Tiny bits send messages in your body. 
Tiny bits help your cells talk. 
Your body uses tiny messengers to send signals. These are called neurotransmitters.
Neurons are cells that send messages. They do not touch each other. A tiny gap sits between them. We call this gap a synapse.
To send a message, a neuron uses a set of steps. First, an electrical signal enters the cell. This signal tells tiny sacs to move. We call these sacs synaptic vesicles. They hold the neurotransmitters. The sacs fuse with the cell wall. This lets the messengers out into the gap.
Next, the messengers float across the gap. They land on special parts called receptors. Think of receptors like locks. The neurotransmitter is like a key. When the key fits the lock, the message is sent. This can tell a cell to start working or to stop.
After the message is sent, the gap must be cleared. If the messengers stay, the cell keeps getting signals. Some messengers are sucked back into the first cell to be used again. This is called reuptake. Other messengers are broken down by proteins called enzymes.
Scientists have found more than 100 different types. Some common ones are dopamine and serotonin. 
These messengers help you move and think.
Neurotransmitters are tiny signaling molecules that help your body work. They are essential for the function of complex neural systems. These messengers allow neurons to talk to other cells. A target cell can be another neuron. It might also be a muscle cell or a gland.
How do these messengers work? It all starts with an electrical signal called an action potential. This signal travels to the end of a neuron. It causes calcium ions to enter the cell. This step triggers tiny sacs called synaptic vesicles to move. These sacs fuse with the cell membrane to release the neurotransmitters. The molecules then float across a tiny gap called the synaptic cleft. They land on special parts called receptors on the target cell.
Once the message is sent, the gap must be cleared. If messengers stay, the cell might receive too many signals. One way to clean up is through reuptake. This is when transporters pump the molecules back into the first neuron. Another way is through enzyme degradation. In this way, proteins called enzymes break the molecules down. For example, an enzyme can break acetylcholine into acetic acid and choline.
Learning about these chemicals took a long time. For many years, scientists thought the brain only used electricity. A scientist named Ramón y Cajal discovered the tiny gaps between neurons. He saw these gaps, which we now call the synaptic cleft. Later, a pharmacologist named Otto Loewi proved chemicals were involved. He used experiments with frog nerves to show this. Loewi is even credited with discovering acetylcholine. This was the very first neurotransmitter ever known.
Neurotransmitters can have different effects on a cell. Some are excitatory, which means they encourage the cell to act. Others are inhibitory, which means they tell the cell to stop. You can think of excitation like a racehorse ready to run. Inhibition is like the starting gate that holds the horse back. Some synapses are Type I, which are excitatory. Others are Type II, which are inhibitory. These different signals help your brain build complex networks to help you think and move.
Neurotransmitters are essential signaling molecules used by neurons to communicate with other cells. These molecules allow the brain and body to function as a complex, connected system. A neurotransmitter is secreted by a neuron to affect a target cell across a tiny gap. This target cell might be another neuron, a muscle cell, or a gland. Scientists have identified more than 100 unique neurotransmitters in humans, though the exact total remains unknown.
The process of communication begins with an electrical signal called an action potential. When this signal reaches the end of a neuron, known as the presynaptic terminal, it triggers a specific sequence. First, voltage-gated calcium channels open to allow calcium ions to enter the terminal. This influx of calcium causes synaptic vesicles, which are tiny storage sacs, to fuse with the cell membrane. This fusion releases the neurotransmitters into the synaptic cleft, the narrow space between cells. The molecules then diffuse across this gap to interact with specific receptors on the target cell.
Neurotransmitters are categorized into several distinct chemical classes. Amino acids, such as glutamate and glycine, are common building blocks. Monoamines are created by altering a single amino acid; for example, the amino acid tryptophan is the precursor for serotonin. Peptides, or neuropeptides, are larger protein transmitters that are often released together to provide a modulatory effect. There are also purine neurotransmitters, like ATP, which are derived from nucleic acids. Some substances, such as the metabolic gases nitric oxide and carbon monoxide, act as neurotransmitters despite not being stored in vesicles.
To prevent continuous, uncontrolled signaling, neurotransmitters must be removed from the synaptic cleft. This occurs through three main mechanisms. First, diffusion allows molecules to drift away, where they are often absorbed by glial cells called astrocytes. These astrocytes help maintain proper function by regulating extracellular levels. Second, enzyme degradation uses specialized proteins to break the molecules down. For instance, the enzyme acetylcholinesterase cleaves acetylcholine into acetic acid and choline.
The effect a neurotransmitter has on a cell depends entirely on the type of receptor it binds to. These interactions generally result in one of three outcomes: excitation, inhibition, or modulation. Excitatory signals, found in Type I synapses, increase the probability that a cell will produce its own action potential. Inhibitory signals, found in Type II synapses, decrease that probability. Modulatory signals do not necessarily change the cell's voltage directly but instead trigger signaling cascades. These cascades can change how sensitive a cell is to future stimuli by recruiting more or fewer receptors to the membrane.
Historically, the understanding of the brain has shifted from purely electrical models to chemical ones. Until the early 20th century, most scientists believed synaptic communication was entirely electrical. However, Ramón y Cajal performed histological examinations that revealed a 20 to 40 nm gap between neurons. This gap, the synaptic cleft, suggested that chemical messengers must traverse the space. In 1921, German pharmacologist Otto Loewi confirmed this through experiments with frog vagus nerves. Loewi demonstrated that chemical concentrations could regulate heart rates and is credited with discovering acetylcholine, the first known neurotransmitter.
Neurotransmitters are vital for the structure and function of complex neural networks. The balance between excitatory and inhibitory signals allows for sophisticated information flow. You can imagine an excitatory signal as a racehorse ready to run down a track. An inhibitory signal acts like the starting gate that holds the horse back. For a neuron to fire, the excitatory messages must often overcome the inhibitory ones. This delicate balance is what allows the nervous system to process information and respond to the world.
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