Vision Process and Photoreceptors

Vision Process

• Perception begins when environmental stimuli activate sensory organs.
• Light entering the eye is adjusted by various cells.
• Bipolar cells transmit visual information to ganglion cells.
• Horizontal cells combine signals from photoreceptors.

Photoreceptors

• Rods and cones are specialized light-sensitive cells in the retina.
• Rods are highly sensitive to low light levels, crucial for night vision.
• Cones are sensitive to color and crucial for detailed vision.
• Phototransduction converts light into electrical signals.
• Rods have a long, cylindrical shape, many photopigments,120 million rods, low light sensitivity, equally distributed.
• Cones have a small, tapered shape, six million cones, color perception, concentrated in the fovea (retina center), high visual acuity.

Receptive Fields

• Capture light in the retina's outer layer.
• ON bipolar cells are responsive to light increase, while OFF cells respond to decrease.
• Lateral inhibition, where neighbouring cells inhibit each other, helps enhance contrast and outlines in vision.

Optical Illusions

• Lateral inhibition is a neural process in the retina that enhances contrast.
• The brain uses this process to create outlines.
• Grid illusions exploit this processing to create a perceived shadow or illusionary dark spot, which disappears when focused.
• Photoreceptor "fatigue" can contribute to visual effects.

Visual Processing Disorders

• Colour blindness can result from abnormalities in photoreceptor function, specifically in the genes that produce pigments for light wavelengths.
• Dichromats have just two types of photopigments.
• Achromatopsia is a disturbance in CNS, causing colour perception dysfunctions.
• Akinetopsia is a disorder affecting motion perception, frequently caused by significant CNS lesions.
• Blind spot (optic disc) is where the optic nerve exits the eye.

Light to Neurotransmission

• Isomerization changes the shape of photopigments in response to light.
• Bipolar cells are either ON or OFF depending on the receptors (mGluR6 or AMPA/kainate)
• ON and OFF activation of cells, changes shape, allowing further transmission of electrical impulse.

Differences in Rod and Cone Cells

• Location: Rods are in the periphery; Cones are concentrated in the fovea.
• Light condition preference: Rods are for dim-light; Cones for bright light.
• Resolution: Rods provide low resolution; Cones provide high resolution.
• Wavelengths detection: Rods detect all wavelengths; Cones detect specific wavelengths (red, green, blue).
• Colour: Rods detect grayscale; Cones detect color.
• Types: Rods have 1 type photopigment (rhodopsin); Cones have 3 types.

Explore the intricacies of the vision process, including how environmental stimuli activate sensory organs and the role of various cells in the eye. Learn about the specialized photoreceptors, rods and cones, and their functions in light sensitivity and color perception.