Glia

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Glia
Glial Cell Types.png
Illustration of the four different types of glial cells found in the central nervous system: ependymal cells (light pink), astrocytes (green), microglial cells (dark red) and oligodendrocytes (light blue)
Details
Precursor Neuroectoderm for macroglia, and hematopoietic stem cells for microglia
System Nervous system
Identifiers
MeSH D009457
TA98 A14.0.00.005
TH H2.00.06.2.00001
FMA 54536 54541, 54536
Anatomical terms of microanatomy

Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system (the brain and the spinal cord) and in the peripheral nervous system that do not produce electrical impulses. The neuroglia make up more than one half the volume of neural tissue in the human body. [1] They maintain homeostasis, form myelin, and provide support and protection for neurons. [2] In the central nervous system, glial cells include oligodendrocytes (that produce myelin), astrocytes, ependymal cells and microglia, and in the peripheral nervous system they include Schwann cells (that produce myelin), and satellite cells.

Contents

Function

They have four main functions:

They also play a role in neurotransmission and synaptic connections, [3] and in physiological processes such as breathing. [4] [5] [6] While glia were thought to outnumber neurons by a ratio of 10:1, studies using newer methods and reappraisal of historical quantitative evidence suggests an overall ratio of less than 1:1, with substantial variation between different brain tissues. [7] [8]

Glial cells have far more cellular diversity and functions than neurons, and can respond to and manipulate neurotransmission in many ways. Additionally, they can affect both the preservation and consolidation of memories. [1]

Glia were discovered in 1856, by the pathologist Rudolf Virchow in his search for a "connective tissue" in the brain. [9] The term derives from Greek γλία and γλοία "glue" [10] (English: /ˈɡliːə/ or /ˈɡlaɪə/ ), and suggests the original impression that they were the glue of the nervous system.

Types

Neuroglia of the brain shown by Golgi's method Neuroglia.png
Neuroglia of the brain shown by Golgi's method
Astrocytes can be identified in culture because, unlike other mature glia, they express glial fibrillary acidic protein (GFAP) Gfapastr5.jpg
Astrocytes can be identified in culture because, unlike other mature glia, they express glial fibrillary acidic protein (GFAP)
Glial cells in a rat brain stained with an antibody against GFAP 2010-3-15 rGFAP 1-4000 1-200 Hip 20x(4).jpg
Glial cells in a rat brain stained with an antibody against GFAP
Different types of neuroglia Blausen 0870 TypesofNeuroglia.png
Different types of neuroglia

Macroglia

Derived from ectodermal tissue.

LocationNameDescription
CNS Astrocytes

Astrocytes (also called astroglia) have numerous projections that link neurons to their blood supply while forming the blood–brain barrier. They regulate the external chemical environment of neurons by removing excess potassium ions and recycling neurotransmitters released during synaptic transmission. Astrocytes may regulate vasoconstriction and vasodilation by producing substances such as arachidonic acid, whose metabolites are vasoactive.

Astrocytes signal each other using ATP. The gap junctions (also known as electrical synapses) between astrocytes allow the messenger molecule IP3 to diffuse from one astrocyte to another. IP3 activates calcium channels on cellular organelles, releasing calcium into the cytoplasm. This calcium may stimulate the production of more IP3 and cause release of ATP through channels in the membrane made of pannexins. The net effect is a calcium wave that propagates from cell to cell. Extracellular release of ATP and consequent activation of purinergic receptors on other astrocytes may also mediate calcium waves in some cases.

In general, there are two types of astrocytes, protoplasmic and fibrous, similar in function but distinct in morphology and distribution. Protoplasmic astrocytes have short, thick, highly branched processes and are typically found in gray matter. Fibrous astrocytes have long, thin, less-branched processes and are more commonly found in white matter.

It has recently been shown that astrocyte activity is linked to blood flow in the brain, and that this is what is actually being measured in fMRI. [11] They also have been involved in neuronal circuits playing an inhibitory role after sensing changes in extracellular calcium. [12]

Human astrocytes are larger and more abundant than any other animals'. [13]

CNS Oligodendrocytes

Oligodendrocytes are cells that coat axons in the CNS with their cell membrane, forming a specialized membrane differentiation called myelin, producing the myelin sheath. The myelin sheath provides insulation to the axon that allows electrical signals to propagate more efficiently. [14]

CNS Ependymal cells

Ependymal cells, also named ependymocytes, line the spinal cord and the ventricular system of the brain. These cells are involved in the creation and secretion of cerebrospinal fluid (CSF) and beat their cilia to help circulate the CSF and make up the blood-CSF barrier. They are also thought to act as neural stem cells. [15]

CNS Radial glia

Radial glia cells arise from neuroepithelial cells after the onset of neurogenesis. Their differentiation abilities are more restricted than those of neuroepithelial cells. In the developing nervous system, radial glia function both as neuronal progenitors and as a scaffold upon which newborn neurons migrate. In the mature brain, the cerebellum and retina retain characteristic radial glial cells. In the cerebellum, these are Bergmann glia, which regulate synaptic plasticity. In the retina, the radial Müller cell is the glial cell that spans the thickness of the retina and, in addition to astroglial cells, [16] participates in a bidirectional communication with neurons. [17]

PNS Schwann cells

Similar in function to oligodendrocytes, Schwann cells provide myelination to axons in the peripheral nervous system (PNS). They also have phagocytotic activity and clear cellular debris that allows for regrowth of PNS neurons. [18]

PNS Satellite cells

Satellite glial cells are small cells that surround neurons in sensory, sympathetic, and parasympathetic ganglia. [19] These cells help regulate the external chemical environment. Like astrocytes, they are interconnected by gap junctions and respond to ATP by elevating the intracellular concentration of calcium ions. They are highly sensitive to injury and inflammation and appear to contribute to pathological states, such as chronic pain. [20]

PNS Enteric glial cells

Are found in the intrinsic ganglia of the digestive system. Glia cells are thought to have many roles in the enteric system, some related to homeostasis and muscular digestive processes. [21]

Microglia

Microglia are specialized macrophages capable of phagocytosis that protect neurons of the central nervous system. [22] They are derived from the earliest wave of mononuclear cells that originate in yolk sac blood islands early in development, and colonize the brain shortly after the neural precursors begin to differentiate. [23]

These cells are found in all regions of the brain and spinal cord. Microglial cells are small relative to macroglial cells, with changing shapes and oblong nuclei. They are mobile within the brain and multiply when the brain is damaged. In the healthy central nervous system, microglia processes constantly sample all aspects of their environment (neurons, macroglia and blood vessels). In a healthy brain, microglia direct the immune response to brain damage and play an important role in the inflammation that accompanies the damage. Many diseases and disorders are associated with deficient microglia, such as Alzheimer's disease, Parkinson's disease and ALS.

Other

Pituicytes from the posterior pituitary are glial cells with characteristics in common to astrocytes. [24] Tanycytes in the median eminence of the hypothalamus are a type of ependymal cell that descend from radial glia and line the base of the third ventricle. [25] Drosophila melanogaster, the fruit fly, contains numerous glial types that are functionally similar to mammalian glia but are nonetheless classified differently. [26]

Total number

In general, neuroglial cells are smaller than neurons. There are approximately 85 billion glia cells in the human brain, [8] about the same number as neurons. [8] Glial cells make up about half the total volume of the brain and spinal cord. [27] The glia to neuron-ratio varies from one part of the brain to another. The glia to neuron-ratio in the cerebral cortex is 3.72 (60.84 billion glia (72%); 16.34 billion neurons), while that of the cerebellum is only 0.23 (16.04 billion glia; 69.03 billion neurons). The ratio in the cerebral cortex gray matter is 1.48, with 3.76 for the gray and white matter combined. [27] The ratio of the basal ganglia, diencephalon and brainstem combined is 11.35. [27]

The total number of glia cells in the human brain is distributed into the different types with oligodendrocytes being the most frequent (45–75%), followed by astrocytes (19–40%) and microglia (about 10% or less). [8]

Development

23-week fetal brain culture astrocyte Human astrocyte.png
23-week fetal brain culture astrocyte

Most glia are derived from ectodermal tissue of the developing embryo, in particular the neural tube and crest. The exception is microglia, which are derived from hematopoietic stem cells. In the adult, microglia are largely a self-renewing population and are distinct from macrophages and monocytes, which infiltrate an injured and diseased CNS.

In the central nervous system, glia develop from the ventricular zone of the neural tube. These glia include the oligodendrocytes, ependymal cells, and astrocytes. In the peripheral nervous system, glia derive from the neural crest. These PNS glia include Schwann cells in nerves and satellite glial cells in ganglia.

Capacity to divide

Glia retain the ability to undergo cell divisions in adulthood, whereas most neurons cannot. The view is based on the general inability of the mature nervous system to replace neurons after an injury, such as a stroke or trauma, where very often there is a substantial proliferation of glia, or gliosis, near or at the site of damage. However, detailed studies have found no evidence that 'mature' glia, such as astrocytes or oligodendrocytes, retain mitotic capacity. Only the resident oligodendrocyte precursor cells seem to keep this ability once the nervous system matures.

Glial cells are known to be capable of mitosis. By contrast, scientific understanding of whether neurons are permanently post-mitotic, [28] or capable of mitosis, [29] [30] [31] is still developing. In the past, glia had been considered[ by whom? ] to lack certain features of neurons. For example, glial cells were not believed to have chemical synapses or to release transmitters. They were considered to be the passive bystanders of neural transmission. However, recent studies have shown this to not be entirely true. [32]

Functions

Some glial cells function primarily as the physical support for neurons. Others provide nutrients to neurons and regulate the extracellular fluid of the brain, especially surrounding neurons and their synapses. During early embryogenesis, glial cells direct the migration of neurons and produce molecules that modify the growth of axons and dendrites. Some glial cells display regional diversity in the CNS and their functions may vary between the CNS regions. [33]

Neuron repair and development

Glia are crucial in the development of the nervous system and in processes such as synaptic plasticity and synaptogenesis. Glia have a role in the regulation of repair of neurons after injury. In the central nervous system (CNS), glia suppress repair. Glial cells known as astrocytes enlarge and proliferate to form a scar and produce inhibitory molecules that inhibit regrowth of a damaged or severed axon. In the peripheral nervous system (PNS), glial cells known as Schwann cells (or also as neuri-lemmocytes) promote repair. After axonal injury, Schwann cells regress to an earlier developmental state to encourage regrowth of the axon. This difference between the CNS and the PNS, raises hopes for the regeneration of nervous tissue in the CNS. For example, a spinal cord may be able to be repaired following injury or severance.

Myelin sheath creation

Oligodendrocytes are found in the CNS and resemble an octopus: they have bulbous cell bodies with up to fifteen arm-like processes. Each process reaches out to an axon and spirals around it, creating a myelin sheath. The myelin sheath insulates the nerve fiber from the extracellular fluid and speeds up signal conduction along the nerve fiber. [34] In the peripheral nervous system, Schwann cells are responsible for myelin production. These cells envelop nerve fibers of the PNS by winding repeatedly around them. This process creates a myelin sheath, which not only aids in conductivity but also assists in the regeneration of damaged fibers.

Neurotransmission

Astrocytes are crucial participants in the tripartite synapse. [35] [36] [37] [38] They have several crucial functions, including clearance of neurotransmitters from within the synaptic cleft, which aids in distinguishing between separate action potentials and prevents toxic build-up of certain neurotransmitters such as glutamate, which would otherwise lead to excitotoxicity. Furthermore, astrocytes release gliotransmitters such as glutamate, ATP, and D-serine in response to stimulation. [39]

Clinical significance

Neoplastic glial cells stained with an antibody against GFAP (brown), from a brain biopsy Anaplastic astrocytoma - gfap - very high mag.jpg
Neoplastic glial cells stained with an antibody against GFAP (brown), from a brain biopsy

While glial cells in the PNS frequently assist in regeneration of lost neural functioning, loss of neurons in the CNS does not result in a similar reaction from neuroglia. [18] In the CNS, regrowth will only happen if the trauma was mild, and not severe. [40] When severe trauma presents itself, the survival of the remaining neurons becomes the optimal solution. However, some studies investigating the role of glial cells in Alzheimer's disease are beginning to contradict the usefulness of this feature, and even claim it can "exacerbate" the disease. [41] In addition to affecting the potential repair of neurons in Alzheimer's disease, scarring and inflammation from glial cells have been further implicated in the degeneration of neurons caused by amyotrophic lateral sclerosis. [42]

In addition to neurodegenerative diseases, a wide range of harmful exposure, such as hypoxia, or physical trauma, can lead to the result of physical damage to the CNS. [40] Generally, when damage occurs to the CNS, glial cells cause apoptosis among the surrounding cellular bodies. [40] Then, there is a large amount of microglial activity, which results in inflammation, and, finally, there is a heavy release of growth inhibiting molecules. [40]

History

Although glial cells and neurons were probably first observed at the same time in the early 19th century, unlike neurons whose morphological and physiological properties were directly observable for the first investigators of the nervous system, glial cells had been considered to be merely "glue" that held neurons together until the mid-20th century. [43]

Glia were first described in 1856 by the pathologist Rudolf Virchow in a comment to his 1846 publication on connective tissue. A more detailed description of glial cells was provided in the 1858 book 'Cellular Pathology' by the same author. [44]

When markers for different types of cells were analyzed, Albert Einstein's brain was discovered to contain significantly more glia than normal brains in the left angular gyrus, an area thought to be responsible for mathematical processing and language. [45] However, out of the total of 28 statistical comparisons between Einstein's brain and the control brains, finding one statistically significant result is not surprising, and the claim that Einstein's brain is different is not scientific (c.f. multiple comparisons problem). [46]

Not only does the ratio of glia to neurons increase through evolution, but so does the size of the glia. Astroglial cells in human brains have a volume 27 times greater than in mouse brains. [47]

These important scientific findings may begin to shift the neurocentric perspective into a more holistic view of the brain which encompasses the glial cells as well. For the majority of the twentieth century, scientists had disregarded glial cells as mere physical scaffolds for neurons. Recent publications have proposed that the number of glial cells in the brain is correlated with the intelligence of a species. [48] Moreover, evidences are demonstrating the active role of glia, in particular astroglia, in cognitive processes like learning and memory. [49] [50]

See also

Related Research Articles

<span class="mw-page-title-main">Central nervous system</span> Brain and spinal cord

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 parts of the bodies of bilaterally symmetric and triploblastic animals—that is, all multicellular animals except sponges and diploblasts. It is a structure composed of nervous tissue positioned along the rostral to caudal axis of the body and may have an enlarged section at the rostral end which is a brain. Only arthropods, cephalopods and vertebrates have a true brain, though precursor structures exist in onychophorans, gastropods and lancelets.

<span class="mw-page-title-main">Myelin</span> Fatty substance that surrounds nerve cell axons to insulate them and increase transmission speed

Myelin is a lipid-rich material that surrounds nerve cell axons to insulate them and increase the rate at which electrical impulses pass along the axon. The myelinated axon can be likened to an electrical wire with insulating material (myelin) around it. However, unlike the plastic covering on an electrical wire, myelin does not form a single long sheath over the entire length of the axon. Rather, myelin ensheaths the axon segmentally: in general, each axon is encased in multiple long sheaths with short gaps between, called nodes of Ranvier. At the nodes of Ranvier, which are approximately one thousandth of a mm (one micrometre in length, the axon's membrane is bare of myelin.

<span class="mw-page-title-main">Schwann cell</span> Glial cell type

Schwann cells or neurolemmocytes 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 ensheathing cells, enteric glia and glia that reside at sensory nerve endings, such as the Pacinian corpuscle. The two types of Schwann cells are myelinating and nonmyelinating. Myelinating Schwann cells wrap around axons of motor and sensory neurons to form the myelin sheath. The Schwann cell promoter is present in the downstream region of the human dystrophin gene that gives shortened transcript that are again synthesized in a tissue-specific manner.

<span class="mw-page-title-main">Nervous tissue</span> Main component of the nervous system

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 and spinal cord, and the peripheral nervous system (PNS) comprising the branching peripheral nerves. It is composed of neurons, also known as nerve cells, which receive and transmit impulses to and from it, and neuroglia, also known as glial cells or glia, which assist the propagation of the nerve impulse as well as provide nutrients to the neurons.

<span class="mw-page-title-main">Oligodendrocyte</span> Neural cell type

Oligodendrocytes, also known as oligodendroglia, are a type of neuroglia whose main function is to provide the myelin sheath to neuronal axons in the central nervous system (CNS). Myelination gives metabolic support to, and insulates the axons of most vertebrates. A single oligodendrocyte can extend its processes to cover up to 40 axons, that can include multiple adjacent axons. The myelin sheath is not continuous but is segmented along the axon's length at gaps known as the nodes of Ranvier. In the peripheral nervous system the myelination of axons is carried out by Schwann cells.

<span class="mw-page-title-main">Astrocyte</span> Type of brain cell

Astrocytes, 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 endothelial cells that form the blood–brain barrier, provision of nutrients to the nervous tissue, maintenance of extracellular ion balance, regulation of cerebral blood flow, and a role in the repair and scarring process of the brain and spinal cord following infection and traumatic injuries. The proportion of astrocytes in the brain is not well defined; depending on the counting technique used, studies have found that the astrocyte proportion varies by region and ranges from 20% to around 40% of all glia. Another study reports that astrocytes are the most numerous cell type in the brain. Astrocytes are the major source of cholesterol in the central nervous system. Apolipoprotein E transports cholesterol from astrocytes to neurons and other glial cells, regulating cell signaling in the brain. Astrocytes in humans are more than twenty times larger than in rodent brains, and make contact with more than ten times the number of synapses.

<span class="mw-page-title-main">Wallerian degeneration</span> Biological process of axonal degeneration

Wallerian degeneration is an active process of degeneration that results when a nerve fiber is cut or crushed and the part of the axon distal to the injury degenerates. A related process of dying back or retrograde degeneration known as 'Wallerian-like degeneration' occurs in many neurodegenerative diseases, especially those where axonal transport is impaired such as amyotrophic lateral sclerosis (ALS) and Alzheimer's disease. Primary culture studies suggest that a failure to deliver sufficient quantities of the essential axonal protein NMNAT2 is a key initiating event.

<span class="mw-page-title-main">Astrogliosis</span> Increase in astrocytes in response to brain injury

Astrogliosis is an abnormal increase in the number of astrocytes due to the destruction of nearby neurons from central nervous system (CNS) trauma, infection, ischemia, stroke, autoimmune responses or neurodegenerative disease. In healthy neural tissue, astrocytes play critical roles in energy provision, regulation of blood flow, homeostasis of extracellular fluid, homeostasis of ions and transmitters, regulation of synapse function and synaptic remodeling. Astrogliosis changes the molecular expression and morphology of astrocytes, in response to infection for example, in severe cases causing glial scar formation that may inhibit axon regeneration.

<span class="mw-page-title-main">Microglia</span> Glial cell located throughout the brain and spinal cord

Microglia are a type of glial cell located throughout the brain and spinal cord of the central nervous system (CNS). Microglia account for about 10–15% of cells found within the brain. As the resident macrophage cells, they act as the first and main form of active immune defense in the CNS. Microglia originate in the yolk sac under tightly regulated molecular conditions. These cells are distributed in large non-overlapping regions throughout the CNS. Microglia are key cells in overall brain maintenance – they are constantly scavenging the CNS for plaques, damaged or unnecessary neurons and synapses, and infectious agents. Since these processes must be efficient to prevent potentially fatal damage, microglia are extremely sensitive to even small pathological changes in the CNS. This sensitivity is achieved in part by the presence of unique potassium channels that respond to even small changes in extracellular potassium. Recent evidence shows that microglia are also key players in the sustainment of normal brain functions under healthy conditions. Microglia also constantly monitor neuronal functions through direct somatic contacts via their microglial processes, and exert neuroprotective effects when needed.

Oligodendrocyte progenitor cells (OPCs), also known as oligodendrocyte precursor cells, NG2-glia, O2A cells, or polydendrocytes, are a subtype of glia in the central nervous system named for their essential role as precursors to oligodendrocytes and myelin. They are typically identified in the human by co-expression of PDGFRA and CSPG4.

<span class="mw-page-title-main">Neuroimmune system</span>

The neuroimmune system is a system of structures and processes involving the biochemical and electrophysiological interactions between the nervous system and immune system which protect neurons from pathogens. It serves to protect neurons against disease by maintaining selectively permeable barriers, mediating neuroinflammation and wound healing in damaged neurons, and mobilizing host defenses against pathogens.

Gliosis is a nonspecific reactive change of glial cells in response to damage to the central nervous system (CNS). In most cases, gliosis involves the proliferation or hypertrophy of several different types of glial cells, including astrocytes, microglia, and oligodendrocytes. In its most extreme form, the proliferation associated with gliosis leads to the formation of a glial scar.

<span class="mw-page-title-main">Radial glial cell</span> Bipolar-shaped progenitor cells of all neurons in the cerebral cortex and some glia

Radial glial cells, or radial glial progenitor cells (RGPs), are bipolar-shaped progenitor cells that are responsible for producing all of the neurons in the cerebral cortex. RGPs also produce certain lineages of glia, including astrocytes and oligodendrocytes. Their cell bodies (somata) reside in the embryonic ventricular zone, which lies next to the developing ventricular system.

<span class="mw-page-title-main">Ben Barres</span> American neurobiologist (1954–2017)

Benjamin Barres was an American neurobiologist at Stanford University. His research focused on the interaction between neurons and glial cells in the nervous system. Beginning in 2008, he was chair of the Neurobiology Department at Stanford University School of Medicine. He transitioned to male in 1997, and became the first openly transgender scientist in the National Academy of Sciences in 2013. Barres is also known for his pioneering activism for equal opportunity in science, often citing his experiences as both a male and female scientist.

<span class="mw-page-title-main">Glia limitans</span> Thin astrocyte membrane surrounding the brain and spinal cord

The glia limitans, or the glial limiting membrane, is a thin barrier of astrocyte foot processes associated with the parenchymal basal lamina surrounding the brain and spinal cord. It is the outermost layer of neural tissue, and among its responsibilities is the prevention of the over-migration of neurons and neuroglia, the supporting cells of the nervous system, into the meninges. The glia limitans also plays an important role in regulating the movement of small molecules and cells into the brain tissue by working in concert with other components of the central nervous system (CNS) such as the blood–brain barrier (BBB).

<span class="mw-page-title-main">Satellite glial cell</span> Cells covering neuron soma in PNS ganglia

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 satellite glial cells (SGCs) and Schwann cells are derived from the neural crest of the embryo during development. SGCs have been found to play a variety of roles, including control over the microenvironment of sympathetic ganglia. They are thought to have a similar role to astrocytes in the central nervous system (CNS). They supply nutrients to the surrounding neurons and also have some structural function. Satellite cells also act as protective, cushioning cells. Additionally, they express a variety of receptors that allow for a range of interactions with neuroactive chemicals. Many of these receptors and other ion channels have recently been implicated in health issues including chronic pain and herpes simplex. There is much more to be learned about these cells, and research surrounding additional properties and roles of the SGCs is ongoing.

Neuroregeneration is the regrowth or repair of nervous tissues, cells or cell products. Neuroregenerative mechanisms may include generation of new neurons, glia, axons, myelin, or synapses. Neuroregeneration differs between the peripheral nervous system (PNS) and the central nervous system (CNS) by the functional mechanisms involved, especially in the extent and speed of repair. When an axon is damaged, the distal segment undergoes Wallerian degeneration, losing its myelin sheath. The proximal segment can either die by apoptosis or undergo the chromatolytic reaction, which is an attempt at repair. In the CNS, synaptic stripping occurs as glial foot processes invade the dead synapse.

Gliotransmitters are chemicals released from glial cells that facilitate neuronal communication between neurons and other glial cells. They are usually induced from Ca2+ signaling, although recent research has questioned the role of Ca2+ in gliotransmitters and may require a revision of the relevance of gliotransmitters in neuronal signalling in general.

<span class="mw-page-title-main">Outline of the human nervous system</span> Overview of and topical guide to the human nervous system

The following diagram is provided as an overview of and topical guide to the human nervous system:

<span class="mw-page-title-main">Brain cell</span> Functional tissue of the brain

Brain cells make up the functional tissue of the brain. The rest of the brain tissue is the structural stroma that includes connective tissue such as the meninges, blood vessels, and ducts. The two main types of cells in the brain are neurons, also known as nerve cells, and glial cells, also known as neuroglia. There are many types of neuron, and several types of glial cell.

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