Decoding the Brain: Understanding the Complex World of Neurons and How They Communicate
The human brain is an incredibly complex machine that is capable of performing extraordinarily difficult tasks in mere milliseconds. Remarkably, humans process information and carry out actions with just a single blink of an eye. It is natural to wonder how our brain completes all of these activities so quickly and how it communicates with the other parts of the body and brain. The key players in this process are neurons - these fascinating cells are responsible for transmitting signals throughout the brain and performing a wide variety of functions. With 86 billion neurons in the brain, these cells are always at work, but contrary to common thought, they are far more complex than most people realize.
Neurons form processing units in the brain to decipher and communicate signals all throughout the body and brain. There is a wide variety of neurons that differin size, shape, function and location. Each neuron consists of main parts such as a cell body, axon, axon terminal, myelin sheath (depending on the type of neuron) and dendrites. To understand how neurons interact with each other, it is first important to understand the structure and function of a single one of these cells.
The cell body of the neuron is the central part of the cell that contains the nucleus, DNA and organelles such as the mitochondria, golgi body, ribosomes and many more. These organelles are responsible for basic functions of the cell, including protein synthesis and energy production. The cell body is protected by the plasma membrane which synthesizes information going in and out of the cell. The energy produced in the cell body eventually generates an electrical signal, which is then transmitted through the axon, which is a long projection that extends from the cell body and transmits electrical signals. This signal is conducted efficiently along the length of a neuron by a fatty insulator called the Myelin Sheath and eventually reaches its destination called the axon terminal which forms connections between neurons called synapses. At the synapse, information is passed between neurons using chemical messengers called neurotransmitters. To receive information, dendrites come into function, which extend from the cell body to receive information and signals coming from other neurons and carry it to the cell body. If the amount of incoming activity is exceeded, neurons begin to fire an action potential which leads to the release of neurotransmitters at the synapse and the transmission of information to the next neuron in the network. In large networks, the collective activity of many individual neurons generates complex patterns of thoughts and behavior, allowing us to perceive, process and respond to the world around us.
Figure 1: https://training.seer.cancer.gov/anatomy/nervous/tissue.html
However, there exist various types of neurons that specialize in their particular function, three of which are particularly important for communication. Sensory neurons are responsible for detecting external stimuli. An example of a sensory neuron in action is when a person touches a piece of ice, which generates an electrical impulse that is transmitted to the brain through sensory neurons.Electrical impulses are converted into physical movement of muscles or glands through motor neurons. They are primarily located in the central nervous system and connect to muscles throughout the body. They play a significant role in the functioning of the spinal cord and are essential for maintaining an active lifestyle. Finally, interneurons act as a bridge between sensory and motor neurons, allowing for information to be transmitted between the two.
The neural firing and action potential process involves the participation of various chemicals. Sodium ion channels can be found on the dendrites of each neuron. Sodium ions, alongside potassium, chloride, and calcium ions pass in and out of the cell through ion channels, contributing to the electrochemical function of action potential. This creates a potential or electrical charge known as the resting state. Only specific ions can pass through the highly selective ion channels found in neurons, which has an effect on the rapid shift in membrane voltage.
Synapses are essential for the communication and functioning of neurons. At a synapse, an electrical or chemical signal is passed from one neuron to another. This information flow passes through the post-synaptic spine, synaptic cleft, and presynaptic terminal.
Synaptic transmission of information follows through with the following steps:
Action potential arrives at the axon terminal.
A rush of calcium follows through the ion channels leading to vesicles fusing with the presynaptic membrane.
The transmitter is released into the synaptic cleft and binds receptor molecules onto the post-synaptic membrane. (Based on this binding, postsynaptic channels close or open).
Ion channels opening causes a possible rush of ions to the post-synaptic neuron.
The balance of ions causes the post-synaptic to depolarize or hyperpolarize.
If the post-synaptic voltage change is large enough it creates an electrochemical pulse which leads to action potential.
Figure 2: https://www.moleculardevices.com/applications/patch-clamp-electrophysiology/what-action-potential
Thus, neurons are a fundamental component of the human brain. They are highly complex and incredibly important cells, crucial for the functioning of the nervous system. Despite the significant amount of research that has been conducted on neurons, new information seems to constantly become available. According to many scientists, like Dr. Kristof Koch, there is still much to be discovered about these incredible cells, which is not surprising given the endless discoveries of the world of neuroscience.
“We humans have approximately 86 billion neurons in our brains, woven together by an estimated 100 trillion connections, or synapses. It’s a daunting task to understand the details of how those cells work, let alone how they come together to make up our sensory systems, our behavior, our consciousness.” - Dr. Kirstof Koch.
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