Astrocytes are part of a diverse group of cells in the nervous system that, unlike neurons, are not capable of producing action potentials or nerve impulses. They therefore lack axons and dendrites designed to transmit and receive them. This group of cells in nervous tissue are glial cells, also called neuroglia or simply glia.

Glia is present in animals, from the simplest invertebrates to humans. It seems that throughout evolution the glia have been diversifying and specializing until they are a key element in the processes of integrating and processing signals to develop responses that, until very recently, we always believed were exclusive tasks of neurons.

Much less known than neurons, and confined to the central nervous system without direct communication with the outside world, these cells began to intrigue scientists since Golgi techniques for staining tissue samples made them visible under the light microscope, in the middle of the 19th century. XIX century. In 1899 Santiago Ramón y Cajal began to ask himself “What functional significance should we give to neuroglia?” [2], because even then he doubted that they simply played that filler role that had led one of the fathers of cell theory, Rudolph Virchow (1821-1902), to give them the name nervenkitt (“nerve glue” in 1846). German) and later glia (glue in Greek). In his “nutritive theory” of him, Golgi considered that they only gave “logistical support” (food, support structure) to the neurons, but Cajal imagined them with much more prominence (and time has proven him right 😉).

At the end of the 19th century Cajal could only “make more or less rational conjectures”, because the lack of methods left the physiologist “totally disarmed”[2]. However, the development of new tools since the 1980s has allowed neuroscientists today to have an arsenal of techniques to unravel the secrets of neuroglia: the patch-clamp (to record the electrical activity of excitable cells). that produce a small electrical current when stimulated), fluorescent probes (to detect, localize and quantify the dynamics that occur at the cellular scale, thanks to molecules that generate fluorescence signals [3]), new microscopy techniques (confocal, multiphoton…) and, of course, the new techniques of molecular biology and genetic editing.
These scientific-technological advances have shown that Cajal’s intuition was good. Without taking away the morphological and functional prominence of the neuron, today we know that glia orchestrate a series of essential functions for the development and proper functioning of the nervous system, and new roles are increasingly being discovered in pathological situations or even related to processing. and the integration of information that neurons make. Divided into two types, microglia (of non-nervous origin) and macroglia (with the same embryonic origin as neurons), glial cells are no longer extraneous and are now as important players in the functioning of the nervous system as neurons.

1. STRUCTURAL FRAME. Astrocytes participate in the physical structuring of the brain and play a secondary mechanical support role.
2. PROTECTION. The endfeet of astrocytes form a continuous layer that surrounds the blood vessels at the periphery of the central nervous system, thereby contributing to the blood-brain barrier that separates blood from the extracellular brain fluid in the central nervous system. Here astrocytes prevent the passage of substances potentially dangerous to the brain and allow access to others, such as water, oxygen or small fat-soluble substances. Recently, the glymphatic system has been discovered, a brain drainage pathway that depends on the proper functioning of neuroglia and especially astrocytes.
3. METABOLIC REGULATION AND ANTIOXIDANT ACTION. Astrocytes are responsible for controlling the amount of substances present in the environment of neurons so that they function correctly and generate clean signals. Specifically, they control pH, potassium (K+) and calcium (Ca2+) levels, capture free radicals (thanks to glutathione), and intervene in the recycling metabolism of neurotransmitters (for example, toxic excess glutamate is absorbed). incorporates glutamate/glutamine into the cycle).
4. ENERGY METABOLISM. Astrocytes manage their cytoplasmic glycogen reserve to maintain it at levels that allow them to cope with the demand for glucose in periods of high neuronal activity. They can also be responsible for transforming glucose into lactate available to the neuron (for the Krebs cycle).
5. CONTROL AND REGULATION OF BLOOD FLOW that reaches the brain and neurons to provide them with the necessary oxygen (O2). The local increase in blood flow supplies more oxygen and nutrients to active brain regions that need more energy.

6. MODULATION OF NEURONAL ACTIVITY. Astrocytes regulate the formation, maturation, maintenance and stability of synapses so that they function correctly, thereby maintaining the connectivity of neuronal circuits, such as those associated with learning and memory. Thus, astrocytes intervene in how the nervous information handled by neurons is processed.

7. REGULATION OF SYNAPSES. In gray matter, astrocytes are closely associated with neuronal membranes, especially in synaptic areas. This is where the terminal feet completely or partially envelop the presynaptic terminals and postsynaptic structures, forming the tripartite synapse.

8. NEURONAL DEVELOPMENT AND PLASTICITY. Astrocytes play an important role in the embryonic development of nervous tissue, and are responsible, for example, for guiding axonal growth or helping neurons and other nerve cells reach the places in the cerebral cortex where they should be.

9. COORDINATION OF MYELIN PRODUCTION. Astrocytes are responsible for transforming adenosine triphosphate (ATP) [11] that releases the electrical activity of neurons into a protein that stimulates the production of myelin in oligodendrocytes.

10. DEFENSE. Astrocytes are involved in inflammatory processes of immunological reactivity of the brain. In response to brain injuries and thanks to a certain capacity to generate an immune response (astrocytes are immunocompetent), they participate with microglia in the formation of the glial scar.

Incredible true? You’re probably thinking that these astrocytes are extraordinary nerve cells that deserve a toast… with the best glasses in the neurodeck!