The Cortex Machina project has its origins in a deeply rooted fascination with neurobiology in general, and the biological origins of consciousness in particular. Unfortunately, it can often be very challenging to discuss and share these fascinating concepts, simply because they generally require a lot of prior knowledge which is, to say the least, quite unfamiliar to most people. That’s why we have started this series of short columns: to kindle interest in the fields of neuroscience and neurobiology and to provide my readers with enough general knowledge on the human brain and cognition to start exploring and sharing these fascinating concepts themselves. We will start with a series of articles on brain anatomy, to provide the reader with an understanding of brain architecture and nomenclature, which will be helpful later on when we discuss other topics. So without further ado, let’s enter now into your Synapses!

Neurons Synapses

A synapse consists of two synaptic terminals (“presynaptic terminal” on the axon side, “postsynaptic terminal” on the dendrite side) separated by a gap called the “synaptic cleft”, which physically separates the two synaptic terminals. It is here that the electrical signal from the axon of one neuron is transferred to a dendrite of another neuron. Signals are sent across the synaptic cleft through the use of neurotransmitters. The presynaptic terminal contains small sacs filled with a chemical neurotransmitter, which is released into the synaptic cleft when a signal is sent down from the emitting neuron. On the receiving end of the synapse (at the postsynaptic terminal), special receptors on its surface bind to the released neurotransmitters, generating a new electrical signal, which will then travel down the dendrite to the receiving neuron’s main body (the “Soma”). 

This “chemical transmission step” means that our nervous systems (and thus our brains), contrary to popular belief, aren’t purely electrical. Instead, they’re hybrid electro-chemical systems. One might believe this is just due to evolutionary limitations, e.g. our brains are “slow” because evolution couldn’t come up with purely electrical systems, but this couldn’t be further from the truth. We do have parts of our nervous systems that are purely electrical, where signal transmission doesn’t need any chemical neurotransmitters, zipping along at the speed of light. So why doesn’t the whole nervous system function like this? Because slower signal transmission enables our brains to selectively slow-down or speed-up signals (this is one of the functions of the myelin “pearls” encasing parts of the axon), which turns out to be one of the major ways our brain controls the flow of information between individual neurons and/or neuron clusters. If our nervous system was purely electrical, all signals would travel at the speed of light, meaning speeding up signals would be physically impossible, while slowing them down would be complicated and energy-intensive (for instance by ‘looping’ signals between neuron clusters at opposite ends of the brain), or rely solely on logic-gate analogues that can block or let a signal through, but are unable to throttle the signal transmission speed. Our brains aren’t ‘slow’ because it’s a disadvantage that evolution couldn’t overcome, our brains are slow because it’s the evolutionary most efficient way to control signal transmission! Maybe this could inspire someone to build computer processors exploiting the advantages of being able to slow-down or speed-up signal transmission at various points, instead of relying on logic gates and light speed signals ☺.

Let’s now go over a couple of definitions that will be useful further on:

Potentiation is the process by which synchronous firing of neurons makes those neurons more inclined to fire together in the future. Long-term potentiation occurs when the same group of neurons fire together so often that they become permanently sensitized to each other. As new experiences accumulate, the brain creates more and more connections and pathways, and may “re-wire” itself by re-routing connections and re-arranging its organization.

The ability of the connection, or synapse, between two neurons to change in strength, and for lasting changes to occur in the efficiency of synaptic transmission, is known as synaptic plasticity or neural plasticity, and it is one of the important neurochemical foundations of memory and learning.

The inverse of long-term potentiation, known as long-term depression, can also take place, whereby the neural networks involved in erroneous movements are inhibited by the silencing of their synaptic connections.

Synaptic pruning, a phase in the development of the nervous system, is the process of synapse elimination that occurs between early childhood and the onset of puberty in many mammals, including humans. Pruning starts near the time of birth and continues into the mid-20s. During pruning, both the axon and dendrite decay and die off

The infant brain will increase in size by a factor of up to 5 by adulthood, reaching a final size of approximately 86 (± 8) billion neurons. Two factors contribute to this growth: the growth of synaptic connections between neurons, and the myelination of nerve fibers; the total number of neurons, however, remains the same

Synaptogenesis is the formation of synapses between neurons in the nervous system. Although it occurs throughout a healthy person's lifespan, an explosion of synapse formation occurs during early brain development, known as exuberant synaptogenesis.

A big thanks for your reading from the entire Cortex Machina team!

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