Wednesday, May 25, 2011

Amazing Eyes

 
The major eye structures include:
Cornea is a clear, thin tissue that covers the surface of the eye. It is extremely sensitive and contains numerous nerve cells.
Lens of the eye allow the refraction of light to occur. These clear tissues are usually bent, so that when the rays of light can be focused to one specific point on the retina.
Retina is a tissue found towards the back of the eye that is layered with multiple sensory tissues. Millions of photoreceptors that are found in the retina capture light rays and convert them into electrical impulses.
Optic nerve is a pathway for the electrical impulses to travel through to the brain from the retina. The electrical impulses by the rays of light are sent to the brain through the optic nerve and are portrayed by the brain as images.  
Lasik surgery begins with the removal of the top layer of the cornea. Afterwards, the doctor uses laser to steepen or flatten the tissue of the eyes. This process in done in order to make sure that the eye is adjusted so that the lenses of the eye bend to focus on a point on the retina. After reforming the eye tissue, the removed layer of cornea is placed back to heal by itself.
Usually, when a person has a 20/20 vision, the refraction of the light through the lenses is focused exactly on the retina of his/her eyes. However, the refractive defect causes nearsightedness, or farsightedness to occur.  Myopia is when the refraction of the light does not quite reach the retina of the eye. Because of this, one cannot see distant objects clearly. On the other hand, hyperopia is the exact opposite of myopia. When a person has a refractive defect of hyperopia, the refraction of the light focuses on a point far beyond the retina. Therefore, he/she cannot see close objects clearly.   

Wednesday, May 4, 2011

Sleep

Neurotransmitters are chemicals that signal the nerves in the brain in order to control our sleeping cycle. It acts on many different groups of nerve cells, or neurons in the brain. For an example, the neurons located near the brainstem produce neurotransmitters such as serotonin and norepinephrine. These neurotransmitters function to keep the brain active.
Circadian clock is also known as biological clock. It describes the physical, mental and behavioral changes that follow a daily (24-hour) cycle, responding primarily to light and darkness in the environment. Hence, our bodies are prone to feel tiredness without sunlight.
REM, also known as the Rapid Eye Movement, is a stage in our sleep cycle when our eyes move around. Although uncertain, there are many theories that conclude that the movements in the eyes are initiated by different phases of dreaming. REM can further be broken down to tonic and phasic. During this phase, REM sleep-on cells are active, and its activity might be an explanation to why such movements occur in the eyes. The researchers found activity in areas of the brain that control sight, hearing, smell, touch, arousal, sleep-wake transitions, balance and body movement, but some parts of the brain were completely shut down. Although some neurons are very active during this phase, some neurotransmitters, such as norepinephrine, serotonin, and histamine, stop functioning during REM.
nREM, also known as non-Rapid Eye Movement, is found to be a dreamless sleep. 80% of the sleep consists of nREM. This phase is when the breathing and the heart rate of the sleeper is slow and regular. The blood pressure is low, and the sleeper is relatively still.
Insomnia is a sleep disorder when the sleeper has trouble falling asleep. It can be caused by many different causes, but some of the main factors that trigger such disorder are alcohol, coffee, anxiety, and/or stress.
Sleep Apnea is a sleep disorder commonly found in overweight people, or children with enlarged tonsil tissues. This is due to the airway that collapse or is blocked during sleep.  This leads to shallow breathing, breathing pauses, snoring, or even gasping in the middle of the sleep. When the airway is blocked, the oxygen flow rapidly decreases. The body signals the brain to stop sleep, which leads to the sleeper to wake up in the middle of the night, gasping for more air.

Restless leg syndrome is caused by the disturbance in sleep due to a sudden urge/ need to move one’s legs. The sleeper feels uncomfortable creeping, crawling, aching, pulling, searing, tingling, bubbling, or crawling sensation that can only be relieved by moving his/her legs. Although it can be considered very minor, it can be very uncomfortable for the sleeper and impact one’s sleep cycle by disrupting the sleep pattern.  
Narcolepsy is caused by reduced amounts of a protein called hypocretin. The disorder is characterized by the numerous sleep attacks throughout the day, and/or excessive sleepiness. Some of the symptoms of this disorder include: dream-like hallucinations involving different senses that occur during the stage in between sleep and wakefulness; sleep paralysis that prevents the body from being able to move around as soon as one wakes up; a sudden loss of muscle tone, also known as cataplexy.
Researches have shown that teenagers need at least 8-9 hours of sleep daily. Without sufficient amount of sleep, our bodies tend to become more vulnerable to sickness and stress. Even from personal experiences, I’ve noticed that whenever I got less than 6.5 hours of sleep, I was dysfunctional. The tiredness was overwhelming, and I was incapable of controlling my brain. I’ve noticed that my lack of sleep plus stress guarantees a sick day.