Neuron Meaning

What is Neuron:

Neuron is a cell of the central nervous system that has the ability to receive and decode information in the form of electrical and chemical signals, transmitting them to other cells.

Neurons are the most important cells, since they are responsible for the transmission of electrical impulses through the synapse process, which constitutes the principle of the brain's functioning.

Neuron comes from the Greek "neûron", which means nerve.

Due to their dimensions, neurons are difficult to observe, even in high-resolution images. For this reason, until the end of the 19th century little was known about its operation, but in 1873 the Italian anatomist Camillo Golgi discovered that silver salts stained neurons black, managing to visualize their structure and identify different types.

This process is known as Golgi staining, and it was not only key to understanding the neural networks that make up the brain (which earned Camillo Golgi the Nobel Prize in Medicine), but it is also a method that, thanks to its efficiency is still used today to identify morphology and possible neuronal pathologies.

Structure of a neuron

Each neuron is made up of four parts or structures:

Nucleus

It is a structure located in the center of the neuron, generally very visible, in which all the genetic information is concentrated. In the nucleus there are also a pair of nucleoli, a substance called chromatin, (in which there is DNA), and the accessory body of Cajal, a kind of sphere in which proteins essential for neuronal activity accumulate.

Perikaryon

Also called the soma, the perikaryon is the cell body of the neuron. Inside it are a series of organelles that are essential to carry out the protein synthesis of the neuron, such as ribosomes, which are supramolecular complexes composed of proteins and RNA (ribonucleic acid) and the mitochondria, responsible for supplying energy for the cellular activity.

Nissl bodies are also found in the soma, granules in which there are accumulations of rough endoplasmic reticulum, whose function is to transport and synthesize the secretion protein. Finally, the cell body is the place where the Golgi apparatus is located, an organelle that is responsible for the addition of carbohydrates to proteins, through a process called glycosylation.

Dendrites

They are multiple branches that start from the prekaryon and that act as a reception area for stimuli and cell feeding, in addition to establishing connections between neurons. They are rich in organelles that contribute to the synapse process.

Axon

It represents the main extension of the neuron and can measure several tens of centimeters. The axon is responsible for conducting the nerve impulse throughout the body and also to other neurons through the dendrites.

Without a coating, the axons would not be able to transmit impulses quickly, as their electrical charge would be lost. By virtue of this, many neurons are covered by a substance called myelin, which is produced by the Schwann cell.

Schwann cells (which are currently called neurolemocytes) cover axons with their myelin content, leaving certain spaces between them, known as nodes of Ranvier. These interruptions in the myelin sheath help the electrical impulse travel at a higher speed.

Neuron function

The main function of the neuron is the transmission of messages in the form of nerve impulses to other cells, which is translated into "instructions" for the body. For example, the voluntary movement of a muscle, or involuntary but necessary reactions such as the perception of pain before a blow or burn, just to name a few.

This process of receiving, processing and sending messages is carried out during the synapse, a process that can be of two types:

  • Electrical synapse: it is characterized by the transmission of ions between one neuron and another through protein connections, called gap junctions or slit junctions, which allow the transmission of the electrical impulse without requiring the intervention of a neurotransmitter. The electrical synapse is bidirectional and faster than a chemical synapse.
  • Chemical synapse: In this case, neurons release and receive neurotransmitters, which are small molecules that carry information to an immediate cell. Some of the best known neurotransmirors are dopamine, acetylcholine, serotonin, norepinephrine, endorphin, and oxytocin.

See also Synapse

Types of neurons

Neurons can be classified according to several criteria:

Neurons according to their function

In this case, the neurons can be:

  • Motor neurons: they are responsible for voluntary and involuntary body movements.
  • Sensory neurons: they are responsible for receiving and processing external information, captured by the senses (smell, taste, touch, hearing, sight).
  • Interneuronal neurons: they are organized in large networks, and their function is to generate cognitive processes, such as thoughts and memories.

Neurons according to their shape

There are five types of neurons according to their morphology:

  • Pyramidal neurons: They are shaped like a pyramid.
  • Spindle neurons: they are cylindrical neurons.
  • Polyhedral neurons: they have a very defined geometric shape, with multiple faces.
  • Stellate neurons: they are characterized by having many limbs, which gives them a shape similar to a star.
  • Spherical neurons: they have a circular or sphere shape.

Neurons according to their polarity

According to the number of their electrical endings, neurons can be classified into:

  • Unipolar neurons: they are neurons that have a unique prolongation that behaves like axon and dendrite at the same time, like neurons found in the ganglia of invertebrate animals.
  • Monopolar neurons: In this case, the neuron has a dendrite that forks into two branches. The posterior ganglia of the spinal nerves, for example, are monopolar.
  • Bipolar neurons: these are neurons with an axon and a dendrite. The vestibular ganglia, which are located in the ear and are responsible for balance, belong to this group.
  • Multipolar neurons: they are neurons with an axon and multiple dendrites. Most neurons are of this type.
  • Anaxonic neurons: dendrites and axons cannot be distinguished due to their small size. The retina of the eye has these types of neurons.

See also Nervous system

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