Wednesday, November 25, 2020

What is the neuron’s or nerve cell

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What is the neuron’s or nerve cell?

The neuron is a cell, like a liver or heart cell , but its primary function is different from the latter two since it is mainly used to propagate information over great distances.The neuron, or nerve cell, has a characteristic function of propagating information over great distances. This results in a very particular shape: the neuron has a cell body surrounded by one or more ramifications which can reach a length sometimes up to a good meter.Neurons form a sophisticated network of connections, which allows information to be redistributed, in parallel or in series, in different cortical areas. The messages pass in two different forms: electrical inside the neuron, and, most often, chemical to pass from one neuron to another.

 

The architecture of the neuron

Before explaining the function of the nerve cell, it is useful to dwell for a few moments on its characteristic form. Like all cells, the nerve cell has a cell body, or soma , but unlike them, branches extend from this cell body in a tree structure.

There are two types of extensions:

  • The information coming from the neurons upstream is transmitted by the intermediary of the dendrites , one speaks then about input signals or  “inputs”. 
  •   The information leaves the neuron via the axon to be transmitted to one or more        neurons downstream, in this case we speak of output signals or  “outputs” .

A neuron maintains contact with many other nerve cells; these contacts are called ” synapses “. On average, there are 10,000 connections for a nerve cell. The signal which propagates inside the nerve ramifications is of an electrical nature, but, at the synapse , the messages which must pass from one neuron to another are sent, most often, via a chemical messenger.

These substances, called ” neurotransmitters “, play a very important role for our health: when they are released in too large quantities, many dysfunctions result. For example, drug abuse will alter the delicate chemical balance at the synapse, in this case, the level of neurotransmitters released with this process is the basis of habituation.A neuron receives a continuous flow of information and it must at all times judge the importance of the messages before transmitting itself the synthesis of the information received further on. We say that the neuron “integrates” all the electrical messages received through its dendrites. This process of integration is localized in the soma. If the information is considered sufficiently substantial, the neuron will warn its neighbors by means of an action potential , otherwise, it will remain silent and the flow of information will stop there.If you want to solve nerve cell problems; then contact a neurologist or health and wellness coach.

 

The different types of neurons

  • Distinction according to the number of neurites :
  • 1 neurite: unipolar neuron;
  • 2 neurites: bipolar neuron ;
  • n neurites: multipolar neuron.
  • Anatomical distinction (3 examples)
  •  Pyramidal cells are found in the gray matter , or cerebral cortex .
  • Star neurons are also found in the cerebral cortex.
  • The Purkinje cells are cells with many ramifications and diffuses that are found-   exclusively in the cerebellum .
  • Distinction according to function:
  • The sensory neurons are directly connected to the sense organs and are responsible for transit sensory information (also called “bottom-information”) to the brain .
  • The motor neurons  are responsible for transmitting the orders coming from the brain (we also say “downward information”) towards the muscles.
  • Interneurons are represented by all neurons which are neither sensory nor motor but which form the junction between these two types of neurons.

Support cells

  • The neuronal architecture is supported by an aggregate of cells known as glial cells or support cells. Here are the main constituents:
  • The astrocytes are involved in regulating the concentration of various substances in the cell medium. They are also believed to have an important role in supporting neurons in information processing.
  • The Schwann cells and oligodendrocytes are special cells forming an insulating sheath, consisting of myelin , which wraps around nerve fibers. This kind of biological isolation serves to optimize the speed of information conduction along the axon.
  • The microglia is a type of cell that deals sort of “clean”, that is to say to release the extracellular medium of all waste surrounding the cell.

 

Excitatory  neurons vs inhibitory neurons

When two neurons are connected to each other, they are distinguished according to the direction of information transit : the presynaptic neuron, i.e. the neuron located before the synapse, transmits information to the neuron postsynaptic, i.e. the neuron located downstream of the synapse. Depending on whether it is an excitatory or an inhibitor, the presynaptic neuron will impose two opposing behaviors on the postsynaptic neuron: 

  • an excitatory neuron which discharges will activate the postsynaptic neuron; 
  • an inhibitory neuron that discharges will prevent the postsynaptic neuron from discharging.

Brief journey to the molecular level

The structure, or cytoskeleton , of the neuron is made up of long, relatively robust molecules , mainly actin and microtubules which are responsible for supporting the architecture of the nerve cell.The mitochondria are a type of important organelles that are found mainly in the soma of all cells. They play a crucial role because they are able to draw energy from the oxygen we inhale and transform it into vital energy for the survival of the neuron.

 

The presence of long ramifications, called “neurites” when the axon is not distinguished from the dendrites, implies that the nerve cell must be able to transfer various factors from the soma to the ends of the neurites. This transit is called “axoplasmic transport” and plays a fundamental role, in particular for the axon which cannot synthesize proteins and which must therefore be sent by the soma. For communication to be properly established, messages must be able to pass in both directions. We speak of “anterograde axoplasmic transport” when the molecules pass from the soma to the extremities and of “retrograde transport” in the opposite direction.

 

The cell membrane , also known as “phospholipid membrane”, separates the intracellular medium from the extracellular medium. Its function as an impermeable barrier plays a critical role for the proper functioning of the nerve cell. It is formed by a double phospholipid layer. These are molecules whose one end is polar ( phosphate group which attracts water) while the other end is nonpolar (repels water, like oil for example).Nested in this membrane, we find ion channels . This protein shunt forms a sort of tunnel connecting the inside and the outside of the cell. A fundamental characteristic of these channels is that they can open and close, allowing only specific substances to enter or escape into the cell. This is the reason why a neuron can be permeable to some ions and not to others.

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