The eye is an organ of vision and light perception. In the human eye, the iris diaphragm regulates the size of the pupil, allowing more or less light to enter the eye as necessary. Light is focused by the combined action of the curved cornea, internal fluids, and lens. When light reaches the retina, located at the back of the eye, the light-sensitive rod and cone cells are stimulated. They, in turn, send signals to the brain via the optic nerve. How do the rods and cones differ in function?
Back in the day
Considered the greatest Abbasid Caliph, Harun al-Rashid was an educated scholar, lover of poetry, and patron of the arts who ruled Baghdad from 786-809. With a vast empire spanning SW Asia and the northern part of Africa, he was known around the world and had diplomatic relations with both China and Charlemagne's Frankish empire. Why did newspapers call future US President Theodore Roosevelt "Harun-al-Roosevelt" when he was a New York Police Department Commissioner?
Born on a day like today
Pavlov was a Russian physiologist, psychologist, and physician. He was awarded the Nobel Prize in Physiology or Medicine in 1904 for his work on the physiology of the digestive glands. He experimented on nervous stimulation of gastric secretions and thus discovered the conditioned reflex, which has had widespread influence in neurology and psychology. How did he conduct these experiments, and what did they show?