Neurofotónica de la Vision La Doctrina de la Neurona

Neurofotónica de la Visión
11/04/2007
Neurofotónica de la Vision
Sistema Visual:
de la Retina al Cortex
NEURONA
Ana González Marcos
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• 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.
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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.
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the achromatic microscope
Teoría de la
Célula 1663R.Hooke
Terminología
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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.
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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.
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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.
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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)
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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).
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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.
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Espectro electromagnético
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Fuentes de Luz (I): El Sol
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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
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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.
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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.
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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).
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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
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