Glial cells

Glial cells of the nervous system are non-neuronal cells of which astrocytes are the most abundant. There are several types of glial cells collectively called neuroglia; (Glial cells of the Central nervous system include - oligodendrocytes, astrocytes, microglia, radial glia, ependymal cells. Glial cells of the Peripheral nervous system include - Schwann cells and Satellite cells). About 70% of the total cell population of the brain and spinal cord are gial cells. Though they are of monocytic origin, they act as macrophages in the brain and are the first cells to respond to injury to the central nervous system (CNS). Their main function is to hold nerve cells in place.

The CNS includes the brain and spinal cord where neurons release “neurotransmitters” across the space between two neurons called the synapses - leading to nerve impulses. It was generally considered that glial cells or astrocytes provide support and do not take part in the neurotransmission. However, it is now known that glial cells produce transmitters named as gliotransmitters that can be recognised by the neurons hence showing that they do participate in transmission.

 

Although the functions of glial cells are still poorly understood, it is believed that the role of glial cells is to provide support to other cells of the brain namely the neurons. For example, it is known that during early development, and neurogenesis, glial cells provide a scaffold for the correct migration and proliferation of neurons. While in adults, gial cells maintain neuronal homeostasis and synaptic plasticity.

In recent years, this view that it provides stability to the nervous system function has drastically changed, as new roles such as roles in the formation of synapses has been identified. In addition to communication, other newly identified roles include; cerebrovascular tone regulation, immune regulation and adult neurogenesis.

References:

Seth P, Koul N. 2008. Astrocyte, the star avatar: redefined. J Biosci. 33: 405

Agulhon C, Petravicz J, McMullen AB, Sweger EJ, Minton SK, Taves SR, Casper KB, Fiacco TA, McCarthy KD. 2008. What is the role of astrocyte calcium in neurophysiology? Neuron. 59: 932