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Touch, taste and smell

Ämne: Biologi, Engelska
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Introduction

Taste and smell are chemical senses. They are made just to give us information about what happens around us. Taste is an immediate sense just to give a clear sign that the food can go down to our body, while the smell is more of a distant sense allowing us to detect small concentrations of airborne substances. Actually smell and taste were separated when animals went up to land. In the water they couldn’t smell things and that’s why they didn’t need it.
Fish and other sea creatures only have one chemical sense. Taste is not just in the mouth. Catfish have chemoreceptor all along their body (a catfish is like a giant tongue), and flies have receptors on their feet so that they can tell immediately upon landing whether an object is good to eat.

Taste

Anatomy of taste
Taste is more of a gateway to test the food before swallowed. Food that’s just going to help our body have a tense of tasting good while things that will harm our body like poison usually taste very bad.
The tongue have many valleys called papillae, there are four types of papillae:
Filiform papillae: Cone shaped and found all over the tongue (Actually that is why the tongue looks so rough.)
Fungiform papillae: mushroom shaped and found at the tip and sides of the tongue.
Foliate papillae: a series of folds along the sides of the tongue.
Circumvallate papillae: shaped like flat mounds surrounded by a trench & found at the back of the tongue.
All papillae except filiform contains taste buds, so the centre of your tongue that only have filiform papillae is “taste blind” you cant taste anything.
Each one of those taste bud contains a number of taste cells which have tips that protrude into the taste pore.

The taste pathway
Transduction (omvandling) occurs when different taste substances cause a change in the flow of ions across the membrane of taste cells.
Different substances affect the membrane in many possible ways here are some of them:
Bitter and sweet substances bind into receptor sites which release other substances into the cell
Sour substances contain H+ ions that blocks channels in the membrane.
Sour substances break up into Na+ ions which flow through the membrane straight into the cell.
Electrical signals generated in the taste cells are transmitted in three pathways:
The chorda tympani nerve conducts signals from the front and sides of the tongue.
The glosso-pharyngeal nerve conducts signals from the back of the tongue
The vagus nerve conducts signals from the mouth and the lynx (struphuvudet)
These three nerves make connections in the brain stem in the nucleus of the solitary tract (NST) before going on to the thalamus and then to two regions of the frontal lobe (the insula and the frontal operculum cortex).

What tastes do we taste?
The four basics are sweet, sour, bitter and salty. In princip all tastes can be explained as either just one or maybe to or three and sometimes all of our basic tastes.
Different taste receptors (and therefore different parts of the tongue) are most sensitive to different tastes.

Food experiences
Your experience of taste depends on your internal state, (things always taste better when you’re hungry) on your past experiences (food that you are familiar with usually taste better than unfamiliar food) and your genes (people have different sensitivities to certain tastes). Taste experience is also subject to effects of adaptation. (Why does orange juice taste gross after you’ve just brushed your teeth?).
Our sensation of taste also depends heavily on smell and texture (touch). Ever notice how food just doesn’t taste that good when you have a stuffed up nose

Aguesia, Chemosensory Disorders – diseases or problems associated with the sense of smell or the sense of taste.
Ageusia (pronounced ay-GOO-see-uh) is the loss of taste functions of the tongue, particularly the inability to detect sweetness, sourness, bitterness, saltiness, and umami (the taste of monosodium glutamate). It is sometimes confused for anosmia
a loss of the sense of smell. Because the tongue can only indicate texture and differentiate between sweet, sour, bitter, salty, and umami most of what is perceived as the sense of taste is actually derived from smell. True aguesia is relatively rare compared to hypogeusia – a partial loss of taste – and dysgeusia – a distortion or alteration of taste.

Smell

Smell is our distant chemical sense. We can discern information about the chemical composition of substances before coming into more direct contact with them. For many animals, smell is the most important sense. Although for humans smell is not as important as say vision or hearing, we do use smell more than we think to guide behaviour. Smell is an important part of taste. Many qualities of foods that we think is taste are actually a function of smell
Anatomy of Smell
The Olfactory Mucosa is a dime-sized region located high inside the nasal cavity and is the site of olfactory transduction. The olfactory mucosa contains olfactory receptor neurons. Olfactory receptor neurons have cilia (little hair-like projections) which contain the olfactory receptor proteins.
The smell pathway
Olfactory transduction occurs when odorant molecules reach the olfactory mucosa and bind to the olfactory receptor proteins on the cilia of the olfactory receptor neurons. When odorants bind to the receptor site, the receptor protein changes shape which in turn triggers the flow of ions across the receptor-cell membrane and an electrical response is triggered in the cilium. Electrical responses in the cilia spread to the rest of the receptor cell, and from there are passed onto the olfactory bulb of the brain in the olfactory nerve. There are about 1,000 different types of receptor proteins each sensitive to different odorants. We have a total of about 10 million receptor neurons. Each receptor neuron has about 1,000 similar receptor proteins. Because there are 1,000 different receptor proteins, there are also 1,000 different receptor neurons. Inputs from similar receptor neurons go to similar glomeruli (collections of cells within the olfactory bulb). Because there are 1,000 different types of receptor neurons, there are 1,000 different types of glomeruli. From the olfactory bulb, mitral cells and tufted cells carry olfactory information to the olfactory cortex, and to the orbitofrontal cortex.
Experience of Smell
Humans can tell the difference between 10,000 different odors. But often it is difficult to name the odors. People who are trained to recognize odors (wine experts or perfume experts) are not necessarily any more sensitive with their nose – just better at retrieving names from memory. Humans can tell the difference between 10,000 different odors. But often it is difficult to name the odors. People who are trained to recognize odors (wine experts or perfume experts) are not necessarily any more sensitive with their nose – just better at retrieving names of smells from memory. Dogs can be 10,000 times more sensitive to odors than humans. Yet, an individual human olfactory receptor is no less sensitive than a dog’s. What makes dogs so sensitive? Although their receptors aren’t any better, they have many more of them (1 billion receptors in dogs compared to only 10 million in humans). Pleasant smells (like fresh baked bread) are used in supermarkets to attract customers to buy it.
Pheromones (often odorless airborne molecules play a crucial role in the behaviour of many animals. For example, a pregnant mouse will spontaneously abort if she is presented with the smell of a non-parent male mouse within a certain critical time period. Do pheromones affect humans too? Although for a long time scientists were sceptical about the possible effects of pheromones on humans, a recent flood of research has established that humans do indeed use an accessory olfactory system (comprised of a vomeronasal organ & projections) just like many other animals. Pheromones have an effect on human attraction to potentional mates. Women prefer the smell of those men whose genetically coded immunities are different from their own.
Pheromones play a role in synchronizing menstrual cycles
Pheromones can affect mood
We can smell fear.
Diseases:
Aguesia, Chemosensory Disorders – diseases or problems associated with the sense of smell or the sense of taste.

Touch!

While your other two senses (smell, and taste) are located in specific parts of the body, your sense of touch is found all over. This is because your sense of touch originates in the bottom layer of your skin called the dermis. The dermis is filled with many tiny nerve endings which give you information about the things with which your body comes in contact. They do this by carrying the information to the spinal cord, which sends messages to the brain where the feeling is registered.
The nerve endings in your skin can tell you if something is hot or cold. They can also feel if something is hurting you. Your body has about twenty different types of nerve endings that all send messages to your brain. However, the most common receptors are heat, cold, pain, and pressure or touch receptors. Pain receptors are probably the most important for your safety because they can protect you by warning your brain that your body is hurt!
Some areas of the body are more sensitive than others because they have more nerve endings. Have you ever bitten your tongue and wondered why it hurt so much? It is because the sides of your tongue have a lot of nerve endings that are very sensitive to pain. However, your tongue is not as good at sensing hot or cold. That is why it is easy to burn your mouth when you eat something really hot. Your fingertips are also very sensitive. For example, people who are blind use their fingertips to read Braille by feeling the patterns of raised dots on their paper.
Diseases
Sensory Integration Dysfunction is the inability of the brain to correctly process information brought in by the senses. Sensory Integration Dysfunction (SID/DSI) or sensory processing deficits can come in many different forms. No two children will be affected in the same ways. SID/DSI was first noticed in children with autism or who had autistic traits but is also seen in children with other disabilities such as cerebral palsy or ADD/ADHD or can be present by itself. Children can have mild, moderate or severe SI deficits. SID/DSI is treatable with therapy and a sensory diet set up by an occupational therapist who is trained in SI. See it from the bright side, You Live.
We know the information on the two first senses are much better that the third one “Touch” but we found some really good information about smell and taste but it didn’t include touch so that’s why we have much more complicated text on the first two.
And it also looks a bit advanced but we could not find another word for some words which are very advanced so we had to use them. We translated them and know their meaning.
Tobias and Louise.

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