There are various kinds of cells present inside the human brain. In this article, we will examine the differences between two types of such cells- neurons and neuroglia.
The neuron is a fundamental unit in the neural system of humans.
Neurons have the metabolic machinery characteristic to somatic cells of other types. They have a nucleus and all other organs that are necessary for a normal cellular life.
Yet, in some other respects, neurons are distinct:
- Neurons show a vast diversity in their morphology, which signifies the diversity in functioning as well, because in the central nervous system the form, structure, and the functions of the components are closely related.
- Neurons are distinct for their unique bioelectrical properties. However, in the human organism, some somatic cells have similar bioelectrical properties, for example, cells that are responsible for generating electrical activity inside muscle cells.
- Neurons are characterized by specialization in intercellular communication. For most neurons in the matured central nervous system, this involves a secretion of special chemical molecules called neurotransmitters. There are other secretory cells in the human organism, but neurons are far more intricate than most of those.
The structure of a neuron:
1. Input zone, which consists of:
- Dendrites -one of the sets of extensions that grow out in different directions from the cell body. They are very short, around 200 microns in length. They are very important for the microanatomy of the neuron because they extend the cell’s surface area, which allows it to receive input from other neurons.
- Cell bodies. They contain all the organelle essential for the cell’s normal functioning. Organelles are abundant, which allows neurons to maintain their morphology; they also provide the support for neurons’ functions, for example, for the synthesis of proteins and molecules, and for the support of energy supply which is necessary for the functioning of neurons within their homeostatic states.
2. The conducting zone of neurons includes axons, which are plasmic extensions that allow neurons to generate electrical signals, which are known as action potential. Axons can be from several nanometers in length to up to half a meter, extending through a whole body. Action potential propagates from the cell body towards the terminal ending of the axon.
3. Output zone. At the ends of the axons, there is a synaptic terminal, which consists of synapses. They can be viewed as specialized contacts that allow one neuron to transfer the signal to another.
Synapses come in two varieties:
- Electrical synapses. These have special junctions that allow charged molecules to move directly from one neuron to another and thus convey the electrical signal.
- Chemical synapses. There is a space, also known as a synaptic cleft, in which a chemical, called a neurotransmitter, which was synthesized in one neuron, passes to another neuron by diffusing across this space and interacting with receptors in another. Essentially, this is a chemical message that mediates an electrical message from one neuron to another.
Neuroglia, or glial cells, are sometimes also referred to as glia. They provide a variety of functions for brain tissue. They support the metabolic and signaling functions of neurons.
Certain types of neuroglia are specialized in making myelin, of which the myelin sheath consists, and which serves as an insulation around axons, aiding significantly the propagations of electrical signals along axons. You can see the myelin sheath on the first picture with neuron structure.
Neuroglia also contribute to the organization and formation of a barrier between the blood and the brain.
The other function of neuroglia is participation in creating an inflammatory response in injured neural tissues, including phagocytosis of cellular debris.
Yet other kinds of neuroglia are responsible for the formation of scar tissue which is a response of the brain in case it or the spinal cord is damaged.
Different types of glial cells:
- Astrocytes. These are found in the grey matter of the brain, and are closely associated with the neuronal cell bodies, dendrites, and synapses. Astrocytes are responsible for taking up and processing neurotransmitters from synaptic clefts, described above.
- Oligodendrocytes. These are found in the white matter of the brain. They primarily responsible for forming myelin. In the peripheral nerve system the analogous cells are called Schwann cells.
They also play a role in presenting antigens which influence the outgrowth of axons in developing and recovering the brain.
One of the peculiar roles of this type of cells is that they are subject to immunological attack in diseases of the central nervous system, for example, multiple sclerosis.
- Microglial cells. These cells are a special type known as mononuclear phagocytes. These cells are derived from the cells that migrate into the brain during early embryonic development.
- Microglia cells are of two types – ramified and amoeboid. The former are initially in a dormant state, they wait until the injury is present in the organism. In the event of injury, they convert in the amoeboid cells, they are activated and ready to help fight with injuries.
- Glial stem cells. These are non-mature cells, which have the capacity to multiply and to differentiate. They are often found adjacent to blood vessels. They can mature to any form of the abovementioned neuroglia, and even to neurons.
In terms of their main function, neurons are primarily responsible for processing of neural signals. Neuroglia, on the other hand, support the electrical and chemical functions of neurons, which often involve simultaneous electrical and chemical processes.
Neurons are organized in circuits, while neuroglia participate in the formation of these circuits and in a variety of forms of synaptic plasticity (these processes are being investigated by a relatively new field of studies in neurobiology).
Neurons are surrounded by extracellular fluids, while neuroglia help maintain the ionic balance of these fluids, which is crucial for the capacity of the neurons to generate and maintain the electrical signaling.
|Are responsible for processing neural signals||Are responsible for support of electrical and chemical functions of neurons|
|Are organized in circuits||Participate in making new synaptic connections in the brain and in maintaining synaptic plasticity|
|Generate electrical signaling with the help of ionic balance in extracellular fluids||Maintain ionic balance of fluids that surround neurons|
In this video you can see a lecture on the basics of the human nervous system; you can also learn about the differences between neurons and neuroglia: