We explain the differences between these biological messengers.
Some of the most well-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 objective of these two organic communication pathways.
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What are these molecules like?
In order to delve into the differences that exist between hormones and neurotransmitters, it is best to first definewhat each of these types of cellular communication molecules lookslike.
1. Hormones
Hormones are cellular productscapable of circulating in organic fluids, such as blood in the case of animals or sap in the case of plants, which also produce hormones. Its main function is to act as a chemical messenger, being able to transport signals that are emitted from the cell that generates them to its target tissue, which may be in a completely different part of the body.
In addition to their abilityto facilitate communication over long distances on a body scale, they are a group of molecules whose shape and composition is very varied, being able to be peptide molecules hormones such as proteins, but also molecules such as terpenes, phenols or some types of lipids, as in the case of steroids.
The contact of a hormone with its target tissue can have a wide variety of effects, which depend on both the hormone and the cell receiving the message. Among the effects produced by hormones we can point out:
- Promoting growth
- The promotion of cell division
- The differentiation of certain cell types
- Changes in food metabolism
- changes in body temperature
- mood swings
- Promotion of sexual maturation
Hormones are single-use molecules . Once they have come into contact with their target tissue or organ, the molecule is destroyed, so it cannot send the message again. These originate mainly in the endocrine glands, those responsible for the production and secretion of hormones. Among them are the liver, the pituitary gland, the thyroid, the ovaries or the testicles.
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2. Neurotransmitters
Neurotransmitters are also biomolecules found in our body , whose main task is intercellular communication. These molecules are transmitted specifically between neurons, the cells of the nervous system, through synapses, the structures found at the ends of neurons allowing the passage of neurotransmitters.
The signals sent by neurotransmitters are modulable. In synaptic communication, different types of neurotransmitter can be sent at the same time, which allows a certain variation of the signal , depending on the proportion and composition of the set of neurotransmitters that are sent from one neuron to another.
Neurotransmitters accumulate in so-called “synaptic vesicles” within the sending neuron . After a nervous stimulus, the neuron expels the neurotransmitters through the end of its axon and these diffuse through the synaptic gap, the “void” between the two cells involved in synapse communication. These neurotransmitters will bind to specific membrane receptors, causing effects in the receiving neuron.
Main differences between hormones and neurotransmitters
Once defined, we can begin to break down 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 noradrenaline, a molecule very similar to adrenaline. It 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 hormone are more varied than those that fulfill the function of neurotransmitter. Among the molecules that can fulfill the function of hormone we will mainly see 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 target organs or tissues of the hormones are usually at a certain distance from the gland that secretes them, connected by the blood supply. An example would be prolactin, which is released from the pituitary gland but has an effect on the reproductive and excretory systems.
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 diffuse through the synaptic space, affecting both adjacent cells as a hormone, and as a neurotransmitter to cells connected by synapses.
3. Tissues affected
The range of tissues affected by neurotransmitters 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 reduced function. They are responsible for transmitting messages, but it is between adjacent cells . These cells also belong to much of the same tissue, except at neuromuscular synapses.
4. Producer 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.
The neurotransmitters are eminently some molecules of the nervous tissue , being able to be secreted only by the 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 method of cellular communication.
6. Living beings that use them
A great curious difference between neurotransmitters and hormones is that although hormones are produced in many other living beings, such as plants, neurotransmitters are, as far as 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 mainly modulated by fluctuations in their blood levels, which depend on the systems that inhibit or promote their release to other tissues, as well asthe availability of receptors (The hormone usually needs specific receptors to act).
The effects of neurotransmitters are mainly modulated by the composition of neurotransmitters that are transmitted at 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 it produces activation of the next cell or not.
References
- Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001. What defines a neurotransmitter? Available in: https://www.ncbi.nlm.nih.gov/books/NBK10957/.
- Campbell M, Jialal I. Physiology, Endocrine Hormones, Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available in: https://www.ncbi.nlm.nih.gov/books/NBK538498/.
To the classic question “what do you do?” I always answer “basically I am a psychologist”. In fact, my academic training has revolved around the psychology of development, education and community, a field of study influenced my volunteer activities, as well as my first work experiences in personal services.