Astrocyte

Astrocytes are cells of the central nervous system (CNS), which means they are located in the spinal cord and brain. They are a type of neuroglia, or specialized cells of the CNS. Astrocytes are the most common type of neuroglia in the brain. These cells play different roles in the CNS, which include sending nutrients to other cells.

Overview

The brain and spinal cord are made up of specialized cells. The most well-known type of specialized CNS cell is the neuron. Neurons are the cells that send messages between the brain and other parts of the body. The other type of specialized cells is neuroglia. Neuroglia help support the neurons in the CNS and are present in roughly similar numbers to neurons in the human brain. Scientists have also learned that neuroglia play other important roles in the CNS, such as helping to generate more neurons and helping to send messages in the brain. The four types of neuroglia found in the CNS are astrocytes, oligodendrocytes, microglial cells, and ependymal cells. Each type plays an important role in supporting neurons and maintaining the health of the CNS.

Astrocytes are among the most abundant glial cells in the brain, though their numbers vary by region and are not consistently greater than neurons overall. These cells get their name from their star shape. They have a cell body that has many thin projections coming out of it. The two main types of astrocytes are protoplasmic and fibrous astrocytes (although additional astrocyte types have also been described in humans). Protoplasmic astrocytes, which are located mostly in the brain's gray matter, help regulate chemicals in the brain that enable it to send signals. These cells are also important because they help form sheets that can surround and protect neurons. Fibrous astrocytes, which grow mostly in the white matter, are important because they can attach to and protect various structures in the brain.

Astrocytes have different jobs in the CNS. One of the most important jobs the astrocyte performs is to help heal injuries that occur in the CNS. Neurons rarely grow in adults. If a neuron dies, a new neuron is unlikely to grow to take its place. For that reason, the neuroglia in the brain have to protect neurons, and they have to remove threats as quickly as possible. When an injury occurs in the CNS, the astrocytes reproduce to create a barrier where the injury occurred. This can help protect other cells in the brain. In addition, astrocytes can send neurons the chemicals and nutrients they need. Astrocytes are also part of the blood–brain barrier maintenance and regulation process, which helps determine what materials can go into and out of the CNS. The cells assist in maintaining homeostasis in the CNS by preventing some harmful materials from entering. Astrocytes also play an active role in communication within the brain by regulating synapses and influencing how neurons send and receive signals.

Although astrocytes are important in maintaining the health of neurons and the CNS, researchers have found that they also play a role in generating new neurons. Most neurons in adults do not regenerate widely, though limited neurogenesis occurs in certain areas of the brain, such as the hippocampus, and scientists have successfully grown new neurons using stem cells. Scientists have found that the new neurons grow much more successfully when astrocytes are present. Scientists hope that growing neurons with stem cells and astrocytes may someday help treat neurodegenerative diseases, such as Alzheimer's disease, and clinical trials using stem cells and astrocytes for treating neurodegenerative diseases are ongoing.

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