When talking about the brain, we immediately begin to think about neurons and their communication networks. It is true, the brain and the nervous system work because the neurons talk to each other, touch each other, exchanging information and playing the role of director in the comedy of life. But what would happen if the glia were missing? In this Psychology-Online article, we will talk precisely about the glial cellsto better understand what they are, the different types and their functions. Let’s look at the definition, classification and characteristics of glial cells.
What are glial cells
Glia, or neuroglia, are the most important cellular component of the nervous system, being 10 to 50 times larger than . The name was introduced in the mid-19th century to indicate the amorphous substance or “nerve cement” that surrounded and supported neurons. Later, the cellular nature of the barrier and the existence of different specialized types were recognized.
By definition, glial cells are a type of cells of the nervous system that make up, together with neurons, the central and peripheral nervous system. Described for the first time by the German physiologist Rudolf Virchow in 1860, they carry out many auxiliary activities to the functioning and survival of neurons, offering them, above all, a mechanical and nutritional support and exercising metabolic control of the intercellular milieu.
Types of glial cells
Just as we can differentiate between various glial cells, we can also find types of glial cells. In the nervous system of vertebrates there are two different types in terms of size and embryonic origin:
Macroglia
The classification of glial cells begins with 3 main types: macroglia and microglia. The macroglia, larger and of neuroectodermal origin, which in the (CNS) includes astrocytes, oligodendrocytes and ependymal cells. The latter are the cellular elements that line the cerebral ventricles and the central spinal canal, where they regulate the production, circulation and resorption of cerebrospinal fluid.
In the (SNP), macroglia is represented by the Schwann cellsequivalent to the central oligodendrocytes and responsible for the formation of the myelin sheaths of the peripheral axons and satellite cells, which delimit the outer surface of the neurons in the spinal ganglia.
Microglia
Microglia, with smaller cells of mesodermal origin, differ from macroglia in size and origin, and represent the population of immunocompetent cells of the central nervous system. The latter have a function similar to that of macrophages and, through the secretion of interleukin, can influence not only the immune response at the level of the nervous system, but also in neuronal activity and reactivity. Microglia represent approximately 10% of the cells of the nervous system and, although present throughout the brain parenchyma, they have a variable density from region to region, reaching the highest concentrations in the hippocampus, basal ganglia, and .
Functions of glial cells
Glial cells, in addition to providing support to neurons, control the internal environment of the brain, participate in the formation of specialized structures such as the blood-brain barrier and the myelin sheath, ensuring the isolation of nerve cells and their protection against foreign agents or trauma. Other functions performed by glial cells are:
- Collect neurotransmitter molecules from the extracellular fluid (many neuroglia are equipped with neurotransmitter receptors).
- Compose the blood-brain barrier which actively controls the passage of nutrients and other molecules from the bloodstream to neurons and vice versa.
- During neurobiological development, some specialized glial cells guide the migration of neurons immature cells to the appropriate places in the brain where they will develop, and support the extension of axons towards their target cells.
The fundamental role of glia in the development and function of the nervous system is also reflected in their involvement in many important neuropathologies. Neuroglia are the source of numerous tumors (called gliomas) of the brain, retina or spinal cord; In fact, in the brain of the adult animal, they face continuous mitotic divisions, which increases the probability of a malignant mutation responsible for uncontrolled proliferation.
After seeing the general functions of glial cells, let’s see what each type of glial cell is used for:
Satellite cells (SNP)
- They surround the cell bodies in the ganglia.
- They regulate the levels of oxygen and carbon dioxide, nutrients and neurotransmitters around the ganglion neurons.
Shwann cells (SNP)
- Wrap around axons in the peripheral nervous system
- Responsible for myelination of peripheral axons
- Participate in damage repair processes
Ependymal cells (CNS)
- They line the ventricles of the brain and the central canal of the spinal cord.
- They contribute to the production, circulation and control of cerebrospinal fluid.
Oligodendrocytes (CNS)
- They myelinate the axons of the central nervous system.
- They provide a structural scaffold.
Astrocytes (CNS)
- They maintain the blood-brain barrier.
- They provide structural support.
- They regulate the concentrations of ions, nutrients and dissolved gases.
- They absorb and recycle neurotransmitters.
- They form scar tissue after an injury.
Microglia (CNS)
- Eliminates waste, cells, residues and pathogens through phagogitosis.
Structure of glial cells
The most abundant type of glial cells, astrocytes, are consisting of numerous excisions that anchor neurons to their blood supply. They are divided into:
- Protoplasmic astrocytes: present in the gray matter and characterized by the presence of short and branched dilations
- Fibrous astrocytes: present in the white matter and characterized by long, subtle cytoplasmic extensions.
- Radial astrocytes: elongated and perpendicular to the ventricular axis.
Astrocytes originate in the ectoderm and differentiate by maturing characteristic morphological structures. In general, The shape of the cells is stellate., with a more or less large cell body depending on the type of astrocyte from which numerous filaments depart that give the cell a digitized appearance. These extroflexions, of variable size and more or less branched, come into contact with brain capillaries, giving astrocytes the ability to interact with the transport of chemicals to the brain.
He Cellular body and the stellate extroflexionscalled pedicelles, can be made up of a variable number of fibrils, called gliofibrilsformed by filaments of small dimensions (approximately 7 nm), gliofilaments, which in turn are characterized by small linear subunits.
Differences between neurons and glial cells
Glia differ from neurons in several ways:
- Neurons have two types of processes; the glia only have one.
- Neurons can generate action potential: Glial cells do not, but they have a resting potential.
- The neurons have synapse that they use; Glia have chemical synapses.
- Neurons do not continue dividing (not the ripe ones, at least); glial cells do.
- Another difference between neurons and glial cells is the amount. There are many more glial cells than neurons (at least 10-50 times more).
This article is merely informative, at Psychology-Online we do not have the power to make a diagnosis or recommend a treatment. We invite you to go to a psychologist to treat your particular case.
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Bibliography
- BRAIN Center (2014). Neuroscienze… per iniziare. Retrieved from: https://www.unibs.it/sites/default/files/ricerca/allegati/Neuroscienze_per%20iniziare_testo%20complementare.pdf
- Dizionario di Medicina (2010). Glia. Retrieved from: https://www.treccani.it/enciclopedia/glia_(Dizionario-di-Medicina)/
- Encyclopedia of Science and Technology (2008). Glial cell. Milan: Mondadori.