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How rattlesnakes can use infrared waves to see in the dark
Rattlesnakes can see without using their eyes
Did you know that rattlesnakes can "see" without using their eyes? All warm-blooded animals emit thermal radiation, and the snakes make use of the heat radiated to find out where their prey is. They can easily hunt at night.
Heat radiation is also called infrared radiation, and the infrared "eyes" of rattlesnakes is called pit organs. They sit on the side of the head, under and above the eyes. The infrared minds of the snakes are very similar to the sense of sight.
In vertebrates there is something called the somatosensory system. That is what we use when we perceive pressure, temperature and pain in the skin. Trigeminal nerve is a cranial nerve that leads somatosensory information from the face to the brain. In rattlesnakes, part of the trigeminal nerve thermal receptors ("Temperature") to detect the infrared radiation with great accuracy.
Pit organs of two small holes above and below the eyes. In each hole there is a heat-sensitive membrane that is about 30 square millimeters wide, but only 15 microns thick (a micron is 0.001 millimeters). The membrane is stretched in the cavity and that is what detects the infrared radiation. The membrane is full of nerve endings, about 7000 pieces! These nerve endings act as thermal receptors, and they belong to nerve fibers that go to the trigeminal nerve. Nerve endings are just a few microns from the membrane surface which makes them very sensitive to even small temperature changes. It is enough that the temperature increases by as little as 0.003 degrees Celsius to nerve endings to transmit the signals to the brain! In addition, the pocket behind the diaphragm is filled with insulating air that makes very little heat can be lost into the body.Instead, all the heat absorbed by the membrane. These characteristics make snakes heat sensitive systems far more advanced than ours.
The actual opening of the pit have only one third of the membrane diameter, making the pit organ work much like a pinhole camera. A pinhole camera is a camera without a lens, in which a small hole acts as a lens. Pit body produces therefore an infrared image of its membrane, just as the eye produces an image of light on the retina. The resolution is worse with hollow body so that its image becomes blurred.
Mouse hunting and accuracy
The area of the brain responsible for processing visual information also deals with information from the thermal radiation sense. Information from the eyes is thus used in conjunction with information from the pit organs to capture prey. A type of neurons in the rattlesnake brain reacts to maximum in small, warm moving objects. These cells receive information from both eyes and from the pit organs.They have been called "mouse-detectors"! With its mouse-detectors the snake can distinguish between a mouse and a stone that have the size and form of a mouse. Stones does not tease the pit organs, but the warm mouse does. It would not be good for the snake to strike against the rocks =)
Rattlesnakes also uses olfaction and tactile as they hunt, but it is the vision and the infrared that plays the greatest role in the hunt for food. Hunting behavior of rattlesnakes can be divided into three phases: before, during and after the blow. The actual blow is very short, lasting only about 0.5 seconds. Yet it is during this phase that the snake moves his head against the switch, tighten the fangs, injecting venom and withdrawing the head. Efficient markets must therefore be very precise, and it is thanks to information from vision and infrared mind that rattlesnakes have this kind of incredible accuracy.