Compendium Review: Reproduction

An image from an electron microscope showing sperm fertilizing an egg, taken from www.sciencemuseum.org.uk/.../lifecycle/40.asp

I. Introduction

II. Human Life Cycle

III. Male Reproductive System

IV. Female Reproductive system

• Ovarian Cycle

V. Birth Control

VI. STDs

VII. Stages of Development

• Pre-Embryonic
• Embryonic
• Fetal

VIII. Birth

IX. Aging

X. Conclusion

Introduction

I enjoyed reading these units because they deal with subjects I have been immersed in over the last 13 years. I spent my early days as a health educator in a women’s health clinic and now serve as the project coordinator of an aging program. I suppose I’ve come full circle. I guess the biggest lesson I have learned from working in a women’s clinic and through these chapters is the importance of understanding your body and how it works. So many women are completely unaware of how their reproductive systems work and are therefore woefully unequipped when making important decisions on pregnancy, contraception, and STD protection. The same is true of men. My husband knew something was “different” when he discovered his cancer but it was not until we looked it up that he knew he might have a serious problem. Over the next few paragraphs I will describe the male and female reproductive organs and their functions, discuss contraception and protection from STDs, and provide an overview of development, pregnancy, and birth.

Human Life Cycle

During puberty, between ages 11 – 13 for girls and 14 – 16 for boys, children reach sexual maturity. Sexual maturity means an individual is now capable of producing children. The reproductive systems of males and females differ significantly but have some similar functions.

Both produce gametes, in males, sperm are produced in the testes, in females the eggs are formed in the ovaries

Eggs reach the uterus via the fallopian tubes, and sperm are carried through ducts through the penis and are ejaculated. The penis delivers sperm to the vagina during sexual intercourse.

Testes and ovaries produce hormones that result in male/ female features and in females facilitate pregnancy. The uterus is the female organ that allows a fertilized egg to grow and develop.

In the human life cycle meiosis occurs in the ovaries (females) and testes (males) resulting in eggs and sperm. Sperm and eggs each contain only 23 chromosomes as compared to other cells that contain 46. Ordinary cells undergo division called mitosis resulting in another cell containing 46 chromosomes. Meiosis requires two cell divisions resulting in the haploid 23 chromosomes. During fertilization the sperm and egg meet to form the zygote which has 46 chromosomes.

Graphic of the human life cycle taken from Human biology page 320, Sylvia S. Mader

Male Reproductive System

The primary sexual organs in males are the testes which are suspended within the scrotum. Sperm are produced in the testes but mature within the epididymis. After maturation, sperm are stored in the vas deferens which consists of two long tubes leading to the ejaculatory duct which leads to the urethra. Ejaculate and urine both exit the penis through the urethra. The seminal vesicles, the prostrate gland, and bulbourethral glands all add secretions to semen which is the fluid that sperm is ejaculated in. Sperm require a particular environment to be more viable and components added by the seminal vesicles and the glands help create this environment. At birth all males have a foreskin over the penis which is usually removed by circumcision.

The penis is the male sexual organ. To facilitate erection, throughout the penis there is spongy tissue with expandable blood spaces. During sexual arousal these spaces fill with blood, causing erection. The sphincter closes off the the bladder so no urine enters the urethra during erection. Sperm enter the urethra via the vas deferens and muscle contractions trigger ejaculation. There are over 400 million sperm expelled during ejaculation.

Graphic of the male reproductive system taken from http://www.riversideonline.com/health_reference/Mens-Health/MC00023.cfm

As stated before, sperm and male sex hormones are produced in the testes. Testosterone is the main male sex hormone and is important for normal development and functioning of the male sexual organs. Testosterone also contributes to male physical characteristics like larger muscles and a deeper voice. The hypothalamus controls the functioning of the testes by secreting a hormone called gonadotropin-releasing hormone, GnRH.

Inside the testes are compartments called lobules which contain seminiferous tubules. This is where the production of sperm takes place. The process is known as spermatogenesis. Spermatogonia divide to produce spermatocytes which undergo meiosis I to become secondary spermatocytes which contain 23 chromosomes. These secondary spermatocytes will then go through meiosis II yielding 4 spermatids which become sperm. Throughout this process, sertoli cells provide support and nourishment. Spermatogenesis is a 74 day process.

A graphic from the text showing testis, sperm, and spermatogenesis. Taken from Human Biology page 323, Sylvia S. Mader

Female Reproductive System

Eggs and the sex hormones, estrogen and progesterone are produced in the ovaries, the female gonads. Oocytes within ovarian follicles mature during the ovarian cycle. Females are born with more then two million follicles but only a few, (400) mature. Usually women only produce one egg per month while they are reproductive.

Meiosis in females is known as oogenesis. An egg bursts from the ovaries during ovulation and is swept into the fallopian tubes, AKA oviducts, by finger-like projections called fimbriae. The egg then travels down the fallopian tubes to the uterus. Fertilization of the egg by a sperm usually takes place in the fallopian tubes. After fertilization, the egg implants on the endometrium of the uterus. If an egg implants in the fallopian tubes it is know as an ectopic pregnancy. The fallopian tubes can not support an embryo and do not expand like the uterus. The uterus is the organ where development of the fetus occurs. The cervix, the opening of the uterus is found at the back of the vagina. During intercourse sperm enter the uterus via the cervix and travel into the fallopian tubes in search of an egg. cervical cancer used to be the leading cause of cancer deaths in women but its incidence has been greatly reduced by the pap smear, a test for changes in cervical cells.

A graphic of the female reproductive system taken from www.northstar.k12.ak.us/.../markey/webpage.html

Ovarian Cycle

The female sex hormones estrogen and progesterone are responsible for female characteristics like breast development and body hair. These hormones also play an important role in the ovarian cycle. The average ovarian cycle lasts about 28 days. The cycle begins when lower levels of estrogen and progesterone cause the endometriun to disintegrate and pass out of the vagina, this is called menstruation. Menstruation is usually a sign that a women is not pregnant. Day one of an ovarian cycle is the first day of menstruation. Around 6-13 days later estrogen is increased by a new follicle and the endometrium begins to thicken in preparation for implantation in the event of a pregnancy. This is known as the proliferative phase. Ovulation usually occurs around day 14. During days 15-28 of the cycle, the corpus luteum increases production of progesterone causing the endometrium to thicken even further. This is the secretory phase and the body is now ready to receive a developing embryo.

A chart showing female hormone levels from Human Biology page 329, Sylvia S. Mader.

During pregnancy the embryo implants on the uterine wall and menstruation does not occur. The corpus luteum will increase the amounts of progesterone because of a hormone secreted by the placenta, human chorionic gonadotropin (HCG). HCG is the hormone detected in a pregnancy test. Later on the placenta will produce its own progesterone and some estrogen.

Hormones during pregnancy, Human Biology page 330, Sylvia S. Mader

Birth Control

There are many different methods available to women wanting to prevent pregnancy. The only sure way is abstinence, abstaining from sexual intercourse. However, contraceptives like birth conrol pills or Depo-provera can be about 98%-99% effective when used correctly. This methods use synthetic hormones (estrogen and/or progesterone) to inhibit ovulation. There are some side effects or risks like menstrual changes, weight gain, headaches, and blood clots that may occur with these methods. Hormonal methods do not provide protection from STDs.

The intrauterine device (IUD) is a piece of plastic, in some cases with copper or hormones, that is placed inside the uterus. It changes the environment of the uterus so that the egg does not implant on the uterine wall. Some women experience heavy cramping and bleeding with the IUD. Infections can also occur and it is recommended to be in a monogamous relationship while using the IUD.

Tubal Ligation and Vasectomy are surgical methods that bring about sterilization. In males the vas deferens is cut. Ejaculation still occurs but the semen is without sperm. In a tubal ligation the oviducts are cut, preventing the sperm and egg from reaching each other.

Barrier methods include the diaphragm and the male and female condoms. The diaphragm is used with a spermicide and is fitted by a clinician. Barrier methods, particularly the male and female condom, offer some protection against STDs but must be used correctly the whole time there is sexual contact. Even when used correctly, barrier methods are not 100% protection against STDs.

Photographs depicting different birth control methods, form Human Biology, page 331, Sylvia S. Mader

STDs

There are many different sexually transmitted diseases that people should be aware of. Some are bacterial, some are viral. Chlamydia and Gonorrhea are examples of bacteria and can be treated by antibiotics. Years ago, when I first started in women's health, Chlamydia was the most common STD. Things have either changed or we just know more. Human Papillomaviruses, AKA HPVs are the most common STDs today. HPVs may cause warts, but not always. What is really scary about HPVs is that some strains are linked to cervical cancer. There is no known cure for HPV but a new vaccine can protect women from some dangerous strains. Unless a woman has regular pap smears she may never know she has the virus. So get your pap smears ladies! By the way, condoms do not necessarily protect from HPV because they may not cover the entire area affected.

Other viruses include HIV and Hepatitis B and C. Hep A is not sexually transmitted. There is a vaccine for Hep B. Hepatitis affects the liver and is actually a more hearty virus than HIV, it just doesn't get the press, go figure.

Some infections like Bacterial vaginosis or yeast are not necessarily sexually transmitted and are fairly common. Yeast is a fungal infection.

Stages of Development

When a sperm meets an egg and a zygote is formed the event is called fertilization. Fertilization usually occurs in the oviducts. Only one sperm fertilizes an egg. The nucleus from the sperm head fuses with the nucleus of the egg. The newly formed zygote has 46 chromosomes. After fertilization the zygote begins to divide, this is called cleavage.

These images show human embryos at various stages of development. Taken from hesc.stanford.edu/research/programs/human.html

Pre-Embryonic Development

The pre-embryonic stage consists of the first week of development. After the zygote has begun to divide it becomes a morula, a complex Ball of embryonic cells. The morula becomes a blastocyst. The cells of the blastocyst will arrange themselves into am inner cell mass with an outer cell layer.

A graphic of pre-embryonic development taken from Human Biology page 356, Sylvia S. Mader

Embryonic Development

The embryonic development stage begins the second week and continues through the second month. Implantation occurs in the second week. HCG is secreted by the chorion which helps maintain the corpus luteum. The inner cell mass becomes the embryonic disk. The amniotic cavity surrounds the embryo and the yolk sac is a site for blood formation.

Gastrulation is morphogenesis in which cell move to form tissue layers called primary germ layers. At the end of gastrulation the embryonic disk becomes the embryo with the ectoderm, mesoderm, and endoderm. Each of these layers is associated with different parts of the body as illustrated below.

Illustration showing the three germ layers and their significance. Taken from Human Biology page 358, Sylvia S. Mader

Development of the heart and nervous system begins in the third week. In the fourth and fifth weeks a body stalk appears, this is the future umbilical cord. Little buds appear that will be future arms and legs. During weeks six through eight the embryo begins to look human. This is an important stage, drugs and alcohol can affect a developing embryo before the mother even knows she is pregnant.

Fetal Development

By the third month it is possible to determine the gender by ultrasound. The placenta is functioning and provides nourishment for the fetus. The placenta also secretes progesterone and estrogen. Cartilage begins to be replaced by bone during the third and fourth months. The skull has six areas where the bone is not fully formed. These are called fontanels. The fontanels provide the skull flexibility during birth.

The mother will usually feel movement around the fifth month. If the child is born at this time it is possible for it to survive, albiet there can be many problems for a premature child. During weeks eight and nine the fetus grows bigger. It positions itself in a head down position in preparation for birth. If a child does not come out head first it is called a breech birth. Because of the dangers in delivering a child in this position many women will have a cesarean section.

Birth

There are three stages to parturition, the process of giving birth. During Stage one uterine contractions cause the cervical canal to thin, a process called effacement. The amniotic membrane often ruptures during this stage, an event that is often referred to as one's "water breaking." Contractions are regular, unlike Braxton Hicks contractions, but they may be relatively far between for some time. Once the cervix is fully dilated, stage one is over.

During stage two, contractions are closer together, about every 1-2 minutes. The woman will feel a desire to push at this point. The baby is delivered during stage two. Sometimes a doctor may have to make a small incision called an episiotomy to enlarge the opening of the vaginal orifice.

Stage three is the delivery of the afterbirth, the placenta and membranes. This can occur as many as fifteen minutes after the baby is born.

The different stages of birth, taken from Human Biology page 370, Sylviia S. Mader.

Aging

There are different stages of life, infancy, childhood, adolescence, and adulthood. development does not end at birth, chidren continue to grow and age. Gerontology is the study of aging. This field, is increasing in interest because it is estimated that by the year 2030 over 20% of our population will be over the age of 65. You should know that Yavapai County is of particular interest because currently 25% of our population is over age 60! You can find this information through the census website, link below.

Aging has an effect on many of our body systems. Bone density decreases and in some cases can lead to osteoporosis. Skin becomes thinner and less elastic causing wrinkles to form.

Women reach menopause somewhere between 45 and 55. Men go through andropause but some sperm continue to be produced until death. It is a myth that older adults are not sexually active. In fact, incidence in STDs in adults over 45 is increasing. This is a particular problem in assisted living communities. There is lots of infomation on this at the CDC website and the Center for Healthy Aging, link below.

I think it is important to point out that there is much wisdom and life experience to be found in older adults. It grieves me that the US is an ageist society that almost worships youth. Many other cultures revere their oldest members. Aging does not mean that we have to become weak and sick. People can stay healthy longer by staying active and eating right. The adults I work with here in town are mostly very active and some are in their nineties. I am a richer person for knowing them.

I got this image from MSN office clipart. I like it because these ladies look like they are having a good time. Good for them!

Conclusion

Reproduction is a fascinating subject. It is even more interesting given the fact that I have had two children and have experienced it firsthand. It is easy for me to get on my soapbox about the aging issue as I live and breathe it every day.

Works Cited

Human Biology, Sylvia S. Mader

Professor Frolich's Power Point

www.sciencemuseum.org

hesc.stanford.edu/research/programs/human.html (this will not go live but you can find it under the photo)

www.northstar.k12.ak.us

www.riversideonline.com

http://www.healthyagingprograms.org/

http://quickfacts.census.gov/qfd/states/04/04025.html

Compendium Review: Movement

Picture from School House Rock's "Not So Dry Bones."

http://www.school-house-rock.com/Bone.html

I Introduction


II Skeletal System

• Function

III Anatomy of Bones

• Bone Growth

IV Muscular System

V Muscle Fibers

• Muscle Contraction


• Energy
  

VI Conclusion

I Introduction

The skeletal and muscle systems work together to give us movement. Skeletal muscle via impulses from the nervous system enable us to move the various parts of our body. In the next few paragraphs I will be discussing the bone, muscles, and skeleton and how they work. I will start with the bones and end with the muscles.

Graphic pointing out the axial and appendicular skeleton found at www.aclasta.co.nz/osteoporosis/index.htm

II Skeletal System

There are 206 bones in the human skeleton. The skeletal system serves several important purposes. First, the skeleton serves as a frame and support for the human body. The design of our skeleton promotes flexibility and enables us to perform different articulations and complex movements. Second, certain bones like those of the skull, rib cage, and vertebral column help protect important body parts for example the brain and lungs. Our bones also produce blood cells and store minerals and fat.

The skeletal system is composed of the axial skeleton and the appendicular skeleton. The axial skeleton consists of the skull the vertebral column, and the ribcage. The skull includes the cranium and the facial bones. The cranium itself (in adults) is composed of 8 bones. The vertebral column includes 33 vertebrae that protect the spinal cord. There are intervertebral disks between vertebrae that serve as a kind of padding to keep vertebrae from grinding against each other. Twelve ribs on each side of the body originate from the thoracic vertebrae. The seven upper ribs connect to the sternum which is also called the breastplate, this bone helps protect the heart and lungs.

An illustration of the skull from www.georgehernandez.com/.../Health/Anatomy.asp

The appendicular skeleton is made up of the bones of the limbs and the pectoral and pelvic girdles. Pectoral means shoulder and pelvic refers to the hip, the arms and legs are attached respectively to the pectoral and pelvic girdles. Because of ball and socket joints our arms and legs are able to perform a wide range of motion. Synovial joints, having cavities filled with fluid to lubricate the joint allow free movement. Synovial joints (AKA hinge joints) allow movement mostly in one direction. Ligaments which connect bone to bone help to make joints stronger. The longest bone in the body is the femur which is the thighbone. The hands and feet are composed of many bones to promote flexibility.

Illustration showing synovial joint movements from Human Biology page 223, Sylvia S. Mader.

III Anatomy of Bones

Long bones have a main portion called the diaphysis. Inside of the diaphysis is the medullary cavity which is filled with yellow bone marrow that stores fat. The ends of long bones are called epiphyses and are coated with a layer of hyaline cartilage. Except for this cartilage at the ends long bones are covered by fibrous connective tissue called periosteum which contains blood vessels.

Compact Bone

Compact bone is composed of osteons and is highly organized. Bone cells called osteocytes are arranged in tiny compartments called lacunae around a central canal. The lacunae are connected to each other by tiny canals called canaliculi. Osteocytes exchange nutrients and wastes with blood vessels.

Spongy Bone

Unlike compact bone, spongy bone is disorganized and contains lots of thin plates separated by unequal spaces. In many cases, the spaces of spongy bone are filled with red bone marrow. Red bone marrow produces all types of blood cells.

Cartilage

Cartilage is more flexible than bone. It is composed of cells called chondrocytes. There are also no nerves or blood vessels in cartilage making it slow to heal.

Fibrous Connective Tissue

Ligaments are made of fibrous connective tissue. Ligaments connect bone to bone at the joints.

Bone Growth

The skeleton of a human embryo begins forming at 6 weeks. Bone growth can continue through age 25. Bones can also heal through bone repair and respond to stress through remodeling.There are different cells involved in bone growth. Osteoblasts are bone forming cells, osteocytes are maintain the structure of bone, and osteoclasts break down bone.

The formation of bone is called ossification. During embryonic development bones are formed in two ways, intramembranous ossification and endochondral ossification.

Intramembranous Ossification: Flat bones like those in the skull are formed in this way. In this form of growth, bones develop between sheets of connective tissue. Osteoblasts are responsible for secreting the living matrix of bone made up of mucopolysaccharides and collagen fibrils.

Endochondral Ossification: This is the way most of our bones are formed. in this process cartilaginous models are replaced by bone. Bone formation spreads from the center to the ends. It starts with the cartilage model, which is made out of hyaline cartilage and shaped like the future bone. Osteoblasts secrete a living bone matrix which calcifies. the result is known as the bone collar. Osteoblasts in the interior begin to lay down spongy bone, this area is called the primary ossification center. Osteoclasts absorb the spongy bone of the diaphysis and the resulting cavern like space is called the medullary cavity. Secondary ossification centers are formed in the epiphyses shortly after birth. Between the primary and secondary ossification centers is the epiphyseal growth plate. The bones will continue to grow as long as this plate is present. There are four layers to this plate. The top layer is the resting zone, then comes the proliferating zone, the degenerating zone and the ossification zone where bone is forming. The growth plates in the arms and legs typically close in women around age 18 and in men around age 20.

This chart shows endochondral ossification of a long bone. Human Biology, page 210, Sylvia S. Mader

This graphic shows bone growth and the epiphyseal growth plate, Human Biology, page 211. Sylvia S. Mader

Bone remodeling helps keep bones strong. remember that bone is constantly broken down by osteoclasts and reformed by osteoblasts. This kind of "recycling" allows our bodies to regulate the amount of calcium we have in our blood. remodeling also helps our bones respond to stress. Exercise and strength training can stimulate the work of oesteoblasts, making our bones stronger. Osteoporosis is a condition of low bone density. Calcium is removed from bones quicker than it is replaced. This can lead to fractures.

Bones can repair themselves when a fracture occurs. First a hematoma (a mass of clotted blood) is formed and fills the space between the broken bones. Tissue repair begins when a fibrocartilaginous callus fills the space and stays there for about two to three weeks. Spongy bone is produced by osteoblasts and begins to join the bones together. Remodeling is the last step, new compact bone is formed at the periphery and a medullary cavity is formed. Fractures can be complete (broken all the way through the bone) or incomplete.

IV Muscular System

Muscle are made to contract and cause some part of the body to move. As we discussed in a past unit, there are three types of muscle, Smooth muscle, cardiac muscle, and skeletal muscle. All of these muscle tissues are made up of muscle fibers but they also have different characteristics. For this compendium I am focusing on skeletal muscle.

The skeletal muscles have many important functions. Our muscles help support us and keep us upright against the force of gravity. They also make our bones move. Muscle contractions are also responsible for movements like facial expressions and breathing. Muscle contraction causes ATP breakdown which results in heat. This helps our body maintain its temperature. Skeletal muscle contraction also plays a role in keeping are blood and lymph moving. Organs and joints are also protected by skeletal muscle by support and padding. I think it is safe to say looking at all these functions that the skeletal muscle system plays a role in homeostasis.

A whole muscle is composed of bundles skeletal muscle fibers known as fascicles. Muscles have a covering of connective tissue called fascia which becomes tendon. Muscles usually work in groups and have an origin, on a stationary bone and an insertion on a moving bone. The single muscle that does most of the work is called a prime mover. Other muscles, called synergists are often working with the prime mover to make the action more effective. A muscle that works opposite a prime mover is called the antagonist. Muscles are named for characteristics like size, shape, location, direction of muscle fibers, attachment, number of attachments, and action.

V Muscle Fibers

Muscle fibers are cells and have the normal cellular componets, except some of these compomponents have different names. The cell membrane is known as the sarcolemma; the cytoplasm is called the sarcoplasm, and the endoplasmic reticulum is known as the sarcoplasmic reticulum.A unique feature of the muscle fiber is the T system. T tubules in the sarcolemma penetrate the cell with larger parts of the sarcoplasmic reticulum. It is here that calcium is stored, and calcium is necessary for muscle contraction. Myofibrils are encased inside the sarcoplasmic reticulum. Myofibrils are contractile portions of muscle fibers. Myofibrils run the length of muscle fibers. Inside of muscle fibers are dark colored striations made up of myofilaments within myofibrils called sacromeres. A sacromere stretches between two dark lines known as Z lines. Within sacromeres are two kinds of protein myofilaments. One is thick and called myosin, the thin myofilament is actin. An I band is light colored and contains actin filaments attached to a Z line. The dark parts of the A band have overlapping actin and myosin filaments. The H zone contains only myosin filaments.

This graphic taken from Human Biology page 233, shows skeletal muscle structure and function. Sylvia S. Mader

Muscle Contraction

Motor neurons stimulate muscle fibers to contract. I talked about nerve impulses in my last compendium. In the case of a muscle contraction the neurotransmitter is acetylcholine (ACh). ACh is released into the synaptic cleft when a nerve impulse arrives at the axon terminal. Once released, ACh diffuses across the synaptic cleft and binds to receptors in the sarcolemma. Next, impulses generated by the sarcolemma spread down T tubules to the sarcoplasmic reticulum.The sarcoplasmic reticulum releases Ca2+ which causes sacromere contraction.

This graphic illustrates a neuromuscular junction. You can see ACh in the lower right corner diffusing across the synaptic cleft. Human Biology, Page 234, Sylvia S. Mader.

When a muscle fiber contracts, the sacromeres (inside myofibrils) shorten. This causes actin filaments to slide past the myosin. The I band shortens, the Z line moves inward, and the H zone almost disappears. This is known as the sliding filament model.

There are two other proteins involved with the actin filament. Tropomyosin winds around the actin filament and troponin is found in intervals along the threads. When released, CA2+ combines with troponin, causing tropomyosin to change position. Now myosin binding sites are exposed and myosin and actin can now bind.

This illustration shows how calcium, and myosin work in muscle contraction. Human Biology, page 235, Slvia S. Mader.

A motor unit is made up of a nerve fiber and all the muscle fibers it stimulates. If one muscle fiber in a motor unit is stimulated, all its counterparts in that unit are as well. The number of muscle fibers within a motor unit varies. Some are very large, like those controlling the gastrocnemius, and some are much smaller like in the case of of the muscles moving the eyes.

Energy

Fuel for excercise can come from stored muscle or blood. Glycogen and fat are stored in muscles and the amount used depends on how hard and how long a person is working their muscles. Energy is also taken from blood glucose and plasma fatty acids. These sources of energy are provided by the blood. Muscle cells can get more ATP by formation of ATP in the creatine phosphate pathway, through fermentation, or through cellular respiration. Normal aerobic exercise relies on cellular respiration.

VI Conclusion

I guess the main thing I got out of this topic is that movement is a very complicated process. We don't often stop and think about the amount of energy and activity that is involved in simple muscle movements. The multitude of funtions of the skeletal and muscular systems was aslo very interesting to me. The roles these systems have in homeostasis was not something I had considered before reading these chapters.

Works Cited:

Human Biology, Sylvia S. Mader

Movement PowerPoint, Professor Frolich

www.georgehernandez.com/.../Health/Anatomy.asp

www.aclasta.co.nz/osteoporosis/index.htm

www.school-house-rock.com (not really a work cited, more for fun)

Ethical Issues Essay: Use It or Lose It

Today, I did something rather odd. I picked up the phone, dialed my supervisor's extension, asked her a question, then hung up. Sound like a reasonable thing to do? Well not really when you consider the fact that my supervisor literally sits ten feet away from me, separated by a line of cubicles. Add to this the fact that I am currently enrolled in the Arizona Take Charge Challenge (ATCC), a program designed to promote physical activity and you can more clearly see how peculiar my behavior actually was. The truth is, I was in the middle of writing a grant and did not want to interrupt my train of thought by getting up and walking across the room, so lifting the receiver to make a quick phone call was much more convenient. Therein lies the problem...convenience. We have created all these amazing inventions to improve our quality of life, automobiles, telephones, washing machines, but there is a trade off. People are living longer but getting fatter. How will the unexpected consequence of obesityand the problems that go with it affect our quality of life.

Ironically, the grant I am currently working on deals specifically with working at the policy level to help change those behaviors that have a direct consequence on our health... number one on the list was lack of physical activity. One of the suggestions was work place interventions. Looking at the various websites and articles on the Internet I was impressed by all the creative and innovative programs different agencies have utilized to encourage physical activity. Some of these programs look very similar to ATCC. The question is, how do you get people to turn these activities into habits.

Three times a week I teach an exercise program for older adults at an assisted living facility. This program is evidence based and when properly implemented can help older adults improve or maintain function. The thing is, most of the adults that are regulars in the program were exercising before I came along. In other words they were already in the habit of exercising. So how do we encourage those that are not already doing it to engage in physical activity?

I was intrigued by the idea of "the built environment of the future." Building our neighborhoods and shopping centers in such a way as to promote physical activity. There was also a reference to video games that promote movement (many assisted living and enhanced care facilities have invested in The Wii for this very reason). When I read these kinds of ideas I cannot help but play devil's advocate. Is fooling someone into becoming physically active really the answer? Does it ultimately solve the problem?

Another idea is to make physical activity fun. There is a social component to exercise. If you have ever watched children on the playground you can see how they interact in very physically active ways. A couple of weeks ago I watched my daughter hop on and off a park bench dozens of times while carrying on a conversation with a friend. Meanwhile the friend twirled round and round a pole. I am not sure what they were doing exactly but they were definitely having fun and getting plenty of exercise at the same time.

Education is obviously important, but how to get the message out and get people to respond. It has been said that it takes three years to completely change a behavior, and even after all that time it can be a struggle. It is almost as if we are culturally conditioned to live sedentary lifestyles. Think about it, office jobs are considered more desirable by many people because of the lack of physical labor. Why would anyone want to be more physically active if a sedentary lifestyle equals higher social status?

Many people finally begin exercising after experiencing a life threatening event like a heart attack. unfortunately this is not the ideal way of changing a behavior. Of course we want people to be physically active before obesity, cardiovascular disease and other issues become a problem. The ideal time to begin the habit of being physically active is during childhood.

It seems that all of these factors need to be considered in order to change the direction society has been heading. Two thirds of american adults are overweight. Technology is a good thing but so is exercise. If we no longer have to do hard labor to make a living we have to find other ways to get exercise, it's a trade off.

This lyric by the Police kept running through my head while I was writing this so I decided to include it for good measure:

"Another working day has ended. Only the rush hour hell to face. Packed like lemmings into shiny metal boxes. Contestants in a suicidal race." -Synchronicity, The police

Online Lab Muscle Function

I wanted to get an idea of how my muscles responded in certain situations. The situations tested were muscle contraction vs. relaxation, muscle reaction to cold, and muscle reaction to fatigue. The tools I used to conduct this experiment can be seen in the photo below.

A bowl of ice cold water, a strip of paper, a rubber ball, and a stop watch.

1. What are the three changes you observed in a muscle while it is working (contracted)?

The muscle became firm to the touch and slightly raised. The circumference of my arm also increased by about half an inch when I formed a fist.

2. What effect did the cold temperature have on the action of your hand muscles? Explain.

My muscle seem ed to get stiffer and slower to respond. I was able to form a fist far fewer times after the cold water. Are my blood vessels constricting to preserve heat and therefore depriving the muscles of needed oxygen?

Soaking my hand in the ice water.

3. In Figure 3, make a line graph of your results of the fatigue experiment. Be sure to fill in the values on the vertical axis.

My graphed results

4. What effect did fatigue have on the action of your hand muscles? Explain.

First of all my arm muscles began to ache. Second, they began to respond more slowly and did not feel as coordinated. The amount of squeezes every 20 seconds began to steadily decline.

Squeezing the ball during the fatigue experiment.

Illustration taken from www.rogers.k12.ar.us/.../musclenotes.html showing how a muscle contraction works.

I think the reason on the cellular level that my muscles responded the way they did to the cold has to do with cell respiration (maybe). Are the cells possibly not getting as much oxygen because my body is responding to the cold? I know that cells require oxygen in order to produce ATP unless they kick into anaerobic mode. I believe that that is the case with the fatigue exercise. After a certain amount of time my muscles kicked into anaerobic mode for energy which can only be sustained for short bursts.

Lab Project: Model of a Working Human Limb

For the lab for this unit we were supposed to construct a working limb, complete with muscles and neurons causing muscles to contract. After much thought I decided to present an arm, using the elbow joint and the biceps and triceps muscles. My problem was that I could not figure out how I was going to create the bones. Finally I decided to use newspaper and masking tape, so all of the bones that you see in the photographs, the humerus, radius, and ulna, were constructed out of rolled up newspaper and masking tape. They turn out a lot better than I expected actually. Obviously the biceps help us to flex the forearm and the triceps helps us extend it.

List of parts an d supplies:

Bones

Newspaper

Masking tape

Muscles and Tendons

Red Cloth

Newspaper

Neuron

Pipe cleaners

Card Stock

Muscle Fiber

Pipe Cleaners

White fabric

Sodium-Potassium Pump

Card Stock

Sequins (Hearts=sodium ions, Snowflakes=potassium ions)

Pipe Cleaners

Muscle cell

Pipe Cleaners

Sequins

These are the supplies I used for the model. The masking tape and newspaper were almost gone by the time I finished.

For the muscles I used red cloth stuffed with newspaper and masking tape as tendons.

Creating the bones, you can see one of them beside me.

Bone model, I think the labels make it pretty easy to understand.

Cutting a dendrite out of card stock.

Twisting pipe cleaners into an axon.

I know this one begs for an explanation. Basically the hearts represent the sodium ions (Na+) and the snowflakes are potassium (K+). The photo above shows resting potential.

In this photo action potential is beginning. This is when depolarization occurs. The Na+ gates have opened and Na+ is moving into the axon.

Here the K+ gates are open and K+ is moving outside of the axon. The action potential is ending.

A model of a neuron, a nerve impulse is traveling down the myelinated axon.

A very lame looking muscle fiber with myofibrils *sigh*.

This photo shows the sacomeres relaxed...

..here they are contracted.

Basically my models show the bones and muscles of the arm and what happens inside those muscles. I actually learned a bit more about how the muscle works from putting this together. I was a little confused about muscle cells and this helped me to get a better feel for the parts of a muscle cell.

Leech Lab

Finding the ganglion




The dye has been injected




Identifying the neuron

1. What is the electrode measuring?

The electrode is measuring the voltage of the neuron.

2. Why use leeches in neurophysiology experiments?

Leeches are popular subjects with neurobiologists because they have relatively few neurons (about 175 pairs) and those neurons are fairly easy to get to. Also, it seem that leeches do not elicit the sympathy that other, cuter animals subjects do.

3. What is the difference between a sensory and a motor neuron?

A sensory neuron carries nerve impulses to the brain, while motor neurons takes nerve impulses or commands to the effectors in the skeletal muscles.

4. Do you think a leech experiences pain? What is pain?

I think leeches can experience pain, they do have a nervous system. The leech was anesthetized prior to the procedure so I don't think it experienced pain in this case. Pain is caused when sensory receptors in the area send nerve impulses to the CNS. Motor neurons in turn send commands to effectors telling our bodies what to do in response. An example is touching a hot surface and reflexively withdrawing our hand.

5. What were the two most interesting things about doing this lab?

It was interesting to me that although the leech is a relatively simple creature, dissecting it is still quite complicated. I also find it interesting that there are some basic similarities between the leech's nervous system and our, like the nerve cord for example.

6. Anything you found confusing or didn't like about the lab?

I did not find anything particularly confusing, but i do not think I could dissect an real leech on my own.

Compendium Review Unit III: Nervous System

This is a storyboard from "Telegraph Line" one of the Schoolhouse Rock videos. This one is about the nervous system.

http://www.thedeeparchives.com/ex_show_top.php4?ex_id=7

I Introduction

II Overview of Nervous System

• Neurons and the Nerve Impulse

III Central Nervous System

• Spinal Cord
  
• Brain

IV The Limbic System

V Peripheral Nervous System

• Somatic System
  
• Autonomic System

VI Sensation

• Sensory Receptors

VII Senses

• Taste
  
• Smell
  
• Sight
  
• Hearing
  
• Equilibrium

VIII Conclusion

An illustration showing the brain, spinal cord and nerves. Taken from Human Biology, page 248. Sylvia S Mader

I. Introduction

How is it that our bodies are able to interact with the world around us? It blows my mind to think that my brain is able to process all the different stimuli around me through the various senses. Furthermore, I am able to thwart injury reflexively through the sensation of pain. The nervous system, which is responsible for this "connection" of body to the environment, is a complex and fascinating subject. My hope is that this short summary will do this amazing system the justice it deserves.

II. Overview of the Nervous System

The nervous system consists of the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS includes the brain and spinal cord while the PNS consists of nerves. These two systems work together to receive sensory input from inside and outside the body, integrate that input, and generate output throughout the body. There are two types of cells found in nervous tissue, neurons and neuroglia. Nerve impulses are transmitted throughout the nervous system by neorons. Neuroglia have the role of supporting and nourishing neurons.

Neurons and the Nerve Impulse

Nerve cells are called neurons. There are approximately 100 billion neurons in the human brain!The three trpes of neurons are sensory neurons, interneurons, and motor neurons. These neurons can be classified based on the direction that they send information. Interneurons reside completely within the CNS and receive input from each other and sensory neurons. Motor neurons take nerve impulses to effectors which are responsible for carrying out our responses to the world around us. These responses can be external like swatting a fly, or internal like body temperature.

Like other cells, neurons have a cell membrane, nucleus, mitochondria, and other organelles. However neurons differ from other cells in that they do not undergo mitosis. Neurons also have special extensions known as dendrites and axons. Dendrites are short extensions that bring information to the cell body from other neurons or sensory receptors. Axons on the other hand can be quite long, these extensions carry information away from the cell body. Axons are responsible for conducting the nerve impulse. Many axons have a protective covering called the myelin sheath. Myelin is often formed by a neuroglia called Schwann cells. The longer axons have the myelin sheath, but not the shorter ones. The gaps in the myelin sheath are known as the nodes of Ranvier. People who have been diagnosed with multiple sclerosis have a loss of myelin from the axons.

An illustration showing the types of neurons, their dendrites, and an axon sheathed in myelin. From Human Biology, page 249, Sylvia S. Mader.

The Nerve Impulse: I learned from the neuroscience for kids website that most of the information we have regarding the nerve impulse comes from studying the giant axons on squid. I guess because of its size, this axon is easy to study. Basically, nerve impulses send information within the nervous system, and it is sent electrochemically. Electrically charged chemicals within the body are called ions. Sodium and potassium ions are each have one positive charge and are the important ions in the nervous system.

When an axon is not not conducting an impulse, it is said to be at its resting potential. During resting potential the charge on an axon will be -65 mV. At this time the inside of the neuron is negative as compared to the outside. Sodium ions are more numerous on the outside than the inside of the axon. Ions will try to balance out on either side of the membrane, but the membrane only allows certain ions to pass through. This unequal distribution of ions is caused by the sodium-potassium pump which transports sodium out of the axon and potassium in.

When a neuron responding to a stimulus sends information down an axon it is known as the action potential. At this point depolarization occurs; depolarization simply means that the charge inside the axon goes from negative to positive. To make this happen, a "gate" or rather a protein structure in the membrane opens to allow sodium to enter into the axon. Then another "gate opens to allow potassium to flow to the outside of the axon. When the potassium flows out this changes the membrane charge from -65 mV to +40 mV. After an action potential has passed the negative charge of a resting potential is restored.

This graphic taken from www.millerandlevine.com/.../898-899-rewrite.html illustrates the sodium-potassium pump

The above graphic nicely illustrates an action potential. Taken from health.howstuffworks.com/nerve4.htm

An action potential will travel the length of an axon. In an axon that is myelinated the action potential will go from one Ravier node to another. This type of conduction is called saltatory conduction. Saltatory conduction is faster and uses less energy. Action potenials along nonmyelinated axons move more slowly. A refactory period occurs after an action potential has passed, preventing it from moving backward along the axon.

An illustration of an action potential moving down a myelinated axon. Taken from Human Biology, page 251, Sylvia S. Mader

At the end of each axon are small swellings called axon terminals. These axon terminals are located either close to a dendrite or the actual cell body of a neuron. The area between the axon and neuron/dendrite is called a synapse. A small gap called the synaptic cleft separates a sending neuron from a receiving one. Nerve impulses are not able to jump this gap so neurotransmitters must aid impulses in getting from one neuron to another. Neurotransmitters are molecules that are stored in synaptic vesicles in the axon terminals. When an action potential reaches the axon terminal, calcium ions enter the terminal, causing the synaptic vesicles to merge with the sending membrane. Then these molecules are released to bind to receptors along the membrane of the receiving neuron.Depending on the type of neurotransmitter, the response of the receiving neuron can be either excitation or inhibition. Neurotransmitters are removed from the cleft after doing their job. There are over 100 known neurotransmitters. A few examples include dopamine, serotonin, acetylcholine, and glutamate.

A graphic showing synapse structure and function. This example shows an excitatory neurotransmitter. Human Biology, page 252, Sylvia S. Mader

III Central Nervous System

The central nervous system (CNS) is composed of the brain and spinal cord. It is in the CNS that sensory information is received and motor control is initiated. The brain is protected by the skull and the spinal cord is protected by vertebrae. For extra protection they are also surrounded by membranes called meninges to provide a cushion. Two types of tissue are found in the CNS. Gray matter includes cell bodies and short nonmyelinated fibers, while white matter has myelinated axons running together in bundles called tracts.

Spinal Cord

Like the brain, the spinal cord contains both gray and white matter. The cord extends from the base of the brain and is protected by the vertebral column. Spinal nerves extend from the spinal cord. There are intervertebral disks between the vertebrae. Cerebrospinal fluid is contained within the central canal. Within the white matter there are ascending tracts that take information to the brain and descending tracts. I have often heard that the right side of the brain controls the left part of the body and vice versa. Apparently this is true as many of these tracts cross as they enter and exit the brain. As far as I can tell, the spinal cord basically hooks up the body to the brain. This is why a spinal cord injury can cause paralysis. the spinal cord is involved in reflex actions as well.

Brain

The brain contains four ventricles, the two lateral ventricles, the third ventricle and the forth ventricle. The ventricles are interconnecting chambers that produce cerebrospinal fluid and serve as a reservoir for it as well. The other parts of the brain I will be discussing are the cerebrum, the diencephalon, the cerebellum, and the brain stem. I should also mention that like the spinal cord, the brain is composed of white and gray matter.

Cerebrum: Another name for the cerebrum is the telencephalon. The cerebrum makes up the largest part of the brain in humans. This part of the brain is the last to receive sensory input and integrate information before commanding voluntary motor responses. The cerebrum also communicates and coordinates activities with other parts of the brain. A grove called the longitudinal fissure divides the cerebrum in to the left and right hemispheres. The hemispheres are divided into lobes by sulci. The frontal lobe is directly behind the forehead, the parietal lobe is behind it, the occipital lobe is at the back of the head, and the temporal lobe lies beneath the frontal and parietal lobes. Each of these lobes carry out certain functions as illustrated below.

The cerebral hemespheres are covered by thin outer layer of gray matter called the cerebral cortex. The cerebral cortex is the part of the brain that handles sensation, voluntary movement, and thought processes we associate with consciousness. Within the cerebral cortex are the primary motor and primary somatosensory areas. The primary motor area is found in the frontal lobe and certain sections control different parts of the body. Commands to skeletal muscles originate in the primary motor area. The primary somatosensory area is in the pariental lobe and receives sensory information from the skin and skeletal muscles.

The different lobes of the brain and their functions, taken from Human Biology page 257, Sylvia S. Mader.

The Diencephalon: The diencephalon covers the third ventricle and includes the hypothalamus and the thalamus. The floor of the third ventricle is formed by the hypothalamus. The hypothalamus has the job of regulating sleep, hunger, thirst, body temperature, and water balance. In this way the hypothalamus has a role in homeostasis. The hypothalamus is a link between the the nervous and endocrine systems by virtue of the fact that it controls the pituitary gland.

All sensory information with the exception of smell is received by the thalamus. Located in the sides and roof of the third ventricle, the thalamus is made out of two chunks of gray matter. The thalamus integrates the information it receives and sends it off to the appropriate parts of the cerebrum.

The Cerebellum: Located below the occipital lobe, the cerebellum is made up of two parts. Input relating to where certain body parts are, sent from the eyes, ears, joints, and muscles, is received by the cerebellum. This information is then integrated and sent as nerve impulses via the brain stem to the skeletal muscles. The cerebellum helps us maintain posture and balance. Maybe I have a problem in the cerebellum because I am a total klutz!

The Brain Stem: Insde the brain stem you will find the pons, the medulla oblongata, and the midbrain. The pons includes bundles of axons that travel between the cerebellum and the rest of the CNS. It also works with the medulla oblongata to help regulate breathing. In addition to breathing, reflex centers within the medulla oblongata regulate heartbeat and blood pressure. These centers also play a role in sneezing, coughing, vomiting and swallowing. The midbrain serves as a relay station between the spinal cord and other parts of the brain. It also contains reflex centers.

Masses of gray matter called nuclei and other fibers make up the reticular formation. This network extends the length of the brain stem. The reticular formation is a big part of the reticular activating system (RAS). The RAS is responsible for sending sensory signals up to the higher parts of the brain. It also sends motor signals to the spinal cord. Injury to this system can result in a coma.

IV The Limbic System

The limbic system is made up of several structures within the cerebrum including the amygdala and the hippocampus. The limbic system plays a role in both our emotions and higher mental functions like memory and speech. I thought it was kind of funny that both of these things come from the same part of the brain as our emotions often seem to get in the way of our minds. The amygdala is responsible for the sense of fear and also gives certain experiences like grief its emotional overtones. In contrast, the hippocampus plays an important role in learning and memory.

There are different kinds of memory. Short term memory is attributed to the prefrontal area of our brains which is effected by Alzheimer disease. Long term memory is broken up into two groups, semantic (numbers, words) and episodic (people, events). I am better at the former than the later. Skill memory involves all the motor areas and has to do with learned skills like riding a bike or driving a car.

V Peripheral Nervous System

The nerves that run throughout our bodies are part of the peripheral nervous system. the nerves that come from the brain are called cranial nerves of which we have 12 pairs. Cranial nerves can be sensory nerves or motor nerves. Nerves that arise from the spine are spinal nerves; there are 31 pairs of spinal nerves. Spinal nerves contain both sensory and motor fibers and are therefore known as mixed nerves. All nerves have the role of taking impulses to and from the CNS.

There are divisions to the peripheral nervous system, the somatic system and the autonomic system.

Somatic System

The somatic system is made up of nerves that serve the skin, skeletal muscles, and tendons. Nerves in this systom can take information from sensory receptors on the skin to the CNS and motor commands from the CNS to the skeletal muscles.

Sometimes the actions our bodies take are not voluntary, these involuntary responses are called reflexes. The illustration below shows the path of a reflex arc when a person touches a pin. This example involves the spinal cord. When skin is pierced by the pin, sensory receptors send nerve impulses along sensory axons through the dorsal-root ganglia to the spinal cord. The data is integrated by interneurons and sent to motor neurons. A nerve impulse is sent down a motor axon commanding skeletal muscles to contract. The result is that the hand moves away from the pin. Of course all of this takes place in a split second!

An example of a reflex arc taken from Human Biology, page 263, Sylvia S. Mader.

Autonomic System

The autonomic system is responsible for regulating the activity of the smooth muscles and glands. Basically this system functions automatically in an involuntary manner, innervates all internal organs, and uses two neurons and one ganglion for each impulse. The system is divided into two parts, the sympathetic division and the parasympathetic division. These two divisions generally produce opposite responses. The sympathetic division is responsble for the fight of flight response. Some of the involuntary aspects of this response include an increased heart rate an dilated bronchi. The parasympathetic system promotes responses that are associated with a relaxed state.

An illustration of the sympathetic and parasympathetic systems taken from http://www.scholarpedia.org/article/Autonomic_nervous_system

VI Sensation

Sensation occurs when sensory receptors responding to external or internal stimuli send nerve impulses to the cerebral cortex of the brain. Sensation is the conscious perception of stimuli.

Sensory Receptors

Dendrites that are specialized to pick up certain types of stimuli are called sensory receptors. Exteroreceptors detect stimuli from outside the body, while interoceptors receive stimuli from inside the body. Interoreceptors respond to change in blood pressure and other internal body conditions that have a direct bearing on homeostasis.

There are four categories of sensory receptors in humans, chemoreceptors, photoreceptors, mechanoreceptors, and thermoreceptors.

Chemorceptors: These receptors respond to chemical substances nearby. These receptors involve taste and smell. Pain receptors (nociceptors) are a type of chemoreceptors and are important because they alert us of danger through the sensation of pain.

Photoreceptors: These receptors are directly involved in the sense of sight. Photoreceptors are sensitive to light rays. Rod cells enable us to see in black and white, while cone cells give us color vision.

Mechanoreceptors: These receptors are stimulated by sound, motion, and gravity. These stimuli result in pressure of some sort. Sound waves for example generate fluid-borne pressure waves that are detected by mechanoreceptors in the inner ear.

Mechanoreceptors involved in reflex actions are known as proprioceptors. These receptors help us maintain muscle tone and therefore keep the body's equalibrium and posture. Muscle spindles are able to send messages to the spinal cord and motor nerve impulses order muscle contraction in order to maintain muscle tone.

An illustration of a muscle spindle taken from Human Biology page 276, Sylvia S. Mader

Thermoreceptors: These receptors can be found in the hypothalamus and skin and respond to changes in temperature. There are both warmth and cold receptors in the body.

The skin contains cutaneous receptors that are sensitive to touch, pain, pressure and temperature. Although the book did not classify the different cutaneous receptors as one of the four sensory receptors it is easy to guess based on their functions.

An illustration of touch and pressure receptors found at www.octc.kctcs.edu/gcaplan/anat/Notes/API%20N...

VII Senses

Taste

The sense of taste is brought about by chemical receptors that respond to in the food we eat. The senses of taste and smell are connected and a lot of our perceived "tastes" are directly related to smell. Adults have about 3,000 taste buds which are found mainly on the tongue, although there are taste buds on other parts of the mouth as well. There are five primary types of taste, sweet, sour, bitter, salty, and umani. Some areas of the tongue are more sensitive to certain tastes than others.

A graphic showing the tungue and the sense of taste taken from embryology.med.unsw.edu.au/notes/tongue.htm

Smell

Humans have about 10 to 20 million olfactory cells. There are olfactory cells found inside olfactory epithelium up in the roof of the nasal cavity. As I mentioned before, our sense of taste is directly related to smell. There is a connection between olfactory cells and the limbic system which causes certain odors to bring up vivid memories.

An illustration showing where olfactory cells are located and how they work. Human biology, page 279, Sylvia S. Mader

Sight

Eyeballs are spherical and made up of three layers, the sclera, the choroid, and the retina. The outer layer, the sclera, includes the cornea which is the window of the eye. The middle layer, the choroid, includes the iris which regulates the size of the pupil. The pupil is a hole in the center of the iris that allows light to enter the eyeball. Behind the iris is the ciliary body on which the lens is attached. The ciliary body helps control the shape of the lens to provide near and far vision. Thelast layer, retina contains photoreceptors. As I mentioned before, rod cells do not see color and cone cells do. The optic nerve, located at the back of the eye is fomed out of sensory fibers from the retina. The optic nerve takes nerve impulses to the visual cortex giving us the sense of sight.

Rhodopsin is a molecule found in rods and is highly sensitive to light. Rhodopsin is made up of the protein opsin and the molecule retinal. When rods are exposed to light signals are sent to the retina. Rods are useful for night vision.

As I mentioned before, cones are responsible for color vision. Cones contain three pigments for blue, green , and red. These pigments contain retinal and opsin.

There are three layers to the retina. The rod and cones cells are contained in the layer of the retina closest to the choriod. Bipolar and ganglion cells in the other two layers of the retina and the sensory fibers of the ganglion cells become the optic nerve. Integration happens when signals are sent to bipolar and ganglion cells. Ganglion cells send nerve impulses via the optic nerve to the visual cortex.

Hearing

There are three parts to the human ear, outer, middle, and inner. The outer ear includes the pinna and the auditory canal. The middle ear begins at the eardrum (AKA tympanic membrane). Three bones called the ossicles are also found in the middle ear. The inner ear includes the semicircular canals, the vestibule, and the cochlea. Of these three parts it is the cochlea that has a role in hearing.

Mechanoreceptors consisting of hair cells in the inner ear are sensitive to mechanical stimulation. Hearing results when sound waves enter the auditory canal and hit the eardrum. The vibration creates pressure which is moved along and multiplied by the ossicles. The stapes (one of the ossicles) strikes the oval window and the pressure is passed on to the cochlea. These pressure waves then move on to the tympanic canal and across the basilar membrane. This is where the hair cells come in. They start to bend, and nerve impulses begin in the cochlear nerve and make their way to the brain.

A graphic showing the anatomy of the human ear, Human Biology, page 286, Sylvia S. Mader.

Equalibrium

Our sense of balance takes place in the inner ear, specifically in the semicircular canals and vestibule. Fluid in these parts of the inner ear is stimulated by movements of the head and/or body giving us a sense of movement and acceleration.

Illustrations of the inner ear and its relationship to balance and equalibrium. From the Power Point presentation and Human Biology, Sylvia S. Mader

VIII Conclusion

Overall I found the nervous system quite interesting. I will say that I obtained a basic grasp of the processes of the central nervous system and its connection to the peripheral nervous system. I can basically understand the "wiring" that links our body parts to our brain. However the five senses and how they are processed (especially sight) are still pretty confusing to me. I do understand the concept of the different neurons and how they are specialized to send messages to the brain, but it is still a mystery to me as to how are brains are able to process the images sent and translate them as well.

Works Cited:

Human Biology, Sylvia S. Mader

Professor Frolich's Power point Presentation

http://faculty.washington.edu/chudler/introb.html

www.thedeeparchives.com

www.millerandlevine.com

health.howstuffworks.com/nerve4.htm ...Great!

www.scholarpedia.org

www.octc.kctcs.edu

embryology.med.unsw.edu.au/notes/tongue.htm