Every movement, thought, and heartbeat begins with a message
sent through the nervous system. But how do nerves actually communicate—with
each other or with muscles and organs?
When the body detects a change—whether internal or from the
environment—nerves are activated. This triggers an electrical signal,
which travels along the nerve fiber until it reaches a synapse, a tiny
gap between cells. From there, the message must jump to the next nerve or to a target
cell such as a muscle, gland, or even the heart.
The big question scientists once faced was this: Is the
message passed across the synapse through electricity or chemistry?
The Early Clues: The Concept of
Chemical Communication
In 1905, John Newport Langley, a leading British
physiologist at Cambridge, proposed that nerve messages were passed by a
chemical released at a specific "receptive substance" on the
target cell. This insight was rooted in experiments by his student, T.R.
Elliott, whose contributions unfortunately went uncredited by Langley.
Over the following years, various scientists confirmed what
Elliott observed: certain chemicals could produce responses in cells that
mimicked nerve stimulation. However, the effect wasn’t always identical, which
raised more questions about how nerves really worked.
The Breakthrough: Otto Loewi and the
First Neurotransmitter
The decisive proof came from Otto Loewi, a
German-born professor of pharmacology working in Austria. For years, Loewi was
haunted by the mystery of neural communication. Then one night in 1920,
inspiration struck—in his sleep. He awoke with an experiment in mind, scribbled
notes, and fell back asleep. But by morning, the notes made no sense.
Luckily, the idea returned during another dream the
following night. At 3 a.m., Loewi rushed to his lab and conducted what would
become one of the most famous experiments in neuroscience.
He used two frog hearts, each in a separate
fluid-filled chamber. When he stimulated the vagus nerve of the first
heart, its beating slowed. Then, he transferred the surrounding fluid from the
first chamber to the second. To his astonishment, the second heart also slowed
down—without direct nerve stimulation.
This demonstrated that a chemical had been released
by the first heart’s nerve endings and carried the message to the second. Loewi
named this substance Vagusstoff, which was later identified as acetylcholine—the
very first neurotransmitter ever discovered.
In 1936, Loewi received the Nobel Prize in Physiology or
Medicine, sharing it with Sir Henry Dale. Sadly, he was later forced to
flee Austria following the Nazi invasion in 1938.
The Expanding Universe of
Neurotransmitters
Since Loewi’s discovery, researchers have identified more
than 100 different neurotransmitters in both vertebrates and invertebrates.
These chemicals are now known to be vital not only for regular nerve function,
but also for understanding complex diseases, shaping new medications,
and unlocking the biology behind emotions, memory, and cognition.
Neurotransmitters are the key messengers in the brain and
body. Their balance—or imbalance—can influence everything from mood and
memory to muscle control and metabolism.
Key Insights to Take With You
- Nerves
transmit signals using both electrical impulses and chemical
messengers.
- John
Langley and T.R. Elliott laid the
foundation for understanding chemical signaling in the nervous system.
- Otto
Loewi’s historic frog heart experiment provided the
first clear proof of neurotransmitter-based communication.
- Acetylcholine,
the first known neurotransmitter, continues to play a crucial role in both
the brain and body.
- Over
100 neurotransmitters have been identified, each with unique roles
in health and disease.
- Modern
medicine increasingly depends on targeting neurotransmitter systems to
treat disorders like depression, anxiety, Parkinson’s, and Alzheimer’s.
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| The neurotransmitter acetylcholine is released from nerve endings to activate receptor sites on the surface of skeletal (voluntary) muscle fibers, causing their contraction. This microscopic view of nerve cell endings in muscular tissue has been magnified 200 times. |
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