Neurons, also called nerve cells, are extremely important. They are mostly located in the brain. Without them, we cannot think, feel, or move our bodies. Life would not be possible without them. It would be unwise to say that neurons are simple. They are actually quite complicated. However, they aren’t too difficult to understand if we just look at the basics of what they look like and what they do.
STRUCTURE
Neurons pick up information from the outside world through the senses of sight, touch, sound, smell, and taste. They share this information with other nerve cells in the brain. Basically, neurons allow the brain to actually think and also to talk with the rest of the body. There are specialized types of neurons, such as sensory neurons and motor neurons, but the basic structure and function is the same for every type.
Communication happens when the electrical charge of the neuron changes. This is the key. The structure of the nerve cell is designed to allow the charge to travel from one end to the other. There are four main parts of the neuron: soma, dendrites, axon, and terminal buttons.
Soma
Also called the cell body, each neuron has one soma. The soma is the control center of the neuron. It contains cytoplasm, mitochondria, and the cell nucleus, all of which control and regulate the neuron’s activities. The cytoplasm is a jelly-like substance in which other materials are suspended. The mitochondria store and release energy as needed by the neuron. The nucleus contains the genes that are responsible for forming different proteins needed by the neuron.
All contents of the soma are enclosed in a membrane, which controls the electrical charge of the neuron. Technically, it is called the membrane potential and it has ion channels which open and close to allow the exchange of differently charged fluids. As we know, the electrical charge must change for the neuron to talk to other nerve cells, so the membrane is where communication really begins.
Axon
Each neuron has one axon, which is a long tubular structure that branches into terminal buttons. The axon allows the neuron to stretch far enough to make physical contact with other cells. It is covered in myelin sheaths, which prevents it from scrambling its electrical signals.
The outside of the axon is covered in a layer called the axon membrane. The axon membrane has ion channels that open and close after the soma is activated. The inside of the axon is lined with microtubules, which are protein strands that allow for the transport of substances.
Terminal Buttons
Each neuron has many small knobs on the end of the axon called terminal buttons. The job of these buttons is to make physical contact with other cells and deliver messages by releasing chemicals.
Each terminal button has a space inside that is filled with cytoplasm and synaptic vesicles; the vesicles are small spheres that hold neurotransmitter. Neurotransmitters are basically chemicals that carry messages from one cell to another.
Dendrites
Each neuron has many tree-like branches called dendrites. Dendrites receive information from other cells via binding sites. All dendrites contain binding sites with which neurotransmitters will connect whenever the nerve cells are communicating.
Most dendrites are smooth, but some of them have dendritic spines, which are larger than average binding sites. The binding site has proteins that detect neurotransmitters. Also near the binding site are ion channels, which open and close when the neuron is activated.
FUNCTION
The main function of a neuron is to send messages to other cells, basically allowing the brain to communicate with the rest of the body. using electrical impulses. An electrical impulse begins with the soma, travels along the axon to the terminal buttons, and ends with the release of neurotransmitters from the terminal buttons.
The electrical impulse can only occur when something strong enough stimulates the neuron into action. In order for this to happen, there must be an action potential.
A neuron is stimulated into action by a strong sensation such as the pain of stepping into a fire. The pain is first detected by the dendrites of a sensory neuron. The dendrites send the information to the soma. The information is exciting enough that the neuron wants to tell the other nerve cells about the pain. An action potential is about to be triggered.
The soma membrane opens its ion channels to allow for the exchange of fluids. The exchange is what changes the electrical charge of the membrane potential from negatively charged to positively charged. This rapid change in electrical charge is the action potential. It is now possible for the neuron to send a message to other cells.
The action potential triggers the membrane of the axon to open its ion channels, allowing the axon to also become positively charged. The electrical impulse travels along the length of the axon until it reaches the terminal buttons.
The terminal buttons react by allowing the synaptic vesicles to fuse with the presynaptic membrane. The vesicles are now able to release neurotransmitters that will cross over and attach themselves to the other neuron.
By this time, the electrical charge of the first neuron has returned to normal, and the ion channels have closed. It has successfully delivered the message that the fire is too hot.
Action potentials may or may not happen, as the neurons will consider many factors including the person’s thoughts and emotions. In this example, the pain is intense enough that the neurons tell the leg muscles to pull away from the fire and therefore stop the pain.
Neurons allow the brain and the body to communicate with each other. People need them to make decisions, feel physical pain, experience thoughts and emotions, and move their bodies. In other words, neurons are the cells that make life possible.
SOURCES
Carlson, N.R. (2005). Foundations of Physiological Psychology. Boston, MA: Pearson Education, Inc.
