Balloonist theory 3230929 197689250 2008-03-12T10:27:29Z Delldot on a public computer 6013586 + info, image '''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.<ref name="Pearn">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. </ref> [[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.<ref>Columbia University. [http://www.columbia.edu/cu/psychology/courses/1010/mangels/neuro/history/history.html History of Neuroscience]. Retrieved on [[January 25]], [[2007]].</ref> In the model, which Descartes used to explain [[reflex]]es, the spirits would flow from the [[brain ventricle|ventricles of the brain]], through the nerves, and to the muscles to animate the latter.<ref name="Cobb"/> 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. ==Debunking== [[Image:Swammerdam frog thigh.PNG|thumb|right|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.]] Also in 1667, [[Jan Swammerdam]], a Dutch [[anatomist]] famous for working with insects, made the first important blow to the balloonist theory. Swammerdam, who was the first to experiment on [[nerve-muscle preparation]]s, showed that muscles do not increase in size when they contract (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.<ref name="Cobb"/> 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).<ref name="Cobb"/> 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.<ref name="Cobb"/> Swammerdam did not believe the results of his own experiment, suggesting that they were the result of artifact.<ref name="Cobb"/> 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".<ref name="Cobb"/> This idea was an important step toward the current understanding of how nerves actually cause muscle contraction.<ref name="Cobb"> {{ cite journal |author=Cobb M |title=Timeline: Exorcizing the animal spirits: Jan Swammerdam on nerve function |journal=Nature Reviews Neuroscience |volume=3 |issue=5 |pages=395–400 |year=2002 |pmid=11988778 |doi=10.1038/nrn806 |url=http://www.janswammerdam.net/NRN.pdf |format=pdf }} </ref> 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. The idea that muscle is inflated by air was further debunked when [[Giovanni Alfonso Borelli]] slit the muscle of an animal under water and watched to see if bubbles of air would rise to the surface; of course, none did. The invention of the [[microscope]] allowed preparations of nerves to be viewed at high magnification, showing that they are not hollow. 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 [[ion]]s), and not air or fluid, is the impetus behind muscle movement. ==See also== *[[Passions of the Soul]] ==References== {{reflist}} [[Category:History of neuroscience]] [[Category:Muscular system]]