Balloonist Theory
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Balloonist theory was a theory in early
neuroscience Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions, and its disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, ...
that attempted to explain
muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...
movement by asserting that muscles contract by inflating with air or fluid. The Roman and Greek physician
Galen Aelius Galenus or Claudius Galenus (; September 129 – AD), often Anglicization, anglicized as Galen () or Galen of Pergamon, was a Ancient Rome, Roman and Greeks, Greek physician, surgeon, and Philosophy, philosopher. Considered to be one o ...
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.
René Descartes René Descartes ( , ; ; 31 March 1596 – 11 February 1650) was a French philosopher, scientist, and mathematician, widely considered a seminal figure in the emergence of modern philosophy and Modern science, science. Mathematics was paramou ...
, who was interested in
hydraulics Hydraulics () is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counterpart of pneumatics, which concer ...
and used fluid pressure to explain various aspects of
physiology Physiology (; ) is the science, scientific study of function (biology), functions and mechanism (biology), mechanisms in a life, living system. As a branches of science, subdiscipline of biology, physiology focuses on how organisms, organ syst ...
such as the
reflex arc A reflex arc is a neural pathway that controls a reflex. In vertebrates, most sensory neurons synapse in the spinal cord and the signal then travels through it into the brain. This allows for faster reflex actions to occur by activating spinal mo ...
, proposed that "animal spirits" flowed into muscle and were responsible for their contraction. In the model, which Descartes used to explain
reflex In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...
es, the spirits would flow from the ventricles of the brain, through the nerves, and to the muscles to animate the latter. In 1667,
Thomas Willis Thomas Willis Fellow of the Royal Society, FRS (27 January 1621 – 11 November 1675) was an English physician who played an important part in the history of anatomy, neurology, and psychiatry, and was a founding member of the Royal Society. L ...
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. This theory has now been superseded by the mainstream scientific community due to the establishment of neuroscience, which is supported by empirical evidence.


Physiological refutations of the theory

In 1667,
Jan Swammerdam Jan or Johannes Swammerdam (February 12, 1637 â€“ February 17, 1680) was a Dutch biologist and microscopist. His work on insects demonstrated that the various phases during the life of an insect—Egg (biology), egg, larva, pupa, and adult†...
, a Dutch
anatomist Anatomy () is the branch of morphology concerned with the study of the internal structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old scien ...
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. 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). 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. Swammerdam did not believe the results of his own experiment, suggesting that they were the result of artifact. 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". This idea was an important step toward the current understanding of how nerves actually cause muscle contraction. Balloonist theory took a second hit from
Francis Glisson Francis Glisson (1597 – 14 October 1677) 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 he ...
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.
Giovanni Alfonso Borelli Giovanni Alfonso Borelli (; 28 January 1608 – 31 December 1679) was a Renaissance Italy, Italian physiologist, physicist, and mathematician who is often described as the father of biomechanics. He contributed to the modern principle of scientif ...
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 balloonist theory. The invention of the
microscope A microscope () is a laboratory equipment, laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic ...
allowed preparations of nerves to be viewed at high magnification, showing that they are not hollow. In 1791,
Luigi Galvani Luigi Galvani ( , , ; ; 9 September 1737 – 4 December 1798) was an Italian physician, physicist, biologist and philosopher who studied animal electricity. In 1780, using a frog, he discovered that the muscles of dead frogs' legs twitched when ...
learned that frogs' muscles could be made to move by the application of
electricity Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...
. This finding provided a basis for the current understanding that electrical energy (carried by
ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
s), and not air or fluid, is the impetus behind muscle movement.


See also

*
Passions of the Soul In his final philosophical treatise, ''The Passions of the Soul'' (), completed in 1649 and dedicated to Princess Elisabeth of Bohemia, René Descartes contributes to a long tradition of philosophical inquiry into the nature of " the passions". ...


References

{{reflist History of neuroscience Muscular system