Balloonist theory

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Balloonist theory was a theory in early neuroscience that attempted to explain muscle movement by asserting that muscles contract by inflating with air or fluid. The Greek physician Galen believed that muscles contracted due to a fluid flowing into them, and for 1500 years afterward, it was believed that nerves were hollow and that they carried fluid. [1] René Descartes, who was interested in hydraulics and used fluid pressure to explain various aspects of physiology such as the reflex arc, proposed that "animal spirits" flowed into muscle and were responsible for their contraction. [2] In the model, which Descartes used to explain reflexes, the spirits would flow from the ventricles of the brain, through the nerves, and to the muscles to animate the latter. [3]

Neuroscience scientific study of the nervous system

Neuroscience is the scientific study of the nervous system. It is a multidisciplinary branch of biology that combines physiology, anatomy, molecular biology, developmental biology, cytology, mathematical modeling and psychology to understand the fundamental and emergent properties of neurons and neural circuits. The understanding of the biological basis of learning, memory, behavior, perception, and consciousness has been described by Eric Kandel as the "ultimate challenge" of the biological sciences.

Muscle contractile soft tissue of mammals

Muscle is a soft tissue found in most animals. Muscle cells contain protein filaments of actin and myosin that slide past one another, producing a contraction that changes both the length and the shape of the cell. Muscles function to produce force and motion. They are primarily responsible for maintaining and changing posture, locomotion, as well as movement of internal organs, such as the contraction of the heart and the movement of food through the digestive system via peristalsis.

Galen Roman physician, surgeon and philosopher

Aelius Galenus or Claudius Galenus, often Anglicized as Galen and better known as Galen of Pergamon, was a Greek physician, surgeon and philosopher in the Roman Empire. Arguably the most accomplished of all medical researchers of antiquity, Galen influenced the development of various scientific disciplines, including anatomy, physiology, pathology, pharmacology, and neurology, as well as philosophy and logic.

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In 1667, Thomas Willis proposed that muscles may expand by the reaction of animal spirits with vital spirits. He hypothesized that this reaction would produce air in a manner similar to the reaction that causes an explosion, causing muscles to swell and produce movement.

Thomas Willis English doctor

Thomas Willis was an English doctor who played an important part in the history of anatomy, neurology and psychiatry. He was a founding member of the Royal Society.

Physiological refutations of the theory

Swammerdam's illustration of a nerve-muscle preparation. He placed a frog thigh muscle in a glass syringe with a nerve protruding from a hole in the side of the container. Irritating the nerve caused the muscle to contract, but the level of the water, and thus the volume of the muscle, did not increase. Swammerdam frog thigh.PNG
Swammerdam's illustration of a nerve-muscle preparation. He placed a frog thigh muscle in a glass syringe with a nerve protruding from a hole in the side of the container. Irritating the nerve caused the muscle to contract, but the level of the water, and thus the volume of the muscle, did not increase.

In 1667, Jan Swammerdam, a Dutch anatomist famous for working with insects, struck the first important blow against the balloonist theory. Swammerdam, who was the first to experiment on nerve-muscle preparations, showed that muscles do not increase in size when they contract (and he supposed if a substance such as animal spirits flowed into muscles, their volume should increase when they contract). Swammerdam placed severed frog thigh muscle in an airtight syringe with a small amount of water in the tip. [3] He could thus determine whether there was a change the volume of the muscle when it contracted by observing a change in the level of the water (image at right). [3] When Swammerdam caused the muscle to contract by irritating the nerve, the water level did not rise but rather was lowered by a minute amount; this showed that no air or fluid could be flowing into the muscle. [3] Swammerdam did not believe the results of his own experiment, suggesting that they were the result of artifact. [3] However, he concluded in his book The Book of Nature II that "motion or irritation of the nerve alone is necessary to produce muscular motion". [3] This idea was an important step toward the current understanding of how nerves actually cause muscle contraction. [3]

Jan Swammerdam Dutch entomologist and beekeeper

Jan Swammerdam was a Dutch biologist and microscopist. His work on insects demonstrated that the various phases during the life of an insect—egg, larva, pupa, and adult—are different forms of the same animal. As part of his anatomical research, he carried out experiments on muscle contraction. In 1658, he was the first to observe and describe red blood cells. He was one of the first people to use the microscope in dissections, and his techniques remained useful for hundreds of years.

Balloonist theory took a second hit from Francis Glisson who performed an experiment in which a man flexed a muscle under water. The water level did not go up (in fact it went down slightly), further supporting the conclusion that no air or fluid could be entering the muscle.

Francis Glisson British doctor

Francis Glisson was a British physician, anatomist, and writer on medical subjects. He did important work on the anatomy of the liver, and he wrote an early pediatric text on rickets. An experiment he performed helped debunk the balloonist theory of muscle contraction by showing that when a muscle contracted under water, the water level did not rise, and thus no air or fluid could be entering the muscle.

Giovanni Alfonso Borelli performed an experiment to test the idea that muscle is inflated by air. He slit the muscle of an animal under water and watched to see whether bubbles of air would rise to the surface. Since no bubbles were seen to rise, this experiment helped to refute the ballonist theory.

Giovanni Alfonso Borelli Italian physicist

Giovanni Alfonso Borelli was a Renaissance Italian physiologist, physicist, and mathematician. He contributed to the modern principle of scientific investigation by continuing Galileo's practice of testing hypotheses against observation. Trained in mathematics, Borelli also made extensive studies of Jupiter's moons, the mechanics of animal locomotion and, in microscopy, of the constituents of blood. He also used microscopy to investigate the stomatal movement of plants, and undertook studies in medicine and geology. During his career, he enjoyed the patronage of Queen Christina of Sweden.

The invention of the microscope allowed preparations of nerves to be viewed at high magnification, showing that they are not hollow.

Microscope instrument used to see objects that are too small for the naked eye

A microscope is an instrument used to see objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using such an instrument. Microscopic means invisible to the eye unless aided by a microscope.

In 1791, Luigi Galvani learned that frogs' muscles could be made to move by the application of electricity. This finding provided a basis for the current understanding that electrical energy (carried by ions), and not air or fluid, is the impetus behind muscle movement.

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Luigi Galvani Italian physician, physicist, and philosopher

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Andrew Huxley English physiologist and biophysicist

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References

  1. Pearn J. 2002. A curious experiment: the paradigm switch from observation and speculation to experimentation, in the understanding of neuromuscular function and disease. Neuromuscular Disorders, Volume 12, Issue 6, Pages 600-607. PMID   12117487.
  2. Columbia University. History of Neuroscience. Retrieved on January 25, 2007.
  3. 1 2 3 4 5 6 7 Cobb M (2002). "Timeline: Exorcizing the animal spirits: Jan Swammerdam on nerve function". Nature Reviews Neuroscience. 3 (5): 395–400. doi:10.1038/nrn806. PMID   11988778.