thus causing increa ...
,
Ependymoma An ependymoma is a tumor that arises from the ependyma, a tissue of the central nervous system. Usually, in pediatric cases the location is intracranial, while in adults it is spinal. The common location of intracranial ependymomas is the fou ...
,
Astrocytoma Astrocytomas are a type of brain tumor. They originate in a particular kind of glial cells, star-shaped brain cells in the cerebrum called astrocytes. This type of tumor does not usually spread outside the brain and spinal cord and it does not usu ...
(
Pilocytic astrocytoma Pilocytic astrocytoma (and its variant pilomyxoid astrocytoma) is a brain tumor that occurs most commonly in children and young adults (in the first 20 years of life). They usually arise in the cerebellum, near the brainstem, in the hypothalamic r ...
,
Glioblastoma multiforme Glioblastoma, previously known as glioblastoma multiforme (GBM), is one of the most aggressive types of cancer that begin within the brain. Initially, signs and symptoms of glioblastoma are nonspecific. They may include headaches, personality c ...
), Dysembryoplastic neuroepithelial tumour,
Oligodendroglioma Oligodendrogliomas are a type of glioma that are believed to originate from the oligodendrocytes of the brain or from a glial precursor cell. They occur primarily in adults (9.4% of all primary brain and central nervous system tumors) but are also ...
,
Medulloblastoma Medulloblastoma is a common type of primary brain cancer in children. It originates in the part of the brain that is towards the back and the bottom, on the floor of the skull, in the cerebellum, or posterior fossa. The brain is divided into tw ...
,
Primitive neuroectodermal tumor Primitive neuroectodermal tumor is a malignant (cancerous) neural crest tumor. It is a rare tumor, usually occurring in children and young adults under 25 years of age. The overall 5 year survival rate is about 53%. It gets its name because the m ...
* Neuroepitheliomatous tumors :
Ganglioneuroma Ganglioneuroma is a rare and benign tumor of the autonomic nerve fibers arising from neural crest sympathogonia, which are completely undifferentiated cells of the sympathetic nervous system. However, ganglioneuromas themselves are fully differ ...
,
Neuroblastoma Neuroblastoma (NB) is a type of cancer that forms in certain types of nerve tissue. It most frequently starts from one of the adrenal glands but can also develop in the neck, chest, abdomen, or spine. Symptoms may include bone pain, a lump in ...
, Atypical teratoid rhabdoid tumor,
Retinoblastoma Retinoblastoma (Rb) is a rare form of cancer that rapidly develops from the immature cells of a retina, the light-detecting tissue of the eye. It is the most common primary malignant intraocular cancer in children, and it is almost exclusively f ...
, Esthesioneuroblastoma *
Nerve sheath tumor A nerve sheath tumor is a type of tumor of the nervous system ( nervous system neoplasm) which is made up primarily of the myelin surrounding nerves. From benign tumors like schwannoma to high grade malignant neoplasms known as malignant peripheral ...
s :
Neurofibroma A neurofibroma is a benign nerve-sheath tumor in the peripheral nervous system. In 90% of cases, they are found as stand-alone tumors (solitary neurofibroma, solitary nerve sheath tumor or sporadic neurofibroma), while the remainder are found in p ...
( Neurofibrosarcoma,
Neurofibromatosis Neurofibromatosis (NF) is a group of three conditions in which tumors grow in the nervous system. The three types are neurofibromatosis type I (NF1), neurofibromatosis type II (NF2), and schwannomatosis. In NF1 symptoms include light brown sp ...
),
Schwannoma A schwannoma (or neurilemmoma) is a usually benign nerve sheath tumor composed of Schwann cells, which normally produce the insulating myelin sheath covering peripheral nerves. Schwannomas are homogeneous tumors, consisting only of Schwann cells. ...
, Neurinoma,
Acoustic neuroma A vestibular schwannoma (VS), also called acoustic neuroma, is a benign tumor that develops on the vestibulocochlear nerve that passes from the inner ear to the brain. The tumor originates when Schwann cells that form the insulating myelin sheath ...
,
Neuroma A neuroma (; plural: neuromata or neuromas) is a growth or tumor of nerve tissue. Neuromas tend to be benign (i.e. not cancerous); many nerve tumors, including those that are commonly malignant, are nowadays referred to by other terms. Neuromas ...


References

{{DEFAULTSORT:Nervous Tissue Tissues (biology)