2007-10-17 - Sense of smell
Smell is essential for taste. It's one of the most primal senses. This is not too far from animal smell sense. Smell is processed in the olfactory bulbs. We smell 1/10th of what cats smell, or 1/100th of what dogs can smell. Think about that, like an overwhelming smell, think about what your dog is thinking if you think the smell is strong. We detect between 4,000 and 10,000 odors. Dogs can remember smells longer than humans can, and they make better connections than we do. Apparently they have dogs that can sniff for cancer for five years in Europe. The salivating and mucous-infested hound dogs, and if it's a good viscosity, it's good for the sense of smell, like for dogs with long, droopy ears and are able to get the odors from the ground to be raised into the air to the nose.
We are the retards of the animal kingdom when it comes to smell. Your sense of smell is processed in your brain, in the amgydala in the limbic system. It gets there by a basic process. When you breath in, molecules are stirred up inside your sinus cavity, those molecules attach to mucus, they dissolve in the mucus, mucus moves the molecules over the olfactory epithelium- the site of transduction. You sense/smell something because the molecule has been rubbed against the skin. The process of smelling anything is called olfaction. Those are connected by nerves that have dropped down through the skull bone, and these nerves are attached to the olfactory bulbs, they are a part of your brain system, so the route happens like, molecules -> mucus -> olfactory epithelium -> stimulation of bulbs -> nerves -> amgydala / hippocampus. This is important, it's a short path. That's why sense of smell is so fast for us. That's why we smell/remember odor connections.
Connection
Neurons from the lateral olfactory tract project for: the limbic system, the amgydala and hippocampus re: motivation, emotion, and certain kinds of memory. Amgydala contains regions known as 'pleasure centers'. The hippocampus has motivational memory, the association of certain stimuli with food. The hippocampus says "Hm, I think I remember this smell," or "hm, this smell is related to another smell I remember," and it recognizes it in terms of its emotion and memory, and it also helps you decide if you are still hungry, it routes information to the hypothalamus from there. The amgydala is the pleasure center: good or bad smell? As the smell information is getting routed, it's being decided immediately as good/bad. Once it's through the limbic system, it's routed out to other parts of the brain. Let's say that you decide it's a bad smell, and you say it reminds you of a bear, then it's going to be routed to the "oh my god" factor in the prefrontal cortex, as well as to the motor cortex to say "Move, it's a bear!"
Anosmia - a complete loss of smell
Hyposmia - partial loss of smell
Hyperosmia - enhanced smell sensitivity
Dysosmia - distortion of odor perception (includes parosmia and phantosmia), somehow your sense of smell is inaccurate.
-- Parosmia- distortion of perception of external stimulus. This could be when the smell is stronger than the stimulus.
-- Phantosmia-- smell perception with no external stimulus. You smell something that's not there, or you have confusion of stimuli, etc. They test this by putting you in a hospital chamber, a vacuum, that has nothing except for clean air, and you report what you smell, and sometimes people report smelling apple pie, and they are sure that they smell it.
Touch
Your sense of touch is equally simple as your sense of smell. Touch is what keeps you alive. It's the most basic survival sense. You can basically survive without sight, hearing, olfaction, or tasting, etc., and touch is what keeps you from being harmed by your environment, just enough to keep you safe. The receptors are put in layers in the skin, such as pain receptors which are deeper in the skin, as opposed to light-touch sensors, or pressure, and pain is deeper. What if pain was on the surface? Even the lightest touch would cause severe pain ... there is a disorder of the skin where the pain receptors are in the wrong place, and then there are some that feel no pain and no pressure. Babies with this disorder will literally chew their fingers off, or bite off their lips and tongues when their teeth come in. These babies can't learn by normal methods, they don't have feedback at all. It's a really yucky disease. The pain receptors are either not there or too deep. In leprosy, the skin has scarred so much that the pain receptors can't do their job.
When your body senses cold, you have hot and cold receptors, when the body senses cold and pressure together it gives you the signal "WET". You don't tend to feel warm water as wet, until you get the other information. You can put your hand into warm water and not really tell that it's wet. You have: pressure, pain, and temperature. It's the combination of those that tell you different textures.
Pressure. Pain. Temperature.
You have about 150 different types of receptors for those three categories. There are highly specialized functions, and highly generalized ones. When you scar your body, you tend to lose the pain receptors that are blocked by the thickness of the skin. That's why burn victims usually become more accident prone, because they don't have the sensation any more.
You have more pain nerve endings than any other type. The least sensitive part of your body is the middle of your back. The most sensitive areas of your body are your hands, lips, face, neck, tongue, fingertips and feet. There are about 100 touch receptors in each of your fingertips (the apex of your finger tips, in the middle of the swirl). Rattlesnakes use their skin to feel the body heal of other animals. We lose between 30,000 and 40,000 skin cells every minute - about 9 pounds a year. Of skin. House dust is mostly skin. Sharks use receptors for tasting their prey first: they will use their sandpaper skin, which will wipe off a layer of your skin, which will make you bleed a bit, and they have receptors in their skin that can taste the blood. So they taste you first by bumping you, before they come back around and take another bite.
Gate-control theory of pain: these gates have pain signals, and then what they route to the brain is "hey, there's something causing pain," so think about it when it becomes overbearing. Shock is for this purpose- so that you can still act and respond. Bruises are broken blood vessels and the pooled blood.