The Unknown Awaits…
There are explorers who choose to go beyond the limits of the “expected” and journey into the unknown. For instance, an individual with a flair for adventure and an urge to understand the unknown may want to explore the inner recesses of a forest, somewhere others dare not venture. Picture yourself as the adventurer, as you stand at the edge of a forest and look into the vast expanse of nature which has so many secrets and mysteries hidden within. In order to go as deep as you can into this forest of mystery, you have to let go of all your fears and inhibitions and trudge forward into the illuminating darkness.
As we stand bewildered and astonished at the neural forest that is the brain, we are awestruck by the deep valleys and large mountains that the fissures and grooves in the brain give rise to. By looking at the brain, standing on one of the main arteries travelling, one can see the illuminating sparks of nerve impulses lighting up various areas of the brain, not unlike flashes of lightning over the neural rainforest. As awe and fear are slowly overcome, we move into the vast forest of brain fluids and jelly, full of uncertainty on what to expect.
Into the Neural Wilderness
As we step foot into the neural forest, we are overtaken by an immense darkness which lasts for a matter of milliseconds, only to give way to tiny sparks of light that illuminate various areas of your perceptual bubble and then die off. Suddenly, a wave of impulses throws the darkness in your surroundings into clarity, as blinding flashes of light from a sudden surge of nerve impulses illuminate everything around us as we see the forest for what it truly is.
All around us, as far as we can see are intricate webs of neurons, so densely interconnected that moving through them while being larger than a millimeter would be quite impossible without severing some connections. Thankfully, owing to the scale that we have reduced ourselves to, we are able to easily navigate through the web of neural circuitry. These immense living circuits with their innumerable wires and connections are the trees that make up the ecosystem of the brain. These neural trees or neurons, are essentially the channel through which information is passed around the various parts and realms of the neural forest.
As we move closer to one of the neurons, we observe that its structure is quite analogous to a tree, consisting of immense branches as well as a long root. The branches which arise from the main cell body or soma, are known as the dendrites. As we look up at the extent of the dendrites and how far they have grown into the foliage of the neural canopy, we see that these dendrites are in turn connected to the dendrites of several other neurons, as well as their roots which are known as the axon terminals.
The axon terminals are the root-tip like structures which arise from the end of a long main root-like structure arising from the soma, known as a the axon. As we observe these axon terminals more closely, we observe that they are in turn connected to the dendrites of the next neuron through connections known as synapses. As we examine this particular connection, we are suddenly struck by a blinding flash of impulse that travels down the axon of the neuron that we were observing. As soon as the impulse reaches the synapse, we observe that the impulse itself is not transferred to the next neuron. In turn, a chemical interaction occurs at the synapse between the two neurons, due to which a new impulse is generated at the second neuron.
First Encounter with the Neural Fauna
As we marvel at the beauty of this connection between two neural trees, we fail to notice as a small yellow blob approaches us from behind. Suddenly, we hear a sound of a liquid oozing out from behind us, which draws our attention to the Microglial cell as it slowly consumes a foreign particle by phagocytosis.
Tripped Out Fact: Microglial cells are the scavengers of the human brain as they eat up dead neurons as well as other brain cells. Another important function that they play is that they eat up any foreign particle that may enter the brain and consumes it through a process known as phagocytosis, where the cell actually engulfs the particle in its own cytoplasm.
We slowly look around and find ourselves surrounded by quite a few of these microglia, some of them roaming around and feeling the cerebrospinal fluid with their long tentacle-like cytoplasmic processes, while others feed on the dead bodies of neurons scattered on the neural forest floor. We quickly and stealthily hide behind some of the interconnected branches of nearby neurons as we ourselves being foreign to the place have a high chance of being consumed by these phagocytotic beasts of the cerebral ecosystem.
As we inch forward into the neural forest, we come across another type of fauna that is indigenous to the neural wildlife. This cell seems to be quite interconnected to the axons of the neurons and seems to be supplying them with some substance. This cell is the oligodendrocyte, which has its long processes embedded onto the axons of nearby neurons. These processes give rise to the myelin sheath which covers the length of the axons.
Tripped Out Fact: The myelin sheath which covers the length of the axons acts like the insulating material on a telephone or cable wire. Essentially, these sheaths prevent the “leaking” of electrical impulses from the neurons and also speeds up the pace of the traveling impulse.
After quite a long walk through the neural forest, we sit down to rest for a while at one of the arteries passing through the forest, pulsating and emitting a strange crimson glow that fills the forest with an eerie and almost mystical atmosphere. Quite fitting for this atmosphere, we encounter a new type of neural fauna, with its immense processes extending out to give it the shape of a star. These are the one of the many calls know as astrocytes which inhabit the forest. This one is seen clinging on to the artery through some of its processes, while using the rest of its processes to cling on to the nearby neurons.
Tripped Out Fact: The astrocytes basically form the basis of the blood-brain barrier by wrapping around the capillaries in order to prevent leakage of the components of the arteries in the brain. Moreover, the astrocytes are also responsible for providing nutrients to the neurons by channelizing them from the arteries to the neurons to which they are connected to.
Welcome to the Jungle!
As we observe the large star-shaped member of the neural fauna, we also notice that these cells are some of the most widely distributed cells in the forest as a whole. We observe some astrocytes in the distance huddling close together in order to cordon off an area of tissue which has been injured. We also observe some astrocytes which huddle close to the synapses between two neurons and clear out the chemicals or neurotransmitters which are released at that site for the transmission of an impulse.
Tripped Out Fact: The neurotransmitters are certain chemicals, such as Serotonin, Dopamine and Acetylcholine, which help in the transmission of an impulse from one neuron to another through the synapse. The neurotransmitters may either serve to excite a neuron or to inhibit the impulse itself.
One of the astrocytes comes hovering over to us, shocking us and putting us in survival mode as we jump behind the neural circuitry in order to hide from it. But, we slowly begin to realize that these gentle giants of the forest mean no harm and are actually the safekeepers of the neural circuitry in the brain as a whole. We soon come out from behind our shelter and pat the astrocyte on one of its processes, acquainting ourselves to the cell. This marks our first direct contact with the fauna of the brain forest.
We soon move forward, with our aim being to reach the inner core of the brain, where the most primitive functions that can be attributed to our inner animalistic desires originate from. This would mean stepping into some of the deepest and darkest recesses of the brain, combing through more and more regions of the neural forest till we reach the core.
Stay tuned for the next episode of “Into the Brain”.