How do neurons work?

A summary of how these nerve cells work.

It is widely known in popular culture that neurons are cells that act as messengers of sorts, sending information back and forth throughout our nervous system.

How neurons, which are the basic functional unit of our brain, spinal cord, and nerves, work is a matter of debate.spinal cord and nerves, is the subject of today's article. Let's discover how these sophisticated engineering works of nature.

How do neurons work? A general description

Neurons are cells that are part of the nervous system, being its basic functional unit. The main function of these cells is to receive and transmit information. in the form of electrical impulses along a complex lattice or network made up of neurons, which constitutes the nervous system, both the central nervous system (CNS), composed of the spinal cord and the brain, and the peripheral nervous system (PNS), made up of the nerves.

It is clear that, based on this definition, the nervous system could not function without neurons, together with glia cells. However, in order to understand more about how they function, it is necessary to make a series of notes regarding their typology, structure and shape, since these directly influence their functioning.

Structure

The functions of neurons cannot be understood without understanding how these nerve cells are organized. These are the parts of the neuron.

1. Soma

The soma is the cell body of the neuron, and is the place where the nucleus is located.The neuron is also very active in protein synthesis, which is fundamental for the functioning of the neuron. It is from here that several protrusions or appendages extend: the dendrites and the axon.

2. The dendrites

The dendrites are tree-shaped protrusions with spines that allow the neuron to receive and process information. Depending on the type of signals it receives, the neuron may be induced to excite or inhibitDepending on the type of signals it receives, it can induce excitation or inhibition of the neuron, causing the action potential to be triggered or not, i.e. to fire a nerve impulse.

3. The axon

The axon consists of a single extension in the neuron with a homogeneous thickness. This structure has its origin in the cell body, specifically in the axon cone.. In motor neurons and interneurons, it is in this axon cone that the action potential is produced.

The axons are coated with a special insulating substance: myelin. This myelin has a fundamental function in the nervous system, since it makes the nerve impulse more efficient and faster.

Reaching the end of the axon are many branches, which form bulb-shaped structures known as axon or nerve terminals. These terminals form connections with the target cells, whether motor or interneuron.

Types of neurons according to their function

According to their functions, we can distinguish between three types: sensory, motor and interneurons.

1. Sensory neurons

Sensory neurons are the ones in charge of capturing information external to the organism or sensations, such as pain, painlessness, pain, motor neurons or interneurons.This information is captured and sent in the form of an electrical impulse, directing it to the central nervous system, where it will be processed.

Motor neurons

Motor neurons receive information from other neurons and transmit commands to muscles, organs and glands.. In this way a movement can be performed or a certain biological function can be carried out, such as the production of hormones.

3. Interneurons

Interneurons are a special type of cell in the central nervous system that are responsible for connecting a are in charge of connecting one neuron to another, i.e. they function as a kind ofthat is to say, they function as a kind of bridge. They receive information from some neurons, whether sensory or other interneurons, and transmit it to others, which may be motor neurons or other interneurons.

Neurons work in networks

Regardless of how healthy a neuron is, if it is isolated from the others, it serves absolutely no purpose. In order for these cells to perform their functions, they must be connected to each other and work together.. Thus, by connecting with each other, these cells stimulate or inhibit each other, process the incoming information and contribute to a motor or hormonal response. These neuronal circuits can become very complex, although there are also quite simple ones, especially related to reflexes.

Working together, neurons can perform three basic functions: receiving nerve signals or information from other neurons; integrating these signals, in order to determine whether the information is important or not; and communicating the signals to target cells, which may be muscles, glands or other neurons.

To further understand these three functions, let us describe an example, a situation involving the three types of neurons based on their function: sensory neurons, motor neurons and interneurons.

Let's imagine that we are preparing a cup of tea, with the teapot on top of the fire.. When we see it we are activating sensory neurons, specifically those in charge of sight, transmitting nervous information captured in the cones and rods of the retina to the brain. In the brain the visual information will be processed and we will be aware that we are seeing the teapot.

As we want to serve ourselves a tea, we get ready to pick up the teapot. In order to move the arm we need to use our motor neurons. These neurons have received the signal from the brain to activate the muscles of the arm, stretch it and pick up the teapot. So we do that movement: we stretch our arm and pick up the teapot, whose handle is made of metal.

It turns out that we had not turned off the fire and that the teapot was very hot. This sensation is picked up by the thermal sensors of the skin when touching the hot handle. This information, captured by sensory neurons, travels rapidly to the spinal cord, which, via an interneuron, sends the information to motor neurons without sending it to the brain. which, by means of an interneuron, sends the information to motor neurons without the need to send it to the brain. We are instructed to move our arm quickly to avoid burning ourselves. Even so, part of the information reaches the brain, which interprets it in the form of pain.

The synapse

Neuron-to-neuron connections are normally formed on the axon and dendrite of two neurons.. The meeting place between these two neurons is known as the synapse or synaptic space, where information is transmitted from the first neuron (presynaptic) to the next, the target neuron (postsynaptic).

The transmission of the information is done by means of chemical messengers, the neurotransmitters, of which there are many types (e.g., neurotransmittersThere are many types of neurotransmitters (e.g. serotonin, dopamine, acetylcholine, GABA, endorphins...).

When an action potential travels along the axon of the presynaptic cell and reaches its terminal, this neuron releases a neurotransmitter into the synaptic space which binds to the receptors of the membrane of the postsynaptic cell and, thus, the transmission of the nerve signal takes place. This signal can be excitatory or inhibitory and, depending on the type of neurotransmitter, it will perform one function or another, as well as depending on which path the nerve impulse follows, going to the corresponding nerve center or target cell.

And what about glial cells?

Although the protagonists are the neurons, we cannot forget their friends, we cannot forget their secondary friends, the glial cells, although "secondary" does not mean "secondary".although "secondary" is not synonymous with "dispensable". If the neuron is the basic functional unit of the nervous system, glial cells are its majority cell. This is why they cannot be forgotten when trying to explain how neurons function, especially considering that they play a very important supporting role in the nervous system.

Broadly speaking, there are four types of glial cells, three of which, astrocytes, oligodendrocytes and microglia, can only be found in the central nervous system. The fourth type is the Schwann cells, which are only found in the peripheral nervous system.

Astrocytes

Astrocytes are the most numerous type of glial cells in the brain.. Their main functions are to regulate Blood flow in the brain, maintain the composition of the fluid surrounding neurons and regulate communication between neurons in the synaptic space.

During embryonic development, astrocytes help neurons reach their destinations, in addition to contributing to the formation of the blood-brain barrier, the part that isolates the brain from toxic substances that may be dissolved in the blood.

Microglia

Microglia are related to the macrophages of the immune system, the "scavengers" that are the "scavengers" of the immune system.The microglia are the "scavengers" that eliminate dead cells and residues that can be toxic if they accumulate.

3. Oligodendrocytes and Schwann cells

Oligodendrocytes and Schwann cells share a similar function, although the former are found in the central nervous system and the latter in the peripheral nervous system. Both are glial cells that produce myelin, the insulating substance found as a sheath around neuronal axons.

Bibliographic references:

• Purves, D., Augustine, G. J., Fitzpatrick, D., Katz, L. C., LaMantia, A.-S and McNamara, J. O. (1997). The organization of the nervous system. In Neuroscience (pp. 1-10). Sunderland, MA: Sinauer Associates.
• Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V and Jackson, R. B. (2011). Nervous systems consist of circuits of neurons and supporting cells. In Campbell biology (10th ed., pp. 1080-1084). San Francisco, CA: Pearson.
• Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V and Jackson, R. B. (2011). Neuron structure and organization reflect function in information transfer. In Campbell biology (10th ed., pp. 1062-1064). San Francisco, CA: Pearson.
• Sadava, D. E., Hillis, D. M., Heller, H. C and Berenbaum, M. R. (2009). Neurons and nervous systems (Las neuronas y el sistema nervioso). En Life: The science of biology (9na ed., pp. 988-993). Sunderland, MA: Sinauer Associates.