24 Dec Neuron Components and Cybernetics
The properties of subcellular neuron components, also known as organelles, are important to this research because they might contribute to the information acquisition, storage, accessing and maintenance systems of the brain. I plan to further discuss the reason for separating storage and maintenance in a post in the section on cognition. These properties may be structurally, mechanically or chemically mediated. They may be governed by the organization of substructures within cells, by the morphology or chemical makeup of the substructures themselves, or by the structural and/or chemical interactions between cells.
In digital computers, all storage and processing functions can be reduced to a simple description of whether each single-bit register in the mechanism is in a state called “set” or “reset.” This can also be described as “on” or “off.” Symbolically, it can even be abstracted to “true” or “false.” These simple abstractions form the basis of all digital computing. Each neuron has mechanisms that are capable of functions similar to a single-bit register. Neurons may, however, perform far more complex functions. We will look at these complex capabilities in cytoskeletal components of neurons, while describing the supporting functions of other components.
|Understanding Context Cross-Reference|
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|Modeling Neural Interconnections|
|neuron cytoskeleton||Linck 1989|
|organelles DNA||Kuffler 1984|
|Symbolic logic||Pickover 1990|
- Structural characteristics (How does the construction contribute to the capabilities?)
- Mechanical functions (How do the pieces interact with one another?)
- Chemical properties (How do chemicals flow in the system and bring about functions?)
- Cell components (What things exist within neurons and why are they interesting?)
- Interactions between cells (How does the structure/componentry of neurons enable interactions?)
The most important part of this natural/artificial intelligence analysis concerns axons and dendrites, sometimes considered neuron organelles. These are described in the next few posts, which deal primarily with the cytoskeleton and how it supports brain networking functions and network components.
Today we will engage in a brief discussion of the organelles that support the functions of the neuron. Major organelles are found in the body or soma of the cell, just as major organs are found in the main part of the body rather than the appendages (arms and legs, fingers and toes). The organelles discussed in this post are the nucleus, mitochondria, and endoplasmic reticulum. We will also look at the other components identified in the illustration above, including the ribosomes that appear as dots on rough ER.
The cell nucleus (sometimes called the nuclear envelope) is the neuron’s control center. The membranes of the cell nucleus contain the DNA of the chromosomes. This is the critical information necessary for the formation, division and differentiation of the cell. Each new neuron is permanent – it will not decay or disintegrate, nor will it be replaced during the organism’s life cycle. The control center in the cell nucleus does, however, go through two stages.
- During development, it controls the process of cell division.
- Throughout the remainder of its lifetime, it maintains all the cell’s subsystems.
The subsystem-maintenance function includes providing the information necessary to facilitate neurite growth. Axons and dendrites actually sprout from the cell; this most often occurs during the developmental stage. Continual neurite growth occurs throughout the life of the organism.
Because it is unlikely that the nucleus participates in cybernetic/ information-processing tasks other than supporting learning by facilitating neurite growth, it will not be described in detail here.
Mitochondria are independent, self-reproducing, sub-cellular particles of oblong shape. They range from .5 to 1 micron wide and 5 to 10 microns long. Mitochondria are surrounded by a double layer of membrane: the outer layer is similar to that of other organelles, but the inner layer is specialized for metabolic and respiratory functions. As a major producer of ATP, a basic source of energy, the mitochondrion is often referred to as the powerhouse of the cell.
Mitochondria membranes are about 30 percent lipids, including enzymes involved in respiration and phosphorylation. These membranes also control the intake and output of calcium ions and those of other molecules. Their possession of chromosomal DNA that resembles that of a procaryotic* cell enables them to synthesize some of their own essential proteins and to replicate themselves, making them relatively autonomous.
* (Procaryotic cells are smaller, independent cells such as bacteria and cyanobacteria. They have few or no organelles. Their DNA is circular instead of linear. RNA and proteins are synthesized together rather than separately as in Eucaryotes. They have no cytoskeleton and are usually unicellular organisms.)
The ability of the mitochondria membranes to open up channels is characteristic of other intracellular membranes, including those that enable the ion exchanges required to restore neuron charges. This ability demonstrates the profound interaction of structure and function, the continual interaction of the constituent parts of neurons to maintain the structural and functional integrity of the cell as a whole, and the ability to serve in their independent roles.Mitochondria membranes serve another important function: they expand and contract to enable the respiratory transfer of enzymes and ions necessary for many cell functions. Enzymes are building blocks for cell components. Neurons actually build the intracellular components that participate directly in cognition – something very relevant to the present study. One intracellular component is the synaptic vesicle that is produced in the cell body area and transferred to synapses by the motion of the cytoskeleton. Synaptic vesicles contain the neurotransmitter chemical necessary for propagation of electrical potential in the brain. The cytoskeleton also needs enzymes. Clearly, the mitochondria are important suppliers for neural manufacture.
Many intracellular components, including mitochondria, can self-replicate like DNA. This ability is essential to coordinated action, growth, development, and day-to-day functioning of the organelle, the cell, and, indirectly, the organism. It may be difficult to equate the balance of calcium within a cell to a person’s well-being or survival. It may be difficult to associate cognition with the controlled permeability of membranes and the ability of a small bundle of proteins to copy itself. While these cell properties only indirectly affect cybernetics, they are part of a massive network of mutually supporting mechanisms that ultimately support all human activities. Without them, cognition would not occur.
Naturally, some processes are more critical to cognition than others, and the breakdown of some functions has more impact than others. The self-replication of mitochondria and other cell components only affects cognition indirectly; however, failure of the process could profoundly limit a person’s cognitive capabilities. If we accept the premise that some neurons require more enzyme production to support greater involvement in cognition, then mitochondria become even more critical.
|Peripheral functions that||support cognitive activity:|
|axon formation and myelination||production/transfer|
|dendrite formation (neurite growth)||maintenance of chemical balance|
|synaptic vesicle||maintenance of resting potential|
Plus many more…
Endoplasmic Reticulum (ER) comes in two forms: rough or granular and smooth or agranular. The grains embedded in the surface of rough ER are actually ribosomes that presumably participate in some of the synthesis functions of ER. Rough ER and smooth ER are often found together, although rough ER is more common in neurons than is smooth ER. They often form contiguous bodies, but rough and smooth ER are made up of different proteins and lipids. They are both manufacturing centers, but they synthesize different products.
Smooth ER (shown in the bottom illustration) is usually tubular in structure. It is primarily specialized for the synthesis of membranes for organelles such as vesicles. Rough ER (shown in the top illustration), on the other hand, can synthesize proteins for ribosomes, for biogenesis, for extracellular transport, and for membranes. It is possible that synaptic vesicles and their neurotransmitter cargo can be combined in the ER, forming cholinergic and adrenergic bodies capable of secreting the chemicals necessary to propagate action potential across synaptic links.
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|4||Perception and Cognition||5||Fuzzy Logic||6||Language and Dialog||7||Cybernetic Models|
|8||Apps and Processes||9||The End of Code||Glossary||Bibliography|