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As discovered by Linda B. Buck and Richard Axel, mammals generally have about 1000 genes for odor receptors. Of these genes, only a portion code for functional odor receptors. Humans have 347 functional odor receptor genes; the other genes have nonsense mutations. This number was determined by analyzing the genome in the Human Genome Project; the number may vary among ethnic groups, and does vary among individuals. For example, some people can smell amyl acetate (which smells like bananas), whereas some others cannot.
Each olfactory receptor neuron in the nose expresses only one functional odor receptor. According to shape theory , each receptor detects a feature of the odor molecule. Odor receptor nerve cells function like a key lock sytem. If the odor molecules can fit into the lock the nerve cell will fire. According to Vibration theory , however, recently proposed by Turin (1996, 2002), odor receptors detect the frequencies of vibrations of odor molecules in the infrared range by electron tunnelling . This would allow encoding of odors to be similar to the way wavelengths of lightLight is electromagnetic radiation with a wavelength that is visible to the eye, or in a more general sense, any electromagnetic radiation in the range from infrared to ultraviolet. The three basic dimensions of light (and of all electromagnetic radiationare encoded by conesCone cells or cones are cells in the retina which only function in relatively bright light. There are about 6 million in the human eye, concentrated at the fovea and gradually becoming sparser towards the outside of the retina. Cones are less sensitive th of the eyeThis article refers to the sight organ. See Eye (disambiguation) for other usages. human eye. Note that not all eyes have the same anatomy as a human eye. An eye is an organ that detects light. Different kinds of light-sensitive organ are found in a varie.
The axons from all the thousands of cells expressing the same odor receptor converge in the olfactory bulbThe olfactory bulb is a part of the brain that is a distinct outgrowth from the forebrain of mammals. As one might guess from the name, it plays a major role in olfaction, which is the perception of smells. In terms of evolution, the olfactory bulb arises. Mitral cell s in the olfactory bulb send the information about the individual features to other parts of the olfactory system in the brain, which puts together the features into a representation of the odor. Since most odor molecules have many individual features, the combination of features gives the olfactory system a broad range of odors that it can detect.
Odor information is easily stored in long term memory and has strong connections to emotional memoryOne element of the Stanislavski system was titled emotional memory. Emotional memory requires the actor to call on the memories he or she felt when they were in a situation similar to that of their charactar. Stanislavski Believed an actor needed to take. This is possibly due to the olfactory system's close anatomical ties to the limbic systemThe limbic system is a group of brain structures that are involved in various emotions such as aggression, fear, pleasure and also in the formation of memory. The limbic system affects the endocrine system and the autonomic nervous system. It consists of and hippocampusThe hippocampus is a part of the brain located inside the temporal lobe (humans have two hippocampi, one in each side of the brain). It forms a part of the limbic system and plays a part in memory and navigation. The name derives from its curved shape, wh, areas of the brain that have long been known to be involved in emotion and place memory, respectively.
To detect pheromones many vertebrates have an auxiliary olfactory sense organ called Jacobson's organ or the vomeronasal organ, located in the vomer, between the nose and the mouth. Snakes use it to smell prey, sticking their tongue out and touching it to the organ. Some mammals make a face called flehmen to direct air to this organ. In humans, the detection of pheromones is subliminal. These subliminal odor messages may transmit opposite immunological sexual compatibility. Finding a partner a of non-similar immunological background may be evolutionarily advantageous because children born with a mixture of immulogical systems are more likely to survive. It has been suggested that human females unconsciously use this process to recognize whom they find attractive.