Difference Between Hormones and Neurotransmitters


Hormones and neurotransmitters are two types of chemical messengers that play critical roles in regulating various physiological processes in the human body. Although both hormones and neurotransmitters are involved in communication between cells, they differ in several key ways. In this essay, we will explore the differences between hormones and neurotransmitters, including their chemical structure, mode of action, target cells, and physiological effects.

What are Hormones?

Hormones are chemical messengers that are produced by endocrine glands and released into the bloodstream to travel to distant target organs or tissues. Hormones are typically large, complex molecules, such as peptides, steroids, or amino acid derivatives. The release of hormones is regulated by feedback mechanisms, which ensure that the levels of hormones in the body remain within a narrow range. Hormones can be classified into three main types: steroid hormones, peptide hormones, and amine hormones.

Steroid hormones are derived from cholesterol and are lipophilic, meaning they can pass through cell membranes to bind to intracellular receptors. Examples of steroid hormones include testosterone, estrogen, and cortisol. Peptide hormones, on the other hand, are composed of amino acids and are hydrophilic, meaning they cannot pass through cell membranes. Instead, peptide hormones bind to cell surface receptors and activate signaling pathways within the cell. Examples of peptide hormones include insulin, growth hormone, and oxytocin. Amine hormones are derived from amino acids and can be either hydrophilic or lipophilic, depending on their chemical structure. Examples of amine hormones include epinephrine, norepinephrine, and dopamine.

Neurotransmitters influence trans-membrane ion flow. These either increase or decrease the chance that the cell will produce an action potential.

The following are the two classifications regarding the facilitation of ion flow −

  • Excitatory Neurotransmitters − Excitatory neurotransmitters stimulate the brain and are somewhat overactive. They allow the postsynaptic neuron to produce action potential which increases the trans-membrane ion flow. Such neurotransmitters include dopamine, norepinephrine, and epinephrine.

  • Inhibitory Neurotransmitters − Inhibitory neurotransmitters help create balance by calming the brain. They decrease the trans-membrane ion flow, thus prohibiting the postsynaptic neuron to produce an action potential. Such neurotransmitters include serotonin, GABA (Gamma-amino butyric acid), and dopamine.

Neurotransmitters are also classified according to chemical or molecular structure −

  • Small molecule neurotransmitterss − These neurotransmitters are synthesized locally within the axon terminal and are smaller than neuropeptides. Such neurotransmitters include the following −

    • Amino acid neurotransmitters: GABA, glycine, and glutamate

    • Biogenic amines: dopamine, norepinephrine, epinephrine, serotonin, and histamine

    • Purinergic neurotransmitters: ATP (Adenosine triphosphate), and adenosine

    • Acetylcholine (does not belong to any structural category)

  • Neuropeptides − These neurotransmitters are known to be larger compared to the molecule neurotransmitters as their structure is made up of three or more amino acids. Neuropeptides are composed of 3 to 36 amino acids. Such neurotransmitters include the following −

    • Endorphins

    • Enkephalins

    • Oxytocin

    • Vasopressin

    • Insulin

    • Glucagon

What are Neurotransmitters?

Neurotransmitters are chemical messengers that are released by neurons to communicate with other neurons or target cells, such as muscle cells or gland cells. Unlike hormones, neurotransmitters are released locally and act within a very short distance. Neurotransmitters are typically small, simple molecules, such as amino acids, monoamines, or acetylcholine. The release of neurotransmitters is regulated by action potentials, which are electrical impulses that propagate down the axon of a neuron.

Neurotransmitters act by binding to specific receptors on the postsynaptic membrane, which triggers a series of biochemical events within the cell. There are two main types of neurotransmitter receptors: ionotropic receptors and metabotropic receptors. Ionotropic receptors are ligand-gated ion channels that open in response to neurotransmitter binding, allowing ions to flow into or out of the cell. Metabotropic receptors, on the other hand, are G protein-coupled receptors that activate second messenger signaling pathways within the cell.

Neurotransmitters can be classified into several categories based on their chemical structure and physiological effects. Amino acid neurotransmitters, such as glutamate and GABA, are the most abundant neurotransmitters in the central nervous system and play critical roles in regulating synaptic transmission. Monoamine neurotransmitters, such as dopamine, serotonin, and norepinephrine, are involved in modulating mood, emotion, and cognition. Acetylcholine is a neurotransmitter that is involved in motor control, learning, and memory.

Differences: Hormones and Neurotransmitters

In terms of their target cells, hormones and neurotransmitters differ significantly. Hormones typically act on cells that express specific hormone receptors, which can be located in multiple organs or tissues throughout the body. For example, insulin acts on cells in the liver, muscle, and adipose tissue to regulate glucose uptake and storage. In contrast, neurotransmitters act on cells that are in close proximity to the presynaptic neuron, such as other neurons or muscle cells. For example, acetylcholine released by motor neurons activates muscle cells to produce muscle contraction.

The following table highlights the major differences between Hormones and Neurotransmitters −

Characteristics

Hormones

Neurotransmitters

Organ System

Hormones are produced by the endocrine system. The adrenals, pancreas, kidneys, gonads, thyroid, and other ductless glands secrete hormones.

Neurotransmitters are produced by the nervous system. Neurotransmitters are released from the terminal end buttons of neurons.

Mode of Transmission

Hormones relay signals through the circulatory system (blood stream).

Neurotransmitters communicate signal across synaptic clefts.

Transmission Speed

Since hormones function to reach distant “target cells”, the speed or signal transmission is much slower (can take minutes to days) than the neurotransmitters’ signal transmission which sends messages in between nerve cells (usually within milliseconds).

Neurotransmitters’ signal transmission which sends messages in between nerve cells (usually within milliseconds) is faster than hormones’ speed.

Transmission Distance

Since hormones are transmitted through the blood stream, these act on distant sites from where these are produced.

Neurotransmitters are transmitted across the synaptic cleft, thus these react in direct proximity to their target cells.

Types

The hormones’ two classifications are “amino acid-based and steroids”.

As for neurotransmitters, it can be classified according to ion flow facilitation: “excitatory and inhibitory” and according to structure (chemical or molecular): “small molecule and neuropeptides”.

Capability

Hormones regulate specific organs and tissues.

The capability of neurotransmitters is humbler as they merely stimulate postsynaptic neurons.

Conclusion

In conclusion, hormones have diverse functions that affect physiological processes such as growth and development, metabolism, mood, sexual function, reproduction, etc. In contrast, neurotransmitters facilitate transmission between neurons by passing action potentials from the axons to the dendrites.

Updated on: 03-Aug-2023

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