Rev. Fac. Med. 2018 Vol. 66 No. 4: 623-7 623 REFLECTION PAPER DOI: http://dx.doi.org/10.15446/revfacmed.v66n4.65552 From substance fermentation to action potential in modern science (part two) De la fermentación de sustancias al potencial de acción en la ciencia moderna (segunda parte) Received: 08/06/2017. Accepted: 12/12/2017. John Barco-Ríos1,2 • Jorge Eduardo Duque-Parra1,2 • Johanna Alexandra Barco-Cano2,3 1 Universidad de Caldas - Faculty of Health Sciences - Department of Basic Sciences - Manizales - Colombia. 2 Universidad de Caldas - Department of Basic Sciences - Caldas Neuroscience Group - Manizales - Colombia. 3 Universidad de Caldas - Faculty of Health Sciences - Clinical Department - Manizales - Colombia. Corresponding author: John Barco-Ríos. Department of Basic Sciences, Faculty of Health Sciences, Universidad de Caldas. Calle 65 No. 26-10, office: M203. Telephone number: +57 6 8781500. Manizales. Colombia. Email: [email protected]. | Abstract | | Resumen | Introduction: After conducting a bibliographical review on the works Introducción. Después de una revisión bibliográfica sobre los trabajos of various researchers at different times to explain the phenomenon de diversos investigadores en distintas épocas para explicar el fenómeno of the transmission of nerve impulses, it is observed that since de la transmisión nerviosa, se observa que a partir del siglo XVIII, the eighteenth century, when modern science was born, scientific cuando surge la ciencia moderna, el conocimiento científico en el campo knowledge in the field of physiology had an accelerated development de la fisiología tuvo un desarrollo acelerado por la creación de nuevas following the creation of new research techniques and the application técnicas de investigación y la aplicación del método científico. Así, of the scientific method. Thus, the philosophical theory of “animal de la teoría filosófica de los “espíritus animales” se llegó al concepto spirits” led to the current concept of action potential, understood as actual del potencial de acción, entendiéndose este como un fenómeno a merely electrochemical phenomenon. meramente electroquímico. Discussion: The establishment of the scientific method and the Discusión. Con el establecimiento del método científico y el desarrollo development of new research techniques led several researchers de nuevas técnicas para la investigación, diversos investigadores en at different times to unravel the molecular mechanisms involved distintas épocas fueron desentrañando los mecanismos moleculares in the transmission of nerve impulses, which took two and a half implicados en la transmisión de los impulsos nerviosos, por lo que centuries to reach the current concept about the origin of action solo bastaron dos siglos y medio para llegar al concepto actual sobre potential. el origen del potencial de acción. Conclusion: The notion “animal spirits” was valid for many centuries, Conclusión. La teoría filosófica de los espíritus animales perduró por while modern science took a little more than two centuries to muchos siglos, mientras que a la ciencia moderna le tomó poco más understand the phenomenon of nerve impulse transmission. de dos siglos para entender el fenómeno de la transmisión nerviosa. Keywords: History; Physiology; Action Potentials; Science Palabras clave: Historia; Fisiología; Potenciales de acción; Ciencia (MeSH). (DeCS). Barco-Ríos J, Duque-Parra JE, Barco-Cano JA. From substance fermentation Barco-Ríos J, Duque-Parra JE, Barco-Cano JA. [De la fermentación de sustancias to action potential in modern science (part two). Rev. Fac. Med. 2018;66(4):623- al potencial de acción en la ciencia moderna (segunda parte)]. Rev. Fac. Med. 7. English. doi: http://dx.doi.org/10.15446/revfacmed.v66n4.65552. 2018;66(4):623-7. English. doi: http://dx.doi.org/10.15446/revfacmed.v66n4.65552. Introduction Modern science, an era for reason Before the birth of modern science, the concepts issued by researchers The first part of this article, entitled From animal spirits to scientific were accepted almost as dogmas, without being proven by other revolution in Medicine (first part), published in volume 66 issue 2 of this researchers. Following the scientific revolution, knowledge began journal, presented a historical review of the way how the functioning of the to acquire a new dimension, slowly detaching itself from religious nervous system based on animal spirits was formerly conceived. This idea influence, leading to dispute and question the concept of animal spirits prevailed until the seventeenth century, during the scientific revolution, when that controlled our nervous system. Giovanni Alfonso Borelli demonstrated that such spirits did not exist. (1) 624 History of action potential: 623-7 This literature review of the period between the eighteenth century, that, after death, the nerves could still retain the ability to drive the when modern science was born, and the first half of the twentieth electrical impulse and transfer it to the muscle fibers to react to it. (8) century, when the phenomenon of nerve impulse transmission Years later, in 1841, the German physician and physiologist Emil was clarified, presents the most outstanding characters and events du Bois-Reymond (1818-1896), at the request of his professor Peter that prompted knowledge about the way how nerve information is Johannes Müller (1801-1858), who was not interested in the field of transmitted through neurons and, consequently, the physiology of electricity, confirmed and expanded the findings reported by Matteucci the nervous system. in 1840 on the existence of an electric current that appeared between a damaged segment and another intact part of a muscle. In fact, Revolution of thought du Bois-Reymond proved the existence of a current in the injured muscle which he called Muskelnstrom and observed, furthermore, Although many historians state that the scientific revolution began that the amplitude of said current decreased by stimulating the nerve; during the Renaissance, modern science took on its avant-garde he called this “negative variation”. (10,11) Later, the researcher role and detached itself from any religious influence only until attached the electrodes of a galvanometer to a nerve and saw the same the eighteenth century. Since then, science developed a way of phenomenon. These works allowed establishing the basic principles interpreting the reality that is attempted to be demonstrated by means of nerve impulse. of the verification of observed facts or data, that is to say, applying In 1850, the German physician and physicist Hermann Ludwig the scientific method proposed by Descartes. Ferdinand von Helmholtz (1821-1894), who was interested in nerve Until the eighteenth century, two hypotheses had been proposed to transmission, which was thought to be impossible to estimate at that explain that the brain was the place where consciousness, sensation time because of the speed at which it was transmitted, designed an and understanding were located (2), and that many bodily structures experiment to measure said speed. For this purpose, he used the were controlled through nerves. The first hypothesis emerged in the newly dissected sciatic nerve of a frog and the corresponding muscle sixth century BC and prevailed until the first half of the seventeenth it innervated, and coupled a clock that started when the nervous century; it proposed the presence of “animal spirits” that were stimulus appeared and stopped at the moment of the contraction. transported by nerves to make organs work. The second hypothesis, After several measurements at different temperatures, Helmholtz was raised in the second half of the seventeenth century, based on the able to calculate that the speed was 27-30 m/s. (8,12) Then, he made experimental work of Giovanni Alfonso Borelli, an advocate of the some measurements on human subjects and found that the driving scientific method, showed that animal spirits were not transported by speed was much faster, about 60 m/s. (13) the nerves and proposed that muscles contract due to the fermentation Wilhelm Friedrich Kühne (1837-1900), a German physiologist, of chemical substances. (3) used fixation and staining and, in the 1870s, described that nerve At the dawn of modern science, a third hypothesis arose to endings reached a small formation on the muscle membrane, calling explain the phenomenon of nerve conduction. In 1713, the physicist, this entire structure “neuromuscular junction”. (14) Kühne proposed mathematician and alchemist Sir Isaac Newton (1642-1727) proposed that the current produced by the nervous impulse excited the muscle that the animal spirits promulgated by Galen were actually “ethereal fibers in this junction. A few years later, Du Bois-Reymond suggested vibrations” that originated in the brain and ran through the nerves to that the nervous transmission could be of chemical nature, where reach the muscles to generate mechanical actions. (4) nerve endings could secrete some chemical agent that excited the In 1752, the Swiss physician and anatomist Albrecht von Haller muscle causing its contraction. (15) (1708-1777), considered as the father of modern physiology, based on At that time, the relationship between nerve fibers and nerve cells his experimental work on animals, concluded that only some parts of was not clear, as it was believed that they were two distinct anatomical the body showed sensitivity and that it was a specific property of the entities. However, Jan Evangelista Purkinje (1787-1869),