Neurotransmitters are chemical compounds that affect how we feel in our mood. Neurotransmitters are chemical messengers. They sit between the post and presynaptic cleft and help jump the action potential or connect the presynaptic neuron to the postsynaptic neuron. Learn about how do neurotransmitters work?
What are neurotransmitters?
Neurons release neurotransmitters, and they can either have an excitatory or inhibitory effect. If we look at a neuron that’s releasing a neurotransmitter, it releases it into the gap. This gap is called a synapse. It’s the gap between one neuron and the next neuron.
Neurotransmitters that will bind to the next neuron will either excite it to send a signal or inhibit it from sending a signal. They don’t just bind to neurons. And they may also bind to muscle, cells, or glands. They can bind to multiple different what we call effectors, which will elicit some change.
Types of neurotransmitters
There are different types, and they serve different functions, so let’s get a closer look at these now.
While many compounds qualify as neurotransmitters, let’s start with the most common ones: Small molecules of three classes.
These are given below:
- Amino acids.
1. Amino acids: Glutamate, aspartate, glycine, and gamma-aminobutyric acid, or GABA for short, which is derived from glutamate.
2. Monoamines: Dopamine, epinephrine, norepinephrine, and serotonin. The first three are categorized as catecholamines, while serotonin qualifies as indolamine.
- The catecholamines are all synthesized by enzymes from tyrosine, converted in a series of steps into L-dopa. Then dopamine, and then norepinephrine, and then epinephrine.
- By contrast, serotonin is synthesized from tryptophan.
3. Acetylcholine: This is in a class of its own, and it is simply a choline molecule that has been acetylated.
- This molecule should be very familiar from our study of the neuromuscular junction in the anatomy and physiology course due to its role in promoting muscle contraction.
4. Unconventional: Another class of unconventional neurotransmitters doesn’t fit into the other categories. This includes small molecules like nitric oxide and carbon monoxide.
These are of a different class because being extremely small and nonpolar.
- They can pass through the cell membrane and thus freely diffuse in and out of cells without passing through membrane proteins.
- Once produced inside a neuron, they move into other cells, stimulating the production of second messenger molecules. Then they are quickly converted into something else, so they are short-lived.
- Sometimes, these molecules are involved in the retrograde transmission, where they travel from the postsynaptic neuron back to the presynaptic, opposite the direction of travel for other neurotransmitters.
Another class of unconventional neurotransmitters is endocannabinoids, which are also retrograde transmitters.
- These are similar in structure to delta-9-tetrahydrocannabinol. The psychoactive agent in marijuana, and similar functions, as they bind to endocannabinoid receptors.
There is also one class of very large neurotransmitters, and that’s the neuropeptides. These are polypeptide chains, some of which are large enough to qualify as a protein.
Each has a different function, which will depend on the amino acid sequence it possesses. And they are categorized primarily according to their location in the body.
- Pituitary peptides in the pituitary gland.
- Hypothalamic peptides in the hypothalamus.
- Brain-gut peptides in the gut.
- Opioid peptides, which resemble opium.
- All the other miscellaneous ones are grouped into a fifth category.
How do neurotransmitters work?
There’s a set of chemicals in the body that cause how you feel, how you think, whether or not you sleep well. They’re called neurotransmitters. They have to do with virtually every function of physical activity, cognitive activity, emotional activity.
If these neurotransmitters have been changed because of stress or trauma, or malnutrition, we may have a child who’s dramatically altered physiologically. Let’s also briefly outline some details regarding function.
- First, neurotransmitters will exhibit two effects when they find their way into their respective receptors’ active site.
- Electrochemical activity propagates along an axon, resulting in one of two things. With an electrical synapse or gap junction, ions can flow from one cell to the next. But with a chemical synapse, neurotransmitters are released at the axon terminals. These interact with receptors on the post-synaptic neuron, and then the signal continues.
- They will either cause excitation or inhibition. This is kind of like flipping a switch on or off. More specifically, an excitatory response will result in depolarization for the post-synaptic neuron, while an inhibitory response will be one that results in hyperpolarization for the post-synaptic neuron. So it’s the difference between propagating a signal and halting it.
- Some neurotransmitters tend to produce one effect over another, like how glutamate is typically excitatory, while glycine and GABA are typically inhibitory.
For others, it depends on the context. Acetylcholine is excitatory at the neuromuscular junction for skeletal muscles but inhibitory in cardiac muscle.
Next, we must distinguish between direct and indirect action.
Direct action: Direct action is when a neurotransmitter binds to an ionotropic receptor and opens it up so that ions can pass through.
- This will affect the membrane potential and promote the rapid propagation of a particular effect.
- Acetylcholine and the amino acid neurotransmitters tend to behave this way.
Indirect action: Indirect action is promoted through second messenger molecules, like the G proteins.
It is similar to the way hormones operate, and metabotropic receptors mediate the activity. The monoamines, neuropeptides, and small gas molecules will tend to exhibit this behavior. And when these act as chemical messengers in this manner, we sometimes call them neuromodulators.
Here are some neurotransmitters and their functions:
Acetylcholine: Acetylcholine has two major types of receptors.
Now depending on what it wants to do depends on the receptor. For example, our peripheral nervous system is divided into the central brain, spinal cord, and peripheral.
- Acetylcholine plays a significant role in skeletal muscle contraction, muscles attached to our bones.
The specific receptor involved here is muscarinic receptors, which means you can have certain drugs that we can use to act on muscular receptors that can affect the way we move our muscles.
- Acetylcholine also plays an essential role in the autonomic nervous system, specifically the parasympathetic division. It is the rest and digests the autonomic nervous system, which is sympathy dick fight-or-flight parasympathetic rest and digest.
- The parasympathetic uses acetylcholine at every single neuron. The sympathetic only use it from the first neuron. The second neuron sends a signal and talks to the target effector. It could be a muscle, gland, cell type, whatever. It’s going to be the digestive system or the heart or the pupils or saliva glands. This is the parasympathetic acetylcholine released at every single point.
It’s essential in rest and digestion, but the spinal cord plays a vital role in memory and cognition in the central nervous system brain. It has been implicated in Parkinson’s disease, which is the most common movement disorder. And Alzheimer’s disease is the most common neurodegenerative disorder.
Catecholamines: Catecholamine is an umbrella for three neurotransmitters. They are:
These three neurotransmitters are produced by the amino acid tyrosine, which we must get from our diet. We can’t create ourselves. We can make it from phenylalanine, but we need to get phenylalanine from our diet as well.
There’s a couple of different receptors that are used. You can have α1, α2, β1, β2, β3. Let’s ignore β3 because they’re only found on fat cells. And we don’t have any drugs that utilize this receptor.
Let’s look at α1 and β1. If noradrenaline or adrenaline balance these receptors, it’s excitatory. For example, what you’ll find is alpha one is found on our blood vessels.
For example, so we’re noradrenaline binds to alpha1 blood vessels will constrict blood pressure. Beta1 is found at our heart when noradrenaline bonds to increase the heart rate and increase the heart’s contractile force.
- Alpha 2 (α2) is found on the postsynaptic neurons, so that’s the second neuron. And what it does is that it auto regulates the sympathetic nervous system. It stops the sympathetic nervous system from firing off any more signals. So it’s like a negative feedback system.
- Beta 2 (β2) if noradrenaline binds to this is found in our lungs. And it opens the airways up some more air come in and out now in the central nervous system.
- Adrenaline and noradrenaline are necessary for opioid release. It is our endogenous opioid system. So opioids are there to pain anxiety. This is involved in opioid release adrenaline.
- Dopamine is a reward molecule, our feel-good molecule. It does play a role in the central nervous system. It’s involved in initiating motor movement and smoothing out motor movement. Now in people with Parkinson’s disease that the neurons that make dopamine are dying off. Dopamine plays a role in blood vessel diameter and the kidney’s role in excrete sodium.
Serotonin: Serotonin is also known as 5-HT. It plays an important role in the central nervous system with sleep and mood, and the peripheral nervous system plays a role in our GRT. If neurons release serotonin in our gut, that’s right. We’ve got neurons in our stomach that released serotonin.
- It stimulates the gastrointestinal tract to contract and push things through too much pushes it through far too quickly.
- It also plays a role in bone remodeling, bone stronger.
Gamma-aminobutyric acid (GABA): GABA is the primary inhibitory neuron of the nervous system. So it inhibits neurons from firing off. That’s a significant role.
- It stops neurons from firing off, usually by throwing negative chloride into the cells. If the cells become super negative, called hyper-polarization, they won’t fire off.
Glutamate: Glutamate is the most common or most abundant excitatory neuron in the nervous system. It has two major types of receptors, NMDA in AMPA. If stimulated and they will tell neurons to fire off. You can have glutamate toxicity too much.
- Glutamate being released can kill brain cells and has been implicated in dementia. This glutamate toxicity theory has been associated with dementia and Alzheimer’s disease.
Substance P: Substance P for pain. This is involved in the pain system. What is going to happen if substance P is released and in the peripheral nervous system?
- The central nervous system stimulates pain and inflammation, so we sometimes want to identify certain drugs that we can use against substance P to help mitigate pain.
I hope you will understand the complete facts of neurotransmitters. If you have any questions, then please feel free to ask. Please write in the comment section. Please share this important biological chapter with your friends that they understand it easily.
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