Math Is Fun Forum

Myopia

Gist

Myopia, or nearsightedness, is a common, often progressive refractive error where the eyeball grows too long or the cornea is too curved, causing light to focus in front of the retina rather than on it. It results in blurred distant vision, with symptoms like eye strain, headaches, and squinting. Affecting roughly 30% of the global population, it is commonly treated with glasses, contacts, or refractive surgery (e.g., LASIK).

Myopia, or nearsightedness, is a common vision condition where distant objects appear blurry because the eye focuses light in front of the retina instead of directly on it, often due to an elongated eyeball or a cornea that is too curved. It allows clear vision for close-up tasks but makes seeing far away difficult, leading to squinting, eye strain, and headaches. It's typically managed with glasses, contacts, or surgery, and its development is linked to genetics and increased near work like screen time. 

Summary

Myopia, also known as near-sightedness and short-sightedness, is an eye condition where light from distant objects focuses in front of, instead of on, the retina. As a result, distant objects appear blurry, while close objects appear normal. Other symptoms may include headaches and eye strain. Severe myopia is associated with an increased risk of macular degeneration, retinal detachment, cataracts, and glaucoma.

Myopia results from the length of the eyeball growing too long or less commonly the lens being too strong. It is a type of refractive error. Diagnosis is by the use of cycloplegics during eye examination.

Myopia is less common in people who spent more time outside during childhood. This lower risk may be due to greater exposure to sunlight. Myopia can be corrected with eyeglasses, contact lenses, or by refractive surgery. Eyeglasses are the simplest and safest method of correction. Contact lenses can provide a relatively wider corrected field of vision, but are associated with an increased risk of infection. Refractive surgeries such as LASIK and PRK permanently change the shape of the cornea. Other procedures include implantable collamer lens (ICL) placement inside the anterior chamber in front of the natural eye lens. ICL does not affect the cornea.

Myopia is the most common eye disorder and is estimated to affect 1.5 billion people (22% of the world population). Rates vary significantly in different areas of the world. Rates among adults are between 15% and 49%. Among children, it affects 1% of rural Nepalese, 4% of South Africans, 12% of people in the US, and 37% in some large Chinese cities. In China the proportion of girls is slightly higher than boys. Rates have increased since the 1950s. Uncorrected myopia is one of the most common causes of vision impairment globally along with cataracts, macular degeneration, and vitamin A deficiency.

Details

Myopia (nearsightedness) is a common condition that’s usually diagnosed before age 20. It affects your distance vision — you can see objects that are near, but you have trouble viewing objects that are farther away like grocery store aisle markers or road signs. Myopia treatments include glasses, contact lenses or surgery.

Overview:

What is myopia?

Myopia is the medical name for nearsightedness, which means that you can see objects that are near clearly but have difficulty seeing objects that are farther away. For example, if you have nearsightedness, you may not be able to make out highway signs until they’re just a few feet away.

Myopia affects a significant percentage of people. It’s an eye focus disorder that’s normally corrected with eyeglasses, contact lenses or surgery.

How common is myopia?

Myopia is common. According to one estimate, more than 40% of people in the U.S. have nearsightedness. This number is rapidly rising, especially among school-aged children. Eye experts expect this trend to continue in the coming decades.

One in four parents has a child with some degree of nearsightedness. Some eye experts believe that if your child spends a great deal of time engaged in “near” activities, such as reading or using smartphones and computers, it may raise their risk of developing myopia.

Are there types of myopia?

Eye specialists divide myopia broadly into simple myopia and pathologic myopia. Pathologic myopia is a newer name for degenerative myopia.

People with simple myopia have contact lenses or eyeglasses that help provide clear vision, while those with pathologic myopia may not be able to have clear vision even with corrective lenses.

Symptoms and Causes:

What are the symptoms of myopia?

If you have nearsightedness, you may notice:

* Faraway objects look blurred or fuzzy.
* Close items appear clear.
* Headaches.
* Eye strain.
* Squinting.
* Tiredness when driving, playing sports or looking more than a few feet away.

Some additional symptoms of myopia to watch for in your children include:

* Poor performance in school.
* Shortened attention span.
* Holding objects close to their face.

Most cases of myopia are mild and easily managed with eyeglasses, contact lenses or refractive surgery.

What causes myopia?

If you have myopia, more than likely, at least one or both of your biological parents do, too. Eye experts are still unsure of the exact cause of myopia, but believe it to be a mix of hereditary and environmental factors.

It’s possible that you can inherit the ability to be myopic. If your lifestyle produces just the right conditions, you’ll develop it. For example, if you use your eyes for a lot of close-up work, like reading or working on a computer, you may develop myopia.

Myopia usually appears in childhood. Typically, the condition can worsen in early childhood but tends to level off by the end of teen years.

Because the light coming into your eyes doesn’t focus correctly, images are unclear. Think of it as being a little like a misdirected spotlight. If you shine a spotlight on the incorrect place in the distance, you won’t be able to see the correct object clearly.

What are the risk factors for myopia?

Risk factors for nearsightedness may include:

* A family history of myopia.
* Spending a lot of time doing “close-up” work, like reading or using screens like those on smartphones or computers.
* Not spending a lot of time outdoors. Certain studies indicate that this may be a factor in developing myopia.
* Ethnicity. Some groups of people have higher rates of myopia than others.

What are the complications of myopia?

In most cases, providers can treat nearsightedness with glasses, contact lenses or corrective surgery, like LASIK. However, some cases of pathologic myopia can lead to more serious eye conditions, including:

* Cataracts.
* Glaucoma.
* Optic neuropathy.
* Neovascularization.
* Retinal detachment.

Pathologic myopia may make you more vulnerable to other more serious eye conditions. These include:

* Developing unwanted blood vessels in your eye (neovascularization).
* Glaucoma.
* Myopic optic neuropathy.
* Retinal detachment.
* Cataracts.
* High myopia happens when your child’s eyeballs are too long, or their corneas are too steep.

Diagnosis and Tests:

How is myopia diagnosed?

An eye care provider can diagnose myopia using standard eye exams. Providers usually diagnose myopia in childhood, but it can also develop in adults because of visual stress or diabetes.

Testing an adult for myopia

Your provider will evaluate how your eyes focus light and measure the power of any corrective lenses you may need. First, they’ll test your visual acuity (sharpness) by asking you to read letters on an eye chart. Then, they’ll use a lighted retinoscope to measure how your retina reflects light.

Your provider may also use a phoropter. A phoropter is an instrument that measures the amount of your refractive error by placing a series of lenses in front of your eyes. This is how your provider measures the lens strength you need.

Testing your child for myopia

Your pediatrician will check your child’s eyes at each well-child visit. A first eye exam should be before age 1, if possible. If your child has no evident eye problems, then schedule a repeat eye exam before kindergarten.

As myopia runs in families, if your child has family members with vision issues, it’s even more important to test their eyes early. If you or your pediatrician notice any vision issues, your child may be referred to an optometrist or pediatric ophthalmologist.

During a children’s eye exam, your eye care provider will do a physical examination of your child’s eyes and check for a regular light reflex. For children between the ages of 3 and 5 years, your provider will also conduct vision screenings using eye chart tests, pictures, letters or the “tumbling E game,” also called the “Random E’s Visual Acuity Test.”

As your child’s vision continues to change as they grow, continue to make sure they get vision screenings by their pediatrician or eye care provider before first grade and every two years thereafter. While most schools conduct eye screenings, they’re usually not complete enough to diagnose myopia. Providers diagnose most children when they’re between the ages of 3 and 12.

Your provider may mention categories — mild, moderate or high myopia. These terms refer to the degree of nearsightedness as measured by refractive error. Refractive errors are issues with the natural shape of your eyes that make your vision blurry. It’s possible to have myopia and another refractive error, like astigmatism.

Management and Treatment:

How is myopia treated?

Glasses or contact lenses can correct myopia in children and adults. For adults only (with rare exceptions for children), there are several types of refractive surgeries that can also correct myopia.

With myopia, your prescription for glasses or contact lenses is a negative number, such as -3.00. The higher the number, the stronger your lenses will be. The prescription helps your eye focus light on your retina, clearing up your distance vision.

* Eyeglasses: The most popular way for most people to correct myopia is with eyeglasses. Depending on the degree of vision correction needed, you’ll wear eyeglasses either daily or only when you need distance vision. You may only need glasses for driving. Some kids with myopia may only need glasses to play ball, watch a movie or view the chalkboard. Some people may need to wear glasses constantly to see clearly. A single-vision lens will make distance vision clearer. But people over 40 who have myopia may require a bifocal or progressive lens to see clearly both near and far.
* Contact lenses: Some people find that their distance vision is sharper and wider with contact lenses. A potential downside is they require more care to keep clean. Ask your provider which type might be right for your myopia level and other refractive errors.
* Ortho-k or CRT: Some people with mild myopia may be candidates for temporary corneal refractive contact lenses that you wear to bed to reshape your cornea temporarily, long enough to see for your daily activities.
* LASIK is a laser-assisted in situ keratomileus procedure, the most common surgery to correct nearsightedness. In a LASIK procedure, your ophthalmologist uses a laser to cut a flap through the top of your cornea, reshape the inner corneal tissue and then drop the flap back into place.
* LASEK is a laser-assisted subepithelial keratectomy procedure. In a LASEK procedure, your ophthalmologist uses a laser to cut a flap through only the top layer (epithelium) of your cornea, reshape the outer layers, and then close the flap.
* PRK is short for “photorefractive keratectomy,” which is a type of laser eye surgery used to correct mild or moderate nearsightedness. It may also correct farsightedness and/or astigmatism. In a PRK procedure, your ophthalmologist cuts off the front surface of your cornea and uses a laser to reshape the surface, which flattens it and allows light rays to focus on your retina. Unlike LASIK, the ophthalmologist doesn’t cut a flap, and your cornea will regrow its top layer in one to two weeks. PRK is better for people with corneas that are thinner or have a rough surface because it disrupts less corneal tissue than a comparable LASIK surgery.
* Phakic intraocular lenses: These are an option for people who have high myopia or whose corneas are too thin for PRK or LASIK. Your provider places phakic intraocular lenses inside of your eye just in front of your natural lens.
* Intraocular lens implant: This allows your ophthalmologist to surgically insert a new lens in your eye, replacing your natural one. This procedure happens before a cataract develops.
* Vision therapy: This is an option if spasms of your focusing muscles cause myopia. You can strengthen the muscles through eye exercises and improve your focus. This treatment isn’t appropriate for everyone with myopia. After an eye exam, your ophthalmologist will let you know if it’s an option for you.

Outlook / Prognosis:

What can I expect if I have myopia?

Myopia is a condition that doesn’t go away. Treatments include using glasses or contact lenses. You may be able to get surgery to correct your vision.

What is the outlook for myopia?

The outlook for being nearsighted may differ depending on the type of myopia.

Usually, providers can treat simple myopia easily. In rare cases of high myopia or pathologic myopia, your outlook may be different.

High myopia usually stops getting worse between the ages of 20 and 30. You’ll still be able to get glasses or contact lenses or you may be able to have surgery.

High myopia may lead to pathologic myopia and the possibility of more serious sight conditions later in life. These complications can lead to loss of sight.

Regular eye exams are important for everyone but are especially if you have high myopia or pathologic myopia. You should follow the schedule set out by your eye care provider.

Prevention:

Can myopia be prevented?

You can’t prevent myopia as it’s a condition that tends to run in families, but you may be able to lower your risk of nearsightedness in some ways.

How can I lower my risk of developing myopia?

Some eye experts believe that you may be able to decrease your or your child’s risk of developing myopia by getting enough time outside and limiting the amount of time spent in front of screens. You may also want to be mindful of the amount of time doing close work like reading or sewing.

Additional Information

Myopia occurs if the eyeball is too long or the cornea (the clear front cover of the eye) is too curved. As a result, the light entering the eye isn't focused correctly, and distant objects look blurred. Myopia affects nearly 30% of the U.S. population. While the exact cause of myopia is unknown, there is significant evidence that many people inherit myopia, or at least the tendency to develop myopia. If one or both parents are nearsighted, there is an increased chance their children will be nearsighted. Even though the tendency to develop myopia may be inherited, its actual development may be affected by how a person uses his or her eyes. Individuals who spend considerable time reading, working at a computer, playing video games or doing other intense close visual work may be more likely to develop myopia. In fact, high levels of screen time on smart devices (i.e. looking at a smart phone) is associated with around a 30% higher risk of myopia and, when combined with excessive computer use, that risk rose to around 80%.

Causes & risk factors

Myopia may also occur due to environmental factors or other health problems:

* Some people may experience blurred distance vision only at night. With "night myopia," low light makes it difficult for the eyes to focus properly. Or the increased pupil size during dark conditions allows more peripheral, unfocused light rays to enter the eye.
* People who do an excessive amount of near-vision work may experience a false or "pseudo" myopia. Their blurred distance vision is caused by overuse of the eyes' focusing mechanism. After long periods of near work, their eyes are unable to refocus to see clearly in the distance. Clear distance vision usually returns after resting the eyes. However, constant visual stress may lead to a permanent reduction in distance vision over time.
* Symptoms of myopia may also be a sign of variations in blood sugar levels in people with diabetes or maybe an early indication of a developing cataract.

Symptoms

People with myopia can have difficulty clearly seeing a movie or TV screen, a whiteboard in school or while driving. Generally, myopia first occurs in school-age children. Because the eye continues to grow during childhood, it typically progresses until about age 20. However, myopia may also develop in adults due to visual stress or health conditions such as diabetes.

Diagnosis

Testing for myopia may use several procedures to measure how the eyes focus light and to determine the power of any optical lenses needed to correct the reduced vision. As part of the testing, you will identify letters on a distance chart. This test measures visual acuity, which is written as a fraction, such as 20/40. The top number of the fraction is the standard distance at which testing is performed (20 feet). The bottom number is the smallest letter size read. A person with 20/40 visual acuity would have to get within 20 feet to identify a letter that could be seen clearly at 40 feet in a "normal" eye. Normal distance visual acuity is 20/20, although many people have 20/15 (better) vision.

Using an instrument called a phoropter, a doctor of optometry places a series of lenses in front of your eyes and measures how they focus light using a handheld lighted instrument called a retinoscope. Or the doctor may choose to use an automated instrument that evaluates the focusing power of the eye. The power is then refined based on your responses to determine the lenses that allow the clearest vision. Your doctor can conduct this testing without using eye drops to determine how the eyes respond under normal seeing conditions.

In some cases, such as for patients who can't respond verbally or when some of the eye's focusing power may be hidden, a doctor may use eye drops. The eye drops temporarily keep the eyes from changing focus during testing. Using the information from these tests, along with the results of other tests of eye focusing and eye teaming, your doctor can determine if you have myopia. He or she will also determine the power of any lens correction needed to provide a clearer vision. Once testing is complete, your doctor can discuss treatment options.

Treatment

People with myopia have several options available to regain clear distance vision. They include:

* Eyeglasses. For most people with myopia, eyeglasses are the primary choice for correction. Depending on the amount of myopia, you may only need to wear glasses for certain activities, like watching a movie or driving a car. Or, if you are very nearsighted, you may need to wear them all the time. Generally, a single-vision lens is prescribed to provide clear vision at all distances. However, patients over age 40, or children and adults whose myopia is due to the stress of near vision work, may need a bifocal or progressive addition lens. These multifocal lenses provide different powers or strengths throughout the lens to allow for clear vision in the distance and up close.
* Contact lenses. For some individuals, contact lenses offer clearer vision and a wider field of view than eyeglasses. However, since contact lenses are worn directly on the eyes, they require proper evaluation and care to safeguard eye health.
* Ortho-k or CRT. Another option for treating myopia is orthokeratology (ortho-k), also known as corneal refractive therapy (CRT). In this nonsurgical procedure, you wear a series of specially designed rigid contact lenses to gradually reshape the curvature of your cornea, the front outer surface of the eye. The lenses place pressure on the cornea to flatten it. This changes how light entering the eye is focused. You wear the contact lenses for limited periods, such as overnight, and then remove them. People with mild myopia may be able to temporarily obtain clear vision for most of their daily activities.
* Laser procedures. Laser procedures such as LASIK (laser in situ keratomileusis) or PRK (photorefractive keratectomy) are also possible treatment options for myopia in adults. A laser beam of light reshapes the cornea by removing a small amount of corneal tissue. The amount of myopia that PRK or LASIK can correct is limited by the amount of corneal tissue that can be safely removed. In PRK, a laser removes a thin layer of tissue from the surface of the cornea in order to change its shape and refocus light entering the eye. LASIK removes tissue from the inner layers, but not from the surface, of the cornea. To do this, a section of the outer corneal surface is lifted and folded back to expose the inner tissue. A laser then removes the precise amount of corneal tissue needed to reshape the eye. Then, the flap of outer tissue is placed back in position to heal.
* Other refractive surgery procedures. People who are highly nearsighted or whose corneas are too thin for laser procedures may be able to have their myopia surgically corrected. A doctor may be able to implant small lenses with the desired optical correction in their eyes. The implant can be placed just in front of the natural lens (phakic intraocular lens implant), or the implant can replace the natural lens (clear lens extraction with intraocular lens implantation). This clear lens extraction procedure is similar to cataract surgery but occurs before a cataract is present.
* Vision therapy for people with stress-related myopia. Vision therapy is an option for people whose blurred distance vision is caused by a spasm of the muscles that control eye focusing. Various eye exercises can improve poor eye focusing ability and regain clear distance vision.

People with myopia have a variety of options to correct vision problems. A doctor of optometry will help select the treatment that best meets the visual and lifestyle needs of the patient.

Prevention

Children who are at high risk of progressive myopia (family history, early age of onset, and extended periods of near work) may benefit from treatment options that have been shown to reduce the progression of myopia. These treatments include the prescription of bifocal spectacle or contact lenses, orthokeratology, eye drops, or a combination of these. Because persons with high myopia are at a greater risk of developing cataracts, glaucoma and myopic macular degeneration, myopia management may help preserve eye health.

Nervous System

Gist

The nervous system is the body's primary command center, controlling actions, sensory information, and involuntary functions by transmitting electrical signals between the brain, spinal cord, and body. Divided into the central (brain/spinal cord) and peripheral (nerves) systems, it enables movement, thought, memory, and, together with the endocrine system, maintains homeostasis.

Core Components

Central Nervous System (CNS): Comprises the brain and spinal cord, which act as the main processing center for information.
Peripheral Nervous System (PNS): Consists of all nerves outside the brain and spinal cord, connecting the CNS to limbs and organs.
Neurons: The basic structural units (nerve cells) that send messages via electrical impulses, featuring axons for transmission and dendrites for reception.

Summary

In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes that impact the body, then works in tandem with the endocrine system to respond to such events. Nervous tissue first arose in wormlike organisms about 550 to 600 million years ago. In vertebrates, it consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord. The PNS consists mainly of nerves, which are enclosed bundles of the long fibers, or axons, that connect the CNS to every other part of the body. Nerves that transmit signals from the brain are called motor nerves (efferent), while those nerves that transmit information from the body to the CNS are called sensory nerves (afferent). The PNS is divided into two separate subsystems, the somatic and autonomic nervous systems. The autonomic nervous system is further subdivided into the sympathetic, parasympathetic and enteric nervous systems. The sympathetic nervous system is activated in cases of emergencies to mobilize energy, while the parasympathetic nervous system is activated when organisms are in a relaxed state. The enteric nervous system functions to control the gastrointestinal system. Nerves that exit from the brain are called cranial nerves while those exiting from the spinal cord are called spinal nerves.

The nervous system consists of nervous tissue which, at a cellular level, is defined by the presence of a special type of cell, called the neuron. Neurons have special structures that allow them to send signals rapidly and precisely to other cells. They send these signals in the form of electrochemical impulses traveling along thin fibers called axons, which can be directly transmitted to neighboring cells through electrical synapses or cause chemicals called neurotransmitters to be released at chemical synapses. A cell that receives a synaptic signal from a neuron may be excited, inhibited, or otherwise modulated. The connections between neurons can form neural pathways, neural circuits, and larger networks that generate an organism's perception of the world and determine its behavior. Along with neurons, the nervous system contains other specialized cells called glial cells (or simply glia), which provide structural and metabolic support. Many of the cells and vasculature channels within the nervous system make up the neurovascular unit, which regulates cerebral blood flow in order to rapidly satisfy the high energy demands of activated neurons.

Nervous systems are found in most multicellular animals, but vary greatly in complexity. The only multicellular animals that have no nervous system at all are sponges, placozoans, and mesozoans, which have very simple body plans. The nervous systems of the radially symmetric organisms ctenophores (comb jellies) and cnidarians (which include anemones, hydras, corals and jellyfish) consist of a diffuse nerve net. All other animal species, with the exception of a few types of worm, have a nervous system containing a brain, a central cord (or two cords running in parallel), and nerves radiating from the brain and central cord. The size of the nervous system ranges from a few hundred cells in the simplest worms, to around 300 billion cells in African elephants.

The central nervous system functions to send signals from one cell to others, or from one part of the body to others and to receive feedback. Malfunction of the nervous system can occur as a result of genetic defects, physical damage due to trauma or toxicity, infection, or simply senescence. The medical specialty of neurology studies disorders of the nervous system and looks for interventions that can prevent or treat them. In the peripheral nervous system, the most common problem is the failure of nerve conduction, which can be due to different causes including diabetic neuropathy and demyelinating disorders such as multiple sclerosis and amyotrophic lateral sclerosis. Neuroscience is the field of science that focuses on the study of the nervous system.

Details

Your nervous system plays a role in everything you do. The three main parts of your nervous system are your brain, spinal cord and nerves. It helps you move, think and feel. It even regulates the things you do but don’t think about like digestion. It contains the central nervous system and the peripheral nervous system.

Overview:

What is the nervous system?

Your nervous system is your body’s command center. It’s made up of your brain, spinal cord and nerves. Your nervous system works by sending messages, or electrical signals, between your brain and all the other parts of your body. These signals tell you to breathe, move, speak and see, for example. Your nervous system keeps track of what’s going on inside and outside of your body and decides how to respond to any situation you’re in.

Your nervous system regulates complicated processes like thoughts and memory. It also plays an essential role in the things your body does without thinking, like blushing, sweating and blinking.

Function:

What does the nervous system do?

Your nervous system’s main function is to send messages from various parts of your body to your brain, and from your brain back out to your body to tell your body what to do. These messages regulate your:

* Thoughts, memory, learning and feelings.
* Movements (balance and coordination).
* Senses (how your brain interprets what you see, hear, taste, touch and feel).
* Wound healing.
* Sleep.
* Heartbeat and breathing patterns.
* Response to stressful situations, including sweat production.
* Digestion.
* Body processes, such as puberty and aging.

How does the nervous system work?

Your nervous system uses nerve cells called neurons to send signals, or messages, all over your body. These electrical signals travel among your brain, skin, organs, glands and muscles.

The messages help you move your limbs and feel sensations, like pain. Your eyes, ears, tongue, nose and the nerves all over your body take in information about your environment. Then, nerves carry that data to and from your brain.

There are different types of neurons. Each type of neuron has a different job:

* Motor neurons take signals from your brain and spinal cord to your muscles. They help you move. They also assist with breathing, swallowing and speaking.
* Sensory neurons take information from your senses (what you see, touch, taste, etc.) to your brain.
* Interneurons communicate between motor and sensory neurons. These neurons regulate your movement in response to sensory information (like moving away from a hot surface) and play a role in how you learn, think and remember.

Anatomy:

What are the parts of the nervous system?

The nervous system has two main parts:

* Central nervous system (CNS): Your brain and spinal cord make up your CNS. Your brain reads signals from your nerves to regulate how you think, move and feel.
* Peripheral nervous system (PNS): Your PNS is made up of a network of nerves. The nerves branch out from your spinal cord. This system relays information from your brain and spinal cord to your organs, arms, legs, fingers and toes.

There are two parts to your peripheral nervous system:

*The somatic nervous system guides your voluntary movements.
* The autonomic nervous system regulates the activities you do without thinking about them (involuntary movements).

What does the nervous system look like?

Nerve cells (neurons) are the basis of your nervous system. There are 100 billion neurons in your brain. These cells connect throughout your entire body.

Imagine your nervous system as a tree. Your central nervous system is the trunk of the tree that contains your brain and spinal cord. The tree branches are your peripheral nervous system (nerves). The branches extend from the truck (brain and spinal cord) to reach all parts of your body.

Conditions and Disorders:

What are common conditions or disorders that affect the nervous system?

There are many conditions that affect your nervous system. Some of the most common include:

* Alzheimer’s disease.
* Cancer.
* Cerebral palsy.
* Epilepsy.
* Huntington’s disease.
* Infection (meningitis).
* Parkinson’s disease.
* Stroke.
* Traumatic brain injury.

What are common signs or symptoms of nervous system conditions?

Signs and symptoms of nervous system conditions vary by type but may include:

* Movement and coordination changes.
* Memory loss.
* Pain, numbness or a pins and needles feeling.
* Behavioral and mood changes.
* Difficulty with thinking and reasoning.
* Seizures.

Some conditions, like a stroke, are medical emergencies that need treatment quickly. If you notice the following symptoms, contact 911 or your local emergency services number:

* Muscle weakness or paralysis in one side of your body.
* Sudden vision loss.
* Slurred speech.
* Confusion.

What tests check the health of your nervous system?

A healthcare provider may use one of the following tests to check the health of your nervous system:

* Computed tomography (CT) scan.
* Electrocardiogram (ECG or EKG).
* Electroencephalogram (EEG).
* Lumbar puncture (spinal tap).
* Magnetic resonance imaging (MRI) scans.

How are conditions that affect the nervous system treated?

A healthcare provider will review your symptoms to diagnose and treat any conditions that affect your nervous system. Treatment varies for each condition. So, your healthcare provider will take into consideration several factors, like your age and general health, to create your treatment plan. This plan may include:

* Taking medications.
* Having surgery.
* Participating in counseling for mental and emotional support.
* Receiving supportive care (to keep you comfortable).

Additional Information:

Key Facts

* The nervous system is made up of the brain, spinal cord and nerves.
* The nervous system is responsible for intelligence, learning, memory, movement, the senses and basic body functions such as your heartbeat and breathing.
* The basic building blocks of the nervous system are the nerve cells (neurons) which are responsible for carrying messages to and from different parts of the body.
* The brain is in constant communication with all parts of the body, sending instructions and receiving input from the senses.

What is the nervous system?

The nervous system is made up of the brain, spinal cord and nerves.

It controls many aspects of what you think, how you feel and what your body does. It allows you to do things such as walk, speak, swallow, breathe and learn. It also controls how the body reacts in stressful situations. The nervous system interprets and responds to information gathered through the senses.

What is function of the nervous system?

The main function of the nervous system is to be the body's communication network. Its main job is to send and receive messages between you and the outside world, and within your own body.

The nervous system is responsible for:

* intelligence, learning and memory: your thoughts and feelings
* physical movement
* basic body functions such as the beating of your heart, breathing, digestion, sweating and shivering
* the senses: sight, hearing, taste, touch and smell

What are the parts of the nervous system?

The nervous system is made up of:

* the central nervous system (CNS), which consists of the brain and spinal cord
* the peripheral nervous system (PNS), which consists of nerves that connect the CNS to the rest of the body

The brain is made up of different parts. These include the:

* cerebrum
* cerebellum
* thalamus
* hypothalamus
* brainstem

The brain's cerebral cortex is the outermost layer of the brain that gives the brain its wrinkly appearance. The cerebral cortex is divided in half lengthways into two sides or hemispheres, the left hemisphere, and the right hemisphere. Each hemisphere specialises in different functions, but they share information and work together seamlessly.

Each brain hemisphere (parts of the cerebrum) has 4 different sections called lobes. These lobes are the frontal, parietal, temporal and occipital lobes. Each lobe carries out different brain functions.

Learn more about the structure of the central nervous system and how it works.

What are nerve cells?

The basic building blocks of the nervous system are the nerve cells, or neurons. The human brain has around 100 billion neurons. These cells are responsible for carrying messages to and from different parts of the body.

Neurons have a cell body which contain the cell's nucleus as well as special extension called dendrites and axons.

The synapse is the gap between the end of one neuron's axon and the tip of next neuron's dendrites. Messages travel from one neuron to the next across synapses.

A neuron and it's parts.

How does the nervous system work?

The brain is in constant communication with all parts of the body, sending instructions and receiving input from the senses.

Outgoing messages from the brain are sent along motor pathways, which carry messages from the brain to the muscles to tell them to move. The neurons that make up these motor pathways are called motor neurons.

Incoming messages from the body to the brain are sent along sensory pathways. The sensory pathways detect things such as light and sound and carry information about these to the brain. The neurons that make up these sensory pathways are called sensory neurons.

The spinal cord carries motor and sensory signals between the brain and nerves. The spinal cord also contains separate circuits for many reflexes.

One part of the nervous system, called the autonomic nervous system, controls a lot of the body processes that function automatically, for example, breathing, sweating or shivering.

There are 2 parts to the autonomic nervous system:

* the sympathetic nervous system, which controls how you respond in an emergency or when you are under stress (for example, it makes your heart beat faster and causes you to release adrenaline)
* the parasympathetic nervous system, which prepares the body for rest

These parts work together to manage how the body responds to your changing environment and needs. For example, your pupils change size to allow the right amount of light into your eyes to allow effective vision.

What medical conditions are related to the nervous system?

There are thousands of conditions that start in or affect the central nervous system, including:

* degenerative conditions such as Parkinson's disease, Alzheimer's disease and multiple sclerosis
* stroke
* seizure disorders, such as epilepsy
* cancer, such as brain tumours
* infections, such as meningitis
* brain injuries and spinal cord injuries
* spinal cord compression (spinal stenosis)

What are the symptoms of problems with the nervous system?

There are many different symptoms that could suggest a problem with the nervous system. They include:

* headaches
* blurry vision
* fatigue
* leg or arm numbness
* loss of coordination, weakness or loss of muscle strength
* slurred speech
* tremors

Other symptoms that might suggest a problem with the central nervous system include:

* emotional problems
* memory loss
* behavioural changes

There are also many diseases that affect the peripheral nervous system. The peripheral nerves include the nerves outside the brain and spinal cord such as nerves of the face, arms, legs and torso. Read more on diseases of the peripheral nervous system.

Come Quotes - IV

1. If you have an important point to make, don't try to be subtle or clever. Use a pile driver. Hit the point once. Then come back and hit it again. Then hit it a third time - a tremendous whack. - Winston Churchill

2. There will be no end to the troubles of states, or of humanity itself, till philosophers become kings in this world, or till those we now call kings and rulers really and truly become philosophers, and political power and philosophy thus come into the same hands. - Plato

3. With mirth and laughter let old wrinkles come. - William Shakespeare

4. Come Fairies, take me out of this dull world, for I would ride with you upon the wind and dance upon the mountains like a flame! - William Butler Yeats

5. The automobile engine will come, and then I will consider my life's work complete. - Rudolf Diesel

6. It is very important to generate a good attitude, a good heart, as much as possible. From this, happiness in both the short term and the long term for both yourself and others will come. - Dalai Lama

7. Let us endeavor so to live so that when we come to die even the undertaker will be sorry. - Mark Twain

8. Nothing brings me more happiness than trying to help the most vulnerable people in society. It is a goal and an essential part of my life - a kind of destiny. Whoever is in distress can call on me. I will come running wherever they are. - Princess Diana.

Oscillator

Gist

An oscillator is an electronic circuit that converts DC (Direct Current) into a periodic, repeating AC (Alternating Current) signal—such as a sine, square, or triangle wave—without needing an external input signal. These devices are essential for generating, timing, and controlling frequencies in systems like radio, clocks, computers, and sensors.

Oscillators are fundamental in electronics, generating precise frequencies for applications like clocks in computers, carrier waves in radios & Wi-Fi, and timing signals in microcontrollers, enabling everything from timekeeping (watches) to data synchronization (Bluetooth) and medical devices (ultrasound), acting as versatile signal generators for diverse needs. 

Summary

An electronic oscillator is an electronic circuit that produces a periodic, oscillating or alternating current (AC) signal, usually a sine wave, square wave or a triangle wave, powered by a direct current (DC) source. Oscillators are found in many electronic devices, such as radio receivers, television sets, radio and television broadcast transmitters, computers, computer peripherals, cellphones, radar, and many other devices.

Oscillators are often characterized by the frequency of their output signal:

* A low-frequency oscillator (LFO) is an oscillator that generates a frequency below approximately 20 Hz. This term is typically used in the field of audio synthesizers, to distinguish it from an audio frequency oscillator.
* An audio oscillator produces frequencies in the audio range, 20 Hz to 20 kHz.
* A radio frequency (RF) oscillator produces signals above the audio range, more generally in the range of 100 kHz to 100 GHz.

There are two general types of electronic oscillators: the linear or harmonic oscillator, and the nonlinear or relaxation oscillator. The two types are fundamentally different in how oscillation is produced, as well as in the characteristic type of output signal that is generated.

The most-common linear oscillator in use is the crystal oscillator, in which the output frequency is controlled by a piezo-electric resonator consisting of a vibrating quartz crystal. Crystal oscillators are ubiquitous in modern electronics, being the source for the clock signal in computers and digital watches, as well as a source for the signals generated in radio transmitters and receivers. As a crystal oscillator's “native” output waveform is sinusoidal, a signal-conditioning circuit may be used to convert the output to other waveform types, such as the square wave typically utilized in computer clock circuits.

Details

Oscillators are essential components in the world of electronics, playing a crucial role in generating periodic signals. From the simplest applications to complex systems, oscillators provide the timing signals needed for synchronization and control. This article explains what oscillators are and how they work, explores the various types and their performance characteristics, highlights their applications across industries, and reviews recent advancements in this essential technology.

What is an Oscillator?

An oscillator is an electronic circuit that produces a continuous, periodic signal - typically in the form of a sine wave, square wave, or triangle wave - without requiring an input signal. These signals are defined by their frequency and amplitude, which can be precisely controlled to suit specific applications. In essence, an oscillator converts energy from a DC power supply into an AC signal.

Oscillators are found in a wide array of devices, including clocks, radios, and computers. They are considered the heartbeat of electronic systems, serving as timing references that enable circuits to synchronize and function properly.

What is an Oscillator in a CPU?

A CPU oscillator is responsible for generating clock signals that regulate the timing and speed of the processor. These clock signals synchronize various CPU components, allowing for the coordinated execution of instructions.

Typically, a crystal oscillator is used, which relies on the mechanical resonance of a vibrating quartz crystal to produce a stable frequency. This precise timing is critical to a CPU’s performance and efficiency, as it directly affects the instruction execution rate.

How Do Oscillators Work?

Oscillators generate a continuous, periodic signal - such as a sine wave or square wave - without requiring an input signal of the same frequency. They achieve this through the combined principles of feedback and resonance.

Basic Components

• Amplifier: Boosts the signal.

• Feedback Network: Determines the frequency of oscillation.

• Energy Source: Supplies power to sustain the oscillation.

The system continuously feeds part of its output back to the input, allowing the signal to regenerate itself. The frequency of oscillation depends on the configuration of components such as resistors, capacitors, and inductors within the feedback loop.

Purpose of an Oscillator

The primary purpose of an oscillator is to generate consistent clock signals that control the timing and synchronization of electronic systems, especially CPUs. These signals are essential for ensuring the coordinated execution of instructions, which in turn impacts overall system performance.

Types of Oscillators:

What is an oscillator? And what are the types of oscillators?

Oscillators, essential components in electronic circuits, can be categorized based on the type of waveform they produce and their method of operation. These components are generally divided into two main categories.

Relaxation vs Linear Oscillators

Relaxation Oscillators: Produce non-sinusoidal waveforms such as sawtooth or square waves.

Linear Oscillators: Generate sinusoidal waveforms.

Specific Types

Crystal Oscillators: Crystal oscillators are linear oscillators, and use quartz crystals to generate precise frequencies. Known for their stability and accuracy, they are ideal for communication devices and clocks.

RC Oscillators: RC oscillators can be both relaxation oscillators and linear oscillators. These oscillators utilize resistors and capacitors to generate sine or square waves. Often used in audio applications due to their simplicity and cost-effectiveness.

LC Oscillators: LC oscillators are considered linear oscillators and use inductors (L) and capacitors (C) to produce oscillations. Typically employed in radio frequency (RF) applications due to their high-frequency capability.

Phase-Locked Loop (PLL) Oscillators: PLL oscillators are primarily considered linear oscillators and are used for frequency synthesis and modulation. Essential in telecommunications for signal processing and frequency control.

Emerging Oscillator Technologies

Recent advancements in oscillator technology focus on performance improvement, miniaturization, and integration with other electronic components.

MEMS Oscillators: Microelectromechanical systems offer smaller form factors, highly stable reference frequencies, and low power consumption - ideal for portable devices.

Programmable Oscillators: Allow for customized frequency outputs, reducing component count and streamlining the design process.

Devices That Use Oscillators

Many electronic devices rely on oscillators for essential functions like timing, signal generation, and frequency control. Their ability to produce consistent waveforms makes them indispensable in both consumer electronics and industrial systems.

Examples:

Quartz Watches: Use crystal oscillators to generate highly accurate timekeeping signals, ensuring the watch maintains precise seconds, minutes, and hours.

Radios: Rely on oscillators to generate carrier frequencies and to tune into specific broadcast channels for both AM and FM signals.

Computers: Employ oscillators in their system clocks to synchronize processor operations, manage data transfer, and maintain stable performance.

Cellphones: Utilize oscillators for network synchronization, frequency hopping in wireless communication, and internal clocking for processors and sensors.

Radar Systems: Depend on high-frequency oscillators to generate the radio waves that detect and measure the speed, range, and position of objects.

Metal Detectors: Use oscillators to produce electromagnetic fields that interact with metallic objects, enabling detection through changes in oscillation frequency or amplitude.

Performance Characteristics of Oscillators

Oscillators are evaluated based on several performance metrics that directly influence their suitability for specific applications. The three most critical are frequency stability, phase noise, and waveform shape.

Frequency Stability

Frequency stability describes an oscillator’s ability to maintain its output frequency under varying conditions over time.

• Short-Term Stability: Covers rapid variations over seconds or minutes, often caused by noise or small environmental changes.
• Long-Term Stability: Considers changes over hours, days, or years, typically influenced by component aging and gradual environmental shifts.
• Environmental Factors: Temperature fluctuations, supply voltage changes, and mechanical vibrations can affect stability.
• Crystal Oscillators: These oscillators excel in this area because the resonant frequency of a quartz crystal is highly resistant to such disturbances, making them ideal for precision timing applications like GPS, telecommunications, and laboratory measurement systems.

Phase Noise

Phase noise measures short-term, rapid fluctuations in the oscillator's phase, which manifest as small, random deviations from the ideal frequency.

• It is usually represented as a power density (dBc/Hz) at a given frequency offset from the carrier signal.
• Low Phase Noise: Essential in high-performance systems, such as satellite communications, radar, and high-speed data links, where timing jitter can degrade system performance or cause data errors.
• High Phase Noise: Can lead to signal distortion, reduced sensitivity in receivers, and degraded performance in frequency synthesizers.

Waveform Shape

The oscillator’s output waveform determines how well it interfaces with downstream circuitry.

• Sine Waves: Preferred in RF applications because they have minimal harmonic content, reducing the need for filtering.
• Square Waves: Common in digital clocking applications, as their fast transitions make it easy for digital circuits to detect logic states.
• Sawtooth or Triangular Waveforms: May be required in specialized systems, such as sweep generators in analog oscilloscopes.
• Poor Waveform Shape: Can cause signal integrity issues, increased electromagnetic interference (EMI), or inaccurate timing in digital circuits.

Are Oscillators Active Components?

Oscillators are classified as active components. They amplify electrical signals and generate power, distinguishing them from passive components like resistors and capacitors. While oscillators incorporate passive elements in their circuits, their role in signal generation qualifies them as active devices.

Industries That Use Oscillators

Oscillators' ability to generate stable, precise signals makes them indispensable for timing, synchronization, and frequency control across a wide range of sectors. The specific oscillator type used often depends on the application's demands - whether it’s ultra-high precision, rugged durability, or low power consumption.

Telecommunications: Oscillators generate carrier signals for data transmission. Their stability and accuracy ensure signal integrity over long distances. Crystal and PLL oscillators are widely used here.

Consumer Electronics: Devices like smartphones and TVs rely on oscillators to generate clock signals for microcontrollers. Their precision directly impacts device performance.

Automotive: Used in engine control units, infotainment systems, and sensor applications (e.g., ABS), oscillators regulate timing for ignition and fuel injection.

Medical Devices: Essential in pacemakers and diagnostic tools, where reliability and precision are critical. Crystal oscillators are often chosen for their long-term stability.

Additional Information

An oscillator is an electronic device that produces repetitive oscillating signals in the form of a sine wave, a square wave, or a triangle wave. Basically, this circuit converts DC (Direct Current) into an AC (Alternating Current) signal at a specific frequency.

An oscillator is essential in various electronic devices. It is used in Bluetooth modules for frequency generation and maintaining a stable connection. In relays, oscillators help with debouncing and pulse generation.

In sensors, they are used for generating carrier signals and stabilizing readings. Integrated circuits (ICs) use oscillators for clock generation and data synchronization. In connectors, oscillators assist with signal integrity and timing matching.

Microcontrollers rely on oscillators for peripheral operation and system clock management. Additionally, oscillators are used in LCD and LED displays for backlight control and data driving.

A basic oscillator circuit typically includes components like an amplifier stage, a feedback network, frequency-determining components, and a power supply.

1. Amplifier

An amplifier in an oscillator can be a transistor, an operational amplifier, or any active device that boosts small signals to maintain continuous oscillations. For that amplifier must provide a gain greater than or equal to one to sustain oscillations.

2. Feedback Network

In this network, it feeds a portion of the output back to the input with the correct phase. This network includes components like capacitive, inductive, or resistive networks like LC circuits or RC circuits.

3. Frequency Determining Components

This component sets the frequency at which the oscillator operates, which includes RC networks, LC networks, and crystal resonators.

4. Power Supply

It provides the necessary voltage and current for operation.

Types of Oscillators

Based on the design, frequency range, and application, oscillators are classified into various types. They are as follows:

1. LC Oscillator

An LC oscillator uses an inductor and a capacitor to determine the frequency of oscillation. It is a high-frequency operation oscillator that gives a smooth sine wave output, and its frequency depends on the values of L and C.

LC oscillator consists of different types like Hartley Oscillator (uses a tapped inductor), Colpitts Oscillator (uses a capacitive voltage divider), and Clapp Oscillator ( it is a variation of the Colpitts with an additional capacitor for better frequency stability.

It is mostly used in radio transmitters, RF communication circuits, and signal generators.

2. RC Oscillator

RC oscillator uses resistors and capacitors to produce oscillations. It produces stable low-frequency sine waves and is ideal for audio frequency generation, which is cost cost-effective design.

This includes the Wien bridge oscillator (for audio applications) and the Phase shift oscillator (produces sine waves using multiple RC stages). RC oscillators are used in audio signal generation, function generation, and low-frequency timing circuits.

3. Crystal Oscillator

To create a very stable frequency oscillation, a crystal oscillator uses the mechanical resonance of a quartz crystal. It generates a pure sine wave output with extremely high frequency stability. They have very low frequency drift due to temperature changes.

These are of the types Pierce oscillator and AT-cut crystal oscillator (widely used in microcontrollers). It is used in microcontrollers and microprocessors, Bluetooth and Wi-Fi modules, digital watches and clocks, and GPS systems.

Working Principle of Oscillator

The working principle of an oscillator is based on the concept of positive feedback and energy conversion from a direct current (DC) source into an alternating current (AC) signal at a specific, stable frequency.

The working of the oscillator is explained in step below:

1. Initial

Due to thermal activity, every electronic circuit has inherent noise, and this tiny noise signal acts as the seed for oscillation.

2. Amplification

At the amplification stage, the amplifier boosts this initial noise signal, and amplification must be sufficient to compensate for any losses in the feedback network.

3. Positive Feedback Loop

A portion of the output is fed back to the input in phase, which reinforces the input signal rather than cancelling it.

4. Frequency Selection

The frequency-determining network (RC, LC, or crystal) controls the frequency of oscillation.

5. Steady State Oscillation

As the feedback sustains the oscillations, the amplitude stabilizes. Non-linear effects or amplitude limiting mechanisms prevent the output from growing indefinitely, ensuring stable oscillations.

Applications of Oscillators

1. Communication Systems

* Oscillators generate high-frequency carrier signals for AM, FM, and digital modulation.
* Used to produce a range of frequencies from a single oscillator source.
* LC and crystal oscillators are used for tuning and frequency control.

Example: Radio Transmitters, Mobile phones, Wi-Fi modules, Bluetooth devices

2. Microcontrollers and Microprocessors

* Oscillators provide the clock signals needed for the timing and operation of microcontrollers and microprocessors.
* Crystal oscillators generate precise timing signals that ensure all processes operate in harmony and within correct timing constraints.

Example: Arduino boards, PIC microcontrollers, Embedded systems.

3. Sensors

* Oscillators are used in sensor circuits for data acquisition and signal processing.

Example: Proximity sensors, Ultrasonic sensors, and Environmental monitoring systems.

4. Display Technologies

Oscillators help maintain the refresh rate of digital displays. Used in the PWM (Pulse Width Modulation) circuits for adjusting display brightness.

Example: LED displays, LCD displays, OLED panels, Digital signage.

Frequently Asked Questions:

1. Is an Oscillator AC or DC?

An oscillator converts DC power into an AC signal by generating a continuous, oscillating waveform without an external input.

2. Is the Oscillator Negative or Positive?

An oscillator uses positive feedback to sustain continuous oscillations.

3. Which Oscillator is Better?

The crystal oscillator is considered better for applications requiring high-frequency stability and accuracy.

4. How Does an Oscillator Differ from an Amplifier?

An oscillator generates its own periodic signal without an external input, while an amplifier boosts the strength of an existing input signal.

5. What is the Difference Between RC and LC Oscillators?

An RC oscillator uses resistors and capacitors for low-frequency generation, while an LC oscillator uses inductors and capacitors for high-frequency generation.

6. What Causes an Oscillator to Fail?

An oscillator can fail due to component aging, temperature variations, power supply issues, or physical damage to the resonator elements, like crystals or inductors.

7. Can an Oscillator be Used as a Signal Generator?

Yes, an oscillator can be used as a signal generator to produce continuous waveforms like sine, square, or triangular signals.

Anion

Gist

An anion is an atom or molecule that carries a net negative electrical charge because it has gained one or more electrons, resulting in more electrons than protons. Formed typically by non-metals, anions are attracted to the positive electrode (anode) during electrolysis and readily combine with positive ions (cations) to form ionic compounds, like chloride or sulfate.

Anions are negatively-charged ions (meaning they have more electrons than protons due to having gained one or more electrons). Cations are also called positive ions, and anions are also called negative ions.

Summary

Anions are atoms or groups of atoms that have a negative electric charge. An anion has more electrons in its atomic orbitals than it has protons in its atomic nucleus. The opposite of an anion is a cation, which has a positive charge.

The name "anion" comes from the words anode and ion. In an electrochemical cell, anions are attracted to the positively charged anode.

Anions can be monatomic, made of only one atom, or polyatomic, made of multiple atoms. Anions can exist on their own only as gases: to make a solid, ionic liquid, or solution the total electrical charge must be zero, meaning a mix of anions and cations.

Properties

In many crystals the anions are bigger; the little cations fit into the spaces between them.

All anions are Brønsted bases: they can make a chemical bond with a proton, H+, to form a conjugate acid.

Examples

Oxide is the most common anion on Earth. It is made from an oxygen atom with two extra electrons. The formula for oxide is written O2−. The oxide ion reacts with water, so it cannot be dissolved to make a solution.

Chloride is a monatomic anion made from an atom of chlorine with an extra electron. The chemical formula is written Cl−. Chloride is the most common anion in seawater.

Sulfate is the second most common anion in seawater after chloride. It is made of a sulfur atom, four oxygen atoms, and two extra electrons. Sulfate is a special type of anion called an oxyanion, which are made of a central element (like sulfur) surrounded by oxygen atoms.

Hydroxide is a polyatomic anion made of one oxygen atom, one hydrogen atom, and one extra electron. It has the formula OH−. Hydroxide is the conjugate base of water, so it is the strongest base that can be mixed with water. Other strong bases, including the oxide anion, react with water to make hydroxide.  

Details

Anions are negatively charged ions formed when an atom or group of atoms gains one or more valence electrons. The term "anion" comes from "anode ions," reflecting their movement toward the positive terminal in an electrolytic solution. Anions, along with positively charged cations, form ionic bonds that are fundamental to many chemical compounds, such as table salt (sodium chloride). Common examples of anions include fluoride, chloride, and sulfate, each named based on their elemental origin or structural characteristics, following specific nomenclature rules established by the International Union of Pure and Applied Chemistry (IUPAC).

The formation of anions is closely tied to the electronic structure of atoms, which consists of a dense nucleus surrounded by electron shells containing orbitals that dictate the arrangement and behavior of electrons. Elements tend to achieve stability by completing their outer electron shell, often following the octet rule, which promotes the formation of anions in various chemical reactions. Understanding anions is essential for grasping broader concepts related to atomic structure, chemical bonding, and the periodic table's organization.

The basic structure of anions is defined, and the development of the modern theory of atomic structure is elaborated. Electronic structure is fundamental to all chemical behaviors and is responsible for the relationships seen in the periodic table.

The Nature of Anions

An anion is any atom or group of atoms that bears a net negative charge due to the presence of one or more extra valence electrons. The term is a contraction of "anode ions," which is a reference to the fact that when a direct electric current is applied to an electrolytic solution, negatively charged ions are attracted to the anode, or positive terminal, of the source of the current. By the same token, cations, from "cathode ions," have a net positive charge and are attracted to the cathode, or negative terminal, of the current source. Anions and cations often combine to form compounds held together with ionic bonds; one common example is sodium chloride (NaCl), better known as table salt, which is created when the sodium cation, Na+, bonds to the chloride anion, Cl−.

The formation of any ion is the result of an atom or molecule gaining or losing one or more valence electrons. This is most apparent in monatomic (single-atom) ions, in which the electrical charge is equal to the oxidation state. For example, the halogens—fluorine, chlorine, bromine, iodine, and astatine—are all highly electronegative, meaning that they readily accept an extra valence electron so that their outer electron shell is completely full and therefore stable. The resulting anions are called fluoride, chloride, bromide, iodide, and astatinide, respectively, and they have an electrical charge of 1− because they gained one electron and thus one unit of negative charge. Similarly, the chalcogens oxygen (O) and sulfur (S) readily accept two extra electrons to form the oxide ion, O2−, and the sulfide ion, S2−.

Compound ions in which a central atom is bonded to a number of oxygen atoms are extremely common. These oxoanions tend to form very stable compounds and are the basic materials of many minerals.

The Electronics of Anion Formation

According to the modern theory of atomic structure, each atom contains a very small, extremely dense nucleus that holds at least 99.98 percent of the atom’s mass and all of its positive electrical charge. The nucleus is surrounded by a diffuse and comparatively very large cloud of electrons containing all of the atom’s negative electrical charge. These electrons are allowed to possess only very specific energies. This restricts their movement around the nucleus to specific regions called "electron shells." Within each shell are well-defined regions called "orbitals." The strict geometric arrangement of the orbitals regulates the formation of chemical bonds between atoms.

Each shell and orbital is subject to a number of restrictions that dictate how many electrons it can hold. There are four different types of electron orbitals, designated s, p, d, and f, each of which can contain a specific number of electrons: s orbitals can hold a maximum of two electrons; p orbitals, a maximum of six; d orbitals, a maximum of ten; and f orbitals, a maximum of fourteen. One or more of these orbitals make up an electron shell. The various electron shells are indicated by an integer value known as the "principal quantum number," starting with 1 for the innermost shell, typically referred to as the "n = 1 shell." The standard notation to describe an electron orbital is the principal quantum number, followed by the type of orbital, followed by a superscript number indicating how many electrons it holds. For example, helium has only one s orbital, which is completely full, so its electron configuration is represented as 1s2. The first p orbital appears in the n = 2 shell, the first d orbital in the n = 3 shell, and the first f orbital in the n = 4 shell. Due to variances in energy levels, electrons usually fill atomic orbitals in the order 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s . . . rather than in strict numerical order.

The outermost electron shell is the valence shell, and in all elements, except the noble gases (helium, neon, argon, krypton, xenon, and radon), the valence shell is incompletely occupied. Because of this, the noble gases are often called "inert gases," reflecting the fact that they are far less chemically reactive than elements whose valence shells are not filled. All noble gases except for helium have eight electrons in their valence shell, as a shell with eight electrons approximates a stable closed-shell configuration of s2p6. This is the basis of the octet rule, which states that atoms of lower atomic numbers tend to achieve the greatest stability when they have eight electrons in their valence shells. The closer an element is to having eight valence electrons, the more likely it is to undergo ionization or a chemical reaction in order to achieve a stable configuration, either by gaining enough electrons to complete the octet or by losing all valence electrons so that the next-highest completed shell becomes the outermost shell. Elements with similar electron distributions in their valence shells typically exhibit similar chemical behaviors, which is the basis on which the periodictable of the elements is arranged.

Naming the Anions

The rules for naming various chemical species are established and standardized by the International Union of Pure and Applied Chemistry (IUPAC). Monatomic anions and polyatomic anions composed of a single element are named by adding the suffix -ide to the name of the element, either instead of or in addition to the existing suffix. Thus a sulfur anion becomes sulfide, a xenon anion becomes xenonide, a potassium anion becomes potasside, and so on. In some cases, the suffix is added to the element’s Latin name instead of its common name; for example, an anion of silver, which has the Latin name argentum, is called argentide.

Oxoanions are generally named for the central atom of the anion and the number of oxygen atoms that surround it, with the charge number given in parentheses at the end. An oxoanion consisting of a sulfur atom surrounded by three oxygen atoms has the formal name trioxidosulfate, while one with a sulfur atom and four oxygen atoms is called tetraoxidosulfate. The common (nonsystematic) names of these two oxoanions are sulfite and sulfate, respectively, following the convention that the oxoanion with fewer oxygen atoms takes the suffix -ite and the one with more oxygen atoms takes the suffix -ate. If one element is capable of forming more than two different oxoanions, as is the case with chlorine, the prefixes hypo- and per- are used as well, so that the common name of ClO− is hypochlorite, ClO2− is chlorite, ClO3− is chlorate, and ClO4− is perchlorate.

Principal Terms

cation: any chemical species bearing a net positive electrical charge, which causes it to be drawn toward the negative pole, or cathode, of an electrochemical cell.
ionic bond: a type of chemical bond formed by mutual attraction between two ions of opposite charges.
ionization: the process by which an atom or molecule loses or gains one or more electrons to acquire a net positive or negative electrical charge.
oxoanion: an ion consisting of one or more central atoms bonded to a number of oxygen atoms and bearing a net negative electrical charge.
valence electron: an electron that occupies the outermost or valence shell of an atom and participates in chemical processes such as bond formation and ionization.

Additional Information

An anion is an atom that has a negative charge. So, given that anion definition, the answer to the question "Is an anion negative?" is yes. Anions are a type of atom, the smallest particle of an element that still retains the element's properties. Atoms are made of three types of subatomic particles: neutrons, protons, and electrons. Neutrons are neutrally charged subatomic particles and, along with protons, they make up the nucleus. Protons have a positive charge. Electrons are very small subatomic particles that orbit the nucleus in levels called shells. Electrons have a negative charge.

Anions are created when an atom gains one or more electrons. The number of electrons gained by an atom is determined by how many are needed to fill their outer shell. For example, fluorine has seven electrons in its outer shell, but a full outer shell contains eight electrons. Thus, fluorine tends to gain one electron to fill its outer shell and generally has a charge of -1. Oxygen, on the other hand, has an outer shell of six electrons. This means it requires two electrons to complete its outer shell and tends to carry a charge of -2.

Uses for Anions

Fluoride ion is widely used in water supplies to help prevent tooth decay. Chloride is an important component in ion balance in blood. Iodide ion is needed by the thyroid gland to make the hormone thyroxine.

Summary

* Anions are formed by the addition of one or more electrons to the outer shell of an atom.
* Group 17 elements add one electron to the outer shell, group 16 elements add two electrons, and group 15 elements add three electrons.
* Anions are named by dropping the ending of the element's name and adding -ide.

Come Quotes - III

1. Put two ships in the open sea, without wind or tide, and, at last, they will come together. Throw two planets into space, and they will fall one on the other. Place two enemies in the midst of a crowd, and they will inevitably meet; it is a fatality, a question of time; that is all. - Jules Verne

2. On two occasions I have been asked, 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?' I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question. - Charles Babbage

3. I've always believed that if you put in the work, the results will come. - Michael Jordan

4. From the deepest desires often come the deadliest hate. - Socrates

5. The most important thing about Spaceship Earth - an instruction book didn't come with it. - R. Buckminster Fuller

6. Hope smiles from the threshold of the year to come, whispering, 'It will be happier.' - Alfred Lord Tennyson

7. Tears come from the heart and not from the brain. - Leonardo da Vinci

8. What goes up must come down. - Isaac Newton.