Dictionary tag: K-L-M-N-O

Optic chiasm

The optic chiasm is the part of the human brain where the optic nerves partially cross. The optic chiasm is located at the bottom of the brain immediately below the hypothalamus.

  • The cross-over of optic nerve fibres at the optic chiasm allows the visual cortex to receive the same hemispheric visual field from both eyes.
  • Superimposing and processing these monocular visual signals allow the visual cortex to generate binocular and stereoscopic vision.
  • For example, the right visual cortex receives the temporal visual field of the left eye, and the nasal visual field of the right eye, which results in the right visual cortex producing a binocular image of the left hemispheric visual field. The net result of optic nerves crossing over at the optic chiasm is for the right cerebral hemisphere to sense and process left hemispheric vision, and for the left cerebral hemisphere to sense and process right hemispheric vision.
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Optic nerve

Optic nerve

The optic nerve is the cable–like grouping of nerve fibres formed from the axons of ganglion cells that transmit visual information towards the lateral geniculate nucleus.

The optic nerve contains around a million fibres and transports the continuous stream of data that arrives from rods, cones and interneurons (bipolar, amacrine cells). The optic nerve is a parallel communication cable that enables every fibre to represent distinct information about the presence of light in each region of the visual field.

Optic nerve

The optic nerve in the human eye is a cable-like bundle of nerve fibres composed of the axons of ganglion cells, responsible for transmitting visual information to the brain’s lateral geniculate nucleus.

  • This nerve contains about a million fibres that carry a constant stream of visual data, received from the eye’s photoreceptors—rods and cones—as well as intermediate neurons such as bipolar and amacrine cells.
  • The optic nerve functions like a parallel communication cable, with each fibre transmitting distinct information about light intensity and patterns from specific regions of the visual field, allowing the brain to construct a cohesive image of the surroundings.
  • The optic nerve exits the eye at a spot called the optic disc, where no photoreceptors are present, creating a natural “blind spot” in the visual field. The brain compensates for this by filling in the missing information.
  • Some fibres from the optic nerve cross over to the opposite side of the brain at the optic chiasm. This crossover allows visual information from both eyes to be processed in both hemispheres of the brain, which is crucial for depth perception and a unified field of vision.

Optic nerve

The optic nerve in the human eye is a cable-like bundle of nerve fibres composed of the axons of ganglion cells, responsible for transmitting visual information to the brain’s lateral geniculate nucleus.

  • This nerve contains about a million fibres that carry a constant stream of visual data, received from the eye’s photoreceptors—rods and cones—as well as intermediate neurons such as bipolar and amacrine cells.
  • The optic nerve functions like a parallel communication cable, with each fibre transmitting distinct information about light intensity and patterns from specific regions of the visual field, allowing the brain to construct a cohesive image of the surroundings.
  • The optic nerve exits the eye at a spot called the optic disc, where no photoreceptors are present, creating a natural “blind spot” in the visual field. The brain compensates for this by filling in the missing information.
  • Some fibres from the optic nerve cross over to the opposite side of the brain at the optic chiasm. This crossover allows visual information from both eyes to be processed in both hemispheres of the brain, which is crucial for depth perception and a unified field of vision.
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Optic radiation

Optic radiation

The optic radiations are tracts formed from the axons of neurons located in the lateral geniculate nucleus and leading to areas within the primary visual cortex. There is an optic radiation on each side of the brain. They carry visual information through lower and upper divisions to their corresponding cerebral hemisphere.

Optic radiation

The optic radiation are tracts formed from the axons of neurons located in the lateral geniculate nucleus and lead to areas within the primary visual cortex.

  • There is an optic radiation on each side of the brain. Each one carries visual information through two divisions called the upper and lower divisions to their corresponding cerebral hemisphere.
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Optic radiation

The optic radiation consists of neural tracts formed by the axons of neurons in the lateral geniculate nucleus (LGN), which project to the primary visual cortex.

  • There are two optic radiations, one on each side of the brain, each responsible for carrying visual information to the corresponding hemisphere.
  • The optic radiation is divided into two main pathways:
    • The upper division, which carries information from the lower visual field,
    • The lower division (also called Meyer’s loop), which carries information from the upper visual field.
  • These pathways ensure that visual information is accurately mapped to the primary visual cortex, where it is processed and interpreted.

Optical density

Optical density is a measure of how much a material resists and slows the transmission of light.

  • The higher the optical density of a material, the slower light travels through it.
  • The lower the optical density of a material, the faster light travels through it.
  • A vacuum is not a medium and has zero optical density.
  • Light travels through a vacuum at the maximum possible speed of light which is 299,792 kilometres per second.
  • Optical density and refractive index are related properties.
  • In general, materials with higher optical density tend to have higher refractive indices and vice versa.
  • The greater the difference in refractive index between two materials, the more they will bend light when they come into contact.

 

 

Optical density

Optical density is a measure of how much a material resists and slows the transmission of light.

  • The optical density of a material is not directly related to its physical density.
  • The higher the optical density of a material, the slower light travels through it.
  • The lower the optical density of a material, the faster light travels through it.
  • A vacuum is not a medium and has zero optical density.
  • Light travels through a vacuum at the maximum possible speed of light which is 299,792 kilometres per second.
  • Optical density and refractive index are related properties.
    • In general, materials with higher optical density tend to have higher refractive indices and vice versa.
    • The greater the difference in refractive index between two materials, the more they will bend light when they come into contact.
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Optical illusion

Optical illusions and other visual anomalies are caused by the way the human visual system processes information.

Physical illusions

Physical illusions result from the limitations and assumptions of the human visual system when interpreting the external world. Examples include:

  • The Sun and Moon appear larger near the horizon as a result of the brain’s interpretation of distance cues.
  • Rainbows are composed of a continuous range of wavelengths across the visible spectrum but appear to be formed from a series of bands of colour.
Physiological illusions

Physiological illusions are often connected with the different attributes of visual perception and occur when visual stimuli are beyond our brain’s processing ability.

Physiological illusions arise due to the way that the human eye and visual system process information from the outside world, such as lighting, contrast, and colour. Examples include:

  • After-images occur when the eye’s photoreceptor cells become fatigued due to overstimulation, resulting in an image appearing after the stimulus is removed.
  • Moiré patterns occur when two similar patterns with slightly different frequencies overlap, creating a new pattern that appears to move or vibrate.
Cognitive illusions

Cognitive illusions result from the brain’s inability to correctly interpret visual information, leading to uncertainties or errors in perception. Examples include:

  • Ambiguous illusions are images that can be read in more than one way, depending on contextual cues and the viewer’s past experiences. They often cause a perceptual “switch” between alternative interpretations.
  • Geometrical illusions occur when the brain uses contextual cues and assumptions to interpret visual stimuli, leading to distortions in size, length, position, or curvature.
  • Paradox illusions occur when visual stimuli contain conflicting information that cannot be resolved by the brain, leading to a perceptual paradox.
  • Fictions are created when the brain fills in missing visual information based on contextual cues and past experiences, leading to the perception of additional content that is not actually present.
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References

Optical illusion

Optical illusions and other visual anomalies are caused by the way the human visual system processes information.

  • Physical illusions: Physical illusions result from the limitations and assumptions of the human visual system when interpreting the external world.
  • Physiological illusions: Physiological illusions are often connected with the different attributes of visual perception and occur when visual stimuli are beyond our brain’s processing ability.
  • Cognitive illusions: Cognitive illusions result from the brain’s inability to correctly interpret visual information, leading to uncertainties or errors in perception.

Optical phenomena

Optical phenomena result from the interactions between light and matter. Optical phenomena include absorption, dispersion, diffraction, polarization, reflection, refraction, scattering and transmission.

  • Optics is the branch of physics that studies the behaviour and properties of light, including visible, ultraviolet, and infrared light.
  • Visible, ultraviolet, and infrared light, along with X-rays, microwaves, and radio waves, are all examples of electromagnetic radiation.
  • Many optical phenomena can be explained using the classical electromagnetic theory that describes light in terms of waves.
  • Geometric optics describes light as travelling in straight lines and changing direction when passing through or reflecting from surfaces. These phenomena can be analysed using ray diagrams.
  • Ray diagrams are useful when explaining the workings of everyday objects such as mirrors, lenses, telescopes, microscopes, lasers, and fibre optic devices.
  • Some optical effects such as diffraction and interference can be explained in terms of the particle-like properties of photons and with reference to the field of quantum mechanics.
  • About photons:
    • A photon is a fundamental particle of light.
    • It is the smallest unit of electromagnetic radiation.
    • It has no mass, but it does have energy and momentum.
    • Photons travel at the speed of light in a vacuum (299,792,458 meters per second).
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References
  • Optical phenomena result from the interactions between light and matter. Optical phenomena include absorption, dispersion, diffraction, polarization, reflection, refraction, scattering and transmission.
  • Optics is the branch of physics that studies the behaviour and properties of light, including visible, ultraviolet, and infrared light.
  • Visible, ultraviolet, and infrared light, along with X-rays, microwaves, and radio waves, are all examples of electromagnetic radiation.
  • Many optical phenomena can be explained using the classical electromagnetic theory that describes light in terms of waves.
  • Geometric optics describes light as travelling in straight lines and changing direction when passing through or reflecting from surfaces. These phenomena can be analysed using ray diagrams.
  • Ray diagrams are useful when explaining the workings of everyday objects such as mirrors, lenses, telescopes, microscopes, lasers, and fibre optic devices.
  • Some optical effects such as diffraction and interference can be explained in terms of the particle-like properties of photons and with reference to the field of quantum mechanics.

Optics

Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it.

Contemporary optics
  • Most optical phenomena can be accounted for using the classical electromagnetic description of light (wavelength, frequency and intensity) but they can also be modelled as particles called photons.
  • Optics is both a field of physics and an area of engineering. It has been used to create many useful devices, including eyeglasses, cameras, telescopes, and microscopes. Many of these devices are based on lenses, which can focus light and produce images of objects that are larger or smaller than the original.
  • New discoveries are being made in the field of optics For example, The first working fibre-optic data transmission system was demonstrated in 1965. Less than 60 years later, fibre optics are now used to send vast amounts of data through thin optical fibre around the world.
  • Contemporary specializations within the field of optics include:
    • Geometrical optics is a branch of optics that deals with the behaviour of light as a collection of rays that propagate in straight lines and are subject to reflection and refraction.
    • Physical optics is a branch of optics that describes the behaviour of light as both a wave and a particle and includes wave phenomena such as diffraction and interference that are not explained by geometrical optics.
    • Quantum mechanics is a branch of physics that describes the behaviour of light as both a wave and a particle and investigates the interactions between light and matter.
About geometrical optics
  • Geometrical optics, also known as ray optics, is one of the two main branches of optics, the other being physical optics.
  • Geometrical optics is based on the assumption that light travels as a straight line and is useful in explaining various optical phenomena, including reflection and refraction, in simple terms.
  • Geometrical optics is a useful tool in analyzing the behaviour of optical systems, including the image-forming process and the appearance of aberrations in systems containing lenses and prisms.
  • The underlying assumptions of geometrical optics include that light rays:
    • Propagate in straight-line paths when they travel in a uniform medium.
    • Bend, and in particular, refract, at the interface between two dissimilar media.
    • Follow curved paths due to the varying refractive index of the medium.
    • May be absorbed as photons and transferred to the atoms or molecules of the absorbing material, causing the absorbing material to heat up or emit radiation of its own.
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References

Optics

Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it.

  • Optics studies the behaviour of electromagnetic radiation in the visible, ultraviolet, and infrared regions of the electromagnetic spectrum.
  • Some fields of optics also study the behaviour and properties of other forms of electromagnetic radiation such as X-rays and microwaves.
  • The observation and study of optical phenomena offer many clues as to the nature of light.
  • Optical phenomena include absorption, dispersion, diffraction, polarization, reflection, refraction, scattering and transmission.
  • Optics explains the appearance of rainbows, how light reflects off mirrors, how light refracts through glass or water, and why light separates into a spectrum of colours as it passes through a prism.

Orders of rainbows

Primary rainbows are sometimes referred to as first-order bows. First-order rainbows are produced when light is reflected once as it passes through the interior of each raindrop.

Secondary rainbows are second-order bows. Second-order bows are produced when light is reflected twice as it passes through the interior of each raindrop.

  • Each subsequent order of rainbows involves an additional reflection inside raindrops.
  • Higher-order bows get progressively fainter because photons escape droplets after the final reflection. As a result, insufficient light reaches an observer to trigger a visual response.
  • Each higher-order of bow gets progressively broader spreading photons more widely and reducing their brightness further.
  • Only first and second-order bows are generally visible to an observer but multi-exposure photography can be used to capture them.
  • Different orders of rainbows don’t appear in a simple sequence in the sky.
  • First, second, fifth and sixth-order bows all share the same anti-solar point.
  • Zero, third and fourth-order bows are all centred on the Sun and appear as circles of colour around it.

https://www.atoptics.co.uk/rainbows/orders.htm

Oscillation

An oscillation is a periodic motion that repeats itself in a regular cycle.

  • Oscillation is a characteristic of waves, including electromagnetic waves.
  • Examples of oscillation include the side-to-side swing of a pendulum and the up-and-down motion of a spring with a weight attached.
  • Electromagnetic waves oscillate due to the transmission of energy by their electric and magnetic fields.
  • An oscillating movement is typically around a point of equilibrium and the motion repeats itself around an equilibrium position.

 

 

Oscillation

An oscillation is a periodic motion that repeats itself in a regular cycle.

  • Oscillation is a characteristic of waves, including electromagnetic waves.
  • Examples of oscillation include the side-to-side swing of a pendulum and the up-and-down motion of a spring with a weight attached.
  • Electromagnetic waves oscillate due to the transmission of energy by their electric and magnetic fields.
  • An oscillating movement is typically around a point of equilibrium and the motion repeats itself around an equilibrium position.
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Stellar light

Stellar light is the term used to describe the electromagnetic radiation emitted by stars, primarily due to the nuclear fusion of hydrogen atoms occurring within their cores.

  • Unlike traditional sources of light on Earth, stars ignite with a far more powerful process – nuclear fusion.
  • Deep within their incredibly dense and hot cores, immense pressure and temperatures fuel nuclear fusion.
  • This process forces hydrogen atoms to merge into heavier elements, primarily helium, releasing tremendous energy.
  • A fraction of this energy escapes the star as the radiant light we call sunlight and starlight.
Nuclear Fusion Process
  • Fuel and Fusion: Nuclear fusion (thermonuclear fusion) primarily occurs in a star’s core, consuming hydrogen and generating energy and light.
  • Immense Conditions: The immense pressure and temperature within the core are crucial for hydrogen atoms to overcome their natural repulsion and fuse.
  • Energy Release: This fusion process releases vast amounts of energy, including the light we see from stars. Fusion reactions release millions of times more energy than traditional chemical reactions, like burning fossil fuels.
  • Temperature and Colour: Hotter stars, fusing at a faster rate, emit more energy and appear blue or white. Cooler stars with slower fusion emit less and appear red or orange.
  • Lifespan and Evolution: Massive stars burn hotter and brighter, but as their hydrogen reserves deplete and their fusion processes change, they produce a dimmer glow.
From Core to Surface
  • The light generated in the core of stars doesn’t immediately escape.
  • It interacts with surrounding layers of hot gas (plasma) within the star.
  • These layers absorb and re-emit light at different wavelengths, ultimately shaping the final spectrum we detect.
  • Finally, the light escaping a star’s surface embarks on its interstellar journey, eventually reaching Earth, our telescopes and eyes.
  • Sunlight originates from the Sun’s core and reaches Earth in about 8 minutes after travelling through its outer layers.
Sunlight and stellar light
  • Light emitted by the Sun and stars is not just a single colour but a spectrum of colours.
  • The electromagnetic spectrum extends far beyond the visible light we perceive.
  • The Sun and stars emit radiation across the whole electromagnetic spectrum, although a limited range of wavelengths make it through the Earth’s atmosphere.
  • Sun and stellar light on Earth include wavelengths stretching into the ultraviolet and infrared.
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