It is widely known in popular culture that neurons are cells that act as a kind of messenger, sending information back and forth throughout our nervous system.
How neurons work, which are the basic functional unit of our brain, spinal cord and nerves, is the topic of today’s article. Let’s discover how these sophisticated works of nature’s engineering work.
Neurons are cells that are part of the nervous system, being its basic functional unit. These cells’ main function is to receive and transmit information in the form of electrical impulses along a complex framework or network made of neurons, which constitutes the nervous system, both the central one (CNS), made up of the spinal cord and the brain, and the peripheral system (PNS) made up of the nerves. .
It is clear that, based on this definition, the nervous system could not function without neurons, along with glia cells. However, to better understand how they work, it is necessary to make a series of notes regarding their typology, structure and shape, given that these directly influence their operation.
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, in addition to having a great protein synthesis activity, essential for the functioning of the neuron. It is from here that several protuberances or appendages extend: the dendrites and the axon.
2. Dendrites
Dendrites are tree-shaped protuberances with spines that allow the neuron to receive and process information. Depending on the type of signals received, the neuron can be excited or inhibited causing the action potential to occur or not, that is, to trigger a nervous 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 axonal cone where the action potential is produced.
Axons are covered 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 there are many branches, which form bulb-shaped structures known as axon or nerve terminals. These terminals form connections with target cells, whether motor or interneurons.
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 They are those responsible for capturing information external to the body or sensations such as pain, light, sound, touch, taste… 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.
2. Motor neurons
motor neurons They receive information from other neurons, being responsible for transmitting orders to muscles, organs and glands In this way you can make a movement or carry out a certain biological function, such as the production of hormones.
3. Interneurons
Interneurons are a special type of cells present in the central nervous system that They are responsible for connecting one neuron to another, that is, they function as a kind of bridge. They receive information from neurons, whether sensory or other interneurons, and transmit them to others, which may be motor neurons or other interneurons.
Neurons work by forming networks
Regardless of how healthy a neuron is, if it is isolated from the others it is of absolutely no use. For these cells to perform their functions, they must connect with others, working together Thus, when these cells connect with each other, they stimulate or inhibit each other, process the incoming information and contribute to the emission of a motor or hormonal response. These neural circuits can be very complex, although there are also quite simple ones, especially related to reflexes.
When working as a team, neurons can perform three basic functions, these being receiving nervous signals or information from other neurons; integrate these signals, with the aim of determining whether the information is important or not; and communicate signals to target cells, which may be muscles, glands or other neurons.
To understand these three functions in more depth, we are going to describe an example, a situation in which the three types of neurons are involved based on their function: sensory neurons, motor neurons and interneurons.
Let’s imagine that we are making tea, with the teapot on the fire When we see it we are activating sensory neurons, specifically those responsible for vision, transmitting nervous information captured in the cones and rods of the retina to the brain. The visual information will be processed in the brain and we will be aware that we are seeing the teapot.
Since we want to serve ourselves some tea, we prepare to grab 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 arm muscles, stretch it and pick up the teapot. So, we make that movement: we stretch out our arm and pick up the teapot, whose handle is made of metal.
It turns out that we hadn’t turned off the heat and the kettle was very hot. This sensation is captured by the skin’s thermal sensors when touching the hot handle. This information, captured by sensory neurons, travels quickly to the spinal cord which, through an interneuron, sends information to motor neurons without having to send it to the brain. It is ordered to move the arm quickly to avoid burning ourselves. Even so, some 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 what is known as a synapse or synaptic space, resulting in the transmission of information from the first neuron (presynaptic) to the next, being the target neuron (postsynaptic).
The transmission of information is done through chemical messengers, neurotransmitters there being many types (e.g., serotonin, dopamine, acetylcholine, GABA, endorphins…).
When an action potential travels through the axon of the presynaptic cell and reaches its terminal, this neuron releases a neurotransmitter into the synaptic space which binds to the receptors on the membrane of the postsynaptic cell and, thus, transmission occurs. of the nervous signal. This signal can be excitatory or inhibitory and, depending on the type of neurotransmitter, one function or another will be performed, in addition to depending on which path the nervous impulse follows, going to the corresponding nerve center or target cell.
Although the protagonists are the neurons, We cannot forget its secondary friends, the glial cells, 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 work, especially considering that they have 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 Schwann cells, which are only found in the peripheral nervous system.
1. Astrocytes
Astrocytes are the most numerous type of glial cells in the brain Its 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.
2. Microglia
Microglia are related to macrophages of the immune system the “scavengers” that eliminate dead cells and waste 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. Both are glial cells that produce myelin, the insulating substance found in the form of a sheath around neuronal axons.
