Body & Sports

10 things you've always wanted to know about your body

Updated: 2015-11-13
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Have you ever wondered why you get pins and needles?
  
Contrary to popular belief, it's not because lying on a limb cuts off the circulation.
 
In fact, it's because sitting awkwardly can trap a nerve.
 
And crying after being hurt is not simply an overflow of emotion, its the body's way of releasing stress hormones which build up when we're in pain.
 
From why our hair goes grey at the temples first, to why our heart is on the left hand side, here, experts answer the burning body-related questions you've always wanted to know...

1. WHY DO I SHIVER WHEN I'M ILL? 
 
 
Shivering is usually associated with being cold, but it actually serves another purpose: it is part of the body's immune response to fight infection.
 
The human body runs at a fixed temperature of 37c, set by the hypothalamus area in the brain.
 
'When we get sick and the hypothalamus detects the immune response to microbes, it then raises the body temperature, which we feel as a fever,' explains Dr Lindsay Nicholson, a specialist in autoimmune infections at the University of Bristol.
 
'You feel cold because technically you are colder than the body's new set-point, and it takes time to adjust.'
 
Research shows that bugs do not like high temperatures, so the body appears to have learned to use heat to slow down germ growth.
Another theory is that our immune system simply works better at higher temperatures, Dr Nicholson says.
 
'The brain tells all cells to work harder in order to produce heat, and this includes muscle cells, which begin contracting and relaxing faster. This quick muscle movement is what we feel as shivering.' 
      
2. WHY DOES HAIR OFTEN GO GREY AT THE TEMPLES FIRST?  
  
 
Hair tends to go grey at different rates across the body — often beginning at the temples or in a man's beard.
 
'This mainly comes down to what happens during embryogenesis — the process by which an embryo forms and develops,' says Des Tobin, a professor of cell biology at the University of Bradford.
 
'This is when our stem cells — the forerunner cells which, in this case, are predetermined to go on to become melanocytes (cells that produce pigment) — are seeded in different parts of the body.
 
'Though we don't know exactly why, it could be that the hair follicles in some areas, such as the temples, receive fewer stem cells than other areas, so these will lose their colour sooner.'
 
There may also be epigenetic factors (environmental factors that influence our genes, such as diet, ultraviolet light or smoking) playing a part in why some stem cells 'burn out' faster than others.
 
Quite why some areas are more affected than others is unclear.
 
3. WHAT EXACTLY IS A KNOT IN THE BACK?     
   
 
Many people complain of 'knots' in their back muscles, but is this description accurate?
 
'Essentially, it is a very localised tender area in a muscle,' says Dr James Selfe, a professor of physiotherapy at the University of Central Lancashire.
 
He adds that it can cause pain in other body parts, too.
 
The tightness is thought to be the result of an irritated nerve. The muscle goes into spasm, or tightens, as a protective mechanism, and tends to become stuck.
 
The best way to treat the pain is slow, firm pressure applied directly to the knot. 
     
4. WHY DO I CRY WHEN I'M HURT?    
  
 
This type of crying — in response to negative feelings or pain — is due to the connections between the tear ducts and the areas of the brain involved with emotion, says Roger Knaggs, a professor in clinical pharmacy practice at Nottingham University, who specialises in pain management.
 
The brain programmes these 'emotional tears' as a way to release stress hormones, which build up when we're in pain. Crying restores a normal balance.
 
'When we hurt ourselves, the tears released when we cry contain stress hormones, so you are literally crying away the stress,' says Professor Knaggs. 'Tears also contain endorphins, the body's natural painkillers.'  
 
5. WHY DO I GET PINS AND NEEDLES?   
   
Typically pins and needles are caused by sitting in an awkward position.
 
Contrary to popular opinion, it's not because it cuts off the circulation, but because it puts pressure on the nerves, says Dr Nicholas Silver, consultant neurologist at the Walton Centre in Liverpool.
 
'One example is "Saturday night palsy", where you fall asleep with your arm over a chair,' says Dr Silver. 'It can compress the radial nerve, a main nerve in the arm, so that you can't lift your wrist properly.'
 
Hyperventilating can also cause pins and needles in the hands and feet. 'It causes changes in the gases in the blood — this has an effect on levels of calcium, needed by nerves.'
 
Those prone to migraines may also get pins and needles in hands, feet or face — one theory is that some brain chemicals become more active, causing the brain to send confusing signals. Some people fear that pins and needles signal a stroke.
 
'But strokes cause loss of sensation, such as numbness, and come on suddenly,' adds Dr Silver. Persistent tingling can be a sign of nerve damage or diabetes — see a doctor if this occurs.
  
6. WHY ARE OUR HEARTS ON THE LEFT SIDE?   
 
  
Like many of our organs, the heart is not in the very centre of the body but is located slightly to the left, behind the sternum (breast bone).
'The reason there are asymmetries in the first phase of our development is to do with evolution,' says Dr Rajay Narain, a research cardiologist.
 
'As our digestive, circulatory and central nervous systems got more complex, Nature had to find ways of packing everything into our bodies. Having everything centrally located is an inefficient use of space.'
 
Some one in 10,000 people have situs inversus, where all the major internal organs are on the opposite side of the body from normal. Yet this is unlikely to cause harm.
 
7. DOES EVERYONE NEED READING GLASSES EVENTUALLY? 
 
 
   
Basically, yes, according to Robert Scott, consultant ophthalmologist at the BMI Priory Hospital. 
  
'Your lens keeps growing throughout life, getting denser and less elastic than it used to be. This means the ciliary muscles [which help squeeze or stretch the lens to help it focus on an object] can't do their job so well.'
 
The process of changing the shape of the lens is called accommodation.
 
From the age of 35, people tend to lose accommodation to the extent that they need reading glasses to help them focus on an object 30cm away — this is known as presbyopia.
 
There are books that aim to teach you how to make these muscles stronger — such as by training your eye to look at smaller and smaller letters — but Mr Scott is not convinced they are effective. 
      
8. WHY CAN I ONLY WINK WITH ONE EYE?    
  
 
With a bit of training you could probably learn to wink with both eyes, says Professor Scott.
 
'Sometimes, people have a damaged nerve, due to injury or disease, and can't wink. But most people should manage it with practice.
'The obicularis muscle, which closes the eyelids, is supplied by nerves on both sides, so can be worked independently.
 
If you can close both eyes, you can probably train yourself to wink.'
 
However, some people still struggle and find they can wink only with the one eye, which tends to be the same side as the hand they write with.
 
In right-handed people, the brain's left hemisphere is thought to be dominant — this hemisphere controls the right side of the body.
 
'Winking is also connected with ear waggling and raising your eyebrows,' adds Professor Scott.
 
'If you can wiggle one ear and not the other, it tends to be the right ear.' So, you may be able to learn to do it on both sides.
 
9. WHY DOES SQUINTING MAKE THINGS CLEARER? 
 
 
 
Squinting reduces the amount of light coming into the eye, explains Professor Scott.
   
By limiting the rays that come through the top and bottom of the pupil, the light that does get in is 'relatively undeviated', allowing rays to pass closer to the centre of the lens.
 
This cancels out the effect of being long or short-sighted, where the light is normally deviated.
 
As a result, the light focuses better on the retina, the layer of cells at the back of the eye that transmit images to the brain. 'It's a bit like looking through a pinhole,' says Professor Scott.
 
You can take advantage of the pinhole effect, which has been known about since the 10th century, to make a DIY pair of reading glasses by putting pinholes in cardboard and looking through them. 
    
10. WHY DOES STICKING FINGERS DOWN YOUR THROAT MAKE YOU THROW UP?  
  
When the brain perceives something that shouldn't be there, the body tries to repel it.
 
Nerves around the tonsils and at the back of the tongue are very sensitive, as their function is to make sure that nothing that is potentially hazardous is swallowed.
 
When these nerves detect we're about to swallow something bad or that might block the airway, we gag.
 
'If the hazard remains, that becomes a retching reflex [dry vomiting],' says Dr Christian Potter, an ear, nose and throat specialist at Torbay Hospital in Devon.
 
'Then it becomes a vomit. It's a throwback to animals that throw up on predators to make themselves less desirable.
 
'Humans are unusual among mammals for being able to vomit.'
  
SOURCE:
dailymail.co.uk   
    
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