Neurology

Neurology refers to the branch of medicine that deals with the diagnosis and treatment of disorders of the nervous system. The Central Nervous System (CNS) is your brain, retina (and joining optical nerves) and spinal cord. Your brain controls every decision you make, stores the experiences that you have, and tells you what is happening right now in the world around you. All of mental health is in your brain. No, your body does not keep score (mental no, physical sometimes).

An interesting way to view the human experience is that we are a mind that is controlling a spaceship made of meat, bones and bits. The mind is the sense of self which is a combination of the quickly changing software that runs on the biological hardware of our brains. All mental health is in our head – and that is because that is where our brain is. Medically, we refer to different aspects of our brain as neurology.

The Central Nervous System

The Central Nervous System (CNS) is comprised of the brain, spinal cord and the retina. Our brain is in the skull, a protective layer of bone. The retina of the eyes has complex nerve and neuronal structure that some argue means it is a part of the brain that is outside of the skull, but most say it is separate. Some similar arguments can be made about the olfactory nerves, however this is most commonly defined as not part of the brain. Running from our skull to sacrum (pelvis) is the spine, where vertebra bones encapsulates the spinal cord. Your spinal cord includes spinal motor neurons, which can make reflex decisions before your brain has been informed of a pain sensation. The spinal cord is an information superhighway between your body and cerebellum, the part of the brain at the hind base of your skull.

Beneath the skull is the meninges, 3 layers (dura mater, arachnoid mater, and pia mater) of web like structure filled with fluid that cushions the brain so that our brain is suspended safely within our skull. This same structure covers your spinal cord. Just like the seatbelt in a car that helps your soft and breakable body not fly around the inside of your hard car when you turn corners, speed up, slow down or suddenly stop, the meninges helps your brain and spinal cord be safe within your bony protection.

The meninges has some other interesting activities around the health of your brain to do with nutrient delivery, flushing toxins and filtering. This circulatory system is a fairly new field of study. For more, look up the Subarachnoidal Lymphatic-Like Membrane for more about this.

Neuronal Cells

Your brain is filled with various different kinds of cells. Some are tiny, some are huge (around 1 metre long).

Common Types of Cells

  • Neurons, aka nerve cells, are made up of:
    • Interneurons,
    • Pyramidal cells including Betz cells,
    • Motor neurons (upper and lower motor neurons), and
    • Cerebellar Purkinje
  • Glial cells, the Neuronal Macroglia is the collective term for the four sub-types:
    • Astrocytes,
    • Oligodendrocytes, and
    • Ependymal cells
    • Microglia
  • Neural stem cells, and
  • Blood vessels

Study of our brains has mostly focused on how neurons interact with each other. Glial cells are a relatively new area of study as it has recently been demonstrated that Glial cells do more than just maintain neurons. Neural stem cells differentiate and become either neurons or glia. Blood vessels are one of two circulatory systems for the brain, and carry the usual blood contents to the brain and waste metabolic products from the brain.

You may have noticed “most of our brain is in our skull”, which begs the question, what part of the brain isn’t? The nose has olfactory sensory neurons that samples the air you inhale through your nose and reports your sense of smell. The olfactory sensory neurons are directly connected to your brain, growing through a part of your skull called the cribriform plate of the ethmoid bone, connecting straight to your cerebellum. Another part of your brain protrudes from your optic foramen, via the optic nerve which is the axons of neurons. The retina is a mini-processing centre converting light into action potentials to be sent along the optic nerve.

Lastly we have the spinal column and the entire body nerve system. The central nervous system is your brain and spine. The neuron in your skull that triggers a muscle to twitch or relax has an axon that travels out of the skull and down the spine and then out to the muscle they trigger. The peripheral nervous system has interconnecting neurons cells that pass on sensory data, such as hot, cold, sharp, blunt and itch.

Neurons

Neurons are polarised cells that are specialised for passing messages via a chemical process called “action potential”, which are conducted from the centre of the neuron down a long branch called an Axon towards another neuron cell. The sender Neuron will use a chemical cascade down the Axon involving calcium and potassium, sending an electrical signal via ions. This signal gets to the end of the Axon, building a charge until it squeezes from reservoirs at the end of the Axon a fluid called a Neurotransmitter. The Neurotransmitter goes from the reservoir into the Synaptic Gap of the Synapse, bridging the Axon and the Dendrite (the receiving branch of the Receiving Neuron). The Neurotransmitter allows the ion charge to go from the end of the Axon to the beginning of the Dendrite, which then continues the signal to the other Neuron.

If the Neurotransmitter level is absent or low, the Axon has to build up much more charge to get a signal across the Synaptic Gap, it may even fail to bridge the gap entirely. If the Neurotransmitter level is too high, the charge crosses prematurely. It is important that the right level of Neurotransmitter is present.

We have a number of different Neurotransmitters that specialise in different profiles and are used to get different effects from the gap and Neuron signal. More on those later.

After the signal has fired, some of the excess neurotransmitter is reabsorbed into the Axon Neurotransmitter Reservoir aka vesicle. This is what “uptake” is referring to in medications called a “reuptake inhibitor”. The uptake is mediated by a neurotransmitter dependent transport chemical. Flooding this chemical with a dummy other chemical inhibits the ability for the transport chemical to take the associated neurotransmitter back to the Axon Neurotransmitter Reservoir. This is “reuptake inhibition”, such as dopamine reuptake inhibitor, or serotonin reuptake inhibitor. These medications cannot reuptake as much of the neurotransmitter, and not as much unabsorbed neurotransmitter is flushed away, leaving some of the neurotransmitter in the synaptic gap, decreasing how much of the neurotransmitter is needed to make the neuron signal cross the synaptic gap, and thus decreasing how much replacement neurotransmitter must be synthesised to refill the Axon Neurotransmitter Reservoir.

Excess neurotransmitter is flushed away, some becoming another related Neurotransmitter.

  • Dopamine -> Noradrenaline -> Adrenaline
  • Serotonin -> Melatonin

Glial Cells

It was assumed for many decades that glial cells merely maintained the neurons We are now aware that glial cells also play a role in neurotransmission, synaptic connections and autonomous actions such as breathing.

Scientific learning on this has been rapid and this is new section of study.

[More at the excellent Glia Wikipedia page]

Neurotransmitters and Synapses

We have a detailed section about how Neurotransmitters work.

Briefly, Neurotransmitters are chemicals that our brain uses to turn signal pathways on and off, much like electronic circuits in a computer. Actually, we based computers off the way that we thought our brains worked. Neurotransmitters are often hormones or other chemicals that are used for very different functions outside of our brain in the general body. Biology is efficient – if it can use the same chemical in multiple ways, then it will so it doesn’t waste resources in making an extra chemical.

Most of the important neurotransmitters are made both in our body for body use, and separately in our brain for use as neurotransmitters. This is because most of our neurotransmitter chemicals cannot pass through the protective Blood Brain Barrier. This means that taking a medication that contains the neurotransmitter generally doesn’t affect our brains, only the rest of the body. As such, the medications we take to help our brains often helps our brain make more of the neurotransmitter, make less, or affect how the neurotransmitter sends signals.

Medial Prefrontal Cortex and the Executive Function

The medial prefrontal cortex (mPFC) is a crucial cortical region. It is one of the primary things that separates our human thinking from other animals, even other primates. The mPFC is poorly developed in children, only starting to mature from the onset of puberty, completing the full growth in our mid 20s. Effectively, the mPFC houses the interconnecting networks of neurons referred to as the Executive Function.

Executive Function

The Executive Function is an oft times used phrase where people think they know what is meant, but when you look deeper, there is no single agreed upon definition of what it means.

Most commonly, it refers to tasks that you consciously and presently do, or the processes involved in doing this, and is separate from autonomous / autopilot tasks. Unfortunately Executive Dysfunction is often used to refer to a failure to do what most people do automatically, that is as autonomous or autopilot tasks.

We explain this more fully on our Executive Function Page.

What the Executive Function Does:

  • Cognitive process (understanding, reasoning, logical, assessment)
  • Regulation of emotion (not too high, not too low)
  • Motivation (planning and execution of behavior)
  • Sociability (interacting with others)
  • Working memory (holding relevant timely information that speeds up tasks)
  • Inhibitory response control (holding back doing the wanted action)
  • Maintenance of focused attention and concentration

Mental Health and the PFC

The vast majority of medical conditions and neurodivergences that are haphazardly lumped under “mental illness” is effectively a dysfunction of the mPFC, which is often connected to the dopaminergic system. [“Medial prefrontal cortex in neurological diseases”, 2019]

Research shows us that perceived external stressors affect how the Mesolimbic Dopamine Pathway operates. These can be physical stressors or psychological stressors. This then affects how the Mesocortical Dopamine Pathway affects our behavioural expression.

References

Subarachnoidal lymphatic-like membrane. (2024, April 22). Wikipedia. https://en.wikipedia.org/wiki/Subarachnoidal_lymphatic-like_membrane‌

‌Xu, P., Chen, A., Li, Y., Xing, X., & Lu, H. (2019). Medial prefrontal cortex in neurological diseases. Physiological Genomics, 51(9), 432–442. https://doi.org/10.1152/physiolgenomics.00006.2019

Wikipedia Contributors. (2019, May 17). Glia. Wikipedia; Wikimedia Foundation. https://en.wikipedia.org/wiki/Glia