(1) The Meaning of Vision
The appropriate stimulus for vision is electromagnetic waves with wavelengths ranging from 380 to 780nm, also known as light waves.
(2) The Physiological Basis of Vision★★
1. Refraction Mechanism (Eyeball)
The eyeball consists of the eyeball wall and the contents of the eyeball, with the contents of the eyeball (lens, aqueous humor, vitreous humor) and the cornea forming the refractive system.
2. Sensory Mechanism (Retina)
The retina consists of rod cells and cone cells (visual receptors).
(1) Rod cells, also known as rod photoreceptor cells, number 120 million and are responsible for night vision and perceiving brightness.
(2) Cone cells, also known as cone photoreceptor cells, number 6 million and are responsible for day vision, perceiving details and colors.
(3) Only cone cells are present in the fovea centralis of the retina, which is the most sensitive to light. As we move away from the fovea centralis, the number of rod cells increases rapidly, reaching the highest concentration at a visual angle of 16° to 20°. Near the fovea centralis, there is an area called the blind spot, which is not sensitive to light. The nerve fibers from the retinal ganglion cells converge here to form the optic nerve.
3. Transmission Pathway
The transmission pathway includes bipolar cells in the retina, ganglion cells, and the lateral geniculate body.
4. Central Mechanism
The visual center is located in the cortical striate area of the occipital lobe.
5. Feedback Regulation
Vision not only relies on the activity of visual receptors but also on the feedback regulation of the central nervous system to the visual organs.