A few neuroscientific basics

What are neurons?

Neurons, also called nerve cells, are special because they can transmit and process information through electrical and chemical signals.

Neurons form the information highway that connects the different parts of our body with the brain. They are therefore found not only in the brain, but also in the spinal cord and peripheral nerves. Because neurons have different functions to perform, there are many different types of them.

However, the basic structure is always the same.

How do neurons work?

Neurons consist of three parts: The cell body or soma, which is the information processing unit, the dendrites, which are the inputs and the axon, which is the output. Neurons have many inputs but only one output.

Dendrites receive signals from other neurons in form of electrically charged molecules, also known as ions. The ions move along the dendrites and end up in the cell body. Here they are accumulated and once a specific threshold is reached, gates or ion channels will open and release them.

All the ions then flow out via the axon. This ion stream is called an action potential and we say the neuron “fired”. The neurons can fire up to 1000 times per second. Modern computers have processing units that execute billions on cycles every second.

To be a little more precise: Neurons are typically negatively charged, and the influx of positively charged ion flow makes them become more positive. The threshold the accumulated charge has to reach before an action potential is generated is about -55 millivolts.

Axons can be long – up to 1 meter – and they divide and connect to dendrites of thousands of other neurons. The interface between neurons is called a synapse. While information processing and transmission within the neurons takes place through electrically charged molecules, communication between the neurons is based on chemical messenger molecules also known as neurotransmitter.

To ensure speedy delivery of information, axons are covered by the myelin sheath. The myelin sheath acts as electrical insulation. Remember that a stream of ions through an electrical conductor is an electrical current. The axon is basically a cable, and the myelin sheath makes sure that action potentials are passed along the axon and reach their destination.

Brain networks and brain patterns

According to our current understanding, the brain is organized in networks and communicates in patterns of action potentials. An action potential can be seen as a binary signal. Either there is one, or not. The information is encoded in the sequence of action potentials, or in the frequency, i.e., how often, a neuron fires.

To produce different behaviours such as running or reading, different networks must be activated, and different action potential sequence patterns must be sent to other networks or to muscles and glands.

What happens if neurons get damaged?

Motor neurons are neurons that sends information from the brain to the muscles.

If, for example, the myelin sheath gets damaged, then without insulation action potentials cannot reach the connected muscles fibers, and the fibers cannot contract. Multiple sclerosis or Amyotrophic Lateral Sclerosis (ALS, also known as Motor Neurone Disease), for example, are diseases in which the myelin sheath degenerates and can lead to paralysis. Imagine a condition where cognitive and emotional functions are fully intact. You can think and feel and hear and smell. But you are not able to control a single muscle. A healthy mind trapped in its body.

There are of course several other situations and medical conditions that lead to the damage or degeneration of neurons. One in six people in the UK have neurological conditions such as dementia, Parkinson’s disease or experience the effects of a stroke. A stroke is a medical condition in which poor blood flow to the brain causes cell death.

Neural engineers have risen to the challenge and are exploring new technological solutions to help people with functional limitations gain more independence and quality of life.

It is now time to learn more about the technological principles and methods.