The central nervous system (CNS) is one of the divisions of the nervous system, along with the peripheral nervous system. It is made up of the brain (which is divided into: cerebrum, cerebellum and brainstem) and the spinal cord.
The cells that are part of all these structures and that therefore enable their biological, chemical and electrical processes are neurons. Responsible for transmitting electrical and chemical information, they are essential for us to walk, think, interact, feel, etc.
But what else do we know about neurons? What characterizes them and what are their functions? What parts is a neuron divided into? At we resolve all doubts!
What is a neuron?
The word “neuron” comes from the Greek νεῦρον neûron, which means ‘string’, ‘nerve’. Neurons are highly specialized cells that control the voluntary and involuntary functions of the body.
It is a type of cell, and constitutes the main component of the nervous system. Thus, neurons are the cells of the nervous system, although they are not the only ones; Glial cells (astrocytes and Schwann cells) are also part of this system.
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Functions of neurons
What is your function? In a generic way, we can say that neurons are responsible for receiving, processing and transmitting information through two types of signals: chemical and electrical (thanks to the electrical excitability of their plasma membrane).
This electrical excitability that characterizes neurons consists of an ability to conduct nerve impulses throughout the network of the nervous system; It allows them to transmit electrical information to other cells.
Thus, neurons are messengers and communicators of the organism. They transmit nerve impulses to other cells in the body (for example, the muscle cells that allow us to move).
They also perceive and communicate external and internal stimuli, and are able to convert them into an organized response (for example, to danger, heat or cold, etc.). On the other hand, they also allow the storage of information, that is, they allow memories to be created and stored in memory.
How are they created and where?
Neurons are created from stem and progenitor cells, specifically in the subgranular zone (SGZ) of the hippocampus and the subventricular zone (SVZ), through neurogenesis (birth of new neurons).
Adult neurons cannot reproduce (although they have been able to see how certain types of neurons do).
Parts of neurons
Neurons can be divided into 9 different parts, with different characteristics and specific functions.
1 . Neuronal body or soma
The body of the neuron is also called the soma. It is here where all the metabolic processes of the neuron occur. It is the widest region, with an oval morphology, where the nucleus of the neuron and the cytoplasm are located.
All the genetic material of the neuron is also found here, and it is where the molecules that allow the survival of the cell are synthesized, and those that guarantee that electrical signals are transmitted.
2. Core
The nucleus of the neuron is its most important part. It is located inside the soma and is delimited with the rest of the cytoplasm. Inside, in turn, is the genetic material of the neuron (DNA).
The nucleus is very important because it controls the expression of genetic material and is also the central base of the neuron, where all processes are regulated.
3. Axon
The axon is a tube that originates from the soma of the neuron, at the opposite end to the dendrites (a component that we will learn about below).
Once the dendrites receive the neurotransmitters and the body has been activated electrically, the axon has the function of conducting the electrical signal to the synaptic buttons. In these buttons, neurotransmitters will be released to inform the next neuron.
4. Dendrites
We have seen how the axon transmits information, but who or what captures it? The dendrites. These are extensions that arise from the soma and that form a type of branches that cover the neuronal center.
In this way, they are responsible for capturing the neurotransmitters produced by the nearest neuron, as well as sending the chemical information to the body of the neuron, which causes it to be electrically activated.
Thus, the dendrites capture information in the form of chemical signals (neurotransmitters), and activate the body that the previous neuron in the network is trying to send an impulse. These impulses are sent either from the sensory organs to the brain or the other way around (from the brain to the organs).
5. Myelin sheath
The myelin sheath covers or surrounds the axon of the neuron. Myelin consists of a substance made up of proteins and fats. It allows the transmission of the electrical signal throughout the entire neuron and for it to propagate at an adequate speed (very fast).
There are diseases where myelin is affected, such as multiple sclerosis; In this case, the electrical impulses become increasingly slower, affecting movement or sensory functions.
6. Nodules of Ranvier
Myelin sheaths are made up of units separated from each other; Each of these separations are called nodes of Ranvier. Thus, electrical impulses are actually transmitted through a “saltatory” signal precisely in those nodes.
They are regions of the axon that are not surrounded by myelin, very small (less than a micrometer in length), and that expose the neuron to the extracellular space. Sodium and potassium electrolytes enter through these nodules, allowing this saltatory conductance; They are essential for the electrical signal to travel properly through the myelin.
7. Nissl substance
Another part of the neuron is the Nissl substance; This substance is also called Nissl bodies. It is a set of granules in the cytoplasm of the neuron (in the body and dendrites, but not in the axon). This substance is responsible for synthesizing proteins for neurons.
8. Synaptic buttons
These are branches located in the terminal part of the axon. They are similar to dendrites, but their function is to release neurotransmitters to the external environment, once the electrical impulse is transmitted throughout the axon. These neurotransmitters, if all goes well, will be captured by the dendrites of the next neuron in the neuronal circuit or network.
9. Axonal cone
Finally, the axon cone is the region of the neuron body that narrows to give rise to the axon. This is an area highly enriched in channels and transporters, which require energy in the form of ATP (a type of molecule).
That is why it is an area with a high concentration of mitochondria (cellular organelles, responsible for supplying most of the energy necessary for cellular activity).
Neurons are essential cells for life since, together with the intervention of a large number of processes involved, they allow us to: think, reflect, move, feel, make decisions and, ultimately, live consciously and “connected” to the environment. around.
It is estimated that a human brain has around 67-86 billion neurons. However, when it comes to functioning properly, the number of cells we have is not so important, but rather that the communication between them is effective; This, in turn, is determined by the quality of neuronal synapses, processes that enable the connection between neurons.
Let’s not forget that our brain is “connected” thanks to neurons, or rather, the communication between them.
References:
- Carlson, N. R. (2005). Behavioral physiology. Madrid: Pearson Education.
- Guyton, A. C. (1994). Anatomy and physiology of the nervous system. Basic neuroscience. Madrid: Panamericana Medical Editorial.
- Knott, G., Molnár, Z. (2001). Cells of the Nervous System. Encyclopedia of Life Sciences.
- Ripoll, D.R. (2010). Fundamentals of psychobiology (Vol. 147). UOC Publishing.