Brain Cells form and function

You can’t understand the brain without first having some idea as to how brain cells work, but before you can understand how they function, you must have some idea as to what they are and how they are constructed. [1]

SO HERE’S THE BASIC PICTURE:
(Graphic from “How Your Brain Cells Talk to Each Other”, by Mike Ludwig)

https://kids.frontiersin.org/articles/10.3389/frym.2017.00039

Brain cells are called neurons. Some authors refer to the neuron’s body as the “Soma”.
Neurons aren’t all the same – some are bigger, some smaller and depending on where they are and what they do, they can be quite different in shape.
Basically they are like other cells, with a nucleus made of DNA (in the chromosomes) and other genetic materials, positioned within a pool of protein jelly.
Suspended in the jelly are sausage-shaped mitochondria [2], which supply energy, other “organelles” (super-tiny organs) which make enzymes and proteins to run the cells’ chemical processes and “microtubules” [3], through which chemicals, including stimulatory or inhibitory “Neurotransmitters” and even organelles, can be transported across the jelly and down the axon or dendrite, to its terminal. Interestingly, the microtubules are supported by a filmy network of “tau” protein – more on tau, in the article on Alzheimer’s!

The connections between axons and dendrites are called “synapses” and the synaptic space between the terminals is only a couple of nanometres.
To message another neuron, a “sending” neuron fires an electrical pulse via its Axon.
This pulse triggers the release of a neurotransmitter chemical from the axon’s terminal, which only has to go a few billionths of a metre to cross the synapse.
On crossing the synapse, the neurotransmitter, whether excitatory or suppressive, immediately binds to its specific “receptor” protein molecule and in so doing, elicits a positive or negative effect (depending on which type of neurotransmitter it is) on the receiving nerve cell. In this way, instructions from a “sending”, to a “receiving” neuron are delivered virtually instantaneously.

However the brain isn’t made up of neurons alone: support cells, called microglia, astrocytes and oligodendrocytes, which vastly (10 to 1) outnumber neurons, provide the neurons with physical support, cleanup services and anti-inflammatory/anti-infection defences.

ENERGY SUPPLY, MAINTENANCE AND REPAIR OF NEURONS

Brain cells of course, need nutrients, oxygen and glucose for energy, a system of enzymes and hormones** for maintenance and repair and a disposal system, for the chemical waste which they generate.
The bloodstream supplies them with the glucose, oxygen and nutrients and carries carbon dioxide and some metabolic waste products away, but some “debris” is simply deposited from the neuron into the surrounding fluid, to be removed by the glial cells or washed away by the brain’s “glymphatic” flow. [4]

The brain’s clean-up system – the Glymphatic Flow

Maintenance and Repair: the hormonal system

The Brain Makes Its Own Neurosteroid Hormones, In Neurons and Glial Cells:

The hypothalamus, along with the pineal and pituitary glands, are quite reasonably regarded as a part of the brain: they make many hormones, including melatonin, antidiuretic hormone, thyrotropin releasing hormone, thyroid stimulating hormone, oxytocin, gonadotropin-releasing hormone, kisspeptin, serotonin, ACTH, growth hormone, hCG, LH, prolactin and a few others.

What is less known is that the brain, using cholesterol as the base chemical and 5-alpha reductase for its main enzyme, does the same job in the neurons and glial cells as the adrenal cortex does, manufacturing Pregnenolone, DHEA, Testosterone, Progesterone, Allopregnanolone and other “neurosteroid hormones” for its own use.

However it does not make enough neurosteroids to supply the entire body and especially because of its very high blood flow rate, its hormones are mostly carried away to the body proper.
So when the adrenals, gonads, thyroid and other hormone-producing glands in the body proper fail [as they do, progressively, with age], the supply of hormones within the brain falls along with the supply in the rest of the body.
Therefore, particularly since the brain is in many ways, more sensitive to hormone loss than any other body part, it is often the first to show evidence of catastrophic hormone failure.

The Difficulty with Maintenance and Repair

DHEA, Pregnenolone [5], Progesterone [6], progesterone’s main downstream product Allopregnanolone [7], Melatonin, Magnesium and Vitamins D, C, B9, B12 etc. combine to do maintenance and repair, particularly repair of the myelin sheath, for the neurons and the long axons which communicate with distant cells.
In addition, it has been shown that estrogen, testosterone and the other “sex hormones” are active in brain maintenance and repair: if they are deficient, simply replacing them can go a long way towards correction of the cognitive deficit which we so often see in aging humans [8].
Finally, Triiodothyronine (T3), the functioning hormone made from the thyroid’s raw material product, “Thyroxine”, does the same in the brain as it does in the entire body: it increases the efficiency of all the cells, thus improving everything from sensory appreciation, to muscle strength, to heart function, memory and cognition.

The human body’s production of every single one of the hormones mentioned above falls to less than 10% by the age of 80 years, in many cases falling to zero.
Deficiency is associated with disease in the case of each hormonal item.
Perhaps maintenance of normal hormonal levels might permit ongoing normal function of all (or most) of our human systems preventing, or delaying, the development of the diseases and conditions of old age.
This possibility exists for the brain:
For details re. mitochondria, microtubules and brain function, see the articles below.
to see the article on Alzheimer’s, click HERE.

REFERENCES

[1] “How Your Brain Cells Talk to Each Other”, by Mike Ludwig, Front Neurosci. 2019; 13: 503.

Published online 2019 May 17. doi: 10.3389/fnins.2019.00503, PMCID: PMC6533804, PMID: 31156378 ……
https://kids.frontiersin.org/articles/10.3389/frym.2017.00039

[2] MITOCHONDRIA the role of mitochondrial function and cellular bioenergetics in ageing and disease,
by m.d. Brand, A.L. Orr, I.V. Perevoshchikova, and C.L. Quinlan
Br J Dermatol. 2013 Jul; 169(0 2): 1–8., doi: 10.1111/bjd.12208, PMCID: PMC4321783, NIHMSID: NIHMS659950

PMID: 23786614 —— this article concerns mitochondria in old age: it is difficult – look up mitochondria in Wikipedia..

[3] MICROTUBULES Stability properties of neuronal microtubules, by Peter W. Baas, Anand N. Rao, Andrew J. Matamoros, and Lanfranco Leo, in Cytoskeleton (Hoboken). 2016 Sep; 73(9): 442–460. ,
doi: 10.1002/cm.21286, PMCID: PMC5541393, NIHMSID: NIHMS877290, PMID: 26887570

[4] “Alzheimer’s: an overview, by G. A. Harry, in “momentary PA explained”, at https://wordpress.com/page/cbhrt.ca/201

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