Brain cell

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Brain cell
Neuron Cell Body.png
Illustration of a neuron, microtubules shown as they enter the axon, and seen enclosed in a myelin sheath.
Anatomical terms of microanatomy

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. [1] There are many types of neuron, and several types of glial cell.

Contents

Neurons are the excitable cells of the brain that function by communicating with other neurons and interneurons (via synapses), in neural circuits and larger brain networks. The two main neuronal classes in the cerebral cortex are excitatory projection neurons (around 70-80%) and inhibitory interneurons (around 20–30%). [2] Neurons are often grouped into a cluster known as a nucleus where they usually have roughly similar connections and functions. [3] Nuclei are connected to other nuclei by tracts of white matter.

Glia are the supporting cells of the neurons and have many functions not all of which are clearly understood, but include providing support and nutrients to the neurons. Glia are grouped into macroglia – astrocytes, ependymal cells, and oligodendrocytes, and much smaller microglia which are the macrophages of the central nervous system. Astrocytes are seen to be capable of communication with neurons involving a signalling process similar to neurotransmission called gliotransmission. [4]

Cell types

Purkinje cells in the cerebellum All that glitters in the brain.jpg
Purkinje cells in the cerebellum

Brain cell types are the functional neurons, and supporting glia.

Neurons

Neurons, also called nerve cells, are the functional electrically excitable cells of the brain. They can only function in collaboration with other neurons and interneurons in a neural circuit. [1] There are an estimated 100 billion neurons in the human brain. [1] Neurons are polarised cells that are specialised for the conduction of action potentials also called nerve impulses. [1] They can also synthesise membrane and protein. Neurons communicate with other neurons using neurotransmitters released from their synapses, and they may be inhibitory, excitatory or neuromodulatory. [5] Neurons may be termed by their associated neurotransmitter such as excitatory dopaminergic neurons and inhibitory GABAergic neurons. [5]

Cortical interneurons only make up around a fifth of the neuronal population but they play a major role in modulating cortical activity needed for cognition and many aspects of learning and memory. Cortical interneurons vary in shape, molecular make-up, and electrophysiology; they function collectively to maintain the balance between excitation and inhibition in the cortex primarily through the use of GABA. Disruption of this balance is a common feature of neuropsychiatric disorders such as schizophrenia. A cause of the disruption can occur in prenatal development through the exposure to chemicals and environment. [6]

In the cerebral cortex different neurons occupy the different cortical layers and include the pyramidal neurons and rosehip neurons. In the cerebellum Purkinje cells and interneuronal Golgi cells predominate.

Glia

Types of glial cell 1209 Glial Cells of the CNS-02.jpg
Types of glial cell

Glial cells are the supporting cells of the neurons. [1] The three types of glial cells are astrocytes, oligodendrocytes, and ependymal cells, known collectively as macroglia, and the smaller scavenger cells known as microglia. Glial stem cells are found in all parts of the adult brain. [1] Glial cells greatly outnumber neurons and apart from their supporting role to neurons, glia – astrocytes in particular have been acknowledged as being able to communicate with neurons involving a signalling process similar to neurotransmission called gliotransmission. [4] They cannot produce an action potential as generated by a neuron but in their large numbers they can produce chemicals expressing excitability that exert an influence on neural circuitry. [7] [4] The star-like shape of the astrocyte allows contact with a great many synapses. [7]

Related Research Articles

<span class="mw-page-title-main">Neuron</span> Electrically excitable cell found in the nervous system of animals

A neuron, neurone, or nerve cell is an excitable cell that fires electric signals called action potentials across a neural network in the nervous system. Neurons communicate with other cells via synapses, which are specialized connections that commonly use minute amounts of chemical neurotransmitters to pass the electric signal from the presynaptic neuron to the target cell through the synaptic gap.

<span class="mw-page-title-main">Nervous system</span> Part of an animal that coordinates actions and senses

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 that impact the body, then works in tandem with the endocrine system to respond to such events. Nervous tissue first arose in wormlike organisms about 550 to 600 million years ago. In vertebrates, it consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord. The PNS consists mainly of nerves, which are enclosed bundles of the long fibers, or axons, that connect the CNS to every other part of the body. Nerves that transmit signals from the brain are called motor nerves (efferent), while those nerves that transmit information from the body to the CNS are called sensory nerves (afferent). The PNS is divided into two separate subsystems, the somatic and autonomic, nervous systems. The autonomic nervous system is further subdivided into the sympathetic, parasympathetic and enteric nervous systems. The sympathetic nervous system is activated in cases of emergencies to mobilize energy, while the parasympathetic nervous system is activated when organisms are in a relaxed state. The enteric nervous system functions to control the gastrointestinal system. Nerves that exit from the brain are called cranial nerves while those exiting from the spinal cord are called spinal nerves.

The development of the nervous system, or neural development (neurodevelopment), refers to the processes that generate, shape, and reshape the nervous system of animals, from the earliest stages of embryonic development to adulthood. The field of neural development draws on both neuroscience and developmental biology to describe and provide insight into the cellular and molecular mechanisms by which complex nervous systems develop, from nematodes and fruit flies to mammals.

<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, 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">Glia</span> Support cells in the nervous system

Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system and 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. They maintain homeostasis, form myelin in the peripheral nervous system, and provide support and protection for neurons. In the central nervous system, glial cells include oligodendrocytes, astrocytes, ependymal cells and microglia, and in the peripheral nervous system they include Schwann cells and satellite 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">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">Basket cell</span>

Basket cells are inhibitory GABAergic interneurons of the brain, found throughout different regions of the cortex and cerebellum.

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">Stellate cell</span> Star-shaped neurons in the central nervous system

Stellate cells are neurons in the central nervous system, named for their star-like shape formed by dendritic processes radiating from the cell body. These cells play significant roles in various brain functions, including inhibition in the cerebellum and excitation in the cortex, and are involved in synaptic plasticity and neurovascular coupling.

<span class="mw-page-title-main">Golgi cell</span>

In neuroscience, Golgi cells are the most abundant inhibitory interneurons found within the granular layer of the cerebellum. Golgi cells can be found in the granular layer at various layers. The Golgi cell is essential for controlling the activity of the granular layer. They were first identified as inhibitory in 1964. It was also the first example of an inhibitory feedback network in which the inhibitory interneuron was identified anatomically. Golgi cells produce a wide lateral inhibition that reaches beyond the afferent synaptic field and inhibit granule cells via feedforward and feedback inhibitory loops. These cells synapse onto the dendrite of granule cells and unipolar brush cells. They receive excitatory input from mossy fibres, also synapsing on granule cells, and parallel fibers, which are long granule cell axons. Thereby this circuitry allows for feed-forward and feed-back inhibition of granule cells.

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">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">Chandelier cell</span>

Chandelier cells or chandelier neurons are a subset of GABAergic cortical interneurons. They are described as parvalbumin-containing and fast-spiking to distinguish them from other subtypes of GABAergic neurons, although some studies have suggested that only a subset of chandelier cells test positive for parvalbumin by immunostaining. The name comes from the specific shape of their axon arbors, with the terminals forming distinct arrays called "cartridges". The cartridges are immunoreactive to an isoform of the GABA membrane transporter, GAT-1, and this serves as their identifying feature. GAT-1 is involved in the process of GABA reuptake into nerve terminals, thus helping to terminate its synaptic activity. Chandelier neurons synapse exclusively to the axonal initial segment of pyramidal neurons, near the site where action potential is generated. It is believed that they provide inhibitory input to the pyramidal neurons, but there is data showing that in some circumstances the GABA from chandelier neurons could be excitatory.

Neuroregeneration involves 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">Ganglionic eminence</span>

The ganglionic eminence (GE) is a transitory structure in the development of the nervous system that guides cell and axon migration. It is present in the embryonic and fetal stages of neural development found between the thalamus and caudate nucleus.

An autapse is a chemical or electrical synapse from a neuron onto itself. It can also be described as a synapse formed by the axon of a neuron on its own dendrites, in vivo or in vitro.

<span class="mw-page-title-main">Glomerulus (cerebellum)</span>

The cerebellar glomerulus is a small, intertwined mass of nerve fiber terminals in the granular layer of the cerebellar cortex. It consists of post-synaptic granule cell dendrites and pre-synaptic terminals of mossy fibers.

References

  1. 1 2 3 4 5 6 Purves, Dale (2012). Neuroscience (5th ed.). Sunderland, Mass. pp. 8–10. ISBN   9780878936953.{{cite book}}: CS1 maint: location missing publisher (link)
  2. ↑ Riedemann, T (17 June 2019). "Diversity and Function of Somatostatin-Expressing Interneurons in the Cerebral Cortex". International Journal of Molecular Sciences. 20 (12): 2952. doi: 10.3390/ijms20122952 . PMC   6627222 . PMID   31212931.
  3. ↑ Purves, Dale; Augustine, George J.; Fitzpatrick, David; Hall, William C.; LaMantia, Anthony-Samuel; White, Leonard E. (2012). Neuroscience (5th ed.). Sunderland, MA: Sinauer Associates, Inc. p. 15. ISBN   9780878936953.
  4. 1 2 3 Mederos, S; Perea, G (October 2019). "GABAergic-astrocyte signaling: A refinement of inhibitory brain networks". Glia. 67 (10): 1842–1851. doi:10.1002/glia.23644. PMC   6772151 . PMID   31145508.
  5. 1 2 Squire (2013). Fundamental neuroscience (Fourth ed.). Amsterdam. pp. 41–47. ISBN   9780123858702.{{cite book}}: CS1 maint: location missing publisher (link)
  6. ↑ Ansen-Wilson, LJ; Lipinski, RJ (January 2017). "Gene-environment interactions in cortical interneuron development and dysfunction: A review of preclinical studies". Neurotoxicology. 58: 120–129. doi:10.1016/j.neuro.2016.12.002. PMC   5328258 . PMID   27932026.
  7. 1 2 Perea, G; Araque, A (January 2005). "Synaptic regulation of the astrocyte calcium signal". Journal of Neural Transmission. 112 (1): 127–35. doi:10.1007/s00702-004-0170-7. PMID   15599611. S2CID   23182200.
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