Notes on Glial cells

Neurons are not the only cells in the brain. Although the brain contains between 86 and 100 billion neurons, it also contains roughly the same number of glial cells. Glial cells, also known as neuroglia, are cells that surround and support the neurons of the central nervous system and the peripheral nervous system. They do not carry nerve impulses (action potentials), but they do perform a variety of important functions. Neurons would not function properly without them.

Glia help neurons in maintaining homeostasis, forming myelin in the peripheral nervous system, and providing support and protection. Glial cells comprise oligodendrocytes, astrocytes, ependymal cells, and microglia in the central nervous system, and Schwann cells, and satellite cells in the peripheral nervous system. 

Glia is derived from the Greek word for “glue,” as these cells were originally thought to serve only as supporting structures for neurons. 

Types of Glial Cells and their functions

CNS and PNS of the brain contain a variety of glial cell types. They represent various functions in the body.

Glial cells are classified into six types, as listed below:

Astrocytes

Astrocytes are the brain’s most abundant type of cell and can be found in the nervous system. Astrocytes are distinguished by their unique star shape. 

There are two types of astrocytes: protoplasmic and fibrous. Protoplasmic astrocytes are found in the grey matter of the cerebral cortex, whereas fibrous astrocytes are found in the white matter of the brain.

Functions

• The principal objective of astrocytes is to enable structure and metabolism to help the neurons.
• Though they do not indicate on their own, astrocytes assist in transmission among nerve cells and central nervous system arteries in order to control the intensity of blood flow.
• They also serve to hold glucose, offer additional nutrition, control ionic strength, and assist in neuron repair.

Ependymal Cells

Ependymal cells are essential cells found in the ventricles of the brain and core line of the spine. They are found in the meninges’ extravascular space.

Functions

• The epithelial tissue blood vessels are lined with microvilli.
• Ependymal cells are responsible for production of CSF, the availability of nutrient content to neurons, filtration of toxic products, and the dissemination of neurotransmission.

Microglia

Microglia are central nervous system cells.

Functions

• They remove cellular waste and defend against the invasion of harmful microorganisms such as bacteria, viruses, and parasites.
• As a result, microglia are thought to be a type of macrophage, which is a white blood cell that protects the body from foreign matter.
• They also aid in the reduction of inflammation in the body by releasing anti-inflammatory chemical signals.
• Microglia also protect the brain by deactivating malfunctioning neurons that become injured or diseased.

Satellite Cells

Satellite glial cells are glial cells that are responsible for covering and protecting neurons in the peripheral nervous system.

Functions

• They help sensory, sympathetic, and parasympathetic nerves by providing structure and metabolic support.
• Sensory satellite cells are frequently associated with pain and, in some cases, the immune system.

Oligodendrocytes

Oligodendrocytes are central nervous system structures.

Functions

• They form the myelin sheath by wrapping around some neuronal axons. The myelin sheath, which is made up of lipids and proteins, acts as an electrical insulator for axons and promotes faster nerve impulse conduction.
• The majority of oligodendrocytes are found in the white matter of the brain, but satellite oligodendrocytes are found in the grey matter.
• Myelin does not form in satellite oligodendrocytes.

Schwann Cells

Schwann cells are neuroglia that form the myelin sheath in peripheral nervous system structures.

Functions

• Schwann cells aid in nerve signal conduction, regeneration, and antigen recognition by T cells. Schwann cells are essential in nerve repair.
• These cells move to the injury sites and release growth factors that help in promoting nerve recovery, and then myelinate newly generated nerve axons.
• Schwann cells are being studied extensively for their potential use in spinal cord injury repair.

Importance of glial cells

• Glial cells are important because of their structural diversity and functional versatility. 
• They have the ability to change the behaviour of firing neurons despite their inability to discharge electrical impulses.
• Glial cells guide early brain development and keep their fellow brain cells healthy throughout life. 
• They have a glymphatic pathway that functionally represents the brain’s lymphatic system.
• Glia are more than just structural fillers; as their name implies (Greek for glue), they help hold things together.
• Glia are functionally the brain’s other half, according to researchers.

Conclusion

Neuroglia are non-neuronal cells of the nervous system. They are also known as glia or glial cells. They form a robust support system that is critical to the proper functioning of nervous tissue and the nervous system. Glial cells, unlike neurons, lack axons, dendrites, and the ability to conduct nerve impulses. Neuroglia are three times more numerous in the nervous system than neurons and are typically smaller.

Glia plays several roles in the nervous system, including physically supporting the brain, assisting in nervous system development, repair, and maintenance, insulating neurons, and providing metabolic functions for neurons.