Müller cells

Müller cells

Müller glia, or Müller cells, are a type of retinal cell that serve as support cells for neurons, as other types of glial cells do.

An important role of Müller cells is to funnel light to the rod and cone photoreceptors from the outer surface of the retina to where the photoreceptors are located.

Other functions include maintaining the structural and functional stability of retinal cells. They regulate the extracellular environment, remove debris, provide electrical insulation of the photoreceptors and other neurons, and mechanical support for the fabric of the retina.

  • All glial cells (or simply glia), are non-neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system.
  • Müller cells are the most common type of glial cell found in the retina. While their cell bodies are located in the inner nuclear layer of the retina, they span the entire retina.

Microscopic images of the Sun

When an observer looks up into the sky and sees an atmospheric rainbow they are looking at tiny images of the Sun mirrored in millions of individual raindrops. This is what produces the impression of arching bands of colour.

  • It is the mirror-like surfaces on the inside of raindrops that reflect microscopic images of the Sun towards an observer.
  • The images are tiny because raindrops are small, but also because the surface they reflect off is concave.
  • At a micro-scale, each image of the Sun is different:
    • Each and every image is a different colour and depends on the wavelength of light each raindrop is reflecting towards an observer’s eyes at any particular moment.
    • For convenience sake, wavelength is usually measured in nanometres, but nanometres can be divided into picometres (or even smaller units). This means that an observer is looking at countless wavelengths of light and so countless colours.
    • The images range in size and shape depending on the dimensions of the droplets and turbulence in the atmosphere. The size and roundness of raindrops also affect the appearance of a rainbow as a whole.
  • The millions of microscopic images of the Sun that produce the impression of a rainbow is similar to the way pixels of light produce the images we see on digital displays.
Notice that:
  • If all the rays of incident light that contribute to the formation of an observer’s rainbow are traced back from each raindrop towards the Sun it transpires that they are produced by parallel rays and that each incident ray is polarized as it passes through a droplet.
  • If all the rays of incident light that travel through a single raindrop as it falls are compared, it transpires that they are all parallel with the axis of the rainbow.

Minimum angle of deviation

The minimum angle of deviation of a ray of light of any specific wavelength passing through a raindrop is the smallest angle to which it must change course before it becomes visible within the arcs of a rainbow to an observer.

  • Any ray of light (stream of photons) travelling through empty space, unaffected by gravitational forces, travels in a straight line forever.
  • When light travels from a vacuum or from one transparent medium into another, it deviates from its original path (and changes speed).
  • The more a ray changes direction the greater its angle of deviation.
  • A ray reflected directly back on itself has an angle of deviation of 1800 – the maximum possible angle of deviation.
  • It is the optical properties of air and raindrops that determines the angle of deviation of any ray of incident light.
  • It is the optical properties of raindrops that prevent any ray of visible light within the visible spectrum from exiting a raindrop towards an observer at an angle of deviation less than 137.60.
  • The angle of deviation and the angle of deflection are directly related to one another and together always add up to 1800.
  • The angle of deviation and the viewing angle are always the same.
More about the minimum angle of deviation
  • The optical properties of an idealised spherical raindrop mean that no light of any particular wavelength can deviate at less than its minimum angle of deviation.
  • The minimum angle of deviation of visible light depends on its wavelength.
  • The minimum angle of deviation for red light with a wavelength of approx. 720 nm is 137.60 but similar rays of the same wavelength but with other impact parameters can deviate up to a maximum of 1800.
  • Different colours have different minimum angles of deviation because the refractive index of water changes with wavelength.
Impact parameter and minimum angle of deviation
  • To form a primary rainbow, incident light must strike each raindrop above its horizontal axis.
  • Rays of incident light of a single wavelength strike a raindrop at every possible point on the side of a raindrop facing the Sun.
  • Only those that strike above the horizontal axis contribute to a primary rainbow.
  • Points of impact of incident light striking a droplet can be measured on an impact parameter scale.
  • It is the point of impact of rays of incident light of the same wavelength that is the variable factor that determines their subsequently different paths.
  • Rays that strike nearest the horizontal axis, so with a value near 0.0 on an impact parameter scale have the largest angles of deviation.
  • Rays that strike farthest away from the horizontal axis (near the topmost point on an impact parameter scale and so near 1.0) also have a large angle of deviation.

Medium

Any material through which an electromagnetic wave propagates (travels) is called a medium (plural media).

Summary

About sections (temp)

Media

Media is the plural of medium. A medium is any material through which an electromagnetic wave propagates (travels).

Magnetic field

A magnetic field is created when electric current flows. The greater the current the stronger the magnetic field.

  • Whilst an electric field is created by a change in voltage (charge), a magnetic field is created when electric current flows. The greater the current the stronger the magnetic field.
  • An electromagnetic wave is the result of the interaction of an electric and magnetic field because an electric field induces a magnetic field and a magnetic field induces an electric field.
  • An electromagnetic wave can be induced when either the charge of an electric field changes or when the current of a magnetic field changes or when they both change together.
  • The waveform, wavelength and frequency of an electromagnetic wave result from the rapid periodic succession of transitions between the electrical and magnetic components and the forward propagation of the wave through space.
  • When electric and magnetic fields come into contact to form electromagnetic waves they oscillate at right angles to one another.
  • The direction of propagation of an electromagnetic wave is at right angles to the electric and magnetic fields.

Monochromatic

Monochromatic colour is produced by a single wavelength of light.

  • Monochromatic colours are produced from a single hue.
  • Monochromatic colour schemes are produced by the HSB colour model by starting with a single base hue and then adjusting saturation and brightness to produce variants between white and black.
  • Monochromatic colour schemes are produced with pigments and paints by adding white to red to create different tints of pink and black to create different shades of maroon

Metameric

Visually indistinguishable colour stimuli are described as being metameric.

  • Metameric stimuli are colour stimuli that are indistinguishable from one another because they evoke the same response by the three cone cell types on which human vision colour vision depends.
  • A class of metameric stimuli can be specified by a set of tristimulus values, defined as the “amounts of the 3 reference colour stimuli, in a given trichromatic system, required to match the colour of the stimulus considered”.
  • Perhaps the most important application of metameric stimuli is to be found in the use of tristimulus values used in additive colour systems.
  • The RGB colour model, for example, uses mixtures of red, green and blue light to produce the impression of a complete range of colours for an observer.

Mass

Mass is the amount of matter in an object and is measured in kilograms (kg).

  • A large object made of a given material has greater mass than a small object made of the same material because it contains less matter.
  • Mass is not the same as weight because an object of a known mass will weigh more on earth than on the moon.
  • An object of a known mass is weightless in free fall.
  • Weight is the force of gravity on an object and is measured in newtons (N).

Magnetic field

A magnetic field is created when electric current flows. The greater the current the stronger the magnetic field.

  • Whilst a magnetic field is created when an electric current flows, an electric field is created by a change in voltage (charge). The higher the voltage the stronger the field.
  • An electromagnetic wave is the result of the interaction of an electric and magnetic field because an electric field induces a magnetic field and a magnetic field induces an electric field.
  • An electromagnetic wave can be induced when either the charge of an electric field changes or when the current of a magnetic field changes or when they both change together.
  • The waveform, wavelength and frequency of an electromagnetic wave result from the rapid periodic succession of transitions between the electrical and magnetic components and the forward propagation of the wave through space.
  • When electric and magnetic fields come into contact to form electromagnetic waves they oscillate at right angles to one another.
  • The direction of propagation of an electromagnetic wave is at right angles to the electric and magnetic fields.
  • The velocity at which electromagnetic waves propagate in a vacuum is the speed of light which is 300,000 metres per second.
  • Once an electromagnetic wave propagates outward it cannot be deflected by an external electric or magnetic field.
  • The reason an electromagnetic wave does not need a medium to propagate through is because the only thing that is waving/oscillating is the value of the electric and magnetic fields.

A magnetic field is created when electric current flows. The greater the current the stronger the magnetic field.

  • Whilst an electric field is created by a change in voltage (charge), a magnetic field is created when electric current flows. The greater the current the stronger the magnetic field.
  • An electromagnetic wave is the result of the interaction of an electric and magnetic field because an electric field induces a magnetic field and a magnetic field induces an electric field.
  • An electromagnetic wave can be induced when either the charge of an electric field changes or when the current of a magnetic field changes or when they both change together.
  • The waveform, wavelength and frequency of an electromagnetic wave result from the rapid periodic succession of transitions between the electrical and magnetic components and the forward propagation of the wave through space.
  • When electric and magnetic fields come into contact to form electromagnetic waves they oscillate at right angles to one another.
  • The direction of propagation of an electromagnetic wave is at right angles to the electric and magnetic fields.

Müller cell

Müller glia, or Müller cells, are a type of retinal glial cells in the human eye that serve as support cells for the neurons, as other glial cells do.

  • An important role of Müller cells is to funnel light to the rod and cone photoreceptors from the outer surface of the retina to where the photoreceptors are located.
  • Other functions include maintaining the structural and functional stability of retinal cells. They regulate the extracellular environment, remove debris, provide electrical insulation of receptors and other neurons, and mechanical support of the neural retina.
  • All glial cells (or simply glia), are non-neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system.
  • Müller cells are the most common type of glial cell found in the retina. While their cell bodies are located in the inner nuclear layer of the retina, they span the entire retina.

Medium

Any material through which an electromagnetic wave propagates (travels) is called a medium (plural media).

Matter

Matter is anything that has mass and energy and occupies space by having volume.

  • Matter describes the physical things around us – earth, air and any object that can be named.
  • Matter is made up of particles – atoms and molecules.
  • Subatomic and atomic particles have mass and energy.
  • Light is a form of energy, not matter.
  • Einstein’s equation E=MC2 suggests that anything having mass has an equivalent amount of energy and vice versa.

Material

Material is the matter from which a thing is or can be made.

  • Material is a broad term for a chemical substance or mixture of substances that constitute a thing.
  • Materials can be classified based on different properties such as physical and chemical properties such as geological, biological or philosophical properties.
  • In the physical sense, materials are studied in the field of materials science.

Material thing

A material thing is something formed or consisting of matter.

  • Things are usually objects.
  • An attribute of an object is called a property if it can be experienced (e.g. its colour, size, weight, smell, taste, and location).
  • Objects manifest themselves through their properties.
  • These manifestations seem to change in a regular and unified way, suggesting that something underlies the properties.