Receptor cells similar in structure

Scientists have always been eager to understand the structure and function of the sense organs. Research has been especially intense in the past few years, after the elec­tron microscope came on the scene. This is understandable since the ordinary microscope only magnifies ten to fifteen hundred times, while the electron microscope has a magni­fication of twenty, forty, sixty, and even a hundred thousand times. Certainly, it has helped scientists to pry out quite a lot of interesting secrets.

They made the astonishing discovery that the receptor cells (the ones that perceive stimulation) in all the sense organs of all animals on the Earth are very similar in struc­ture. Each of them has a tiny mobile hair, or flagellum. These flagella are also very similar in diflerent receptor cells. Each flagellum contains two central fibrils surrounded by a ring of nine pairs of motile fibrils. The structure of the flagellum rarely varies.

The flagella in a receptor cell play the same part as the antennae in radio sets, and are therefore called recep­tor antennae. Through these antennae we perceive the outside world. The antennae in the receptor cells of the eye, for example, respond to light energy, or photons. The antennae of the organ of smell perceive the energy of the molecules of odoriferous substances. The antennae of the auditory cells respond to the energy of sound waves, or sounds.

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