Ain't About Those Mixed Signals
Have you ever thought about your thoughts? Maybe you have in the philosophical way of ‘why do I think?’ or when a really random thought passes by, you think ‘that was weird, where did that come from?’. But have you ever considered the physiology of what makes a thought? What processes are going on in that noggin to make you think of that really funny situation when you are sat in a serious meeting and you cannot stop yourself spluttering with laugher? Or just as you are drifting off to sleep, you remember every embarrassing thing you have ever done and die inside? The entities responsible for generating not only thoughts, but your movement, senses, interpretation and memories are neurons; the brain-specific cell type packed inside your skull in their millions. Before we can get into the many jobs these cells perform, we need to get to know them as individuals and how they have adapted for their complex functions
What are you looking at: Neuroanatomy
All cell types of the body contain some similar features, such as the organelles mitochondria and ribosomes, but have slight or major adaptations enabling them to carrying out specific actions. The neuron looks nothing like the ‘basic’ pumpkin-spice animal cell. The neuron is extra.
The first thing you may notice about the neuron compared to the animal cell is its spidery appearance. And while some arachnophobes may recoil at those spindly processes, they play a vital role in the neuron’s main job; signalling. Neurons signal to many other neurons rapidly to allow you to function in real time. There are a few essential anatomical adaptations involved in neuronal signalling:
Dendrites: a neuron has many dendrites coming off the cell body. These processes are the area at which a signal is received.
Axon: each neuron has a single axon. This process is where the neurons outgoing signal is delivered.
Synapse: this is the junction formed between one neuron’s axon and another neuron’s dendrite. It is the site of signal transmission.
So, if a neuron receives a signal at a dendrite, this signal is sent to the cell body which can then be passed on down the axon to a synapse with another neuron’s dendrite. This is the route of transmission in all neurons.
No Service: What is Neuronal Signalling?
When you think of signal, you think of that ancient technology you used to use to text people and have to hang out of your window to stop your call breaking up. Now, the word ‘signal’ is normally replaced with ‘data’ or ‘Wi-Fi’, but both of the latter are still types of signals. They allow you to receive information and send out responses in the blink of an eye. So how do neurons communicate?
Well, the technology a neuron uses to signal may not appear to be quite as fancy as the new IoS or windows update, but the principals are similar to the very basic code these software’s are built on. Neurons communicate using an ‘all or none’ signal called an action potential. At the synapse, action potentials are passed from one neuron to another. These signals are sometimes described as ‘electric’ signals as they use ions inside and outside the neuron for their conduction, similar to electrical conduction.
The all-or-none nature of the action potential means the neuron either sends a full action potential or nothing at all. There is no ‘half’ or ‘small’ action potential; each one is the exact same size. This is similar to binary code (something I know verrrrry little about). Everything on your screen right now is coded by a series of 1’s and 0’s and everything in your head is coded by action potentials (1) or not (0). When an action potential is triggered, there is a short period when no other signal can be transmitted. This is known as the refractory period and prevents constant action potential signalling.
I’ve got 99 signals but can only send 1
A single neuron can receive thousands of signals all at once. This is because of the numerous dendrites an individual neuron has, allowing axons from many different neurons to form synapses along the dendritic branches. But how does a neuron process these signals and decide which is important if every signal is made of identical action potentials? The best way to think of this situation is to consider dendrites as Wi-Fi signals, synapses as routers and the cell body as your phone. There are a few situations which permit some signals to be stronger than others.
1. Proximity of signal to cell body: the closer the synapse and its incoming signal, the more likely it will reach the cell body and trigger action potential conduction down the axon. Signals made at dendrites far away from the cell body (distal dendrites) fade before they reach the main part of the neuron. Like with Wi-Fi, if the router is far away from your device, you cannot get a signal but if you sit next to the source of the signal, you can stream live Monday night football as clear as day.
2. Repetition of signal: What if a signal at a distal dendrite is really important? The way these signals make it to the cell body is by constantly sending action potentials in very quick succession so the signal does not fade. This is like buying a Wi-Fi booster; the signal is almost retransmitted in a location distant from the router and closer to your device.
3. Synapses near each other amplify signals: This is a phenomenon neurons have developed to amplify smaller signals which may not have reached the cell body. If two synapses on a single dendrite receive sub-threshold signals, a larger signal can be produced leading to the cell body generating an action potential. This would be like having multiple routers with pretty poor bandwidth on the same network; they poor signals would sum to generate a signal worthy of updating all your apps.
So once all the ‘important’ signals reach the cell body, the neuron compiles them and transmits a combination signal of action potentials along its axon. The axon terminals can branch out to many dendrites of many other neurons so this signal can be sent far and wide. The same scenario applies concerning strength of signal and distance in the axon too; with far-reaching terminals sometimes receiving signals considered too ‘weak’ to pass on to a neighbouring dendrite.
The reason the neuron is picky with the signals it receives and sends creates a dynamic signalling system. This prevents really vital signals being lost but makes sure crucial energy is not wasted transmitting non-important signals throughout your neural network.
It really is amazing what goes on in your brain. Every fleeting thought, small movement and random memory flash-back are caused by fine-tuned networks of neurons signalling to one another. We have one of the most intricate and essential social networks sat inside our own heads and while you have been reading this article, your collective neuronal network has been signalling hundreds of thousands of times a second. If your Wi-Fi router had that type of bandwidth, websites would load instantly, YouTube videos would be in ultra-4K HD and live-streaming really would be live streamed. Your neuronal network is a work of genius so next time that random thought passes by, appreciate the little guys who generated it.