Haley+Col.

What is a Neuron?
A neuron is a nerve cell that is the basic building block of the nervous system. Neurons are specialized to transmit information throughout the body and are responsible for communicating information in both chemical and electrical forms.



How do Neurons Fire?
The signal output of a neuron can either cause excitation or inhibition in the neuron it is connected to. When a neuron sends an excitatory signal to another neuron, this signal will be added to all of the other inputs of that neuron. If it exceeds a given threshold then it will cause the target neuron to fire an action potential, if it is below the threshold then no action potential occurs.



The action potential is an electric pulse that travels down the axon from the dendrites to the synapses where it the causes the release of neurotransmitters. The synapses are extremely close to the dendrites of the target neuron which allows the neurotransmitters to diffuse across the small space and fit into the receptors that are located on the target neuron. This causes some action to take place in that neuron that will either decrease or increase the membrane potential of the neuron. If it increases the membrane potential then it is exciting the neuron, and if it decreases the membrane potential it is inhibiting the neuron. If it causes the membrane potential to pass the firing threshold then it will activate an action potential in the target neuron and send it down its axon.

Neurons at their resting potential are around -70mV. This means that the voltage difference between the fluid on the inside of the cell relative to the fluid on the outside of the cell is negative. This is maintained by ions like Na+, K+, Cl-, and protein anions. The cell membrane prevents charged particles like these to go freely diffusing into and out of the cell. There are two basics ways that they can get in or out. The first is with passive transport when the cell has a protein in the cell membrane that it can open and close. When it opens, then the ions can flow down their gradient from the more concentrated area to the less concentrated area. The other way to get ions in or out of cells is to by active transport which is when the cell uses some of its own energy to actively pump the chemicals //against// their gradient. The neuron has a pump that actively pumps three Na+ ions out and takes in two K+ ions. This means that a net positive charge flows out of the neuron. This is what gives the cell its negative potential. Ions are also what are for the initiation, and transmission of action potentials. When the neurotransmitters from other firing neurons come in contact with their corresponding receptors on the dendrites of the target neuron it causes those receptors to open or close some of the passive ion transports. This allows the ions to flow into the cell and temporarily change the membrane voltage. If the change is big enough then it will cause an action potential to be fired.


 * 1) Na+ channels open allowing a flood of sodium ions into the cell causing the membrane potential to become positive.
 * 2) K+ channels open allowing the potassium ions to flow out of the cell.
 * 3) Next the Na+ channels close stopping inflow of positive charge. Since the K+ channels are still open it allows the outflow of positive charge so that the membrane potential plunges.
 * 4) Neuron begins reaching its resting potential so the K+ channels close.
 * 5) The sodium/potassium pump does its work and starts transporting sodium out of the cell, and potassium into the cell so that it is ready for the next action potential.

The action potential travels down the length of the axon as a voltage spike. As a section of the axon goes through this process it increases the membrane potential of the neighboring section and causes it to spike. This is like a mini chain reaction that proceeds down the length of the axon until it reaches the synapse.

media type="youtube" key="ZjTbz_RyENM" width="560" height="315" align="center"

A team of MIT neuroscientists have developed a way to monitor how brain cells coordinate with each other to control specific behaviors, such as initiating movement or detecting an odor. This quick video shows their work.

For more information, check out these sites!
http://www.examiner.com/article/so-you-wanna-know-how-a-neuron-fires-the-action-potential-or-nerve-impulse http://apps.childrenshospital.org/clinical/animation/neuron/ http://www.nvo.com/scullari/unitii/ http://www.mind.ilstu.edu/curriculum/neurons_intro/neurons_intro.php

Sources.
http://psychology.about.com/od/aindex/g/actionpot.htm http://faculty.washington.edu/chudler/ap.html http://neuroblog.stanford.edu/?p=4541 http://library.thinkquest.org/28807/data/nervous3.htm

What is Evolution?
Evolution in general is described as any process of formation of growth(development). // Biological evolution // is described as a change in the gene pool of a population from generation to generation by mutation, natural selection, and genetic drift. Continuous changes over many generations can result in the development of entirely new species. Organisms grow to adapt to their environment and this shows as they evolve. Scientists believe that there has been life on earth for around 3.5 billion years. They believe that it all started with marine invertebrates then onto fish, amphibians, reptiles, birds, and finally mammals. They know this because of fossils that are left behind in sedimentary rocks. Fossils have played a huge role in helping scientist uncover the earth's history!

Charles Darwin.
Contrary to popular belief, the idea of evolution did not start with Charles Darwin, who is now considered the father of evolution. People started exploring the idea of evolution when religion could no longer explain questions posed about how the earth as we know it came into existence. Charles Darwin was born in 1809. Darwin's father was a physician and evolutionist. Darwin had originally planned to become a clergyman, but became interested in evolution while studying natural history in Cambridge.

Natural Selection.
Charles Darwin is most famous his ideas on natural selection. He believed that all species evolved over time from common ancestors. This process involved favorable traits becoming more common in successive generations of living things while unfavorable traits becoming less common. Essentially this means survival of the fittest. In 1859, Darwin released his theories on evolution in a book titled //On the Origins of Species.// Darwin had been hiding these findings since 1844 but was worries it wouldn't be accepted, but by 1859 he had enough evidence to confidently release the book.

The March of Progress.
The //March of Progress// is a popular image often used when discussing evolution. This original version, called //The Road to Homo Sapiens//, shows a series of fifteen males from an ape(left) to a human(right). The original image is usually shortened into six pictures for simplicity. The progression from left to right in reality took millions of years, but the image helps break down how we have evolved from dryopithecus to homo sapiens, or modern day humans.



The following video helps explain the //March of Progression//. media type="youtube" key="xpo8SdY1JSw" width="560" height="315" align="center"

For more information, check out these sites!
[] [] [] []

Sources.
Images: [|Charles Darwin Image] [|Road to Homo Sapiens]

Webpages: [|Charles Darwin Facts] [|Darwin] [|Theories on Evolution] [|Early Evolution]

** What is it? **
Noonan syndrome is one of many genetic disorders found in humans. Noonan syndrome prev ents normal development in different parts in the body. Effects of the disorder include unusual facial characteristics, short stature, heart defects, and other physical problems or developmental delays.

** Causes. **
Noonan syndrome is caused by the mutation of certain genes. There are currently eight different genes that are known to cause Noonan syndrome. This mutation can be inherited from a parent or can develop in children who don't have a genetic predisposition for the disease. The mutation of the genes causes you to produce proteins that are always active. These genes play a role in the formation of several tissues through the body and the constant activity of the proteins effects the normal process of cell growth and division. Children who have one parent with Noonan syndrome have a 50% chance of developing this genetic disorder.



** Symptoms. **
About 80% of people with Noonan syndrome have some form of heart disease including valve disorders, hypertrophic cardiomyopathy and various structural defects. **Growth** Children's birth weight tends to be normal but they often have trouble with feeding which causes poor weight gain. This leads to delayed growth spurts and delayed bone maturity. By adulthood, about one third of people with Noonan syndrome are "regular" height. Most people with Noonan syndrom are not affected intellectually but there is an increased risk of learning disabilities. Most people with Noonan syndrome complete high school, college and go onto have careers. **Eye Conditions** People with Noonan syndrome commonly have abnormalities in their eyes and eye lids including different shapes and sizes of the eyes. The iris is usually pale blue or green. Problems with eye movement and nerves are quite common.
 * Facial Features(Visual Symptoms)**
 * Early infancy:** Babies younger than a month old can have a wide-set face, down-slanting eyes, low-set ears, short necks and a low hair line on the back of the neck.
 * Infancy:** Prominent eyes with downward slant and thick eye lids.
 * Childhood:** The child's face can seem expressionless.
 * Adolescence:** Typically wide at the forehead and thinning out at the chin. Their facial features become sharer and less prominent. The neck lengthens and appears webbed.
 * Adulthood:** Lines from the edge of the nose to the corner of the mouth becomes prominent and skin looks wrinkled.
 * Heart Disease**
 * Learning Disabilities**



media type="youtube" key="Ctp6Msz3Kgc" width="560" height="315" align="center"

This video was made my The Traveling Awareness Bears, a nonprofit organization started by a 7 year old boy who wants to raise awareness about Noonan syndrome.

Prevention.
There is no definite way to prevent Noonan syndrome. If you have a history of Noonan syndrome in your family, it is suggested that you consider genetic counseling before having children. There is no way to completely prevent a child from being born with Noonan syndrome, but early detection can help lessen the chances of complications like heart disease.

For more information check out these sites!
//Parents Guide to Noonan Syndrome(all you need to know)// [] //Support Group// [] //Before Going to the Doctors, read this!// [] //Gene Testing// []

Sources.
Images: http://openi.nlm.nih.gov/imgs/512/40/3232501/3232501_IPC-3-19-g005.png http://manbir-online.com/grafics/noonan-syndrome2.jpg

Webpages: [] [] [] []