What are neurons?
Neurons are information processing units in the brain responsible for sending, receiving, and transmitting electrochemical signals throughout the body.
Neurons, also called nerve cells, are basically the cells that make up the brain and nervous system. Neurons do not touch each other, but when one neuron approaches another, a synapse forms between them.
According to new research, the human brain contains approximately 86 billion neurons (Herculano-Houzel, 2009). These cells are fully developed at birth, but unlike other cells, they cannot reproduce or regenerate after death.
How do neurons work?
The neurons are next to each other but are not connected. There is a small space between neurons calledsynapse.
The function of a neuron is to transmit nerve impulses along a single neuron and across the synapse to the next neuron. The electrical signals transmitted by neurons are calledaction potentials.
The electrical signal must cross the synaptic cleft to continue its journey to or from the CNS. This is done by chemicals that diffuse through the space between the two neurons. These chemicals are called neurotransmitters.
During synaptic transmission, an action potential (electrical impulse) causes the synaptic vesicles of the presynaptic neuron to release neurotransmitters (chemical message).
These neurotransmitters diffuse across the synaptic cleft (the space between pre- and postsynaptic neurons) and bind to specialized receptor sites on the postsynaptic neuron. This will trigger an electrical impulse in the adjacent cell.
HeCentral Nervous System, which includes the brain and spinal cord, and the peripheral nervous system, which consists of sensory and motor nerve cells, contain neurons that process information.
What are the parts of a neuron?
A neuron contains a soma (cell body) that spans the axon (nerve fiber that conducts electrical impulses from the soma) and dendrites (tree-like structures that receive signals from other neurons). Hemyelin sheathIt is an insulating layer that forms around the axon and allows nerve impulses to travel faster along the axon.
Neurons do not touch each other, and there is a space between the axon of one neuron and the dendrite of the next, called a synapse.
The unique structure of neurons allows them to receive and carry messages to other neurons and throughout the body.
Dendrites are the tree-root-shaped part of a neuron that is typically shorter and more numerous than axons. Their job is to receive information from other neurons and transmit electrical signals to the cell body.
The dendrites are covered with synapses that allow them to receive signals from other neurons. Some neurons have short dendrites while others have longer dendrites.
In the central nervous system, neurons are long and have complex branches that allow them to receive signals from many other neurons.
For example, cells called Purkinje cells, which arefound in the cerebellum, have highly developed dendrites that receive signals from thousands of other cells.
Soma (cell body)
The soma, or cell body, is essentially the nucleus of a neuron. The function of the soma is to maintain the cell and the proper functioning of the neuron (Luengo-Sanchez et al., 2015).
The soma is surrounded by a membrane that protects it but also allows it to interact with its immediate environment.
The soma contains the cell nucleus, which produces genetic information and directs protein synthesis. These proteins are necessary for the functioning of other parts of the neuron.
An axon, also called a nerve fiber, is a tail-like structure in a neuron that connects to the cell body at a place called the axon mound.
The function of the axon is to carry signals from the cell body to the terminal buttons to transmit electrical signals to other neurons.
Most neurons have a single axon, the size of which can range from 0.1 millimeters to more than 3 feet (Miller and Zachary, 2017). Some axons are covered by a fatty substance called myelin, which insulates the axon and helps it transmit signals faster.
Axons are long neural processes that can branch and transmit signals to multiple areas before terminating in connections called synapses.
The myelin sheath is a layer of fatty material that covers the axons of neurons. Its purpose is to isolate one nerve cell from another, thus preventing the impulse from one neuron from interfering with the impulse from another. The second function of the myelin sheath is to speed up the conduction of nerve impulses along the axon.
Axons that are wrapped in cells calledglial cells(also known as oligodendrocytes andschwann cells), form the myelin sheath.
The myelin sheath that surrounds these neurons is designed to insulate and protect the axon. Thanks to this protection, the speed of transmission to other neurons is much higher than that of demyelinated neurons.
The myelin sheath consists of broken spaces called Ranvier nodes. Electrical signals can jump between Ranvier nodes, helping to speed up signal transmission.
The axon terminals (end buttons) at the end of a neuron are responsible for transmitting signals to other neurons.
At the end of the terminal button there is a slot, the so-calledsynapse. The terminal buttons support vessels that contain neurotransmitters.
neurotransmitters are releasedfrom the terminal buttons to the synapse and transmits signals across the synapse to other neurons. During this process, electrical signals are converted to chemical signals.
The final buttons then have the function of capturing the excess neurotransmitters that have not passed to the next neuron.
types of neurons
Although there are billions of neurons and they are highly diverse, neurons can be divided into three basic groups based on their function: sensory neurons (long dendrites and short axons), motor neurons (short dendrites and long axons), and relay neurons (short dendrites and long axons). short and short axons). dendrites and short axons) axons). short or long axons).
Sensory neurons (sometimes called afferent neurons) are nerve cells that carry nerve impulses from sensory receptors to the central nervous system and brain.
When these nerve impulses reach the brain, they are transformed into "sensations" such as sight, hearing, taste, and touch.
This sensory information can be physical (through sound, heat, touch, and light) or it can be chemical (through taste or smell). An example would be touching a very hot surface. When this happens, the sensory neurons will send signals to the central nervous system about the information received.
Most sensory neurons are pseudounipolar. This means that they have one axon that splits into two branches.
motor neurons(also called efferent neurons) are nerve cells responsible for transmitting signals from the central nervous system to the muscles, causing movement. They release neurotransmitters that trigger reactions that lead to muscle movement.
Motor neurons are located in the brainstem or spinal cord (parts of the central nervous system) and connect to muscles, glands, and organs throughout the body.
These neurons transmit signals from the spinal cord and brain stem to skeletal and smooth muscles to directly or indirectly control muscle movements.
For example, when your hand touches a hot surface, sensory neurons receive a message. The motor neurons then cause the hand to move away from the hot surface.
There are two types of motor neurons:
- lower motor neurons– these are the neurons that travel from the spinal cord to the muscles of the body.
- upper motor neurons– these are neurons that travel between the brain and the spinal cord.
Motor neurons are multipolar. This means that they have one axon and several dendrites that protrude from the cell body.
A relay neuron (also known as an interneuron) allows communication between sensory and motor neurons. Transmitter neurons connect different neurons in the brain and spinal cord and are easily recognized by their short axons.
Like motor neurons, interneurons are multipolar. This means that they have one axon and several dendrites.
In addition to acting as a connection between neurons, interneurons can also communicate with each other by forming circuits of varying complexity.
Communication between interneurons helps the brain perform complex functions such as learning and decision making, and plays a vital role in reflexes and neurogenesis, which means thatregeneration of new neurons.
Herculano-Houzel, S. (2009).The Human Brain in Numbers: Linearly Expanded Primate Brain.The frontiers of human neuroscience, 3, 31.
Luengo-Sanchez , S. , Bielza , C. , Benavides-Piccione , R. , Fernaud-Espinosa , I. , DeFelipe , J. and Larrañaga , P. (2015).Unequivocal definition of neuronal soma morphology using Gaussian mixture models..Neuroanatomical limits, 9, 137.
Miller, MA and Zachary, JF (2017). Mechanisms and morphology of damage, adaptation and cell death.Pathological bases of veterinary diseases., 2.