What can we learn about cells and neurons?

November 26, 2024

What can we learn about cells and neurons?

A lot. We're just beginning and we are enjoying it. Human life is a complex cellular network. Our guess or hope is that by learning more about cells and how they work, we can gradually learn more about how we can stay in that state of being "alive" and how we can manage to enjoy this experience called life. 

All life on Earth is cellular life. There are no exceptions. If it's alive, it is composed of one or more cells. Humans are composed of trillions of cells. Men are in average a cluster of 37 trillion cells. Women are a cluster of 28 trillion cells. The difference is due that men have more red blood cells. By the way, about 80% of all cells in the human body are red blood cells. Not counting red blood cells, it can be said that both men and women are about 7 trillion cells. We are trillionaires no matter how we look at it. 

Cells can be categorized as generic (stem) or specialized. All cells, specialized or not, conduct all the same generic activities that generate the physical phenomena called life. These are metabolic, genetic, maintenance (MGM) activities. In addition, cells perform specific functions depending on their differentiation and specialization. 

In this post we touch briefly on the generic functions or activities of all cells, we list about 20 specialized cells, and discuss the basic framework about how neurons work. This is just part of generic learning and the process of accumulating knowledge that we know for sure we will be able to apply and benefit from in the future somehow. Enjoy. 

Generic Activities of Every Cell: Metabolic; Genetic; Maintenance (MGM)

1. Metabolic Activities: Energy, Growth, Division, and Migration 

Energy Production. 

Cells metabolize organic matter, which leads to energy production, cell growth, and cell division.  Glycolysis is the first stage where digestive enzymes break down glucose into an organic molecule called pyruvate. The citric acid cycle (Krebs Cycle) is when mitochondria processes the pyruvate into another compound (acetyl-CoA), which then enters the citric acid cycle that produces high energy electrons. These high-energy electrons interact with oxygen (are oxidized), which produces a compound called adenosine triphosphate (ATP), which works as fuel energy for cell functions. 

Cell Growth

The ingestion of nutrients together with interactions with hormones and "growth factors" cause cell growth. Nutrients are sugars, fats, and proteins. Hormones are organic molecules that serve as messengers. Growth factors are polypeptides like platelets, fibroblasts, and nerve cells that bind to surface receptors on cells.

Cell Division. 

Mitosis is the process by which regular cells divide, producing two genetically identical daughter cells. Stages: Prophase, Metaphase, Anaphase, and Telophase (PMAT). Prophase (chromosomes condense and become visible); Metaphase (chromosomes line up in the middle of the cell); Anaphase (sister chromatids separate and move to opposite poles); and Telophase (new nuclear membranes form around the separated chromosomes). Meiosis is cell division of germ cells (sperm and egg cells). Chromosome number is reduced by half, which leads to genetic diversity and stability in sexual reproduction.

Cells Migration

Cell migration is the process by which cells move from one location to another in response to external or internal input. Cell migration is a fundamental process that occurs throughout life, from embryonic development to death. Cell migration is essential for many biological processes, including: embryonic development; tissue repair / regeneration; and immune response. Cell movement is aided by cytoskeleton dynamics. The cytoskeleton is a network of protein filaments that provide structural support to the cell, aid in intracellular transport, and allow for cell movement. 

2. Genetic Activities: RNA and DNA Interactions 

Interactions between RNA and DNA within the cell have the effect of regulating cell functions including the production of proteins. 

Protein Production

Ribosomes in the cytoplasm of the cell serve as "factories" that assemble different amino acids in different orders to produce different proteins. RNA serves as an electromagnetic template for the assembly. After interacting with DNA in the nucleus of the cell, RNA goes out to the cytoplasm carrying with it (unbeknownst to it) a copy of segments of DNA. 

• RNA Transcription: RNA comes in contact with the DNA in the nucleus. The "information" in the DNA is electromagnetically transcribed into this "messenger" RNA (mRNA).
• RNA Translation: The mRNA travels out of the nucleus into the cytoplasm where it interacts with the ribosomes and other RNA referred to as "transfer" RNA (tRNA). RNA serves as an electromagnetic template for the assembly of amino acids into proteins in the ribosomes. 

Gene Regulation 

The cell is continuously interacting with input from the external environment and from input from internal processes. The biochemical processing of that input has the effect of regulating the "expression" of genes, meaning which ones are exposed or activated "on" and which ones are not. The different binary "expressions" (exposures or activations; "on" or "off") leads to different adaptations and developments causing cell differentiation and specialization. 

DNA Replication

Interactions between RNA and DNA unwrap the DNA and facilitate replication. When the cell divides, each new cells carries a complete copy set of the 46 chromosomes (23 pairs) holding the DNA wrapped in histones. 

3. Maintenance Activities: Autophagy, Apoptosis, Communication

Cells undergo generic activities that have the effect of keeping them active, dynamically interacting with their environment. In other words, these maintenance activities keep cells in the state that we refer to as being alive. Generic cell activities that promote their maintenance and wellbeing include autophagy, apoptosis, input / output operations that lead to the effect of communication and stabilization (homeostasis). 

• Cell autophagy is the process by which cells break down and remove damaged or unnecessary components (like organelles), which helps them maintain cellular health. Cell apoptosis is cell suicide or programmed death by which cells undergo self-destruction in response to damage or other triggers. This feature is naturally selected because it has the effect of removing damaged or unneeded cells without allowing them to cause inflammation, harm to surrounding tissue, or abnormal growth (cancer).

• Cell maintenance activities include lysosomal activity and endoplasmatic activities. Lysosomes are organelles filled with enzymes that break down waste materials, cellular debris, and foreign substances. They are involved in the digestion of macromolecules, old organelles, and pathogens. Endoplasmic Reticulum (ER) functions include the rough ER (involved in protein synthesis and processing) and smooth ER (involved in lipid synthesis, detoxification, and calcium storage). As part of these and other generic operations, cells take in and emit different organic molecules (e.g. hormones, neurotransmitters) that serve as "signals" between cells. The output of a cell is received as input by neighboring cells. This communication triggers a cascade of intracellular events that have the effect of regulating functions (e.g., growth, metabolism, immune response). Technical terms include endocytosis (cells taking in substances from the external environment by engulfing them in a membrane vesicle) and exocytosis (cells expelling substances like waste, proteins, or neurotransmitters by vesicles fusing with the cell membrane).

• Cell maintenance activities generate electrically charged atoms or molecules (ions) like sodium, potassium, calcium, and chloride, which travel across cell membranes through ion channels and pumps. This channeling of electrical energy helps maintain electrical gradients, pH balance, and osmotic pressure in well balance for normal cell functioning.

These processes keep the cells and the organism interacting dynamically within the environment in what is referred to as being "alive". Cells are dynamic systems, constantly responding to internal and external conditions, adapting to changes, and carrying out necessary functions that lead to the physical phenomena known as life.

Specialized Activities 

During embryonic development, generic or "stem" cells undergo processes that make them different and that eventually lead to their migration and specialization. The differentiation and specialization are regulated by the different "notes" or "tunes" played or streamed by RNA from the DNA "playlist". Note that each cell contains the entire playlist with about 25,000 songs (genes). However, not all songs are played. RNA interactions with DNA and other factors (internal and external) have the effect of having different segments of songs streamed in different orders, mixes, and remixes. All that leads to differentiation and specialization. 

Below is a sample of 20 specialized cells in the human body, each performing unique functions:

1. Red Blood Cells (Erythrocytes): Carry oxygen from the lungs to the rest of the body and return carbon dioxide to be exhaled.
2. White Blood Cells (Leukocytes): Defend the body against infections and foreign invaders.
3. Platelets (Thrombocytes): Involved in blood clotting to prevent excessive bleeding.
4. Muscle Cells (Myocytes): Responsible for muscle contraction and movement.
5. Nerve Cells (Neurons): Transmit electrical signals throughout the nervous system for communication.
6. Sperm Cells (Spermatozoa): Male reproductive cells involved in fertilization.
7. Egg Cells (Oocytes): Female reproductive cells involved in reproduction and fertilization.
8. Skin Cells (Keratinocytes): Form the outer layer of skin, providing a barrier and protection.
9. Fat Cells (Adipocytes): Store energy in the form of fat and help insulate the body.
10. Bone Cells (Osteocytes): Maintain bone structure and regulate calcium levels in bones.
11. Cartilage Cells (Chondrocytes): Produce and maintain the cartilage that provides cushioning in joints.
12. Liver Cells (Hepatocytes): Involved in detoxifying chemicals, metabolizing nutrients, and producing proteins.
13. Kidney Cells (Nephrons): Filter blood to remove waste products and regulate fluid balance.
14. Pancreatic Cells (Beta Cells): Produce insulin to regulate blood sugar levels.
15. Intestinal Cells (Enterocytes): Absorb nutrients from food during digestion.
16. Glial Cells: Support and protect neurons in the central nervous system.
17. Photoreceptor Cells (Rods and Cones): Found in the retina, these cells detect light and allow vision.
18. Endothelial Cells: Line blood vessels and regulate the exchange of nutrients and waste.
19. Ciliated Cells: Found in the respiratory tract, these cells move mucus and trapped particles out of the lungs.
20. Melanocytes: Produce melanin, the pigment responsible for skin color and protecting the skin from UV radiation.

All cells, specialized or not, perform all the same generic functions. Specialized cells perform specific functions that end up being essential for the body's overall health and stability (homeostasis). All of the above specialized cells are critically important. Our favorites are neurons because they make up the functions of the brain, the central processing unit of this thing that we call intelligent life.  

What are Neurons?

Neurons are specialized cells in the nervous system. They are the basic building blocks of the brain, spinal cord, and peripheral nervous system. Neurons transmit electrical and chemical signals. Networks of thousands, millions, or billions of neurons "firing" on and off in different sequences create the brain processes that we refer to as cognition (feeling, association, thinking, remembering, understanding, learning, etc) (Mnemonic FATRULE). 

Neurons perform basic cellular functions like other cells, including protein synthesis, energy production, and maintaining their own structure, with the majority of these functions occurring within the cell body (soma) of the neuron. However, their unique structure allows neurons to also conduct specialized functions such as receiving and transmitting electrochemical signals, which becomes their primary function in the nervous system.

Neurons consist of three main parts: Soma, Axon, Dendrites (SAD)

• Soma (body): Contains the nucleus and other cellular structures.
• Axon: A long extension that transmits electrical signals to other neurons, muscles, or glands.
• Dendrites: Branch-like extensions that receive signals from other neurons.

How Neurons Work?

Neurons generate electrical impulses (action potentials) and chemicals (neurotransmitters) at synapses (the gaps between neurons). 

• A neuron synapse is a junction between two neurons where a nerve impulse is transmitted from one neuron to another, essentially acting as the point of communication between these nerve cells. 
• A synapse allows signals to pass between neurons through the release of chemical messengers called neurotransmitters across a small gap called the synaptic cleft.
• There are about 100 billion neurons in the brain. Each neuron can have thousands of synapses. It is estimated that there are about 100 trillion synaptic connections in the adult brain.

The synaptic emissions of one neuron are received by other neuron, and vice versa, in what becomes neural communication. That network communication is what ultimately create the processes like sensation, perception, emotions, thoughts and actions (SPETA) of the brain. 

Electrochemical Communication Across Neural Synapses

Electrical Impulses

• When a neuron is not actively transmitting an electrical signal, it is at its resting potential, which is typically around -70 millivolts. This resting potential is maintained by the sodium-potassium exchange. Sodium ions are emitted out of the cell and potassium ions into the cell.
• When a neuron receives a sufficient stimulus (from sensory input or another neuron), the membrane potential becomes less negative, a process known as depolarization. This occurs because sodium channels open, allowing sodium ions to flow into the neuron, making the inside of the cell more positive. When depolarization reaches a threshold level, an action potential is generated. This is an all-or-nothing electrical signal that travels down the axon. During the action potential, voltage-gated sodium channels open, and sodium ions rush in, causing further depolarization. This is followed by potassium channels opening, allowing potassium ions to flow out and repolarize the cell. The action potential travels down the axon toward the axon terminals, where the signal is transferred to the next neuron. 

Chemical Emissions. 

• Once the action potential reaches the axon terminals, it triggers the release of chemicals (neurotransmitters) stored in vesicles. These neurotransmitters cross the synaptic cleft and bind to receptors on the dendrites of the next neuron, muscle, or gland. Depending on the type of neurotransmitter, this binding can either stimulate or inhibit the next cell, allowing the signal to continue or stop.
• After the neurotransmitters have transmitted the signal, they are either reabsorbed by the original neuron (a process called reuptake) or broken down by enzymes. Thus the signal is not continuously active and neurons can reset for the next transmission.

How are Neurons Categorized?

Neurons can be categorized based on their function:

• Sensory Neurons: These neurons carry signals from sensory receptors (e.g., in the skin, eyes, or ears) to the central nervous system (CNS). They help detect changes in the environment, such as light, sound, or temperature.
• Motor Neurons: Motor neurons transmit signals from the CNS to muscles or glands, causing them to contract or secrete. For example, motor neurons allow us to move our muscles or make glands secrete hormones.
• Interneurons: Interneurons are found within the CNS and connect sensory and motor neurons. They play a crucial role in processing information and coordinating responses.

How Neurons Generate Cognition

Neurons generate cognition through a series of electrical and chemical processes. The generation of thought is linked to the interactions between large networks of neurons across different regions of the brain. 

1. Neural Activity (Action Potentials and Synaptic Transmissions)

• Neurons communicate by transmitting electrical signals along their axons to other neurons. When one neuron receives a sufficient stimulus (for example, from sensory input or a previous neuron’s signal), it generates an action potential. These action potentials travel down the axon and, upon reaching the axon terminals, trigger the release of neurotransmitters (chemical signals) into synapses (the gaps between neurons).
• Synaptic Transmission. The neurotransmitters cross the synaptic gap and bind to receptors on the dendrites of neighboring neurons. This can either excite or inhibit the next neuron, depending on the type of neurotransmitter and receptor involved. When neurons receive enough excitatory signals and reach a certain threshold, they generate their own action potential. This process propagates through a network of interconnected neurons.

2. Association, Pattern Recognition, Regional Activation

• Neurons in the brain form associations between different pieces of information. The brain is constantly comparing new sensory input and existing knowledge, which is why thoughts are often influenced by what we already know or have experienced.
• Pattern recognition plays a big role in how we generate ideas and thoughts. The brain recognizes patterns in sensory information and memories, which helps form coherent thoughts and allows us to make sense of new information by relating it to what we already understand.
• Different regions of the brain are responsible for different types of thoughts and mental processes: The prefrontal cortex plays a key role in higher-level cognitive functions such as decision-making, problem-solving, and self-reflection. The hippocampus is involved in memory formation and recall, linking past experiences to present thoughts. The temporal lobes are associated with processing sensory information, language, and auditory thoughts.The parietal lobes help integrate sensory information and contribute to spatial thinking and mathematical reasoning. The occipital lobes are primarily involved in visual processing and can contribute to visual thoughts or imagery.

3. Memories, Emotions, Thoughts, Actions (METAs)

• Neurotransmitters like dopamine, serotonin, and norepinephrine play a crucial role in shaping our memories, emotions, thoughts, and actions (METAs). 
• Memories are synaptic connections that can be strengthened or weakened over time, a process known as synaptic plasticity. When you think about something, the relevant neural circuits that were activated during the original experience are reactivated. This is how memories influence thought patterns. The brain uses working memory (short-term memory) to hold information temporarily for processing and reasoning, while long-term memory stores more permanent information and experiences.
• Emotions often arise in response to thoughts and vice versa, with both emotions and thoughts influencing actions. 
• Thoughts are generated by the collective firing of neural networks. These networks are made up of neurons in various parts of the brain that become activated in response to specific stimuli or internal thought processes.
• Conscious thoughts are those we are aware of, and they are typically processed in the prefrontal cortex, which is responsible for executive functions like planning, judgment, and decision-making.
• Unconscious thoughts arise from deeper parts of the brain and may be related to instinctual behavior or automatic processes, such as memories, learned habits, and emotions. These thoughts can influence our behavior without us being fully aware of them. 
• Subconscious thoughts and memories exist between the conscious and the unconscious, surfacing occasionally what we refer to as intuition, insight, or creativity.

Conclusion

Human life is a complex cellular network. Human cells are tiny machines where biochemical processes occur and generate the physical phenomena that we call life. Cells begin as generic (stem) and later undergo differentiation and specialization. All cells regardless of specialty conduct basic or generic operations that have the result or effect of keeping the overall organism alive. Generic functions include metabolic, genetic, maintenance (MGM) activities. There are many different types of specialized cells in the human body. Red blood cells are the most abundant by far, accounting for about 80% of all cells in the body. Neurons are the most complex and fascinating in our opinion, leading to the complex functions that we call cognition. Neurons perform functions that serve as communication and regulation of all bodily functions. Their ability to transmit electrical signals and communicate through chemical messengers underpins nearly all bodily functions, from simple reflexes to complex cognitive processes. Neurons work together in intricate networks to process information, coordinate actions, and help maintain homeostasis. Thoughts, for example, are generated through the complex interplay of neurons, neurotransmitters, and various brain regions. Neurons transmit electrical impulses, release neurotransmitters, and form networks that activate certain mental processes and memories. The brain integrates sensory input, memories, and associations to produce thoughts, which are influenced by both conscious and unconscious processes. This vast network of interconnected neurons enables the rich and dynamic experiences that we recognize as thoughts.

Keep thinking. Keep learning. Keep simplifying. It can be fun.

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