{"id":594,"date":"2021-03-26T12:00:00","date_gmt":"2021-03-26T16:00:00","guid":{"rendered":"https:\/\/anyonecanscience.com\/?p=594"},"modified":"2021-03-26T11:58:37","modified_gmt":"2021-03-26T15:58:37","slug":"the-architecture-of-thought-part-3-neural-coding-and-neurotransmitters","status":"publish","type":"post","link":"https:\/\/anyonecanscience.com\/index.php\/2021\/03\/26\/the-architecture-of-thought-part-3-neural-coding-and-neurotransmitters\/","title":{"rendered":"The Architecture of Thought: Part 3\u2014Neural Coding and Neurotransmitters"},"content":{"rendered":"\n

So far, in our series on the architecture of thought, we\u2019ve dissected the conductive power<\/a> of neurons and the vast interconnected web of the peripheral nervous system<\/a>. The nervous system is an incredibly complex machine, so you may be feeling overwhelmed by now (if you\u2019re not overwhelmed, consider this: your nervous system is currently trying to understand the nervous system). Before we dive into the next section, let\u2019s take a moment to ground ourselves using my favorite grounding exercise. Take a deep breath and settle into the space around you. Now, look around you and name five things you can see, four things you can hear, three things you can feel, two things you can smell, and one thing you can taste. Not only does this exercise soothe anxiety by helping to trigger the parasympathetic division of the autonomic nervous system, but it is also a useful demonstration of the range of sensory information our nervous system manages from moment to moment. During the exercise, you forced your brain to consciously focus on fifteen discrete pieces of sensory information. But at any given moment, your nervous system collects thousands of individual information \u201cpackets\u201d from your various sensory organs. In order to transmit this cache of raw information to the brain, neurons have to convert it into a complex binary language of electrical signals and chemical neurotransmitters. These signals influence how you perceive those sensations\u2014whether they all dissolve into an overwhelming jumble of stimuli or if one stimulus rises to the front of your consciousness. And the way we perceive the world can even change day to day, moment to moment, based on the levels of certain neurotransmitters in the brain and the complex interplay of neurons.<\/p>\n\n\n\n

\"Neurons
Neurons use their vast network of interactions to convey information through neural coding and neurotransmitters.
“aman_geld 03.01.04 (neural network)”<\/a> by Cea.<\/a> is licensed under CC BY 2.0<\/a><\/figcaption><\/figure><\/div>\n\n\n\n

At the level of an individual neuron, excitation is an all-or-nothing affair\u2014either the neuron reaches the threshold potential and completely depolarizes, or it doesn\u2019t. But that excitation doesn\u2019t have to all come at once or from the same source. Smaller excitations\u2014called graded potentials<\/a>\u2014can sum together in succession or from different points of contact to create a full depolarization. On the sensory level, a single physical or chemical stimulus from the environment may not be enough to trigger full depolarization, but if it is persistent, the summation of the potentials over time will generate an action potential. This is called temporal summation, where graded potentials build up over time to trigger the neuron. Temporal summation can also affect how signals travel from one neuron to the next. Repetition of a relatively weak signal from an adjacent neuron can sum together to create an ongoing action potential. Graded potentials from multiple inputs\u2014spatial summation\u2014can also generate an action potential. Depending on their function, neurons can often form vast connection webs where their dendrites interface with multiple adjacent axons. An incoming signal from just one of those neurons may not be strong enough to trigger ongoing change, but signals from multiple sources can sum together to generate the full action potential. Temporal and spatial summation often work together, allowing the nervous system to filter stimuli and coordinate the electrical propagation of information. They also help to minimize the risk of random misfiring by preventing the propagation of isolated signals.<\/p>\n\n\n\n

Graded potentials can come in many different shapes, strengths, and flavors. Stronger stimuli push the membrane potential up more than weaker stimuli. More consistent stimuli may result in a longer, more drawn out graded potential. Some stimuli can even result in graded potentials that are hyperpolarizing\u2014they reduce the membrane potential. In the summation of signals, hyperpolarizing graded potentials act as subtractors, reducing the likelihood of an action potential. Hyperpolarization helps neurons carefully orchestrate the patter of firing neurons, which influences how a sensation is perceived. But you may be wondering how neurons modulate and control the movement of graded potentials. While some of these potentials are conducted electrically, the real nuance of graded potentials comes from the chemical interactions of neurotransmitters.<\/p>\n\n\n\n

\"Graded
Graded potentials come in various strengths of depolarization or hyperpolarization that can sum together to create an action potential. OpenStax, CC BY 4.0<\/a>, via Wikimedia Commons<\/figcaption><\/figure><\/div>\n\n\n\n

When an action potential reaches the end of the axon, it triggers the release of packaged neurotransmitters into the synaptic cleft between the presynaptic axon and the postsynaptic dendrite. As neurotransmitters flood this intercellular space, they diffuse and bind to specific receptors on the dendrite. Different receptors can have different responses to different neurotransmitters, so changing the receptor makeup of its dendrites is one way a neuron can modulate how it receives signals. There are hundreds of diverse neurotransmitters that affect neuron signaling, but many of them fall into a few general categories.<\/p>\n\n\n\n

One of the primary neurotransmitter systems of peripheral motor neurons is the cholinergic system<\/a>, which involves the binding of the organic cation acetylcholine to specific dendrite receptors. In most cases, acetylcholine triggers depolarization by opening ion channels. But when it binds to specific receptors that are not associated with ion channels, the same neurotransmitter can trigger hyperpolarization instead. The release of acetylcholine by motor neurons directly interfacing with muscle cells triggers muscle contraction. In the central nervous system, acetylcholine also acts as a neuromodulator\u2014a chemical signal that modulates the activity of many local neurons. As a neuromodulator, acetylcholine helps us maintain attention and focus on specific stimuli.<\/p>\n\n\n