How Your Nervous System Works Part 1 🧠

The Nervous System is the most complex thing in existence, here's what we know so far. (8min Read)

TL;DR Summary:

• What the spinal cord is and its role in getting our nerves to our body

• The 12 cranial nerves, and how they function

• What a Neuron is, and how does it work to help our Nervous System function

• How the Neuron is structured & its function

The Nervous System is the most complex thing in existence. There’s nothing more complex in the entire universe.

That being said, we’ve learned quite a lot about it since the start of the 20th century.

In this blog series, I will break down some of the basic units of the Nervous System so you can learn about the thing you’re learning with! (Neuroscience joke, couldn’t help myself.)

The Peripheral Nervous System

Before we get too deep into the individual cells that make up the Nervous System which we will spend most of our time on today, let’s talk about how these cells get out of our skull.

The brainstem is the last part of the “Brain” before we move into the Spinal Cord & body.

This is why before we break down what a nerve is, it makes sense to understand how they get out of our brains.

The Spinal Cord's most vital role is to transmit nerve impulses for movement, sensation, pressure, temperature, pain, and much more from the brain to the body, and vice versa.

The Spinal Cord is also responsible for our reflexes! This function is so crucial that the Spinal Cord even acts independently of the brain to control them.

How Reflexes Work

Most people think that when the doctor taps on your knee that your knee sends signals to your brain, and then your brain back down to your knee causing the kick reflex, but that’s not actually how it works.

This all happens right inside the Spinal Cord, which is why they happen nearly instantly!

Another great example is hot water! Have you ever gone to put your hands under water to wash them only to realize it’s near boiling temperature causing you to pull your hands away quickly?

The next time this happens pay close attention, if you do, you’ll notice that you pull your hands out from under the water before you feel the pain.

This is because your Spinal Cord fired an instant signal to hand & arm muscles to pull your hands away, and shortly after that signal hits your hand and arm muscles, the pain receptors in your skin have gotten their pain signal to the brain, which then signals to you that you’re hurt and you then feel the pain.

The nerve path from your Spinal Cord to your muscle is a much shorter distance than the one from your skin all the way up to your brain, this distance difference is what explains this phenomenon.

Spinal Nerves & Cranial Nerves

Nerves that originate from the Spinal Cord are aptly called Spinal Nerves. These types of nerves make up the vast majority of the nerves in our Peripheral Nervous System!

While the Spinal Cord & its nerves make the largest 2 -way highway between our brain & body, there is another pathway that our brain gets information from outside of the skull, the 12 Cranial Nerves.

The Cranial Nerves are a set of 12 nerves that are directly connected to the brain allowing it to interface with the outside world quickly!

Some of the most important of these nerves are the primary drivers of our senses.

We aren’t going to go in-depth on every single one in this blog, but we will hit a couple of the most important ones!

The Optic & Vagus Nerve

The Optic Nerve is an example of one of these Cranial nerves.

Its job is massive considering vision is one of our most used senses, so much so that nearly 70% of the total brain plays a part in it.

The Vagus Nerve is another example of a Cranial nerve. The Vagus Nerve is the boss of the Parasympathetic Nervous System!

It is also the longest nerve in the body, running all the way from the center of the brain to the top of the small intestine!

The Parasympathetic Nervous System is part of our Autonomic Nervous System and is responsible for our Rest & Digest functions. This is the system that is active when we are calm, cool, and collected.

When active, it clears out stress chemicals like cortisol from our bodies and decreases inflammation in our brain.

This makes the Vagus nerve a direct connection to this calming system inside of us!

We also have Cranial nerves for smell, eye movement, sensory information in the face, and motor movements of the face and mouth!

Nerve Cells

By now, you’re probably wondering what a “nerve” even is, they seem important, but how do they work?! Let’s dissect these powerful cells!

Whenever you hear the word “nerve” it is a catch-all term for any type of neuron. Neurons are the main cells that make up the Nervous system.

Just like a brick wall is made of individual bricks, each of the parts of the Nervous System we’ve talked about so far are made up of neurons and their lesser-known cousins, glial cells.

To be exact, we have about 170.68 billion cells in our Nervous System, 86.1 billion of which are neurons and 84.6 billion of which are glial cells or neuron support cells.

Let’s break down the Neuron! There are multiple types of neurons that break down into super-specific cell types, however, for the purposes of this blog, we are going to classify them into 3 main categories.

Motor neurons, Sensory neurons, & Interneurons or sometimes called Association Neurons.

Motor neurons are efferent nerves, which again means they’re going from the Central Nervous System (CNS) out to the Peripheral Nervous System (PNS) to affect muscles or glands.

Sensory neurons are afferent nerves, which are the opposite of efferent neurons. They bring information from the PNS back to the CNS for processing!

Interneurons or Association neurons sit right in the middle of sensory & motor neurons helping them communicate with one another more effectively.

The 3 Parts of a Neuron

Neurons themselves have 3 main parts no matter what type of neuron they are. Those 3 parts are a cell body, axons, and dendrites.

The cell body or “soma” as it is commonly called in relation to neurons, is where the neuron creates neurotransmitters, and other proteins necessary for the cell's survival.

The axon is the long tail-looking portion of the neuron. It extends from the soma (cell body) and is the main communication cable for signals leaving the neuron.

Dendrites on the other hand are the branch-looking parts that extend off the soma.

These are like antennas for the neuron, they connect the axons of other neurons to pick up the signals they are sending.

Where a dendrite & an axon meet is called a synapse, you’ve probably heard of this term before but may not have understood what it was.

Synapses are where the communication between neurons happens at the smallest level. They sit right at the junction of an axon & a dendrite.

Synapses & Math

This is where the numbers get a little crazy… As we talked about earlier, on average, the human brain contains about 100 billion neurons.

Each neuron has roughly 10-15k dendrites and may be connected to up to 10,000 other neurons, which brings the number of synapses in our brains to well over 1,000 trillion synapses.

That’s 1 quadrillion (1,000,000,000,000,000) synapses…

Here are some examples to get a feel for how many that is:

• A quadrillion words would take up 11 billion books

• It would take over 200 million years to count to 1 quadrillion

• A quadrillion hours is longer than the age of the universe itself…

And all of these synapses fit between your ears… Crazy right?

I hope you enjoyed today’s Neuroscience lesson! Next week we will learn about neural communication, neurotransmitters & brainwaves.

Thanks for tuning it, and until next time, live heroically!