CNS Retinal Function and Visual Perception

The process where the eye's lens changes shape to focus on objects at different distances.

The point where light rays converge and are focused on the retina.

Seeing objects close to the eye; requires more lens curvature.

Seeing objects far away; requires a flatter lens.

Bending of light as it passes through different mediums (e.g., the eye's lens).

Sharpness or clarity of vision; ability to see fine details.

The image formed on the retina is upside down and reversed.

Muscles that control the shape of the lens, enabling accommodation.

Ganglion cells are the only neurons that transmit signals out of the retina, their axons form the optic nerve.

Photoreceptors detect light as photons, the smallest unit of light. The light we see is part of the electromagnetic spectrum.

Rods are photoreceptors sensitive to light intensity, they detect how much light is present but not color.

Cones are photoreceptors that provide information about color, they also contribute to sharper vision.

Rods are mainly found in the peripheral retina, while cones are most concentrated in the macula, especially the fovea.

Photoreceptors have an outer segment containing discs where light is absorbed, and an inner segment with mitochondria and organelles.

The signal from photoreceptors flows to bipolar cells, which then communicate with ganglion cells, whose axons form the optic nerve.

Rods are highly sensitive to light, they can even detect a single photon. They also converge onto the same ganglion cell, resulting in low acuity.

Cones are found in higher density at the fovea, they don't contribute to color vision, but they help focus on details.

The retinal structure varies with more rods in the periphery, allowing for sensitivity in low light. The center has higher cone density for sharp vision.

Specialized cells in the retina that convert light into electrical signals. They contain photosensitive pigments like rhodopsin.

A light-sensitive pigment found in rod cells. It's composed of opsin (a protein) and retinal (a light-absorbing molecule).

A light-absorbing molecule derived from vitamin A. It changes shape when it absorbs light, triggering a cascade of events in phototransduction.

A decrease in the membrane potential of a cell, making it less likely to fire an action potential. Photoreceptor cells hyperpolarize when they absorb light.

A G protein activated by rhodopsin. It initiates a signaling cascade leading to the closure of ion channels in rod cells.

An enzyme activated by transducin. It breaks down cGMP, causing ion channels to close and reducing the cell's electrical activity.

A cyclic nucleotide that keeps ion channels open in rod cells in the dark. When light enters the eye, cGMP is broken down, leading to hyperpolarization.

A series of biochemical reactions that reset the system after light absorption. It converts all-trans-retinal back to 11-cis-retinal and reforms rhodopsin.

When light hits a photoreceptor, it causes the cell to become hyperpolarized (more negative). This is because light triggers a cascade of events that lead to the closure of sodium channels, reducing the flow of positive ions into the cell.

Photoreceptor cells normally release glutamate, a neurotransmitter that inhibits bipolar cells. However, when light hits the photoreceptor, it hyperpolarizes the cell, causing a reduction in glutamate release.

When light reduces glutamate release from the photoreceptor, the bipolar cell is no longer inhibited. This allows the bipolar cell to depolarize, becoming more positive.

The signal from the photoreceptor is transmitted through the bipolar cell to the ganglion cell. The ganglion cell then generates an action potential (nerve impulse) that travels to the brain.

There are two types of bipolar cells, "on-center" and "off-center". On-center bipolar cells are excited by light, while off-center bipolar cells are inhibited by light.

Cone cells are less sensitive to light than rod cells. They need hundreds of photons to activate, compared to rod cells which only need a few photons to activate.

Cone cells achieve high acuity (sharpness) because they have a lower degree of convergence in their wiring patterns. This means that each cone cell connects to fewer bipolar cells, resulting in a more precise signal.

There are three types of cone cells: blue cones, green cones, and red cones. Each type of cone contains a different form of opsin, a light-sensitive protein, which determines its peak sensitivity to different wavelengths of light.

A condition where an individual lacks certain cone pigments, leading to an inability to distinguish between certain colors, most commonly red and green.

Photoreceptor pigments located in cones that are responsible for color vision. Different cones are sensitive to different wavelengths of light, allowing us to perceive a wide range of colors.

Vision in low light conditions, dominated by rod photoreceptors, which are more sensitive to light intensity than color.

The process of our eyes adjusting to low light conditions. It involves a shift from cone to rod vision and the regeneration of rhodopsin.

Vitamin A is crucial for the synthesis of rhodopsin, the photopigment in rods. A deficiency can lead to impaired night vision.

Photoreceptor cells in the retina that are highly sensitive to low light levels but do not perceive color.

The amount of light energy present, which influences the type of photoreceptor used for vision.

The ventral stream is responsible for object recognition. It's nicknamed the 'what' pathway because it helps us identify and understand what we're seeing.

The optic chiasm is where the optic nerves from each eye cross. This allows signals from the left visual field of each eye to be processed by the right hemisphere of the brain, and vice versa.

The Lateral Geniculate Nucleus (LGN) acts as a relay station in the thalamus for visual information coming from the retina. It's where signals are organized and sent to the visual cortex.

The visual processing happens primarily in the visual cortex, located in the occipital lobe of the brain.

Neurons in the visual cortex that respond to specific visual features like lines, edges, or angles. They help the brain analyze and recognize patterns in images.

The images projected on the retina are inverted. Through complex processes in the visual cortex, the brain re-inverts these images to allow us to see things correctly.

Both the LGN and the visual cortex contain topographical maps. This means that there's a point-by-point correspondence between the retina and these brain regions.

The fovea is responsible for high-acuity vision, so it has a large representation in the visual cortex. This means that more brainpower is dedicated to processing the center of our field of view.

The eye's ability to adjust to different light intensities, shifting from low to high illumination levels. This involves changes in the use of photoreceptor cells, specifically rod and cone cells.

Rod photoreceptor cells become overwhelmed and lose sensitivity in bright light conditions. Their photopigment, Rhodopsin, bleaches out, leading to a decrease in visual sensitivity.

In bright light, cone photoreceptor cells become the primary source of visual information, leading to high-acuity (sharp) and color vision.

The point where the optic nerves from each eye cross. Fibers from the nasal side (inner) of each eye cross over to the contralateral hemisphere, while fibers from the temporal side (outer) remain ipsilateral.

The Lateral Geniculate Nucleus (LGN) in the thalamus receives visual information from the optic nerve. It acts as a relay station, organizing and filtering signals before sending them to the visual cortex.

The area in the occipital lobe of the brain responsible for processing visual information. It receives signals from the LGN and further analyzes them to interpret images.

Specialized cells in the visual cortex that respond to specific features in visual stimuli, such as lines, edges, and angles.

The LGN and visual cortex contain spatial representations of the visual field, maintaining the relative location of objects as they are processed.

The Snellen chart is a common test to measure visual acuity, which is the sharpness or clarity of vision.

20/20 vision indicates normal visual acuity. This means a person can see at 20 feet what a person with normal vision can see at 20 feet.

The Fovea is a small, central pit in the retina that is responsible for sharp central vision, also known as high visual acuity.

Retinal ganglion cells are neurons located in the innermost layer of the retina. Their axons form the optic nerve, transmitting signals from the eye to the brain.

Photoreceptors are light-sensitive cells in the retina responsible for converting light into electrical signals that the brain can interpret.

Each hemisphere of the brain exclusively processes visual information from the opposite visual field, integrating them for complete visual perception.

The pathway from the primary visual cortex to the parietal lobe, responsible for processing spatial location, motion, and control of eye and arm movements. Often referred to as the "where" pathway.

The pathway from the primary visual cortex to the temporal lobe, responsible for processing shape, color, and detail information. Often referred to as the "what" pathway.

Involved in perception of movement, spatial orientation, and coordination of eye and arm movements.

Responsible for perception of shape, color, and recognition of objects. Crucial for understanding what we see.

A series of steps where light absorption by rhodopsin triggers a chain reaction that ultimately leads to hyperpolarization of the photoreceptor cell.

The final step in the transduction cascade, where the closure of ion channels leads to the hyperpolarization of the photoreceptor.

A leading cause of blindness in Western countries, resulting from the loss of photoreceptor cells, primarily in the macula.

Rod cells are partially depolarized due to the presence of cGMP, which keeps sodium channels open, allowing sodium influx. This results in continuous glutamate release from the synaptic terminals.

Light triggers a cascade that reduces cGMP levels, causing sodium channels to close and the cell to hyperpolarize. This reduces glutamate release from the rod cells.

Light triggers a chain reaction that reduces cGMP levels, which in turn closes sodium channels. This reduces sodium influx, making the cell more negative (hyperpolarized).

Hyperpolarization of the rod cell due to light reduces glutamate release, which is an inhibitory neurotransmitter in the retina.

Rod cells are incredibly sensitive to light, capable of being activated by a single photon. This allows for excellent vision in low light conditions.

Cone photoreceptors are specialized cells in the retina that are responsible for color vision. They are most concentrated in the fovea, the central part of the retina, providing sharp, detailed central vision.

Color blindness is a genetic condition where an individual lacks one or more cone pigments, leading to an inability to distinguish between certain colors, most commonly red and green.

Scotopic vision is vision in low light conditions, dominated by rod photoreceptors. It lacks color discrimination and allows us to see in dim light.

Dark adaptation is the process where our eyes adjust to low light conditions, shifting from cone to rod vision and allowing us to see better in the dark.

Vitamin A is crucial for the synthesis of rhodopsin, the light-sensitive pigment in rods. A lack of vitamin A can lead to impaired night vision, making it harder to see in low light conditions.

Rhodopsin is a light-sensitive pigment found in rod cells. It absorbs light, triggering a cascade of events that lead to the transmission of visual signals to the brain.

Visual processing is the way our brain interprets and understands the information received from our eyes. It involves a complex series of steps from the retina to the visual cortex.