The Brain Electrical Signals
Electrical impulses are the fundamental mechanism used to transmit information from one place to another. They are very common in all living organisms.
They have been known since ancient times. There are two types of electrical impulses: those which are transmitted through nerves and those which are transmitted through muscles.
Nerves carry signals from one part of the body to another. These signals are made up of small electric charges, or currents, which travel along nerve fibers.
Nerve impulses may originate anywhere in your body. They are sent to the brain for interpretation. The brain then decides on a response, which is then sent back to the body.
Muscles may also contract if an impulse reaches them. This happens without conscious thought.
For example, if you step on a sharp object, a signal is sent from your foot to your brain. The brain sends an impulse back down to the muscles in your foot. These contract, causing you to jerk your foot. Your body has learned over time that this reaction will help avoid damage to the foot.
The way that the brain sends messages to muscles is slightly different. There are two types of muscle tissue: voluntary and involuntary.
Voluntary muscles are ones that we can control, such as the ones in our arms and legs. Involuntary muscles are ones over which we have no control, such as those in the heart or stomach.
If you want to raise your arm, you decide to do so. Your brain sends an electrical impulse down to the nerves in your arm, which then send a signal to the muscles.
These contract, and the arm moves.
When you are hungry, your stomach growls. This is the stomach muscles contracting involuntarily.
Your brain sends a signal through the appropriate nerve, which causes the muscles to contract.
The difference between these two types of muscles is how they react to electric signals. Voluntary muscles react to electric signals sent from the brain.
In order for you to raise your arm, the signal originating in your brain must reach your arm.
Involuntary muscles react to electric signals generated by nerves coming from elsewhere in the body. These signals travel along the nerves until they reach the involuntary muscles, which then contract.
An example of this is your heartbeat. Your heart contains two chambers, and a set of muscles for each chamber.
These muscles contract and push the blood along through the veins and arteries.
How Does the Brain Interprets these Electrical Impulses?
The brain does not directly react to the electrical signals sent through the nerves. It instead reacts to tiny chemicals known as neurotransmitters. These are released by the nerves in order to send their signal. These neurotransmitters drift through the space between two neurons, which is known as a synapse. When they reach a neuron, the neuron reacts to them. This reaction is known as a synaptic event.
The way that the brain interprets these synaptic events, is through synapses which are designed to react to specific neurotransmitters. These are known as receptors.
There are two types of receptors: excitatory and inhibitory.
Excitatory receptors react to specific neurotransmitters which cause the neuron to fire. Inhibitory receptors work the opposite way.
They cause a neuron to not fire, which prevents it from react to stimuli.
In order for a neuron to react to a synaptic event, it must have both excitatory and inhibitory receptors. These receptors are either on or off.
They cannot be half on or half off. For a neuron to react, the amount of on and off receptors must reach a certain level.
This means that the brain cannot have a set level of firing. It is constantly either firing or not firing.
If there are too many excitatory receptors, or not enough inhibitory ones, the neuron will react every time it is stimulated. If there are too many inhibitory ones, or not enough excitatory ones, then the neuron will never react.
Our brain has an enormous number of neurons, with an enormous amount of variation between them. Some have a lot of excitatory receptors, with very few inhibitory ones.
Others have the opposite make-up. Some have very few of either, and fire randomly.
The net result of all of this is that our brain does not react to stimuli in a set way. Instead, it creates reactions unique to us.
When we observe something, listen to something, or otherwise sense something, our unique brain makes a unique reaction.
This is how we are conscious. These reactions, over time, create our personality and our consciousness.
Without these reactions, we would be nothing.
Are We Conscious?
If our consciousness is simply a bunch of reactions taking place in our brain, then are we conscious?
Sources & references used in this article:
- Making sense of taste (DV Smith, RF Margolskee – Scientific American, 2001 – JSTOR)
- How neural networks learn from experience (GE Hinton – Scientific American, 1992 – JSTOR)
- What does fMRI tell us about neuronal activity? (DJ Heeger, D Ress – Nature Reviews Neuroscience, 2002 – nature.com)