Self Evaluation

Self Evalutation Unit 4

1. What were the aspects of the assignments I've submitted that I am most proud of?

I'm most proud of my online pregnancy lab. I really like the pictures and stages I represented.

2. What two aspects of my submitted assignments do I believe could have used some improvement?

An improvement I would make is to research the species I used for my lab project to determine the interaction type and how each other do or dont benefit from one another.

3. What do I believe my overall grade should be for this unit?

I believe overall it was a succesful unit that I enjoyed. I really think I portrayed most of the important details from the chapters.

4. How could I perform better in the next unit?

If there were another unit I would say that I would work harder to make my reviews longer.

5.At what moment during this unit did you feel most engaged with the course?
I really felt engaged with the online lab concerning pregnancy. I found it very interesting and loved reading about the stages of development.

6.At what moment unit did you feel most distanced from the course?
The second online lab about population didn't really grab my interest and would have to be my least favorite part about this unit.

7.What action that anyone (teacher or student) took during this unit that find most affirming and helpful?
The powerpoint presentation turned out to be very useful for this unit, expecially for the Lab project.

8.What action that anyone (teacher or student) took during this unit did you find most puzzling or confusing?

I did not really find anyone's actions puzzling but I did find the lab project a bit confusing. When we were to decided the interaction type with the species. I was not sure if I was supposed to simply give my opinion or if I were to research the species to determine if they benefit me or visa versa.

9.What about this unit surprised you the most? (This could be something about your own reactions to the course, something that someone did, or anything else that occurs to you.)

What suprised me the most about this unit would have to be how easy the information was to learn and still very informative.

Unit 4 Online Lab Human Population

Human Population Lab

1. What was your high fertility rate country and what was its fertility rate?

My high fertility rate country Haiti with a rate of 6.20 Children.

2. What was your low fertility rate country and what was its fertility rate?
My low fertility rate country is Australia at 1.80 children.

3. The initial demographic "shape" of your high fertility rate country should have been a pyramid, with high population in young age groups. Explain why high fertility rate results in a high percentage of young people in the population. How does this affect future population growth?
When there is a high fertility rate it means that more people are able to have kids than not, as this large age group starts having children the result is a higher percentage of young age groups. When there is a low fertility rate like in this country and people start having children and there children grow up to have children of there own there is a dramatic increase in poplulation. This is because the majority of the poplulation is fertal and reproducing.
(below shows the World vs. Haiti)

4. Your low fertility rate country might have had a more oval-shaped curve with high population in middle age groups. This is especially exaggerated if the fertility rate is below 2.00. Explain why low fertility rate leads to lots of middle-aged people. When fertility rates are low there are less people that are young since they are the onces who are able to reproduce resulting in an older popluation. (Below is World vs. Australia)



5. Write ten adjectives or descriptive phrases for what you might expect life, people's attitudes, conditions on the streets, etc. will be like in each of those situations. Imagine a situation with lots of middle-aged and older people in the population and write ten quick "brain-storm" descriptors for you think it would be like (Prescott, Arizona?). Then do the same for a situation with lots of children in the population.

A town with high poplulation of young people might have:
lots of loud cars and trucks
Increase in car accidents
Speeding
Shoplifting
Parties
more schools
more fast food places
night clubs
bar/bar fights
more activities like bowling, skating, movies
lots of pregnancies

Town with older poplulation:
Increase in illness
more retirement homes
Quite
less crime
well maintained neighborhoods
slower/calmer atmosphere
decrease in population
low demand of resources
more medical facilities and drug stores
lack of activities
deserted streets at night

Work cited

http://simon.cs.vt.edu/geosim/IntlPop/IntlPop.html

Unit 4 Lab Project

Unit 4 Lab Project

In this lab I will show some of the species that I have come across in my life. I will present the common name they are referred to and the scientific name. Along with the names I will give the type of interaction with the different species and if they are domesticated.





Scientific name (Common name)/Domesticated?How?





Crotalus atrox (diamond back rattle snake)/no


The type of interaction would have to be mutualistic since we benefit from them eating unwanted pests and they benefit from us since our waste produce attract their prey.





Geococcyx californianus (roadrunner)/no


The interaction would be commensal since we benefit since they eat unwanted pests but they dont really benefit from us.



Callipepla gambelii (quail)/yes,food


Quail are domesticated since some people hunt and eat them. The interaction would also be parasitic since we benefit from them by what they eat and as food but they are harmed when people eat hunt them.



Cyprinus carpio( Koi fish)/yes,pets,food


Interaction would have also be predator/prey since both can benefit from each other but also one is harmed in other situations. As pets they koi benefit and as food we benefit.

Demodex folliculorum (Eyelash bugs)/no

The interaction is mutualistic both benefit they have a place to live and eat and we benefit since they protect us from harmful bacteria and fungi.

Phodopus Sungorus (dwarf russian hamster) /yes,pets

The interaction is symbiotic we provide them with food and home and they provide us with a pet to care about.

Felis silvestris (Cat)/yes,pet

This relationship would also be symbiotic like hamsters, they become apart of our lives and we give them food and a home.

Herbaceous (Bananas)/yes,food

Relationship would have to be commensal since we benefit from the nutrients they provide us but they dont benefit from us but are not harmed either.

Pinnipeds (Seals),sometimes

I would have to say seals are not really domesticated since they dont become pets but in a way when kept in zoo's they are unable to return to the wild and become some what domesticated. The relationship would have to be mutualistic since we benefit from them in zoo's by being abe to witness a wild animal and when they are in zoo's they are taken care of provided for.

Cimex lectularius (bed bugs)/no

Interaction is parasitic since they benefit from bitting us since they live off of blood and we are harmed by the bitting.

Tabanus atratus(black horse fly)/no

Relationship is commesal since we dont really benefit from them but they benefit from our trash and food.

Atta sexdens (ant)/yes,pets

The interaction type is symbiotic since we benefit from each other they help recycle organic material in the soil for our lawns and they benefit from our food and waste.

Sylvilagus audubonii (rabbit)/yes,pets,food,livestock

The relationship is predator/prey since people do hunt and eat rabbits but also keep them as pets and apart of the family.

Canis lupus familiaris (dog)/yes,pet

Interaction type would be symbiotic since we provide them with food,love and a home while they provide us with happiness and something to care for.

Equus caballus (horse)/yes,pets,livestock

The interaction is the same as dogs, symbiotic, since we care for them.

Nemobiinae (ground crickets)/no

Interaction would be commensal since they benefit from us I suppose, like the food we drop on the floor.

Chiroptera (bats)/no

The interaction type would symbiotic since they eat insects that we dont want in our house.

Hemiptera Gerridae (Water Strider)/no

The interaction type might also be symbiotic since they too eat insects like bats.

Capra hircus (domestic goat)/yes,food,pets,livestock

The relationship would be perdator/prey since we care for them giving them food and shelter while they help us as food and as apart of the family

Holbrookia maculata (Lizard)/yes,pet

The interaction type would be symbiotic since we benefit from them as pets and since the eat bugs and they benefit from us when they are our pets.

Class Chilopoda(centipedes)/no

The interaction type is preditor/prey since they can harm us and we harm them.

Avicularia (Tranchula)/yes,pet

The interaction type would be mutualistic since as pets both owner and spider benefit each other. They also eat unwanted insects.

Acronicta (moth)/yes,pets

As pets they are symbiotic but otherwise the are parasitic when they eat holes in clothing.

Citrullus lanatus (watermelon)/yes,food

The interaction would becommensal since we benefit from the nutrience and they are not harmed by us.

Salix Matsudana 'Navajo" (Globe willow)/yes

The interaction is symbiotic since we benefit from there shade and oxygen and they benefit from the carbon dioxide we produce.

Triticum (Wheat)/yes,food

The interaction is commensal since we bennefit by making food product and the nutrience we gain and its not harmed in the process

Ananas comosus (Pineapple)/yes,food

This too is commensal for the same reason as wheat we bennefit from the nutrience.

Rosa (rose)/yes

This too is commensal since we bennefit from the look and smell.

Pediculus Humanus Capitis (Lice)/no

The interaction is parasitic since it bennefits from eating and living in our hair while we are harmed because it can cause hair loss and damage.

Unit 4 Review #2 Human Evolution

Unit 4 Review#2 Human Evolution
Deep Time Evolutionary History
Natural Selection

Human Ecology

Deep time Evolutionary History
The origins of the earth started 4.6 billion years ago and has been evolving slowly ever since. Its believed that a chemical evolution produced the first cells on earth and they have been evolving into the different creatures that have existed and that do exist today. There have been fossil findings of creatures that do not exist today but have distinct characteristics about them that resemble ones that do live today. These findings lead to the idea of a common descent, that everything living today came from common ancestors that evolved into different creatures. Humans and chimpanzee’s genomes are 99% identical to each other. Other fossil findings and research has shown humans to resemble apes as well. This does not mean we evolved from apes or chimpanzee’s but instead its believed that both apes and humans evolved from a common ancestor which makes apes our distant cousin. These findings show how a common ancestor could have evolved into humans, apes, chimpanzee’s and other animals over the years. [Picture of human (left) and ape (right)]



Natural Selection
Darwin’s idea of natural selection was the most significant description of adaptation. Through many years of research he observed animals such as finches that all had unique difference that helped them in daily life. He believed that they all came from a common “ancestor whose offspring had spread out among the islands and become adapted to different environments.”(Mader 474) This research lead to natural selection that over time a species becomes suited for their environment in order to survive. Giraffes for example Darwin believed neck lengths varied and that competition for food and resources lead to giraffes with long necks having more offspring slowly eliminating those with short. Over time due to natural selection most giraffes now have long necks. Just like with other creatures over time they adapt to their environment and if certain traits and need more for survival then those traits would be passed on to future generations. Darwin believed this is why there are so many different types of one creature. That depending on its environment it adapted making it different from creatures living in different environments.



Human Ecology
Scientists are continuously studying the environment and the effects we have on it. Everything on this plant contributes from and to the environment. There is a natural occurring cycle in the ecosystem and each component relies on each other in order to keep functioning properly. The picture below is a simple demonstration of the ecosystem.



This diagram though simple shows how everything works in a continuous cycle. Trees use carbon dioxide and let off oxygen while we need oxygen and let off carbon dioxide. When animals die and decompose they release organic carbon and replenish the soil. Everything effects the ecosystem for good and bad. As humans we tend to do more harm to the ecosystem from our factories, cars, streets, buildings and waste. Our environment is slowly becoming polluted by our luxuries. The abundance of burning fossil fuels in factories has lead to acid deposition that has dramatically effected forest and lakes. It also reduces agricultural yields and corrodes marble, metal, and stonework. The burning of fossil fuels has lead to a thermal inversion where warm air gets trapped not being able to escape into the atmosphere causing pollutants to be trapped. This is what give phoenix or any large city its dirty orange sky. (picture of inversion layer)


Along with fossil fuels human are also damaging the ecosystem with daily chemicals and products like; Freon a coolant found in refrigerators and air conditioners, cleaning agents and foaming agents. These all contain chlorine atoms that are breaking down the ozone layer which maintains earths temperature and protects us from the suns harmful rays. As the ozone layer depletes the earths temperature rises and the glaciers will melt causing flooding. Also as the “earth’s surface warms due to global warming, less heat reradiates into the stratosphere.”(Mader506) Stratospheric cloud are lasting longer and are expected to increase causing colder winters. Cloud cover also contributes to the breakdown of the ozone layer. Scientist are continuously trying to find new ways of protecting our atmosphere but it is up to everyone to do there part in preserving our world.
(picture of ozone layer)




Work Cited:
Madder, Sylvia S. “Human Biology” 10th ed. New York: McGraw-Hill, 2007
http://www.visitandlearn.co.uk/factfiles/images/eco4.gif (ecosystem)

Unit 4 Review #1 Human development

Unit 4 Review #1 Reproduction
Human Life Cycle
Meiosis---eggs and sperm
Fetal Development and Birth

The human life cycle starts at birth when we are first introduced to this world. From there we grow into young adults where puberty sets in and then into adulthood. Boys and girls both go through puberty with girls starting between ages 11-13 and boys between 14-16. During this stage is when the reproductive system goes through many changes and is then capable of producing offspring.

Meiosis
There is two types of cell division that takes place in the human body mitosis and meiosis. Mitosis discussed before it a cell making an exact copy of its self. A cell has 46 chromosomes and after cell division the copies also have 46 chromosomes. This type of cell division takes place during tissue repair or growth. While meiosis cell division takes place during the production of sperm and eggs. During this process the cell starts with 46 chromosomes (called a diploid 2n) like before but after division the offspring or copies only have 23 chromosomes each (called haploid n). Meiosis goes through two successive divisions meiosis 1 and meiosis 2. When the sperm with 23 chromosomes meets with the egg also having 23 chromosomes the zygote will have 46 chromosomes and will grow into a baby. If meiosis did not occur then the offspring or baby would have too many chromosomes and the cells would not be able to function properly. So because of this process you have equal traits from both parents.
The sperm produced from male and the eggs produced by females are very important to the reproduction of children. During puberty males start to produce sperm in the testes, sperm has three distinct parts; a head, middle piece, and tail. The head is covered in enzymes needed to penetrate the egg while the middle provides energy for the tail made of flagellum to propel its self threw the cervix to an egg. The only function of sperm is too carry the 23 chromosomes to the egg.

(picture of sperm)

The ovaries of women produce eggs along with hormones. A women usually ovulates once a month which is when the ovary releases an egg to be fertilized. If the egg is not fertilized then menstruation takes place. If the egg is fertilized the it will attach it’s self to the lining of the uterus.

(picture showing sperm entering egg to be fertilized)

Fetal Development

Once the egg is fertilized and attached to the uterus it is considered an embryo and starts to grow. Many cell divisions take place to create your child. An average pregnancy last 40 weeks and is calculated starting from the first day of your last menstrual cycle. Which means by the time you notice that your pregnant by missing a period you are already around 3 weeks pregnant. Pregnancy is broken down into three main stages of development pre-embryonic, embryonic, and fetal development. Pre-embryonic is considered the first week of pregnancy when ovulation occurs in the mother and fertilization has occurred starting cell division of the zygote. The next stage embryonic development is the second week through the second month. There are many things that take place to both mother a child during this time. A few of the events the baby goes through are as follows;
2nd week: implantation occurs, the embryo has tissue, and the placenta is forming
3rd week: the nervous system starts to develop and blood vessels are present
4th week: limb buds form, heart is noticeable and beating, and the nervous system is prominent
5th week: head is fairly large while the nose, eyes and ears are now noticeable
6th week: the fingers and toes are now present and the skeleton is cartilaginous
8th week: all systems are under development and bone is replacing cartilage
The last stage of pregnancy is fetal development which is the third month through the ninth month. Below are some of the developments of the baby during fetal development. During the;
3rd month: the gender may be determined with ultrasound and fingernail are now present.
4th month: skeleton is visible, and hair starts growing
5th month: Heartbeat can be heard and a protective coating surrounds the baby called vernix caseosa
6th month: fat has developed, the ears can now hear sound, and the baby now has eyelids and eyebrows.
7th month: eyes are now open and facial features now resemble what your baby is going to look like
8th month: lungs and digestive tract are almost complete and baby eyes can now distinguish light and dark
Finally the in the 9th month all the body hair is gone and the fetus is ready for birth.

(Below a new born)

Work Cited:
http://parenting.ivillage.com/pregnancy/0,,nc26,00.html
http://faculty.uca.edu/~johnc/human%20life%20cycle.bmp (meiosis)
http://www.thetilleychannel.com/sarah/month01/princess.jpg (newborn)
http://www.lions.odu.edu/~knesius/miniunits/gamma/sperm.jpg (sperm)
http://www.siue.edu/~cbwilso/203con4.jpg(fertilization)

Unit 4 Online lab Fetal Development

Unit 4 Online Lab Fetal Development

During this lab I will be explaining some of the stages during pregnancy and when they take place. I will be referencing the time frame in weeks starting with 4 weeks, which is counting from the first day of the last menstrual period.
The four week of pregnancy is when the placenta is under construction if you will and the baby is in the yolk sac awaiting its permanent home. The beginning of the connecting stalk which becomes the umbilical cord has appeared. This is very significant because the embryo needs the placenta for development and the umbilical cord provides nutrients to the baby during development.
The brain starts forming three separate parts in the sixth week of pregnancy. Along with the heart is now circulating blood and the kidneys and liver are growing. A very significant part of this week is that the spinal cord in now connected to the brain. Which makes up the central nervous system and is very important. (below is 6 weeks)

At nine weeks the major organs, muscles, and nerves have developed and the embryo is very active. The testes or ovaries are developed but gender still cant be determined by ultra sound. This is a very exciting time because the heart beat can now be heard using a Doppler.(shown below 9 weeks)
At the end of ten weeks the baby will have noticeable fingers and toes, the tail disappears, and the external ear and upper lip are now complete as well. This is a very significant time since from here on out the baby is referred to as a fetus.
At eleven weeks the irises are now forming, the primitive tail is gone, and the baby’s head starts to slow in grown. This is an important stage since now that most of the major organs such as liver, brain and intestines are ready for operation the details start to form such as hair.

(shown below 11 weeks)
In the thirteen week the baby is growing fingernail and toenails, organs are functioning on there own now. The intestines are now inside the abdomen and the baby has reflexes and will respond to external forces. This is a very important stage because the baby is now functioning and responding to stimuli and growing to become strong enough to live outside the uterus.
At fourteen weeks it can be very exciting for the mother since the baby is now starting to move around and its possible to feel a fluttering sensation. Another important part of this week is that the neck is complete along with little fingerprints. (Shown below 14 weeks)
Sixteen weeks is another very important stage since the gender can now be determined if you have an extroverted fetus. Coordination and sucking reflex can be noticed with an ultrasound and the baby is now 3 ounces and 12 centimeters long.
At nineteen weeks permanent teeth buds are forming and the reproductive organs are under fast development. An ultra sound can easily determine the gender of the child now and this is the time when most mothers choice to know if they are having a boy or girl. (shown below 19 weeks)
Twenty two weeks is an exciting time for the baby since now he or she can hear sound from the outside. The development of eyelids, eyebrows, and fat under the skin to keep the baby warm and maintain body temperature are all happing at this time. (shown below 22 weeks)
Work Cited:
http://parenting.ivillage.com/pregnancy/calendar?ivNPA=1&prd=sch&sky=gglivlfetalppPPC192Dc

http://www.babycenter.com/pregnancy/fetaldevelopment

Unit 3 Lab Project "joints"

Unit 3 Lab Project

For this lab I will be demonstrating the inner workings of a human elbow. I will show how muscle contraction works to move a limb. Starting with motor neurons that take information from the central nervous system to muscles fibers. To how the action potectial takes place in neurons and how they stimulate muscle contraction.

This picture represents the elbow. Shown in the three main bones involved; humerus, ulna, and radius. Along with the bicep muscle which is responsible for flexion. The bicep is conected to the bone by tendons allowing movement to take place. When the bicep contracts the lower region of the arm (radius and ulna bone) are pulled upward towards the humerus and bicep muscle. The parts are made from play dough and vegetables.


When a muscle contracts what is really happening is that the central nervous system sends a nerve impulse by means of a motor neuron to the bicep. A motor neuron has a cell body where the nucleus and other organelles reside, dendrites that receive signals from sensort receptors and other neurons. The axon and axon terminals. On the axon myelin sheath wraps form where neuroglia cells called Schwann cells wrap themselves around the axon in many layers. Gaps occur making nodes of Ranvier because neuroglia cells only cover part of the axon. Axon terminals lie very near dendrites or the cell body of other neurons. A motor neuron is shown in the following photo.


The following five photos show action potential (nerve impulses). When the central nervous system generates a motor response, a nerve impulse travels throught motor neurons to the muscle. When this nerve impluse or action potential happens a few things take place along the axon. First being that sodium gates open allow Na+ to flow into the axon changing the membrane potential from negative to possitive ,depolarization, as shown in right picture. The second thing that takes place is the potassium gates open allowing K+ to flow to the outside of the axon. As this happens the action potential changes from possitive back to negative, repolarization.







































The following three photos are a close up view of above two photos. The first one is showing a resting potential. No nerve impulse is taking place in the neuron.




The next two show action potential taking place. The photo on the left is the begining of action potential. Depolarization occurs since the Na+ gates are open allowing Na+ to flow to inside of the axon. The photo on the right is the ending of action potential. Repolarization in the axon takes place since the K+ gates are opening allowing the flow of K+ to move to the outside of the axon.




























After action potential takes place and the nerve impulse the muscle it travels down the T tubule which causes calcium to be released from the sarcoplasmic reticulum. The Ca2+ that is released combines with troponin, protein apart of actin filament, causing the tropomyosin (another protein) threads to shift their position. Resulting in myosin binding sites. This is where ATP in the form of ADP + are bound to myosin as a myosin head and attaches to actin. A power stroke takes place moving the actin fiber resulting in muscle contraction. This procedure is repeated until muscle is contracted to the desired position. The following two photos are showing an actin filament before and after calcium is released exposing myosin binding sites.





These last two photos are showing how when the myosin head attaches to the actin at the myosin binding sites a pulling or sliding action takes place resulting in a contraction of a muscle. Below a sarcomere is being show which by definition is one of many units arranged linearly within a myofibril, whose contraction produces muscles contraction. A sarcomere is composed of actin filaments and myosin filaments. The first photo shows a relaxed sarcomere or relaxed muscle.
This photo shows the sarcomere contracted which results in a contracted muscle.

In conclusion it is really important to understand how all these different parts all aid in contracting a muscle. From the nerve impulse sent from our central nervous system to the bones, joints and tendons that support and allow movement. The system works together and without one compont it will not function properly.


Work Cited: Madder, Sylvia S. “Human Biology” 10th ed. New York: McGraw-Hill, 2007.

Unit 3 Ethical Essay "exercise"

Do you exercise?

Everyone knows that a healthy diet includes exercise of some type. There a millions of diet pills, diets and exercise equipment available so why is it that Americans are still over weight and suffer from obesity? Our children should be taught to eat right and to participate in physical activities instead of video games and fast food joints.

This brings me to my first issue, why should we exercise besides the obvious reason of being over weight. Well exercise improves cardio respiratory endurance which helps to prevent plaque build up in the arteries preventing heart attacks. Routine exercise and a healthy diet helps to prevent certain cancers like colon, breast, and cervical cancers. Exercise improves muscular strength, endurance, flexibility, and improves bone density and strength preventing osteoporosis. Not only does exercise and eating right physically help the body it also helps with depression and gives a person a feeling of tranquility.

Now we have a basic understanding of why exercise is so important to the mind and body why don’t we do it. Well today people are to busy watching television and playing video games that we are missing out on great opportunities to improve our health. The continually growing fast food places that are fast and convenient are hitting society hard and adding serious poundage. In most schools, gym class has been eliminated to one day a week and extracurricular activities require money to join. Most people can’t afford to pay for their child to be on the soccer or football team and not having a regular gym class is the only time their children have to exercise, which too is being taken away.

What should we do? The first thing is to teach our children the importance of exercise and eating right. Instead of buying those video games for your child play a physical activity or get them signed up for one. This way both you and your child are exercising and improving your health today. We need to teach our selves and our children that exercising and eating right can be fun. Instead of taking the family to KFC make a healthy meal together, get everyone involved so that it is fun, educational, and mind and body satisfying.

Eating right and exercise needs to be looked at as an enjoyment and a family activity. Communities could even start evening walks or activities for them and their children to do together. If together we don’t start taking control of our lives the obesity epidemic will not go a way instead it will increase along with preventable diseases.

Unit 3 Review #1

Unit 3 Review #1Nervous system
>What does the nervous system due
>Diffusion & Action potentials in Neurons- rapid transmission of messages
>Reflex arc (simple somatic function) and autonomic function
>What can we sense

Function of nervous system
The nervous system has three major functions and consists of two major parts the central nervous system (CNS) and the peripheral nervous system (PNS). The brain and spinal cord and considered the CNS and the nerves throughout the body are the PNS. These two systems work together to perform the following; sensory input, integration, and motor output. When internal or external stimuli is detected by sensory receptors and nerve impulse is generated and travels through the PNS to the CNS. The CNS then takes the information it is receiving and the generates motor out put. Which are more nerve impulses but coming from the CNS to PNS and then specific muscles or organs. For example when you eat food the sensory receptors in the stomach send an impulse through PNS to your CNS saying that there is food in here. Then your CNS sends out an impulse to your stomach, pancreases, liver, gallbladder all the organs associated with digestion to get to work.

Diffusion & Action potentials in Neurons- rapid transmission of messages
Nerve impulses are transmitted throughout the body by cells called neurons. Neurons consist of a cell body, dendrites, and an axon. The nucleus and organelles are located in the cell body. The dendrites receive messages from sensory receptors and other neurons. While the axon conducts nerve impulses. As a nerve impulse occurs a rapid change in polarity across the axonal membrane called action potential takes place. It takes a certain level called threshold for an action potential to occur. An action potential strength stays constant but an intense stimulus can cause the start of an axon potential. Meaning that nerve impulses (action potential) is an either takes place or doesn’t and the intensity of the message is determined by how many nerve impulses take place in a given time frame. Axon length varies for each type of neuron and most are covered in myelin sheath a protective lipid substance. The myelin sheath wraps forms where neuroglia cells called Schwann cells wrap themselves around the axon in many layers. Gaps occur making nodes of Ranvier because neuroglia cells only cover part of the axon. There are also unmyelinated axons which are usually short axons while the long axons have the myelin sheath. Not only does the myelin sheath protect it also acts as a passageway for new fiber growth in nerve regeneration. At the end of an axon many branches with axon terminals on the end extend outward towards another neurons dendrites or cell body. The area between the axon terminals (sending neuron) and the receiving neuron is called a synaptic cleft. Neurotransmitters from the axon of the sending neuron are released crossing the synaptic cleft and bind with the receiving neuron.

Nerve impulse travel at 1.0 m/sec in unmyelinated axons and 100m/sec in myelinated axons and this type of conduction is referred to as salutatory conduction. This is because in myelinated axons a nerve impulse jumps from node to node while unmyelinated axons the action potential (nerve impulse) at one location stimulates an adjacent part of the axon’s membrane to produce an action potential. When people are diagnosed when multiple sclerosis and leukodystrophies, demyelization ,the loss of myelin, has occurred which effects the function of the nervous system.

Reflex arc (somatic function) and Autonomic function
The somatic system has many nerves that serve the skin, skeletal muscles and tendons. These nerves take messages to the CNS from external sensory receptors and then motor commands from the CNS to skeletal muscles. Now while actions are voluntary like walking or eating some are also automatic referred to as a reflex. A reflex occurs when an external sensory receptor is triggered like touching a hot surface. The sensory receptors in your skin send a message to your CNS where a response is then sent back the muscles in your hand and arm to pull away and to feel pain. This happens very fast and without thinking about it resulting in the quick movement known as a reflex. The autonomic system on the other hand is involuntary. After you eat you no longer think about the food or what happens to it but you autonomic system does. It regulates all your organs telling them when to function and when not too. This system is divided into two part the sympathetic division and parasympathetic both consisting of fibers . The sympathetic division is located in the middle portion of the spinal cord and branches out into ganglia, collection of cell bodies outside of CNS) almost immediately. The preganglionic fiber is short while the postganglionic fiber is long and is the fiber that makes contact with an organ. This part of the autonomic system is very important during emergency situations. The sympathetic division accelerates the heartbeat, dilates air passages and inhibits the digestive tract. An example being when walking outside in the dark if you hear something frightening and don’t know what it is your heart starts beating really fast and you feel the need start to run. The sympathetic division has many other function some being; stops tears, dilates pupils, and stimulates the release of glucose from liver. The parasympathetic division includes a portion of the bottom of the spinal cord and a few cranial nerves. Unlike the sympathetic division the preganglionic fiber is long and the postganglionic fiber is short. This is because the ganglia is either near or inside the organ. The parasympathetic division is known as the housekeeper of the rest and digest system. It promotes the responses we associated with rest like slowing the heartbeat and stimulates the organs associated with digestion of food.

What can we sense?
First off the reason why we can sense anything is because we have sensory receptors which are dendrites that are specialized to detect certain stimuli from both internal and external. Exteroceptors sense stimuli from outside the body while interceptors sense stimuli from inside the body. The four types of sensory receptors are chemoreceptors, photoreceptors, mechanoreceptors and thermoreceptors. Chemoreceptors recognize stimuli from taste, smell, and they monitor blood pH. Pain receptors are a type of chemoreceptors that consist of special dendrites that respond to chemicals produced by damaged tissue. Pain receptors also alert us to danger like when touching something sharp or hot. Photoreceptors are stimulated by light energy. Our eyes have photoreceptors both rod cells and cone cells giving us the ability to see black, white and different colors. Mechanoreceptors allow use to hear by meaning of sound waves, sense changes in gravity and motion allowing us to keep our balance, and the sense of touch from pressure receptors. These pressoreceptors detect changes in blood pressure and how much the lungs have inflated. There are also proprioceptors that make us aware of our limbs. Lastly we have thermo receptors that are stimulated my temperature and are located in the skin and hypothalamus. All of these receptors allow us to sense by means of hearing, seeing, taste, touch, and smell. Our nose gives use the ability to smell both good and bad aromas. While the taste buds that cover our tongue allow us to taste the food we are eating. Our ears sense sound waves alerting us and our eyes sense light allowing us to see the world and our skin lets us feel everything we come into contact with. The many different senses and sensory receptors send these impulses to our brain for interpretation so that we may experience what is taking place whether good or bad.

Work Cited:
Madder, Sylvia S. “Human Biology” 10th ed. New York: McGraw-Hill, 2007
http://www.infovisual.info/03/img_en/038%20Nervous%20system.jpg
(Nervous system)
http://mustang.millersville.edu/~bduncan/465/anatomy/brain-anatomy/cellular-level/neuron.gif
(Neuron)
http://www.wooster.edu/psychology/intro/autonomic.gif
(autonomic system)
http://fig.cox.miami.edu/~cmallery/150/neuro/c7.49.3.skin.jpg
(touch)
http://www.rennard.org/alife/img/biom/eye_anatomy.jpg
(eye)
http://www.lincoln.dubuque.k12.ia.us/images/Fifth%20Grade/2004_2005/human_body/tongue.jpg
(tongue)
http://www.hf.faa.gov/Webtraining/NonVisDisplays/Non_vis%20images/earcrop.jpg (Ear)