Neurofotónica de la Visión 11/04/2007 Neurofotónica de la Vision Sistema Visual: de la Retina al Cortex NEURONA Ana González Marcos AGM - abr-07 1 • Microscopio Primeros Pasos until, in the years from 1836 to 1838 (roughly a decade after the new microscopes were available), the first cells in the nervous tissue were described by several anatomists, such as Gabriel Gustav Valentin (1810-1863) – 1595 by Hans and Zacharias Jansen (1588-1631) in Holland – in the 17th century in several countries, including by Robert Hooke (1635-1703), in England but most notably by a Dutchman, Anton van Leeuwenhoek (1632-1723). Siglo XIX Another influential scientist of this period, Robert Remak (1815-1865), described in 1836 how the nervous tissue seemed to be entirely suffused with a very fine and exceedingly complex mesh of filamental processes, which had escaped the eyes of previous microscopists. He also described for the first time the existence of two types of nerve processes: myelinated and unmyelinated. No one knew for sure what was the function of these filaments, but they seemed to be important. Purkinje proposed that there should be some connection between these processes and the nucleated cell bodies. Remak suggested in no uncertain terms that the nerve fibers could be processes which arose from the nerve cell. Jan Evangelista Purkinje (1787-1869) La mielina es la sustancia lipídica que recubre las neuronas con la finalidad de hacer más rápidas las conexiones entre unas neuronas y otras (sinapsis). Recubre una parte de las neuronas llamada axón. AGM - abr-07 3 AGM - abr-07 Otto Friedrich Karl Deiters (1834-1863), using chromic acid and carmine red. "dendrites" in 1889, by Wilhelm His (18311904), "axons" in 1896, by Rudolph Albert von Kölliker. The cell itself was christened only in 1891 as "neuron", by Heinrich Wilhelm von Waldeyer (1836-1921). Drawings of stained neurons in the spinal chord with soma, nucleus, dendrites and axons, by Otto F K. Deiters, in 1865. AGM - abr-07 2 the achromatic microscope Teoría de la Célula 1663R.Hooke Terminología AGM - abr-07 5 4 La Doctrina de la Neurona officially enunciated by Wilhelm Waldeyer (1836-1921) in 1891 The neuron doctrine is the now fundamental idea that neurons are the basic structural and functional units of the nervous system. The theory was put forward by Santiago Ramón y Cajal in the late 19th century. It held that neurons are discrete cells (not connected in a meshwork); that neurons are genetically and metabolically distinct units; that they have cell bodies, axons, and dendrites; and that neural transmission goes only in one direction, from dendrites toward axons. Particularly relevant were Cajal s conclusions about the way action currents propagate in neuronal networks, always in the direction of dendrites to axons, and there to the dendrites or soma of other neurons. He called this the Law of Dynamic Polarization , which was another fundamental contribution to neurophysiology. AGM - abr-07 /http://www.tfo.upm.es/WebNeurof/Neurofot3.htm 6 1 Neurofotónica de la Visión 11/04/2007 Santiago Ramón y Cajal Synapsis anatomist Camillo Golgi (1843-1926) Golgi and Cajal, compartieron el Premio Nobel en 1906 por sus estudios sobre el sistema nerviosos . Se conocieron en Estocolmo en la entrega de premios. Golgi mantuvo la Teoría Reticular en su discurso frente a la Teoría de la Contigüidad. Microscopio electrónico A photograph of dendritic spines made by Cajal Cajal was almost clairvoyant in proposing that the increase in the number of synapses could be one of the mechanisms of learning and memory, a fact that was ascertained only much later. AGM - abr-07 morphological proof y in 1954, with the work of George Palade, Eduardo de Robertis and George Bennett distinct presynaptic and postsynaptic elements, a synaptic cleft and presynaptic vesicles. 7 AGM - abr-07 8 Transmisión Química/Eléctrica Sir Henry Dale again came to rescue, by Otto Loewi described his beautiful proving, in a series of elegant experiments experiments, showing that stimulation between 1929 and 1936, that acetylcholine of the vagus nerve produced its is also a neurotransmitter in the inhibitor effects on the frog's heart by neuromotor synapse the liberation of a chemical substance They shared the Nobel Prize of 1936 for their discoveries. in 1951, Eccles succeeded for the first time in inserting microelectrodes into nerve cells of the central nervous system and in recording the electrical responses produced by synapses Bernard Katz, was able to study the neuromuscular junction with intracellular electrodes, and the role of acetylcholine in this synapse was completely demonstrated. Sir John Eccles and Sir Bernard Katz were both honoured with the Nobel Award of 1963 and 1970, respectively. LA LUZ when excited by the release of neurotransmitters: the excitatory and inhibitory post-synaptic potentials (EPSP and IPSP, respectively) AGM - abr-07 9 AGM - abr-07 10 Concepto de Fotón Interacción radiación-materia Dualidad onda-partícula hv = E1 - E0 1 eV = 1.602 x 10-19 J h = 6.626 x 10-34J s (joule second). AGM - abr-07 11 AGM - abr-07 /http://www.tfo.upm.es/WebNeurof/Neurofot3.htm 12 2 Neurofotónica de la Visión 11/04/2007 • En 1900, Max Planck demuestra que la energía se emite en pequeños paquetes discretos, a los que denomina cuantos, y no de manera continua, tal y como proponía la teoría de ondas de la radiación electromagnética entonces imperante. • Desarrollando la teoría de Plank, Albert Einstein, en 1905, sugiere que la luz misma no está compuesta por ondas, sino por cuantos de energía (a los que denomina fotones), estando relacionada la energía del fotón con su longitud de onda (o frecuencia). • Einstein demostró cómo bajo determinadas condiciones los electrones podían absorber y emitir la energía de los fotones, y utilizó esta demostración para explicar lo que se denominó el efecto fotoeléctrico (la descarga de electrones de la materia por el impacto de la radiación, especialmente de la luz visible). Por la explicación del efecto fotoeléctrico fue galardonado con el Premio Nobel de Física en 1921. • En 1913, Niels Bohr formula un modelo del átomo en el que los electrones ocupan órbitas específicas, o estados de energía, alrededor del núcleo, determinados por los niveles de energía de los electrones • En 1917, nuevamente Albert Einstein, identifica el fenómeno conocido como emisión estimulada, uno de los principios fundamentales en los que se basará el láser. AGM - abr-07 13 Espectro electromagnético AGM - abr-07 Fuentes de Luz (I): El Sol 14 Fuentes de Luz(II) Espiga o Spica es una estrella blanco-azulada: su magnitud aparente en banda B (filtro azul) es igual a 0.91 mientras que en banda V (filtro verde) es igual a 1.04. Situada en la constelación de Virgo, se le conoce también como α Virginis. Se encuentra a 260 años luz de la Tierra; su movimiento orbital la aleja de nuestro planeta a la velocidad de 1 km/s. Incoherentes Coherentes Antares es el nombre propio de la estrella α Scorpii, la estrella más brillante de la constelación de Escorpio. Se aproxima a la Tierra a la velocidad de 3.4 km/s AGM - abr-07 15 AGM - abr-07 16 Radiación y Seres Vivos light rays (~400–700 nm), the somewhat longer infrared or heat rays, and the somewhat shorter ultraviolet rays El componente tipo C de la radiación ultravioleta emitida por el sol (UV-C) es mayoritariamente absorbido por la capa estratosférica de ozono, y la mínima cantidad que llega a la superficie terrestre no es potencialmente nociva para los ojos. UV-A, 400–320 nm — the most abundant in sunlight; UV-B, 320–290 nm — responsible for tanning and the synthesis of vitamin D; The shorter wavelengths of ultraviolet can be UV-C, < 290 nm — a powerful germicidal absorbed by DNA and damage it — causing agent. mutations. X-rays and gamma rays also damage DNA by generating ions within the cell. Thus these wavelengths represent ionizing radiation. AGM - abr-07 Sin embargo, la exposición ocular repetida o muy intensiva a los tipos A y B de radiación solar ultravioleta (UV-A y UV-B) puede conducir a la aparición de alteraciones oculares severas, que van desde inflamaciones agudas en la conjuntiva (conjuntivitis) y en la córnea (queratitis), hasta la aparición de procesos degenerativos en la superficie ocular (pingüécula, pterigion), cataratas, diferentes formas de retinopatía, e incluso lesiones cutáneas predisponentes a desarrollar un cáncer en la piel de los párpados. Sin embargo, los rayos UV no son siempre perjudiciales. Toda radiación procedente del sol es necesaria para mantener ciertas funciones de los seres vivos (hormonales, del crecimiento, síntesis de vitaminas, inmunológicas, etc.) pero basta con una exposición de media hora al día. 17 AGM - abr-07 /http://www.tfo.upm.es/WebNeurof/Neurofot3.htm 18 3 Neurofotónica de la Visión 11/04/2007 El visible Light makes possible a number of essential functions in living things: photosynthesis ("essential" is too mild a word here: photosynthesis provides the organic molecules upon which virtually all life depends) vision plant growth responses photoperiodism phototropism setting the biological "clocks" that adjust many metabolic functions in virtually all organisms (e.g., circadian rhythms). Approximately one-half of the energy reaching the earth from the sun is light; that is, it is within the visible portion of the spectrum. The remainder arrives as heat and a small amount of ultraviolet light (which can, however, have a large effect on the aging of skin and the development of skin cancer). AGM - abr-07 19 AGM - abr-07 20 Autotrophic Capable of synthesizing organic molecules from inorganic raw materials. •Photoautotrophs - plants, algae, and some bacteria - use light as the source of the needed energy. [Photosynthesis] •Chemoautotrophs use the energy secured by oxidizing some inorganic substance in their surroundings. Characteristic of certain bacteria and archaea. The heart of photosynthesis as it occurs in most autotrophs consists of two key processes: the removal of hydrogen (H) atoms from water molecules The electrons (e−) and protons (H+) that make up hydrogen atoms are stripped away separately from water molecules. 2H2O -> 4e− + 4H+ + O2 2H2O -> 2H2 + O2, Δ G = +118 kcal. the reduction of carbon dioxide (CO2) by these hydrogen atoms to form organic molecules. The second process involves a cyclic series of reactions named (after its discoverer) the Calvin Cycle AGM - abr-07 21 /http://www.tfo.upm.es/WebNeurof/Neurofot3.htm 4