Are neurons the only kind of cell in the brain?

In this brief guide, we are going to answer the question ”Are neurons the only kind of cell in the brain?” Let’s discover what’s inside our brain!

Are neurons the only kind of cell in the brain?

No, the neurons are not the only kind of cell in the brain. The brain is a puzzle made up of different types of cells. The most common is the neuron. However, there is another type of cell but less popular, known as glia.

The brain is the computer that controls the human being. The ability to perceive our environment through smell, sensation, touch, taste and sight is the response given by our brain and the tissues that compose it.

It’s common to think of neurons when talking about the brain and its tissues. Neurons were the fundamental structure that helped us understand how our mind works, the way we feel, think, act and move.

The neuron is the principal cell that makes up the brain’s nervous tissue having the function of being responsible for receiving and transmitting information through nerve impulses. However, these cells wouldn’t be able to carry out this work if it weren’t for their partners the glial cells.

At the end of the 19th century, Santiago Ramon, father of modern neuroscience discovered two types of cells in histological exams; neurons and glial cells. 

Glial cells, unlike neurons, are smaller and more numerous cells. The human has 86 million neurons and approximately 20-40 million glial cells.

Glial cells are as important as a neuron. Glial cells don’t transmit nerve impulses. It’s in charge of sustaining, isolating, nourishing and defending neurons to ensure their survival because, as is known, once a neuron dies doesn’t regenerate.

Neurons Structure

All neurons have three essential parts; 

• Cell body or soma; Is a spherical zone of the neuron that contains the nucleus
• Dendrites; Are terminal branches present in neurons that guarantee the reception of nerve impulses that arrive from an axon.
• Axon; It’s a thin neural stretch that conducts electrical impulses away from the cell body of the neuron or soma.

Are there different types of neurons?

In the nervous system, neurons are divided into three classes; sensory neurons, interneurons and motor neurons.

Sensory Neuron

A sensory neuron or afferent neuron is a cell activated by external information such as light, sound and temperature, to be processed by the CNS (Central Nervous System) and gives a response. At the same time sensory neurons can be classified in; 

• Gustatory. 
• Thermoreceptors.
• Mechanoreceptors.
• Olfactory.
• Nociceptors.
• Proprioceptors.
• Photoreceptors. 

For example, when we touch a hot pot with our hands; we immediately withdraw our hands due to the heat we perceive. This reflex occurred for the thermoreceptor neurons located in our skin which are responsible for the human capture of different temperatures.

Interneurons

Interneurons or associative neurons are the most common type of neuron. Working as a kind of bridge. In charge of connecting motor neurons with sensory neurons. Participating in the processing and retention of information. Ubicated in the brain and spinal cord.

For example, if we touch a hot pot, sensory neurons on our hand, send a signal to interneurons in our spinal cord. And others interneurons transmit a signal to the motor neurons in our hand, allowing us to move away from the hot pot.

Motor Neuron

Motor neurons, also known as motoneuron, are a group of neurons localized in the CNS (Central Nervous System) with the mission of sending a series of nerve impulses to the glands or muscles or glands.

Structure of Glial cells

The name Glial, in Latin, means ”glue” name awarded by the pathologist Rudolf Virchow, he said that the glia was a kind of adhesive that joined neurons to form nervous tissue. However, unlike neurons, glial cells do not have axon and dendrites.

Are there different types of Glial cells?

There are two types of glial cells in the central nervous system (CNS) and peripheral nervous system (PNS) of humans; these are; microglia and macroglia. 

The microglia are white blood cells (phagocytes) that appear in conditions of damage or diseases of the nervous tissue, protecting against microorganisms (bacteria, viruses and parasites) and also helping reducing inflammations through the release of anti-inflammatory cytokines.

There are three types of macroglial cells; 

• Oligodendrocytes: Are small cell bodies with some thin extensions; there are no filaments in its cytoplasm. It’s found exclusively in the central nervous system, that is, in the brain and spinal cord. 

They have the function of creating myelin sheaths around the axons of neurons, isolating them and increasing the speed of transmission of the electrochemical impulses that run through them.

• Astrocytes: They are star-shaped cells with numerous extensions, the nucleus is light, and the cytoplasm contains glycogen granules. The astrocytes are in the central nervous system (brain and spinal cord) playing supporting roles concerning neurons.
• Ependymal cells: Are cells involved in creating cerebrospinal fluid (CSF). Ubicated in the spinal cord and ventricles.
• Radial glia: The radial glia has a bipolar morphology that extends throughout the cerebral and cerebellar cortex. These cells have the function of serving as a structural pillar contributing to the development of the nervous system.
• Schwann cells: They’re a type of glial cell in the peripheral nervous system that help form the myelin sheath around nerve fibres.
• Satellite cells: Glial satellite cells are glial cells that cover the surface of nerve cell bodies in the sensory, sympathetic, and parasympathetic ganglia.

Do neurons and glial cells communicate?

Glial cells have been little studied in the communication and information processing of the nervous system (SN) because they have long been considered as simple elements of the structural support of neurons. 

However, in recent years numerous studies have implicated glial cells in different processes required for the proper functioning of the nervous system. 

Glial cells are involucrated in the proliferation, migration, and differentiation of neuronal precursors, as well as in synaptogenesis and myelination, during NS development. 

Glial cells in the adult can control the intensity or strength of synaptic activity; they can change the membrane potential that occurs when postsynaptic neurotransmitter receptors are activated, they can also participate in information processing by coordinating the activity between groups of neurons. 

Conversely, neurons can also regulate a wide range of glial activities such as proliferation, differentiation, and myelination.

How did we discover there were cells in our brain?

It was in 1665 that Robert Hooke, designer of magnifying glasses, first observed cells.

In 1831, the botanist Robert Brown, observing plant tissues, discovered the nucleus of the cell, an internal circular structure.

In 1838 Matthias Jacob Schleiden launched a cell theory; All plants are made up of cells, the structural unit. Theodor Schwann extends this theory to all living things.

The first microscopic image of a nerve cell, with its nucleus and nucleolus, was published in 1836, by Gabriel Gustav Valentin. A year later, Jan Evangelista Purkinje presented for the first time the layered cytoarchitecture of a region of the nervous system.

In 1873, Camillo Golgi developed the method that he became known as the  ´´reazione nera ’’ (black reaction). The technique is based on the use of potassium dichromate and silver nitrate, which reacts to form opaque intracellular silver chromate deposits. Applied to histological preparations, it allows the visualization in black of sets of nerve cells, their components and branches in three dimensions. Using the same preparation.

In 1886, Golgi published several works, using his staining method. In them, he supported the reticular theory. He observed the ramifications of the axons and dendrites.

In 1846, Rudolf Virchow observed cells in the walls of the cerebral ventricles and postulated in one of the most famous science books of the 19th century, that the brain contained a second population of cells, different from neurons. He thought they were part of a Bindegewebe (connective tissue) and called them glia or Nervenkitt. 

In 1888 Santiago Ramon said that each nerve cell is an absolutely autonomous physiological unit.

In 1906 the neural theory was the most accepted within academic circles. However, the discussion was not settled and there was not yet a demonstration so strong that it defeated that of its detractors. Thus, when the winner of the Nobel Prize had to be chosen, there was no agreement on a clear winner.

In 1955 that issue could be settled. The creation of the electron microscope and the improvements in the processes to prepare the tissues for study allowed Palay and Palade to take an electron photomicrograph where the synapse of a neuron could be observed. The distance between neurons was only 20 nanometers. The neural theory was correct.

Are neurons the only kind of cell in the brain?

No, the neurons are not the only kind of cell in the brain, in the year 1846 the pathologist and biologist Rudolf Virchow affirmed the existence of another type of cell different to the neuron.

The scientists thought the glial cells didn’t fulfil an important role as neurons making it less popular or known, over the years this belief was collapsed. 

Currently, it is known that glial cells are as important as a neuron, glial cells don’t transmit nerve impulses as neurons but without the help and existence of these cells the neuron would be unable to perform its function and that means that even the nervous system wouldn’t exist.

FAQS: Are neurons the only kind of cell in the brain?

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References

‌Jäkel, S., & Dimou, L. (2017). Glial Cells and Their Function in the Adult Brain: A Journey through the History of Their Ablation. Frontiers in Cellular Neuroscience, 11. 

Jessen, K. (2004). Glial Cells. The International Journal of Biochemistry & Cell Biology, 36(10), 1861-1867.

Penttila, N. (2019, August 8). Cells of the… Retrieved September 15, 2020, from Dana Foundation website: https://www.dana.org/article/cells-of-the-brain/

Von Bartheld, C., Bahney, J., & Herculano-Houzel, S. (2016). The search for true numbers of neurons and glial cells in the human brain: A review of 150 years of cell counting. Journal of Comparative Neurology, 524(18), 3865–3895. 

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