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The Five Senses

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on 17 December 2013

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Transcript of The Five Senses

The five senses
By Timmy Hyams
Sense 2 - Touch
Sense 3 - Smell
Sense 1 - Sight
How the eyes work
and how they can be manipulated
When you look at an object, the light from it enters your eye through the pupil. The iris changes the size of the pupil, depending on how bright the light is. The lens focuses the light onto the back of the eye: the retina. The retina is a mass of light-sensitive neurons, called photoreceptors, which change light signals into electrical ones.
Photoreceptors contain chemicals that change when they are hit by light. This causes an electrical signal, which is then sent to the brain along the optic nerve. Different types of photoreceptor allow us to see an enormous range of light: from starlight to full sunshine, and all the colours of the rainbow.
What are Photoreceptors?
A magnified picture
of photorecepters
What is colour
The most common form of 'colour blindness' is red-green colour deficiency, which affects 7-10% of people. This is not actually blindness, but a difficulty in distinguishing shades between red and green. It is caused by a change to or loss of the light responsive chemical in certain photoreceptors. Total absence of colour vision, where everything is seen in shades of black and grey, is very rare, and is usually caused by brain damage.
A colour blindness test-what number is it?
Nerves in the hand
Congenital insensitivity to pain (CIPA), also known as congenital analgia is a very rare condition in which you cannot feel any sort of pain. Sounds good, right? Wrong. What many people don't realize is that this can be extremely dangerous.
This disorder is caused when the nerves that sense pain do not connect with the part of the brain that recognizes pain. The reasons why this happens or what causes this to happen are unknown. Other sensory areas of people with CIPA are completely normal.
How some people cannot feel pain
As mentioned before, this is disease is incredibly rare and only 35 United States citizens have CIPA. Unfortunately, many people with CIPA don't live to see the age of 25. The rarity of this disease and the very low survival rate of it makes it difficult to study.
How touch can be manipulated
A commonly known manipulation of touch test: if you are blindfolded, and someone slowly taps their fingers up your forearm, you will think that they have reached your inner elbow before they actually have. I decided to put this to the test:
Test results
My prediction is, that, on average, I will be about 5cm off my inner elbow.
My prediction was reasonably accurate, as I was only 0.3cm off. I conclude that this statement is true, and, on average, you will be about (rounded) 5cm away from your inner elbow.
As mentioned earlier, nerve endings known as receptors gauge what is happening to the body's surface, but there are different receptors for different things:
Hair follicle ending
responds to displacement of hair
Ruffini ending
responds to pressure on skin
Krause corpuscle
responds to pressure (lips, tongue)
Pacinian corpuscle
responds to vibration (most sensitive in 150-300Hz range)
How we smell
The sense of smell, called olfaction, involves the detection and perception of chemicals floating in the air. Chemical molecules enter the nose and dissolve in mucous within a membrane called the olfactory epithelium. In humans, the olfactory epithelium is located about 7 cm up and into the nose from the nostrils. Hair cells are the receptors in the olfactory epithelium that respond to particular chemicals. These cells have small hairs called cilia on one side and an axon on the other side. In humans, there are about 40 million olfactory receptors; in the German Shepherd dog, there are about 2 billion olfactory receptors.
More on how we smell
No one knows what actually causes olfactory receptors to react - it could be a chemical molecule's shape or size or electrical charge. The electrical activity produced in these hair cells is transmitted to the olfactory bulb. The information is then passed on to mitral cells in the olfactory bulb. The olfactory tract transmits the signals to the brain to areas such as the olfactory cortex, hippocampus, amygdala, and hypothalamus. Many of these brain areas are part of the limbic system. The limbic system is involved with emotional behavior and memory. That's why when you smell something, it often brings back memories associated with the object.
Smell manipulation?
Many top supermarkets and stores actually use smell to make you buy more! This may seem unreal, but one experiment carried out in a local clothing store in America showed that when “feminine scents” such as vanilla were sprayed in the women’s clothing sections, sales of female apparel actually doubled.
This is also the case in other types of shops. In fact, the whiff of baking bread has proven a profitable exercise in increasing sales across many product lines. Some Northern European supermarkets don’t even bother with actual bakeries; they just pump artificial fresh-baked-bread smell straight into the store aisles from ceiling vents.
But it gets even stranger! 84 percent of subjects preferred a type of running shoe they’d looked at in the florally scented room. Moreover, the people assessed the scented Nikes as costing roughly £10 more than the pairs in the unscented room. In a related experiment in Germany, the fragrance of freshly cut grass was sprayed into a home improvement store. From the second the pumps started emitting the grassy mist, 49 percent of all customers surveyed before and after claimed that the staff appeared to be more knowledgeable about the store’s products.
All credit for this goes to Martin Lindstrom, and his book 'Buyology: Truth and Lies About Why We Buy'
Sense 4 - Taste
How we taste
Taste buds are what allow us to taste. They are sensory organs that are found on your tongue and allow you to experience tastes that are sweet, salty, sour, and bitter. How exactly do your taste buds work? Well, stick out your tongue and look in the mirror. See all those bumps? Those are called papillae, and most of them contain taste buds. Taste buds have very sensitive microscopic hairs called microvilli. Those tiny hairs send messages to the brain about how something tastes, so you know if it's sweet, sour, bitter, or salty.
The average person has about 10,000 taste buds and they're replaced every 2 weeks or so. But as a person ages, some of those taste cells don't get replaced. An older person may only have 5,000 working taste buds. That's why certain foods may taste stronger to you than they do to adults. Smoking also can reduce the number of taste buds a person has.
You also have different tastebuds in different areas, to taste different things:
But before you give taste buds all the credit for your favourite flavours, it's important to thank your nose. Olfactory receptors inside the uppermost part of the nose contain special cells that help you smell. They send messages to the brain.
Here's how it works: While you're chewing, the food releases chemicals that immediately travel up into your nose. These chemicals trigger the olfactory receptors (see Sense 3-Smell) inside the nose. They work together with your taste buds to create the true flavor of that yummy slice of pizza by telling the brain all about it!

When you have a cold or allergies, and your nose is stuffy, you might notice that your food doesn't seem to have much flavour. That's because the upper part of your nose isn't clear to receive the chemicals that trigger the olfactory receptors (that inform the brain and create the sensation of flavour).
Try holding your nose the next time you eat something. You'll notice that your taste buds are able to tell your brain something about what you're eating — that it's sweet, for instance — but you won't be able to pick the exact flavor until you let go of your nose.

Sense 5 - Hearing
How we hear
Sound waves travel into the ear canal until they reach the eardrum. The eardrum passes the vibrations through the middle ear bones or ossicles into the inner ear. The inner ear is called the cochlea, and is shaped like a snail. Inside the cochlea, there are thousands of tiny hair cells. Hair cells change the vibrations into electrical signals that are sent to the brain through the hearing nerve. The brain finally tells you that you are hearing a sound and what that sound is.

The outer ear, the part that is visible on the side of your head, is called the pinna or auricle. It's made of tough cartilage covered by skin. The pinna's main job is to gather sounds and funnel them to the ear canal, which leads to the middle ear. The pinna, which includes the earlobe, is the part that people pierce to wear earrings.
The ear canal, the hollow passage that leads to the eardrum, is also part of the outer ear. Glands in the skin lining the ear canal produce earwax, which protects the canal by cleaning out dirt and helping to prevent infections.

The middle ear is an air-filled cavity about the size of a pea. It turns sound waves into vibrations and delivers them to the inner ear. The middle ear is separated from the outer ear by the eardrum, or tympanic membrane, a thin, cone-shaped piece of tissue stretched tight across the ear canal.

To hear properly, the pressure on both sides of your eardrum needs to be equal. When you go up or down in elevation, the air pressure changes and you may feel a popping sensation as your ears adjust. Ears are able to adjust thanks to the narrow Eustachian tube that connects the middle ear to the back of the nose and acts as a sort of pressure valve, opening to keep the pressure equalized on both sides of the eardrum.

The inner ear consists of two tiny organs called the cochlea and the semicircular canals. The snail-shaped cochlea act as a sort of microphone, converting the vibrations from the middle ear into nerve impulses that travel to the brain along the cochlear nerve, also known as the auditory nerve.

The semicircular canals look like three tiny, interconnected tubes sticking out in loops from the top of the cochlea. It's their job to help you balance. The canals are filled with fluid and lined with tiny hairs. When your head moves, the fluid in the canals sloshes around, moving the hairs. The hairs send this position information as impulses through the vestibular nerve to your brain. The brain interprets these impulses and sends messages to the muscles that help keep you balanced.

When you spin around and stop, the reason you feel dizzy is because the fluid in your semicircular canals continues to slosh around for awhile, giving your brain the idea that you're still spinning even when you aren't. When the fluid stops moving, the dizziness goes away.

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