How does contrast help in vision?
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It helps detect edges, shapes, and patterns.
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How does contrast help in vision?
It helps detect edges, shapes, and patterns.
What is the primary function of photoreceptors in the retina?
To generate photosensory data.
By what age is accommodation about half of what it was at age 10?
By age 40.
What happens to the lens when no tension is placed on it by the ligaments?
It assumes its natural rounded shape due to elasticity.
How does the retina recognize objects in the environment?
By using contrast rather than absolute light intensity.
What barrier do Müller cells form in the retina?
The inner limiting membrane.
Where do some optic fibers project after leaving the optic chiasm?
To the midbrain for control of eye movement and coordination with sensory information.
What regions of the retina have the most acute vision?
The fovea and the narrow ring of tissue surrounding it, the macula.
What are the five types of neurons found in the retinal layers?
Photoreceptors, bipolar cells, ganglion cells, amacrine cells, and horizontal cells.
What allows us to see objects clearly at different distances?
The ability of the eye to accommodate.
What is the role of aqueous humor in the eye?
It bathes and nourishes the lens and maintains pressure within the eye.
What causes near-sightedness (myopia)?
When the focal point falls in front of the retina.
What is one advantage of using contrast in visual processing?
It allows better detection of weak stimuli.
What happens to a person's eyes when they enter a dark room after being in bright light?
Their eyes initially have low sensitivity to light, making it difficult to see.
What is the process called that increases sensitivity to light in the dark?
Dark adaptation.
How long does it take to reach maximum sensitivity during dark adaptation?
About 20 minutes.
What more complex aspects can the information from ganglion cells translate into?
Color, movement, and detailed structure.
How does the organization of information from ganglion cells help in visual perception?
It helps to establish edges and contrast in the visual field.
What is crucial for recognizing shapes and patterns in visual perception?
The brain's ability to detect the direction and angle of lines.
How are light-on bipolar cells affected by glutamate in the dark?
They are inhibited by glutamate release.
What is the second way light is modified?
By changes in the shape of the lens.
What does the consensual reflex refer to?
The automatic, simultaneous constriction of both pupils when light is shone in one eye.
What is phototransduction?
The process that occurs when light hits the retina, the sensory organ of the eye.
At what age does the accommodation reflex begin to diminish?
From the age of 10.
What gives the pigment epithelium its black color?
Granules of the pigment melanin.
What is the macula responsible for?
Detailed central vision, such as reading, known as visual acuity.
What two factors influence the angle of refraction when light passes from one medium to another?
The difference in density of the two media and the angle at which the light rays meet the surface.
Where is the fovea located in relation to the optic disk?
Lateral to the optic disk.
What are the two types of photoreceptors in the eye?
Rods and cones.
Where do most optic axons project after the optic chiasm?
To the lateral geniculate body of the thalamus.
How is information from ganglion cells translated in the simplest pathways?
Into sensitivity to line orientation.
How is information from adjacent objects processed in the visual cortex?
It is processed together due to topographical organization.
Where is the final destination of the vision pathway?
The occipital cortex.
What is convergence in the context of the retina?
It is when multiple neurons synapse onto a single postsynaptic cell.
What is the role of collateral pathways from the thalamus?
They synapse with efferent neurons of cranial nerve III that control pupil diameter.
What is the shape of ganglion cell visual fields?
Roughly circular.
What is the main function of horizontal cells?
To increase contrast between light and dark areas in the visual field.
What does contrast refer to in the context of vision?
The difference in light intensity between two areas of an image.
What is the distance from the center of a lens to its focal point known as?
Focal length (or focal distance).
What are the three main components of the eye?
What is presbyopia?
The loss of accommodation, leading to the need for reading glasses in the 40s.
What is the remaining one-third of refraction attributed to?
The lens.
What causes far-sightedness (hyperopia)?
When the focal point falls behind the retina.
What assumption is made about the density of the lens when light passes through it?
The density of the lens is assumed to be the same as the density of air.
What is the role of the optic nerve in the vision pathway?
It carries signals from the retina to the brain.
What is the function of rods?
They are sensitive to low-intensity light and function well in darkness.
What is the role of the dark pigment epithelium in the eye?
It absorbs extra light and prevents distortion of vision.
What happens to parallel rays striking a convex lens?
They bend inward and focus to a point.
What is the function of convex lenses in terms of light waves?
Convex lenses converge light waves.
Where do vision neurons terminate after synapsing in the thalamus?
In the occipital lobe at the visual cortex.
How many axons leave the eye in each optic nerve?
Approximately 1 million axons.
What do ganglion cells generate that is different from other retinal cells?
Action potentials.
What characterizes an on-center/off-surround field?
It responds most strongly when light is brightest in the center.
What is the role of amacrine cells in the visual pathway?
They connect bipolar cells and ganglion cells, refining signals sent to the brain.
What is the process called that the eye uses to adjust the shape of the lens for focusing?
Accommodation.
What are the two main functions of the ciliary body?
What is the response of the ganglion cell when light is uniform across a visual field?
The ganglion cell responds weakly.
What are Müller cells?
A special type of glial cell found only in the retina.
What is the first structure in the vision pathway?
The retina.
What does the integration of visual information from both eyes allow us to perceive?
Depth and three-dimensionality.
What occurs when parallel light rays strike a concave lens?
They are refracted into a wider beam.
Where do the optic nerves from the eyes go?
To the optic chiasm in the brain.
What is the primary function of cones?
They are responsible for high-acuity vision and color vision during the daytime.
Which photoreceptors are responsible for early adaptation in the dark?
Cones.
What is the sensitivity of cones to light intensity?
Cones are not sensitive to low-intensity light.
What are the two molecules that compose rhodopsin?
Opsin and retinal.
What causes dilation of pupils?
Contraction of radial muscles under the influence of sympathetic neurons.
What happens in an off-center/on-surround field?
The ganglion cell is inhibited when light is brightest in the off-surround region.
Which structures of the eye comprise the refractive mechanism?
The cornea and lens.
What is the point called where parallel light rays converge in a convex lens?
The focal point.
What role do bipolar cells, horizontal cells, ganglion cells, and amacrine cells play in the retina?
They process visual signals.
How does the lens of the eye change shape if it has no muscle fibers?
Through the action of the ciliary muscle and zonules.
What is the role of neuroglia in the retina?
They provide essential support to the neurons.
What is the fovea?
A small depression at the center of the macula where light is focused.
What is astigmatism?
A condition caused by a cornea that is not a perfectly shaped dome, resulting in distorted images.
What happens when parallel light rays strike a lens surface that is perpendicular?
The light passes through without bending.
What is the organization of the lateral geniculate body?
It is organized in layers corresponding to different parts of the visual field.
What are optic radiations?
They are pathways that transmit visual information from the thalamus to the occipital cortex.
What happens at the optic chiasm?
Some of the fibers cross to the opposite side.
Where is the fovea located and what is its significance?
The fovea is the region of sharpest vision and has a very high density of cones.
What pigment do rods produce that significantly increases sensitivity in dim light?
Rhodopsin.
What happens to light-off bipolar cells in the dark?
They are excited by glutamate release.
What is the first step in the process of photosensory transduction?
When light strikes the photoreceptors, rhodopsin is activated.
What mediates the consensual reflex?
Parasympathetic fibers running through cranial nerve III.
What pigment do rods contain that is crucial for detecting light?
Rhodopsin.
What must happen for the focal length of a lens to change?
The shape of the lens must change.
What is the function of the pigment epithelium in the retina?
To absorb light rays that escape the photoreceptors, preventing distortion of the visual image.
Where does most refraction occur in the eye?
About two-thirds occurs at the cornea.
What occurs when the ligaments pull on the lens?
The lens flattens out for distance vision.
What is the term for the slightly different images received by each eye due to their separation?
Monocular vision.
Which part of the brain combines information from both eyes to create a binocular view?
The visual cortex.
How can vision problems be corrected?
By placing a lens with the appropriate curvature in front of the eye.
What is the role of photoreceptors in the retina?
They convert light energy into electrical signals.
How do rods compare to cones in terms of quantity?
Rods outnumber cones by a 20:1 ratio, except in the fovea.
Where does light transduction occur in photoreceptors?
In the outer segment of the photoreceptor.
What is the structure of the visual cortex?
It has six layers of neurons grouped into vertical columns.
What are the two types of bipolar cells?
Light-on and light-off bipolar cells.
What are visual fields in relation to ganglion cells?
Areas of the retina from which a ganglion cell receives information.
What occurs to retinal when it is activated by light?
It changes shape and is released from opsin in a process known as bleaching.
What does a decrease in cyclic GMP levels cause in photoreceptors?
It closes Na+ channels, reduces inward Na+ current, and produces hyperpolarization.
What is refraction?
The bending of light rays as they pass from one object to another.
What happens at the optic chiasm?
Nerve fibers from each eye cross to the opposite side of the brain.
What part of the electromagnetic spectrum can our brains perceive?
Only a small portion of it.
What contributes to increased sensitivity in the dark?
The production of more visual pigments by photoreceptors.
What alters neurotransmitter release onto bipolar cells?
Changes in photoreceptor membrane potential.
What aspects of visual information are sorted within each portion of the visual field?
Form, color, and movement.
How is the amount of light reaching photoreceptors modulated?
By changes in the size of the pupil.
What is the response of a ganglion cell to strong contrast?
It elicits a strong excitatory response or a strong inhibitory response.
What neurotransmitters do horizontal cells usually release?
Inhibitory neurotransmitters like GABA or glycine.
What chemical change occurs in rods when light hits them?
It causes a chemical change in the pigment molecules within the membranous discs.
Why does rhodopsin appear purple?
It reflects light in the red and blue parts of the spectrum while absorbing primarily in the green region.
