Which type of neuron is most common in the brain?

This article answers the question “Which type of neuron is most common in the brain?” The article will also cover information on what neurons are, how they communicate, and the different kinds of neurons we have. The article will also answer some frequently asked questions in the end.

Which type of neuron is most common in the brain?

The most common neurons in the brain are interneurons. Interneurons work as intermediaries and are found in the brain as well as the spinal cord. 

What are neurons?

The brain consists of brain cells called neurons that are responsible for processing and transmitting information in the brain, and from the body to the brain and vice versa. In order to communicate with each other, neurons in the brain use electrical as well as chemicals known as ions. Ions are electrically charged particles that enable neurons to communicate with each other. 

Neurons are thus said to have electrochemical signs consisting of both electrical and chemical charges. These charges change on the basis of whether the neuron is on rest or active. When the neuron is active, it is either sending a message or receiving it (Furber, 2012). 

Neurons consist of fluids inside them that contain ions. These ions either have a positive or a negative charge. When at rest, the neuron consists of more negative ions on the inside and positive ions on the outside. This gives its membrane a negative charge. Whenever there is a signal of brain activity, positive ions rush through the channels into the neuronal membrane. When the charge is strong enough, it starts sending signals to nearby neurons to communicate with them. 

What are the different types of neurons?

Neurons differ from each other in their structure, function, as well as their genetic makeup. We have a billion neurons in our brain and thus we have thousands of different kinds of them.

Below we describe five major kinds of neurons, each of them has several characteristics of the basic neuronal shape.

Multipolar neurons

Multipolar neurons consist of a single axon and they have symmetrical dendrites extending from the axon. Multipolar neurons are commonly found in the central nervous system.

Unipolar neurons

Unipolar neurons are generally found only in invertebrate species. They only have a single axon. 

Bipolar neurons

Bipolar neurons are found to have two extensions that extend from the cell body. One side’s end contains the axons while the other has dendrites. These neurons are usually found in the eye’s retina. However, depending on their functions, they can also be found in parts of the nervous system that assists in the functioning of the nose and ears.

Pyramidal neurons

Pyramidal neurons have only one axon but they have several dendrites. This makes them look like a pyramid shape. Pyramidal neurons are the largest neuron cells and are most likely to be found in the cortex.

Purkinje neurons

Purkinje neurons have several dendrites and they spread out from the cell body. They are inhibitory neurons. This means that they release neurotransmitters that work to keep other neurons from firing or getting activated.

When it comes to the functions of neurons, scientists classify neurons into three types namely, sensory, motor, and interneurons.

Sensory neurons

Sensory neurons function to help you taste, smell, hear, see, and feel things around you. They are activated by physical and chemical inputs that you encounter in your environment. From these, sound, touch, heat, and light are considered to be physical inputs whereas smell and taste are chemical inputs.

Motor neurons

Motor neurons have a role to play when it comes to movement. This includes controlling both voluntary and involuntary movements. These neurons help the brain and the spinal cord to communicate with other muscles, organs, and glands of the brain. 

There are lower motor neurons that carry messages from the spinal cord to the smooth muscles as well as skeletal muscles. Upper motor neurons carry out messages between the brain and the spinal cord. 

Interneurons

Interneurons carry out signals from the sensory neurons and other interneurons. It also carries messages from motor neurons to other interneurons and vice versa. They help in forming complex circuits which help us in reacting to external stimuli.

What are the different types of Neurotransmitters?

Neurotransmitters can be categorised into two types: small-molecule transmitters and neuropeptides. 

The difference between the two is that small-molecule transmitters such as dopamine and glutamate generally have direct access to act on their neighbouring cells. Neuropeptides consist of smaller molecules such as insulin and oxytocin. These work in subtle ways and regulate the communication of cells at the synapse. 

More often than not, the way neurotransmitters are talked about, it seems as if they have only one function. For instance, dopamine is given the role of being the pleasure chemical, while GABA is considered to be involved only in learning. 

However, as time passes, neuroscientists are discovering newer and more multifaceted functions of neurotransmitters. They are trying to study how neurotransmitters work for and against each other, and how they send neural signals to the cortex. Below we will discuss some of the most studied and well-understood neurotransmitters.

Acetylcholine

The first neurotransmitter to ever be discovered was Acetylcholine (Ach). Ach is said to be a small-molecule neurotransmitter which involves muscles, and it helps us to convert our intentions into actions. Ach is passed from the neurons into the fibre of the muscle. Ach also plays a role in directing attention, and facilitating neuroplasticity in the brain, especially across the cortex.

Dopamine

Dopamine is one of the most-studied neurotransmitters. This is because dopamine has links to various kinds of human behaviour which includes motivation, and pleasure-seeking, and it plays a role in addiction behaviours. Dopamine also has a role in attention, memory formation, learning, movement, as well as our ability to anticipate pleasure. 

Glutamate

Glutamate (GLU) is known as the most excitatory neurotransmitter in the cortex. Too much glutamate can be detrimental to the person, as it can lead to excitotoxicity. Sometimes, excess release of glutamate can cause the death of neurons as it leads to strokes, traumatic brain injury, or amyotrophic lateral sclerosis. It can also cause Lou Gehrig’s disease, which is a neurodegenerative disorder.

However, the excitement glutamate causes in the brain is also useful in various functions, including learning and memory. Long-term potentiation (LTP) occurs in glutamatergic neurons located in the hippocampus and cortex. LTP is the molecular process which enables the formation of memories. 

Serotonin

The calming chemical, serotonin (5HT) affects mood modulation. A lack of serotonin has been associated with depression, as well as other psychiatric disorders. Serotonin also helps in the management of appetite, sleep, memory, as well as decision-making.

Low levels of serotonin and dopamine cause similar symptoms. However, one stark difference is that dopamine deficiency affects muscles, while serotonin deficiency does not. 

Norepinephrine

Norepinephrine (NE) is a hormone as well as a neurotransmitter. It is also known as noradrenaline. Norepinephrine affects moods, arousal, vigilance, memory, and stress. Researchers are now focusing on whether norepinephrine plays a role in post-traumatic stress disorder (PTSD) as well as Parkinson’s disease. 

Gamma-Aminobutyric acid (GABA)

Gamma-Aminobutyric acid (GABA) is the antithesis of glutamate, where it is the most inhibitory neurotransmitter. GABA’S function is to inhibit neural signalling. However, if it over-inhibits cells too much, the results of this can be detrimental. It can lead to epileptic seizures and other problems. GABA plays an important role in laying down important neural circuits in childhood, during early development. GABA is known to be the “learning chemical” because it plays a crucial role in deciding whether learning has successfully taken place or not. 

Conclusion

This article answered the question “Which type of neuron is most common in the brain?” The article also covers information on what neurons are, how they communicate, and the different kinds of neurons we have. The article will also answer some frequently asked questions in the end.

Frequently Asked Questions: Which type of neuron is most common in the brain? 

What is the most common neurotransmitter in the brain?

Glutamate is the most common chemical in the brain. It is an excitatory neurotransmitter which is found across the brain and spinal cord. Its functions include early brain development, thinking, memory, and learning. 

What are brains made up of?

Soft tissue, including the grey matter, white matter, nerve cells, and non-neuronal cells make up the brain. The brain also includes small blood vessels. Brains also have high water content and nearly 60% of fat.

What are neurons made up of?

Neurons are made up of three parts. These are the cell body, dendrites, and axons.

References

Furber, S. (2012). To build a brain. IEEE spectrum, 49(8), 44-49.