Is the human skull made up of one bone or two?



It surprises many to learn that the human skull is not one solid bone as is usually thought. Nor does it consist of just two bones---the top of the head and everything underneath. The skull (cranium) is actually composed of (count them!) twenty-two separate bones. There are eight cranial bones around the brain and fourteen facial and jaw bones in the human skull. Just one of these bones moves - the jaw bone (mandible). In infants and very small children, the cranial bones are disconnected segments held together by connective tissue stripes called sutures. At certain sites, these sutures are especially weak, creating the so-called “soft spots” (fontanels) in an infant’s head. The most prominent of these is a little way up from the infant’s forehead. When growing is complete, the bones of the skull fuse together along the suture lines. These unions contain small amounts of fibrous connective tissue similar to those of the joints of arms and legs. Although the skull may structurally appear to be one piece when fully developed, it is still composed of separate bones. Many fossil skeletal remains that anthropologists find often appear to have cracked or broken skulls. But these skulls are actually just missing some of their pieces. The softer connective tissue having decomposed, little support is left between the individual pieces in the skull. This causes them to fall out and perhaps get left behind over thousands and thousands of years.

Sleep is one of those funny things about being a human being -- you just have to do it. Have you ever wondered why? And what about the crazy dreams, like the one where a bad person is chasing you and you can't run or yell. Does that make any sense?


If you have ever wondered about why people have to sleep or what causes dreams, then read on. In this article, you'll find out all about sleep and what it does for you.

Characteristics of Sleep

We all know how sleep looks -- when we see someone sleeping, we recognize the following characteristics:

* If possible, the person will lie down to go to sleep.

* The person's eyes are closed.

* The person doesn't hear anything unless it is a loud noise.

* The person breathes in a slow, rhythmic pattern.

* The person's muscles are completely relaxed. If sitting up, the person may fall out of his or her chair as sleep deepens.

* During sleep, the person occasionally rolls over or rearranges his or her body. This happens approximately once or twice an hour. This may be the body's way of making sure that no part of the body or skin has its circulation cut off for too long a period of time.

In addition to these outward signs, the heart slows down and the brain does some pretty funky things (we'll get to this later).

In other words, a sleeping person is unconscious to most things happening in the environment. The biggest difference between someone who is asleep and someone who has fainted or gone into a coma is the fact that a sleeping person can be aroused if the stimulus is strong enough. If you shake the person, yell loudly or flash a bright light, a sleeping person will wake up.

For any animal living in the wild, it just doesn't seem very smart to design in a mandatory eight-hour period of near-total unconsciousness every day. Yet that is exactly what evolution has done. So there must be a pretty good reason for it!

**Reptiles, birds and mammals all sleep. That is, they become unconscious to their surroundings for periods of time. Some fish and amphibians reduce their awareness but do not ever become unconscious like the higher vertebrates do. Insects do not appear to sleep, although they may become inactive in daylight or darkness.

By studying brainwaves, it is known that reptiles do not dream. Birds dream a little. Mammals all dream during sleep.

Different animals sleep in different ways. Some animals, like humans, prefer to sleep in one long session. Other animals (dogs, for example) like to sleep in many short bursts. Some sleep at night, while others sleep during t*he day.

Sleep and the Brain

*If you attach an electroencephalograph to a person's head, you can record the person's brainwave activity. An awake and relaxed person generates alpha waves, which are consistent oscillations at about 10 cycles per second. An alert person generates beta waves, which are about twice as fast.

During sleep, two slower patterns called theta waves and delta waves take over. Theta waves have oscillations in the range of 3.5 to 7 cycles per second, and delta waves have oscillations of less than 3.5 cycles per second. As a person falls asleep and sleep deepens, the brainwave patterns slow down. The slower the brainwave patterns, the deeper the sleep -- a person deep in delta wave sleep is hardest to wake up.

At several points during the night, something unexpected happens -- rapid eye movement (REM) sleep occurs. Most people experience three to five intervals of REM sleep per night, and brainwaves during this period speed up to awake levels. If you ever watch a person or a dog experiencing REM sleep, you will see their eyes flickering back and forth rapidly. In many dogs and some people, arms, legs and facial muscles will twitch during REM sleep. Periods of sleep other than REM sleep are known as NREM (non-REM) sleep.

REM sleep is when you dream. If you wake up a person during REM sleep, the person can vividly recall dreams. If you wake up a person during NREM sleep, generally the person will not be dreaming.

You must have both REM and NREM sleep to get a good night's sleep. A normal person will spend about 25 percent of the night in REM sleep, and the rest in NREM. A REM session -- a dream -- lasts five to 30 minutes.

Medicine can hamper your ability to get a good night's sleep. Many medicines, including most sleeping medicines, change the quality of sleep and the REM component of it.

REFARDS

__________________
Always do what you are afraid to do
Saqib Riaz(TIPO KHAN)

Missing Sleep

One way to understand why we sleep is to look at what happens when we don't get enough:

* As you know if you have ever pulled an all-nighter, missing one night of sleep is not fatal. A person will generally be irritable during the next day and will either slow down (become tired easily) or will be totally wired because of adrenalin.

* If a person misses two nights of sleep, it gets worse. Concentration is difficult, and attention span falls by the wayside. Mistakes increase.

* After three days, a person will start to hallucinate and clear thinking is impossible. With continued wakefulness a person can lose grasp of reality. Rats forced to stay awake continuously will eventually die, proving that sleep is essential.

A person who gets just a few hours of sleep per night can experience many of the same problems over time.

Two other things are known to happen during sleep. Growth hormone in children is secreted during sleep, and chemicals important to the immune system are secreted during sleep. You can become more prone to disease if you don't get enough sleep, and a child's growth can be stunted by sleep deprivation.

But the question remains -- why do we need to sleep? No one really knows, but there are all kinds of theories, including these:

* Sleep gives the body a chance to repair muscles and other tissues, replace aging or dead cells, etc.

* Sleep gives the brain a chance to organize and archive memories. Dreams are thought by some to be part of this process.

* Sleep lowers our energy consumption, so we need three meals a day rather than four or five. Since we can't do anything in the dark anyway, we might as well "turn off" and save the energy.

* According to ScienceNewsOnline: Napless cats awaken interest in adenosine, sleep may be a way of recharging the brain, using adenosine as a signal that the brain needs to rest: "Since adenosine secretion reflects brain cell activity, rising concentrations of this chemical may be how the organ gauges that it has been burning up its energy reserves and needs to shut down for a while." Adenosine levels in the brain rise during wakefulness and decline during sleep.

*What we all know is that, with a good night's sleep, everything looks and feels better in the morning. Both the brain and the body are refreshed and ready for a new day.

Dreams and Improving Sleep Habits

* Why do we have such crazy, kooky dreams? Why do we dream at all for that matter? According to Joel Achenbach in his book Why Things Are:

*The brain creates dreams through random electrical activity. Random is the key word here. About every 90 minutes the brain stem sends electrical impulses throughout the brain, in no particular order or fashion. The analytic portion of the brain -- the forebrain -- then desperately tries to make sense of these signals. It is like looking at a Rorschach test, a random splash of ink on paper. The only way of comprehending it is by viewing the dream (or the inkblot) metaphorically, symbolically, since there's no literal message.

This doesn't mean that dreams are meaningless or should be ignored. How our forebrains choose to "analyze" the random and discontinuous images may tell us something about ourselves, just as what we see in an inkblot can be revelatory. And perhaps there is a purpose to the craziness: Our minds may be working on deep-seated problems through these circuitous and less threatening metaphorical dreams.

Here are some other things you may have noticed about your dreams:

* Dreams tell a story. They are like a TV show, with scenes, characters and props.

* Dreams are egocentric. They almost always involve you.

* Dreams incorporate things that have happened to you recently. They can also incorporate deep wishes and fears.

* A noise in the environment is often worked in to a dream in some way, giving some credibility to the idea that dreams are simply the brain's response to random impulses.

* You usually cannot control a dream -- in fact, many dreams emphasize your lack of control by making it impossible to run or yell. (However, proponents of lucid dreaming try to help you gain control.)

Dreaming is important. In sleep experiments where a person is woken up every time he/she enters REM sleep, the person becomes increasingly impatient and uncomfortable over time.

To learn more, check out How Dreams Work.

How Much Sleep Do I Need?
Most adult people seem to need seven to nine hours of sleep a night. This is an average, and it is also subjective. You, for example, probably know how much sleep you need in an average night to feel your best.

The amount of sleep you need decreases with age. A newborn baby might sleep 20 hours a day. By age four, the average is 12 hours a day. By age 10, the average falls to 10 hours a day. Senior citizens can often get by with six or seven hours a day.

Tips to Improve Your Sleep

* Exercise regularly. Exercise helps tire and relax your body.
* Don't consume caffeine after 40 p.m. or so. Avoid other stimulants like cigarettes as well.
* Avoid alcohol before bedtime. Alcohol disrupts the brain's normal patterns during sleep.
* Try to stay in a pattern with a regular bedtime and wakeup time, even on weekends.

Regards

__________________
Always do what you are afraid to do
Saqib Riaz(TIPO KHAN)

What is a black hole?

A black hole is an object with such powerful gravity that nothing can escape from it, including light. The black hole's mass is concentrated in a point of almost infinite density called a singularity. At the singularity itself, gravity is almost infinitely strong, so it crushes normal space-time out of existence. As the distance from the singularity increases, its gravitational influence lessens. At a certain distance, which depends on the singularity's mass, the speed needed to escape from the black hole equals the speed of light. This distance marks the black hole's "horizon," which is like its surface. Anything that passes through the horizon is trapped inside the black hole. Black holes come in several varieties, depending on mass.

How does a black hole form?

A black hole forms when any object reaches a certain critical density, and its gravity causes it to collapse to an almost infinitely small pinpoint. Stellar-mass black holes form when a massive star can no longer produce energy in its core. With the radiation from its nuclear reactions to keep the star "puffed up," gravity causes the core to collapse. The star's outer layers may blast away into space, or they may fall into the black hole to make it heavier. Astronomers aren't certain how supermassive black holes form. They may form from the collapse of large clouds of gas, or from the mergers of many smaller black holes, or a combination of events.

Are any black holes close to Earth?

The closest black holes yet discovered are several thousand light-years away. They are so far that they have no effect on Earth or its environment. A super massive black hole appears to inhabit the center of the Milky Way galaxy, about 27,000 light-years away. Although it is several million times the mass of the Sun, its great distance insures that it won't affect our solar system.

Will our Sun become a black hole?

No. Stars like the Sun just aren't massive enough to become black holes. Instead, in several billion years, the Sun will cast off its outer layers, and its core will form a white dwarf - a dense ball of carbon and oxygen that no longer produces nuclear energy, but that shines because it is very hot. A typical white dwarf is about as massive as the Sun, but only as big as Earth, which is one percent of the Sun's present diameter.

Will our universe become a black hole?

Unlikely. Recent developments that show our universe is expanding at an ever-increasing rate. The cause of the expansion, called dark energy, is not understood, but it appears that the universe is destined to undergo a slow and cold death. If there were enough mass in the universe, and if dark energy did not exist, then it might have been possible for the universe to collapse in on itself, condensing all matter and energy to an almost infinitely small point, like a black hole.

__________________
The future belongs to those who believe in the beauty of their dreams.
.::Be Different::.
M$. L!|y

What Your Bathtub Can Teach You About Tornadoes

If you've ever watched a whirlpool form in your bathtub or sink while draining the water, then you've witnessed the fundamentals of a tornado at work. A drain's whirlpool, also known as a vortex, forms because of the downdraft that the drain creates in the body of water. The downward flow of the water into the drain begins to rotate, and as the rotation speeds up, a vortex forms.
Why does the water start rotating? There are many explanations, but here's one way to think about it. Imagine yourself as a particle in the water, suddenly pulled toward the suction that the drain creates. At first, you'd find yourself accelerating toward the drain. Then, quite literally, there's a twist. Because of your previous momentum and the number of other particles rushing toward the drain at the same time, chances are that you're going to be pushed off to one side of the point of suction when you arrive. That deflection sets you on a spiraling path into the point of suction, like a moth spiraling in toward a light. Once the spiral has started in one direction, it tends to influence all the other particles as they arrive. A very strong spiraling tendency is created. Eventually, there's enough spiraling energy to create a vortex.

Vortices are obviously a common phenomenon. After all, you see them in tubs and sinks all the time. Small dust devils sometimes form when winds flow over hot deserts, and wildfires have been known to produce climbing vortices of flame and ash called fire whirls. Scientists have even observed dust devils on Mars and spotted solar tornadoes whipping out from the sun.

In a tornado, the same sort of thing happens as with our bathtub example, except with air instead of water. A great deal of the Earth's wind patterns are dictated by low-pressure centers, which draw in cooler, high-pressure air from the surrounding area. This airflow pushes the low-pressure air up to higher altitudes, but then the air heats up and is pushed upward as well by all the air behind it. The air pressure inside a tornado is as much as 10 percent lower than that of the surrounding air, causing the surrounding air to rush in even faster.

H*ow do weather conditions pull the plug on atmospheric conditions? Skip to the next page to find out how tornadoes form.

Tornadoes and Thunderstorms

*Tornadoes don't just pop into existence -- they develop out of thunderstorms, where there's already a steady, upward flow of warm, low-pressure air to get things started. It's kind of like when a rock concert erupts into a riot. Conditions were already volatile; they merely escalated into something even more dangerous.
Thunderstorms themselves form like many other clouds: A warm, moist air mass rises and cools, causing the water vapor to condense into clouds. However, if the updraft continues, this cloud mass will continue to grow and rise 40,000 feet (12,192 m) or more up into the troposphere, the bottommost layer of the atmosphere that we live in. A typical thunderstorm cloud can accumulate an enormous amount of energy. If the conditions are right, this energy creates a huge updraft into the cloud, but where does the energy come from?

Clouds are formed when water vapor condenses in the air. This change in physical state releases heat, and heat is a form of energy. A good deal of a thunderstorm's energy is a result of the condensation that forms the cloud. Every gram of water condensed results in about 600 calories of heat -- and another 80 calories of heat per gram of water results from freezing in the upper atmosphere. This energy increases the updraft temperature, as well as the kinetic energy of upward and downward air movement. The average thunderstorm releases around 10,000,000 kilowatt-hours of energy -- the equivalent of a 20-kiloton nuclear warhead [source: Britannica].

In supercell thunderstorms, the updrafts are particularly strong. If they are strong enough, a vortex of air can develop just like a vortex of water forms in a sink. This precursor to the tornado is called a mesocyclone, and is typically 2 to 6 miles (3 to 10 kilometers) wide. One a mesocyclone forms, there's a roughly 50 percent chance that the storm will escalate into a tornado in around 30 minutes.

Some tornadoes consist of a single vortex, but other times multiple suction vortices revolve around a tornado's center. These storms-within-a-storm may be smaller, with a diameter of around 30 feet (9 meters), but they experience extremely powerful rotation speeds.

The tornado reaches down out of a thundercloud as a huge, swirling rope of air. Wind speeds in the range of 200 to 300 mph (322 to 483 kph) aren't uncommon. If the vortex touches ground, the speed of the whirling wind (as well as the updraft and the pressure differences) can cause tremendous damage, tearing apart homes and flinging potentially lethal debris.

The tornado follows a path that is controlled by the route of its parent thundercloud, and it will often appear to hop. The hops occur when the vortex is disturbed. You've probably seen that it is easy to disturb a vortex in the tub, but then it will reform. The same thing can happen to a tornado's vortex, causing it to collapse and reform along its path.

Smaller tornadoes may only thrive for a matter of minutes, covering less than a mile of ground. Larger storms, however, can remain on the ground for hours, covering more than 90 miles (150 km) and inflicting near continuous damage along the way.

At this point, you might be wondering just how tornadoes eventually dissipate. Scientists still debate exactly how these deadly storms die, but one of the prime suspects is none other than the parent thunderstorm: the rotating mesocyclone. Tornadoes need instability and rotation. Disrupt the airflow, take away its moisture or destroy its unstable balance of hot and cold air, and it can't function. Often, a tornado will die because the cold outflow of air from falling precipitation upsets the balance.

__________________
Always do what you are afraid to do
Saqib Riaz(TIPO KHAN)

What produces Thunder?

Thunder is the sound made by lightning. Depending on the nature of the lightning and distance of the listener, it can range from a sharp, loud crack to a long, low rumble (brontide). The sudden increase in pressure and temperature from lightning produces rapid expansion of the air surrounding and within a bolt of lightning. In turn, this expansion of air creates a sonic shock wave which produces the sound of thunder.

The cause of thunder has been the subject of centuries of speculation and scientific inquiry. The first recorded theory is attributed to the Greek philosopher Aristotle in the third century BC, and an early speculation was that it was caused by the collision of clouds. Subsequently, numerous other theories have been proposed. By the mid-19th century, the accepted theory was that lightning produced a vacuum. In the 20th century a consensus evolved that thunder must begin with a shock wave in the air due to the sudden thermal expansion of the plasma in the lightning channel. In a fraction of a second the air is heated to a temperature approaching 28,000 °C (50,000 °F). This heating causes it to expand outward, plowing into the surrounding cooler air at a speed faster than sound would travel in that cooler air. The outward-moving pulse that results is a shock wave, similar in principle to the shock wave formed by an explosion, or at the front of a supersonic aircraft. More recently, this consensus has been eroded by the observation that measured overpressures in simulated lightning are greater than what could be achieved by the amount of heating found. Alternative proposals rely on electrodynamic effects of the massive current acting on the plasma in the bolt of lightning.

__________________
The future belongs to those who believe in the beauty of their dreams.
.::Be Different::.
M$. L!|y

Arteries are blood vessels that carry blood away from the heart. All arteries, with the exception of the pulmonary and umbilical arteries, carry oxygenated blood.

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