Neurodevelopment in Humans and Specialization of Cells

by Claire O'Sullivan
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As a constant student of anatomy and neuroanatomy, taught by Marion Diamond of UC Berkeley, it’s been one of my favorite subjects when I practiced in the medical field.

Today, I’ll present a very small portion regarding the development of the neurological system. The neural tube: here is both the first part of the embryo’s development and the last – and that last, after birth. Mind you, these processes are far more complex than I can present here.

It’s a complicated system but involves our ability throughout life (beginning in the embryo) to think, feel, and move. It’s perhaps the most vital development and there are many things that affect this development both positively and negatively. I might add specialization of these cells is intricate to the point of awe, cells weaving among each other, knit together and work with amazing accuracy while developing each individual with its own abilities and personalities. Cloning cells falls far short, as the DNA strands are shortened with each replication. In essence, humans, adapted over the years, and bright as we are, we cannot replicate what 2 cells do in the beginning.

At 16 days post-ovulation/insemination, the neural tube forms, folding into a groove so to speak, which can be seen on MRI. The embryo continues, and by day 17-18, the development of glial and neurons can be seen. Not quite three weeks post insemination, this amount of growth and specialization occur and currently with our science can be seen on MRI. At the third week, the fetal heartbeat can be detected, and by the fourth and fifth week, the embryo has electrical activity in the developing brain and the fetus is already moving within the womb, and by a month, the fetus is curling fingers, and then sucking its thumb, hiccupping, and yawning.

The neural tube is vastly important. Neurons create what are known as ‘action potentials,’ sending messages from the brain to different body parts. Glial cells are non-neuronal, but they 1. Protect the neurons 2. Are found in the central nervous system (CNS) as well as the peripheral nervous system (PNS) 3. Maintain homeostasis and 4. Protect myelin. 5. Glial cells support and nourish neurons.1

Glial cells specialize into astrocytes, which provide support; oligodendrocytes, which form the myelin; and microglia, which produce antigens and destroy bacteria.2

Astrocytes not only provide support but protect against trauma, cell damage, death, ischemia (i.e. stroke), metabolic disorders, and neurodegenerative diseases.3 Astrocytes are so numerous and important that without astrocytes all cell function would fail.4, 5

Oligodendrocytes develop the myelin and grey matter. They are progenerator cells (ancestor cells, not to be confused with stem cells),6 develop astrocytes and oligodendrocytes not only in the development of the human brain, but in the remyelination of cells in degenerative disorders such as multiple sclerosis in the adult brain. Schwann cells are similar to oligodendrocytes but in the PNS, also developing myelin sheath. As Schwann cells develop, they wrap neuronal axons in myelin. Myelin is one thin bilipid layer (bilipid refers to cells in the brain and the periphery, as bound by two lipid or cholesterol layers) which protects from movement disorders and in the brain, protection from memory loss.7

Myelin disorders include multiple sclerosis perhaps as the most—known PNS disorder while Alzheimer’s and memory loss in found in CNS disorders.8

In my own practice I had seen these things occur, not just in patients, but myself. This becomes important when patients with high cholesterol take lipid-blocking medications or lose so much weight their cholesterol drops. In the skin, one will note bruising and even muscle damage, tears, and loss. The heart is pure muscle, so the question, ‘how low should cholesterol go?’ is not simply an irrelevant topic, it is dangerous for all body systems to entertain as a positive move. In the brain, the lipid bilayers simply fall apart and people become forgetful. I noticed when I was eating a low fat diet, my cholesterol dropped to a total cholesterol of 113 and I was had spontaneous bruising.

Over the years, we have found many simple things to improve the appropriate neural tube development, the maintenance of a healthy brain as well as adverse behaviors. Here are both negative and positive outcomes:

  1. Smoking causes arteries to constrict, decreasing blood flow, causing unintended cardiovascular problems leading to stroke.9 “The prefrontal cortex is one of the last areas of the brain to mature.

  2. Evidence suggests that exposure to nicotine during adolescence interferes with the normal course of brain maturation and has lasting effects on cognitive abilities, mental health, and personality. The adolescent brain is in a vulnerable state of imbalance and particularly susceptible to the influence of brain-altering substances like nicotine. Nicotine is a psychoactive and addictive substance that directly interferes with all brain areas involved in emotional and cognitive processing. Nicotine use during adolescence results in cell damage and cell loss throughout the brain, and particularly in the hippocampus, the mind’s memory bank.”10

  3. In the prenatal developing brain, nicotine starting in the first trimester, show endocrine abnormalities in sex differentiation, increased cortisol (weight, stress, immune system negative effects), cellular proliferation (cells that produce rapidly as in cancer), and early apoptosis (early cell death), and decreased brain cell production.11

  4. Lest you think only women should not smoke, the DNA/RNA of men’s sperm is also affected, and these effects passed onto the developing embryo.

  5. High sugar (an inflammatory) and high fat diet leading to obesity is just as damaging as too little cholesterol. Extra weight means increased inflammation and stress (cortisol) and has been shown to decrease brain size leading to cognitive impairment and dementia.12 It would be safe to assume that smoking is bad for men and women, fetuses at conception, and adolescents.

  6. In a Harvard study, research showed that regular exercise improves not just your bodily health, but brain health. Cognitive, prefrontal lobe (where we make our everyday executive decisions), improvement, hippocampus (our internal memory drive), and can increase the volume (size) of the brain.13 Regular exercise in rats has shown that at 5 weeks, embryos had 40{44c8773cfc5435cd81ad20e0c4d9124b8149e87e023df21bb722cbe5a8d7cc51} more neurons than non-exercising rat moms.

  7. Ever wonder why there is folic acid (folate) in your cereal? In the US and other countries, this is a national mandatory for most cereals. Adolescents (and some adults) eat cereal for at least breakfast. Folic acid is a requirement during the embryonic stage to fully form the neural tube, which closes at last 28 days after birth of the baby.14, 15 The mitochondria (energy packets within each cell, their engines) contain 40{44c8773cfc5435cd81ad20e0c4d9124b8149e87e023df21bb722cbe5a8d7cc51} of the total cellular folate, so it’s evident that folic acid is required for the cells to have the energy to complete the task of neural tube formation.16 Spina bifida is one neural tube defect most known, where the neural tube does not fully close, and often the spine is open to the skin surface.

  8. Eat healthy fats, including polyunsaturated and saturated. Your diet should include 20-35{44c8773cfc5435cd81ad20e0c4d9124b8149e87e023df21bb722cbe5a8d7cc51} calorie intake from fats.17

  9. Everyone understands the problems with fetal alcohol syndrome, so I won’t even go into that, nor the endocrine changes noted in adolescent brains since the brain does not reach maturity until age 25. But for adults, drinking a glass of wine a day may be great for the heart, but not for the brain. There is no amount of alcohol useful to cognitive ability or survival of brain cells. I don’t know about you, but I’d like to keep every brain cell in good working order!18

  10. More bad news: Marijuana use, medically or for morning sickness can cause significant problems in neural tube development, fertility in parents, and a host of other problems. Forget the bad juju regarding meth, cocaine and heroin (which we all know), even the most benign considered drug can cause mild damage to death in the fetus.19

And that is the beginning of brain health, memory, cognitive factors which begin in the ova and sperm—before insemination.



Claire O'Sullivan
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