Our body needs hormones and neurotransmitters to function properly.
Neurotransmitters allow communication between neurons and other cells, crossing the synaptic space and using nerve impulses. Hormones, meanwhile, are secreted by the endocrine glands, intervening in the regulation of a multitude of basic bodily functions.
Although they share structural and functional characteristics, there are also aspects that differentiate them.
In this article we explain what they are, how they work and what are the main characteristics of hormones and neurotransmitters, as well as the most important differences between them.
Difference between neurotransmitter and hormone
A neurotransmitter when released only communicates to an immediate neuron, through the synapse. Instead, a hormone communicates with another cell no matter how far away it is, traveling through the bloodstream.
Living beings with multiple cells and diverse organizational systems, such as animals, have the need for multiple tissues to maintain communication pathways, to allow the coordination of the body’s actions. Thanks to the communication pathways that exist at the cellular level, we can coordinate complex responses that involve various parts of our body.
Some of the best-known communication pathways at the cellular level are hormones and neurotransmitters.
Both are types of chemical messengers, which are excreted at the cellular level to stimulate other cells or tissues in some way, but they have marked differences mainly due to the purpose of these two organic communication pathways.
Hormones: definition, characteristics and classification
Hormones are chemical substances that act as messengers and activate different processes for our body to function properly. They are produced in the endocrine or secretory glands (such as the hypothalamus, pituitary or thyroid, for example) and are released into the extracellular space, diffusing through the blood vessels into the blood.
The main characteristics of these chemical messengers are that they intervene in metabolism and other functions (immune system, sexual reproduction, etc.); they act on tissues of the body that may be at long distances from the point of origin from where the hormone is released;
The effect they cause depends on the number of hormones there are, being directly proportional to their concentration.
Almost all hormones can be classified, chemically, into three large groups: peptide hormones, made up of amino acids, polypeptides or oligopeptides, such as insulin or vasopressin; hormones derived from amino acids, which use these to synthesize, such as adrenaline; and lipid hormones, from the group of eicosanoids or steroids, such as cortisol and testosterone.
Hormones can produce stimulating effects, promoting activity in a tissue (eg prolactin); inhibitory effects, decreasing activity (eg somatostatin, which inhibits the release of growth hormone); antagonistic effects, when two hormones have opposite effects to each other (eg insulin and glucagon); and synergistic effects, when two hormones together produce a more powerful effect than separately (eg, growth hormone and thyroid hormones).
Neurotransmitters: definition, classification and characteristics
Neurotransmitters are chemical substances that our body uses to send information from one neuron to another, through the synaptic space that mediates between them. These signals travel to and from the central nervous system, with the aim of coordinating our body, regulating muscle activity, body secretions and the activity of different organs.
Chemical messengers that act as neurotransmitters share some basic characteristics: they are stored in synaptic vesicles, they are released when calcium ions (Ca2 +) are introduced into the terminal axon in response to the action potential, and they produce their effect by binding to membrane receptors. of the post-synaptic cell.
The main function of neurotransmitters is to inhibit or stimulate the activity of post-synaptic cells, depending on the type of receptor on which they exert their effect, triggering changes in the permeability of the neuronal membrane and in its enzymatic activity, with the mediation of other neuromodulators (such as cAMP and cGMP).
There are different types of neurotransmitters that can be classified as follows:
- Amines: neurotransmitters that are derived from different amino acids. In this group we can include dopamine or serotonin.
- Amino acids: they are the precursor substances of amines (eg glutamate or glycine).
- Purines: substances such as ATP or adenosine, can act as chemical messengers as well.
- Peptides: distributed throughout the brain, the best known are opioid peptides (eg enkephalins and endorphins), responsible for modulating pain, among other functions.
- Gases: the most representative, nitric oxide, which produces vasodilator effects.
- Esters: in this group, the most representative neurotransmitter, acetylcholine, which is involved in the regulation of sleep or muscle activity, among many other functions.
Main differences between hormones and neurotransmitters
Once defined, we can begin to unravel the main differences between these two types of molecule.
It is worth mentioning that there are neurotransmitters with hormonal function and vice versa, as is the case of norepinephrine, a molecule very similar to adrenaline. This is also the case of dopamine, a neurotransmitter with hormonal functions on the pituitary gland, blocking the release of prolactin.
1. Type of molecule
The molecules that fulfill the function of hormones are more varied than those that fulfill the function of neurotransmitters. Among the molecules that can fulfill the function of hormones, we will see mainly peptides, amines, terpenes or steroids, while neurotransmitters are usually peptide molecules, amino acids or gases.
2. Range of action
Hormones have “long-range” functions. This means that the organs or tissues that target hormones are usually at a certain distance from the gland that secretes them, communicated by the blood supply. An example would be prolactin, which is released in the pituitary gland but has an effect on the reproductive and excretory system.
Neurotransmitters, on the other hand, have a very limited range of action. Molecules that act as neurotransmitters only affect cells that connect through synaptic junctions. Of course, some neurotransmitters spread through the synaptic space, affecting adjacent cells as a hormone and cells connected by synapses as a neurotransmitter.
3. Affected tissues
The range of tissues that neurotransmitters effect is much smaller than that of hormones. Hormonal function tends to be multi-targeted, apart from long distance. Hormones usually produce coordinated responses from various organs or tissues, as in the case of adrenaline, which affects muscles, connective tissue, liver …
Neurotransmitters, on the other hand, have a much smaller function. They are responsible for transmitting messages, but it is between adjacent cells. These cells also belong to mostly the same tissue, except in neuromuscular synapses,
4. Producing tissues
Hormones affect different types of tissues, but they are also produced by very different organs. The endocrine system, which is responsible for producing and releasing hormones into the bloodstream, is made up mainly of the hypothalamus, the pituitary gland, the thyroid and parathyroid glands, the adrenal glands, the reproductive organs, and the pancreas.
Neurotransmitters are eminently molecules of the nervous tissue, and can only be secreted by neurons.
5. Response time
Hormones produce effects that tend to last for some time, since their effects can take from minutes to days after they come into contact with the target tissue. The time window of action of neurotransmitters is much faster, fractions of a second.
They are released by the electrical action of the nervous system, so it is an extremely fast cellular communication method.
6. Living things that use them
A great curious difference between neurotransmitters and hormones is that although hormones are produced in many other living things, such as plants, neurotransmitters are, so far as it is known, molecules unique to animals.
7. Transmission mode
When comparing the definitions of both molecules, this difference becomes apparent. Hormones travel through the bloodstream to affect other tissues, while neurotransmitters are a strictly synaptic method of communication between cells.
8. Modulation of its effects
Hormones are modulated mainly by fluctuations in their blood levels, which depend on the systems that inhibit or promote their release to other tissues, as well as the availability of receptors (The hormone generally needs specific receptors to act).
The effects of neurotransmitters are mainly modulated by the composition of neurotransmitters that are transmitted in the synapse, in addition to the effect they produce depends on the affected cell type. This effect is usually “all or nothing”, depending on whether or not the next cell is activated.
In short, what are the differences between hormones and neurotransmitters?
Hormones and neurotransmitters share a basic characteristic, which is that they both act as chemical messengers, intervening in the regulation of different bodily functions. However, there are important differences between a hormone and a neurotransmitter. Next, we will see which ones.
One of the differences between hormones and neurotransmitters is that the former is released by the endocrine glands into the bloodstream; instead, neurotransmitters are released into the synaptic space between neurons. This leads us to point out another basic difference, and that is that the effect produced by hormones is, in general, much longer than that of neurotransmitters.
Another characteristic that differentiates these two types of chemical messengers is that the neurotransmitter, when released, only communicates with the closest neuron, through the synaptic space; however, the hormones communicate with other cells that may be at a great distance as they travel through the bloodstream.
The difference would also lie in the fact that neurotransmitters act specifically in the nervous system, while hormones could do so anywhere in the body.
Sometimes the distinction between hormone and neurotransmitter is not entirely clear. Some neurotransmitters also act as hormones, such as catecholamines (adrenaline, norepinephrine, and dopamine).
These can be produced by the adrenal glands and discharged into the bloodstream, exerting a hormonal effect; and at the same time, they are released in the nerve endings, acting as neurotransmitters. In these cases, they are also called neurohormones.
According to the French doctor, Roger Guillemin, a neurotransmitter would be nothing other than a paracrine secretion hormone (a type of cellular communication by chemical secretion), although due to their specific characteristics, they are often considered to be another type of messenger other than the hormone.
However, at present there are still authors who consider that a hormone is any substance that is released by one cell to act on another, either close or distant, and regardless of its origin or location, as well as the route used for its transport (blood circulation, extracellular fluid or synaptic space).
The definitions of hormone and neurotransmitter are thus open to interpretation.
FAQS: Difference between neurotransmitter and hormone
Which neurotransmitters are also hormones?
Some neurotransmitters also act as hormones, such as catecholamines (adrenaline, norepinephrine, and dopamine).
How do hormones differ from neurotransmitters quizlet?
A distinction in that neurotransmitters does use an electrical charge to deliver and chemically activate hormones. Another distinction is that target cells are perceived differently by them.
Is Dopamine a neurotransmitter or a hormone?
Dopamine is a neurotransmitter that occurs in many parts of the nervous system, especially in the substantia nigra. Dopamine is also a neurohormone released by the hypothalamus whose function here is to inhibit the release of prolactin from the anterior lobe of the pituitary.
Are neurochemicals and neurotransmitters the same thing?
Molecules (called neurochemicals) that function on receptors but do not follow neurotransmitter requirements are often created by the brain.
What are the 2 types of neurotransmitters?
In this article we explained what neurotransmitter and hormone are, how they work and what are the main characteristics of hormones and neurotransmitters, as well as the most important differences between them.
If you have any questions or comments please let us know!
Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001. What Defines a Neurotransmitter?
Campbell M, Jialal I. Physiology, Endocrine Hormones, Treasure Island (FL): StatPearls