Brain cell
Brain cells are the fundamental units of the brain, primarily categorized into two types: neurons and glial cells (glia). Neurons serve as the main communicators, transmitting electrochemical signals that facilitate brain functions and coordinate responses throughout the body. These specialized cells have distinct structures, including a soma (cell body), axons (long extensions for signal transmission), and dendrites (branch-like structures for receiving signals). There are various neuron types, such as motor neurons, sensory neurons, and interneurons, each with specific roles in processing and relaying information.
In contrast, glial cells, which outnumber neurons by a significant margin, provide essential support functions, contributing to the health and efficiency of neurons. They do not transmit signals like neurons but play crucial roles in maintaining the brain's environment, insulating axons, and assisting nutrient delivery. Key types of glia include astrocytes, which help hold neurons in place and support their functions, and microglia, which serve as the brain's immune defense. Recent research has expanded our understanding of glial cells, suggesting they may play a more significant role in brain function than previously recognized. Overall, the intricate relationship between neurons and glial cells is vital for the brain's operations and overall health.
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Brain cell
Brain cells are the small units, or cells, that make up the brain. There are two main types of brain cells: neurons and glia (glial cells). Each has a different structure and function. Neurons are the main brain cells, while glia provide support for the functions of the neurons. There are several different types of neurons and glia, each of which performs different tasks in the complicated workings of the brain and spinal cord.
Background
A human brain has about one hundred billion neurons, or cells that send and receive signals from the brain and the nervous system. There are also several trillions of glia, or helper cells that make it possible for the neurons to perform their tasks and to help protect the neurons. It has only been within the past two centuries that scientists were able to begin to study brain cells and how they function.
Scientists in the nineteenth century knew that living matter was made up of small parts called cells that were each a small self-contained unit of the organism. However, at that time, researchers lacked the equipment and technique to examine brain cells in the same way as other cells. Unlike other cells that seemed to be individual blocks, brain cells under the microscopes of the time seemed to be tangled in a web of long tendrils. This led scientists to adopt a theory put forth by German anatomist Joseph von Gerlach that the brain and spinal cord were made of a web, or reticulum, instead of individual cells.
It took the development of a new technique for making the cells visible in 1873 for researchers to realize that the brain was a series of individual cells, like all other living matter, but that the cells did have long extensions. This new technique for staining some cells with a chemical to make them more visible was developed by Italian physician Camillo Golgi. It paved the way for physicians to study brain cells and determine that there were several types of cells with different functions and designs.
Overview
Neurons are the functional cells of the brain. They send and receive electrochemical signals that determine not only the function of the brain but also the functions and responses of other parts of the body. This ability to transmit electrochemical signals over distances of several feet within the body and the way they communicate are what differentiate neurons from other cells in the body.
There are three main parts to a neuron. These are the soma, the axon, and the dendrites. The soma is the main cell body, which contains the nucleus and cell deoxyribonucleic acid (DNA), as well as all the parts the cell needs to function. The axons are the long tendrils that made the nineteenth-century scientists think there were no individual brain cells. These axons carry the electrochemical signals and pass them along from cell to cell. There are two types of axons: myelinated and non-myelinated. Myelin is an insulator made of protein and fat. The main brain and spinal cord are made up of non-myelinated cells, while the neurons of the peripheral nervous system—the part farther away from the brain—include myelinated axons. Finally, dendrites are the very ends of the cells. They have fine tendrils that help make the connections between cells and also detect changes in the environment around the cells.
Neurons come in different shapes and sizes, depending on their function. Some are very small, while others can have axons a foot long or more. There are four main shapes of neurons: unipolar, bipolar, multipolar, and pyramidal.
These neurons can perform a number of different functions. Motor neurons transmit signals to the furthest parts of the body, such as the skin, muscles, and glands, while sensory neurons bring information to the brain from other parts of the body. For example, sensory neurons detect that a person is touching something hot and motor neurons tell the person to pull back his or her hand. Interneurons help the various parts of the brain and spinal cord communicate with each other. In 2015, researchers uncovered six previously unknown types of interneurons that seem to develop as the brain ages.
For each neuron in the brain, there are an estimated ten to fifty times as many glia. They make up about 90 percent of the brain. Glia are helper cells that support the function of the neurons. These cells differ from neurons in several ways. First, they do not have axons and dendrites, therefore, do not function in the same way as neurons. They also do not have neurotransmitters that send and receive the electrochemical signals like neurons. However, the glial cells provide a number of key functions that help neurons complete their functions.
For example, Schwann glial and oligodendroglia cells make up the myelin that insulates the axons. This insulation helps the axons transmit their signals up to thirty times faster than they could without it. Astrocytes, or astroglia—so named for the Greek word astron, or "star," because of their star shape—help hold neurons in place. They also help nutrients reach the neurons and assist with the removal of dead parts of neurons. Twenty-first-century scientists have discovered that astrocytes have more ability to communicate than was previously thought, and may play a larger role in the function of neurons than was previously believed.
Another type of glial cell, microglia, play a role in helping to keep neurons healthy. These cells, which only appear in the brain, serve an important immune function by protecting the brain from bacteria and viruses, and by removing dead, damaged, or infected neurons. Microglia also send out a signal to indicate the potential for trouble in that area of the brain; they incorporate portions of the damaged neuron on their own outer surface to alert other neurons of the need for repair or replacement. Scientists continue to investigate the function of glial cells; some think these cells could be the origin of imagination.
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