Topic

2.1 The Neuron

The Neuron

Neurons are one of the most important things to understand when it comes to any aspect of nervous system health. Their structure and function can be very profoundly affected by nutrition, and even the slightest lack of key nutrients can have effects on the nervous system that may be an intense experience for anyone affected. Let’s first look at the parts of the neuron and how each individual part works:

neuron

Axon

The axon is essentially the long fibrous projection of a neuron. Axon’s can vary massively in length. Some can get as long as a metre and some as short as a millimetre. Their function is to transmit information. This could be sensory information like our earlier example of touching something hot or it could also be information that instigates movement. Axons (almost) touch other neurons, muscles and glands. They carry their signal in the form of a special electrical impulse called an action potential. This electrical impulse moves across the axon at an insanely fast pace, until it reaches the axon terminal, which is the very endpoint of the neuron that you can see on the diagram. For neurons that aren’t directly feeding muscles or tissues, it appears that they are touching each other back to back. However, there is, in fact, a gap between them, known as the synapse. When the action potential reaches the terminal end of the axon it has to deliver the impulse across the gap. This gap is called the synapse.

Synapse & Communication Between Neurons

The synapse is the gap between two neurons. As previously outlined, the signal that moves along a neuron is electrical, in the form of an action potential. This signal, however, cannot jump across the synapse, it needs to be carried across by different means. Enter the neurotransmitter. Neurotransmitters are chemical communication molecules that take the message that is being delivered by the action potential and translate it into a chemical message that is capable of jumping the gap between neurons.

Once it reaches the neuron it is then translated back into an action potential, and so it continues. As the action potential moves along the axon and reaches the terminal, it triggers a different set of processes. At the terminal, there are small vesicles (sacs) filled with different neurotransmitters that cause different types of responses to take place.

Different signals activate the vesicles containing different neurotransmitters. These vesicles then move to the very edge of the membrane at the axon terminal and release their contents, the neurotransmitters, into the synapse. On the neighbouring neuron, there are specialised receptors that are designed to recognise specific neurotransmitters. When they recognise a specific neurotransmitter, they know what signal (in the form of an action potential) to trigger in the neuron.

So, the electrical signal gets to the end of the axon, gets translated into a chemical signal that can move across the synapse, gets picked up by a receptor, then gets translated back into an action potential where the process continues, until the response is given. This response may be moving your arm or trying to remember an important date. Whatever the neurological response, the same principles essentially apply.

The Myelin Sheath

The myelin sheath is a very important structure indeed. It is required for proper nerve function and is designed to maximise a neuron’s communication capacity. The myelin sheath is an outcropping of cell membranes that are composed of proteins and specialised fatty material.

It is there to allow the electrical impulses in neurons – the action potential, to actually jump across the axon rather than simply flowing across it. This makes the action potential travel like lightning. If you see on the earlier diagram, the myelin sheath is not a single envelope that wraps the axon, but rather is laid out as a series of little capsules along the length of the axon. Between these little capsules are tiny areas of exposed axon. These are called ‘Nodes of Ranvier’. The action potential jumps from node to node, travelling across the axon quicker. Even the slightest degradation of the myelin sheath can drastically affect the functioning of the neuron.

In extreme circumstances, where the immune system attacks the myelin sheath, the results can be devastating and life-threatening. As such, the body constantly maintains the myelin sheath and requires key building blocks to do this. These are the all-important dietary fats!

meylin-sheath