Self and Unit Evaluation

REGARDING YOUR OWN PERFORMANCE
1. What were the three aspects of the assignments I've submitted that I am most proud of?

I am most proud of my compendium reviews. I feel that I spend a lot of time on those and use the internet as a resource to supplement the class material in a way that makes the learning interesting and the information easy to recall. I am also proud of my quiz grades. I've taken the time to review the material and this is reflected in them. Lastly, I'm proud of the fetal development lab. I learned a lot when picking and choosing the events I felt to be most relevant during the development process.

2. What two aspects of my submitted assignments do I believe could have used some improvement? I could have spent more time on the last lab assignment. We lost electricity for several days this past week and I waited until the last minute to finish that one. I would have liked to use personal pictures instead of ones online, but was under a time constraint to get it done. Also, I would have spent more times with the weblinks this unit. I didn't focus as much on them as I had in other units.

3. What do I believe my overall grade should be for this unit? I feel that I should get an A in this unit. All of my work is complete and on time, as per the directions.

4. How could I perform better in the next unit? Now this makes me happy. This is the last unit.


REGARDING THE UNIT (adapted from Stephen Brookfield, University of St. Thomas "Critical Incident Questionnaire")
At what moment during this unit did you feel most engaged with the course? I felt most engaged during the Fetal Development Lab. A lot of my friends are going through pregnancy so it was the assignment of the most interest to me.

At what moment unit did you feel most distanced from the course? When our power went out this weekend from a monsoon--I couldn't access the coursework and had luckily completed most of it early.

What action that anyone (teacher or student) took during this unit that find most affirming and helpful? I was pretty much on my own in this unit.

What action that anyone (teacher or student) took during this unit did you find most puzzling or confusing? Again, I was pretty much on my own here.

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.) I was surprised about how much of the information I already knew. I'd taken one biology course in high school, and much of this information was covered then. The unit was a good review, though I'd expected more new information.

Lab Project Four: Species Interaction

1. horses EQUUS CABALLUS Horses are a domesticated species. They have been used by humans for agriculture, companionship, transport, and recreation for a good deal of time. *mutualistic

2. dogs CANIS FAMILIARIS Dogs are a domesticated species. They have been used by humans for companionship, hunting, etc. for quite while. *mutualistic

3. humans HOMO SAPIEN *symbiotic (only one species is present here, but both parties of that species benefits)

4. cat FELUS CATUS Cats are domesticated for companionship. *mutualistic

5. fire ants SOLENOPSIS CONJURATA *parasitic

6. lemongrass plant CYMBOPOGON CITRATUS *symbiotic

7. egg/hen GALLUS DOMESTICUS Hens are domesticated for agricultural purposes. *mutualistic

8. kale BRASSICA OLERACEA *mutualistic

9. soybeans GLYCINE MAX *mutualistc

10. alfalfa MEDICAGO SATIVA *mutualistic

11. amaranth GOMPHRENA GLOBOSA *mutualistic

12. quinoa CHENOPODIUM QUINOA *mutualistic

13. pine nuts PINUS EDULIS *mutualistic

14. cottonwood tree POPULUS DELTOIDES *commensal

15. plum tree PRUNUS ANGUSTIFOLIA *mutualistic

16. apricot tree PRUNUS ARMENIACA *mutualistic

17. lizards (SKINK) EUMECES GILBERTI *mutualistic

18. javelina TAYASSU TAJACU *commensal

19. corn ZEA MAYS *mutualistic

20. quail (CALIFORNIAN) CALLIPEPLA CALIFORNICA *predation

Embryonic and Fetal Development Lab

Significant Events During Embryonic and Fetal Development

1. Fertilization begins when the sperm penetrates the egg and ends with the production of a zygote. This normally takes 24 hours. This is significant as it is the very first stage of embryonic and fetal development.

2. Implantation takes place after 7-12 days. The egg attaches to the womb in order to survive.

3. Placenta forms usually around the 13th day. This provides nourishment and blood to the fetus.

4. Cardiac Muscle Contraction Begins

Neural Folds/Heart Folds begin to fuse. This happens within 21-23 days from fertilization.

The two endocardial tubes formed previously now fuse. Together they form one single tube generated from the cells of the "roof" of the nueral tube. The heart tube takes on an S-shape establishing the asymetry of the heart. As the S-shape forms, cardiac muscle contraction begins.

5. Kidneys Start to Produce Urine- this happens around 44-48 days. Kidneys remove toxins and waste from the body and are essential to survival.

6. Brain Structure Complete - at 61-68 days. This is necessary to control thinking, breathing, movement, etc.

7. Fetus is Able to Hear- 22 weeks.

8. Lung Development- at 26 weeks the lungs are developed enough to breath oxygen.

9. Use of Eyes- at 32 weeks the baby can open and close its eyes.

10. Birth- the baby is fully developed and ready to be born at 40 weeks.

Demographics Online Lab

These images show a human population simulation. The time frame for this simulation extends to the year 2050. The first simulation shows the world population versus that of Yemen. The second simulation shows the world population versus that of the United States.

1. My high fertility rate country was Yemen. The fertility rate for this country is 7.3 children.

2. My low fertility country was the United States. The fertility rate for this country is 2 children.

3. High fertility rate results in a high number of young people in a population. In Yemen for instance, the fertility rate is 7.3. If each family has seven children, there is a good possibility that many of those children are young in age. Also, the life expectancy is not that high in Yemen (only to the average age of 50). The pyramid shape results because there are many more young people than old people. As far as future population growth--there will be a substancial increase in population. (If each of those 7 children reproduce even one child there will be a dramatic increase in population).

4. Low fertility rate leads to a lot of middle aged people. If the fertility rate is low, people are not reproducing at a high level of frequency so the youngest demographic will taper off. Also, the oldest generation will be smaller in number because of natural death. The result of the two will be a more in-between population demographic.

5.

Middle Aged/Older: quiet, reserved, calm, organized, efficient, scheduled, maintained, orderly, strict, understimulated

Children: loud, chaotic, overstimulated, reckless, unorganized, unscheduled, disorder, free-spirited, mess, fun

Unit Four Ethical Issue

World Resource ABUSE

World resource use--particularly energy use has gotten out of control. Economic development has put the world on a fast track to destruction. Stereotypically, Americans are one of the most wasteful of societies. Population growth will naturally contribute to the depletion of resources. How much depletion, however, will result in the demographics of that population increase.

In the third world island nation of Vanuatu for instance population growth may not have that much effect on energy use. Typically, there is no electricity, no vehicles, no running water. When a family increases in size they adapt to the addition by planting extra crops. Bathing is done in streams, the ocean, or in rain. Composting toilets are used.

In America, however, an addition to the family generally means a larger (less full efficient) vehicle and one more person to use an abundance of unnecessary electricity and water resource. "A typical U.S. child will consume the same resources as 30 children in India and 300 children in Ethiopia. A typical U.S. resident consumes energy as if they were a 30,000 kg primate".


We should stop encouraging economic development in "under-developed" countries. The fact is, we are over-developed and enabling an abuse of world resources. America would do well to take others into consideration for once: un-develop and waste less.

Compendium Review: Chapters 22,23,24

Human Landscapes

Evolutionary History (text, page 488)

Natural Selection (text, page 474, 488)

Human Ecology (Powerpoint)

-Physical Landscape (text page 508, http://epa.gov/climatechange/kids/greenhouse.html)

-Biological Landscape (domestication) Powerpoint

Biological evolution explains the unity and diversity of life. (Descent from a common ancestor explains the likeness of living things. Adaptation to different environments explains the diversity of living things).

Fossil evidence supports evolution.

Darwin discovered much of the evidence for common descent.

Biographical Evidence: the distribution of organisms on Earth is explainable by assuming that organisms evolved in one locale.

Anatomical Evidence: the common anatomies and development of a group of organisms are explained by descent from a common ancestor.

Biochemical Evidence: all organisms have similar biochemical molecules.

Darwin developed a mechanism for adaptation known as natural selection. The result of natural selection is a population adapted to its natural environment.

The critical elements of natural selection are variation, competition for limited resources (such as food), and adaptation.

Over time the environment "selects" members of a population for better-adapted traits. (Those with more advantageous traits capture more resources and are more likely to reproduce and pass on those traits).

The classification of humans is traced to our ancestry. The first hominid (this includes humans) is thought to have lived around 6-7 MYA.

There are two hypotheses of modern human evolution. The multiregional continuity hypothesis suggests that modern humans evolved separately in Europe, Africa, and Asia. The out-of-Africa hypothesis says that humans evolved in Africa, but then migrated to Asia and Europe.

Human Ecology: Species, including humans, live in communities or ecosystems. A diagram of a human ecosystem is shown below.

Physical Landscape:

The Water Cycle: The reservoir of the water cycle is freshwater that evaporates from the ocean. Water that falls on land enters the ground, surface waters, or aquifiers and evaporates again. All water returns to the ocean.















The Carbon Cycle

The reservoirs of the carbon cycle are organic matter. (forests and dead animals for fossil fuels), limestone, and the ocean. The exchange pool is the atmosphere. Photosynthesis removes carbon dioxide from the atmosphere. Respiration and conduction add carbon dioxide to the atmosphere.









The Greenhouse Effect

The Greenhouse Effect is the rise in temperature that the Earth experiences because of certain gases in the atmosphere that trap energy from the sun. The gases are referred to as greenhouse gases because they warm the world. These gases include carbon dioxide, water vapor, methane, etc).









Biological Landscape: Domestication

The basis for our relationship with domesticated species includes the following:

-Food and Agriculture (food crops and animals)
-Transportation (animals)
-Care and Protection (pets)

Wikipedia provides a great, in-depth look at the history of domestication.

Chapter 16, 17 Compendium Review

Major Topic One: Reproduction

Human Life Cycle

Meiosis

How an Organism is Started

Fetal Development and Birth

Why We Develop and Age

The life cycle of higher organisms requires two types of cell division.

Mitosis: growth and repair of tissues

Meiosis: gamete production

Meiosis happens in the ovaries for females. One egg per month bursts from the wall of the ovary to be taken up into the Fallopian tube. This is Phase I. Phase II occurs if the egg is fertilized.

For males, meiosis is undergone constantly by sperm in the walls of tubules.

The image to the left illustrates the human life cycle. A detailed explanation is as follows: "This figure illustrates the human life cycle. Adults produce gametes by meiosis, and each gamete contains only one-half the number of chromosomes found in the somatic cells of the parent. Parental cells (containing 46 chromosomes) are called diploid cells, and are abbreviated as "2n." The gametes (containing 23 chromosomes) are called haploid cells, and are abbreviated as "n." When a haploid ovum and a haploid sperm unite through fertilization (also termed syngamy), a diploid zygote is produced. The life cycle describes how diploid (2n) individuals produce haploid (n) gametes, which then unite to form a new diploid (2n) zygote.

This alternation of meiosis and fertilization is found in the sexual life cycles of all sexually reproducing organisms, but its timing can differ considerably, depending on the organism. The human life cycle typifies the most common life cycle found in animals, where the gametes are the only haploid cells. They combine to form a zygote, which divides by mitosis (cell reproduction; discussed in more detail in tutorial 25) and grows to form a new individual.

In a second type of life cycle, as seen in most fungi and some protists (unicellular eukaryotes and their somewhat simple multicellular relatives), the diploid zygote produces haploid cells by meiosis; these develop into free-living, haploid, multicellular organisms. The haploid organisms then produce modified gametes by mitosis (they are already haploid, therefore, they cannot undergo meiosis), and these gametes unite to form diploid zygotes. Some plants and algae exhibit a third type of life cycle, termed alternation of generations. This life cycle contains both haploid and diploid, free-living, multicellular stages. The diploid multicellular stage, the sporophyte, produces spores by meiosis, which develop into a multicellular haploid stage, the gametophyte. The gametophyte produces gametes by mitosis, and these unite to form a new sporophyte. Although these three types of life cycles differ in the timing of fertilization and meiosis, they all produce genetic variation in their offspring ".

The image to the right is an overview of the process of meiosis.

Another really informative site with great illustrations on meiosis can be found at this link.

An organism is "started" when the sperm nucleus enters the egg and bonds with the egg nucleus.

The image to the left shows both the sperm and the egg. If an egg and a sperm meet in the Fallopian tube there is a good chance that one sperm will join with the egg, resulting in fertilization.

Fetal Development and Birth At the end of the embryonic period, all organ systems are in place and there is a mature and functioning placenta.

Fetal development extends from the third through the nine months. During the third and fourth months the skeleton is becoming ossified. (bone formation is occurring). The sex of the fetus also becomes evident. The fetus continues to grow and gain weight until it reaches nine months/birth.

During the first stage of birth the cervix dilates. Stage two takes place as the child is born. Stage three is the expelling of the afterbirth. Development after birth includes infancy, childhood, adolescence, and adulthood.

Aging may have a genetic basis and may be due to changes that affect the whole body. (the decline of the hormonal system for example). Aging can also be due to diet and exercise. Deterioration of organ systems can possibly be prevented (in part) by good health habits.

Unit Three: Model of a Working Limb

I used playdough for this lab to build a model of a working limb. I chose to create a model of the arm--showing the forearm both contracted and relaxed.


















I began by forming the bone structure. First is detail of the ball and socket joint that connects the pectoral (shoulder) girdle and the upper limb.

The large bone at the top of the arm is the humerus. This is joined to the two lower bones in the arm: the radius and the ulna. (The humerus is connected to the ulna with a hinge joint).

Next is detail of the arm at rest.

The muscles here are represented by the pink playdough.
Tendons are represented by the blue. Tendons enable the muscle to move the bone.

In the first image below, the bicep muscle is relaxed, while the tricep muscle is contracted.

In the second image the opposite is true. (This is because the bicep and the tricep muscles are antagonistic--meaning that they work in opposition).














Prior to the change in arm position, a neuron would carry a message to the muscle, signaling the muscle to contract. The image below shows a neuron signaling the bicep to contract.

A neuron is represented by orange colored playdough. The signal being sent by the neuron is also known as a nerve impulse or action potential. The Schwann cell (and myelin sheath) are represented by the smallest blue pieces of playdough within the orange (*not to be confused with the blue tendons--I ran out of colors!).

Ugh, I can not get these pictures to format. From left to right they are A, B, and C.

A

D

Image A shows a motor neuron. Again, Schwann cells are represented by blue. Neurotransmitters are located at the end of the strands in axon terminals. These send messages between the neurons.

Image B shows sarcomeres that are contracted. Image C shows sarcomeres that are relaxed. Both images represent the sliding filament process. Actin is represented by the pink, while myosin is represented by the orange. During this process the sarcomere shortens and actin filaments slide past the myosin filaments.

Image D shows action potential. The nerve impulse passes/is sent rapidly from one section to another.

Thus, the entire systems works together to enable movement. Movement begins as the central nervous system transmits a message via neurons. Nerve impulses then initiate the action. In conclusion, the process of initiating human movement likely simulates the process of initiating movement of other organisms. (image)

(Also, an informative page on the sliding-filament theory of muscle action can be found here).

*source: Mader, Sylvia. Human Biology, tenth edition.

Unit Three, Muscle Lab

This lab was a muscle testing. We began by observing our bicep at rest, and then observing changes as it was extended. Next, we repeatedly made a fist with one hand over a period of twenty seconds. Then we introduced ice to the testing to see how change in temperature would effect muscle activity. Following this we introduced a rubber ball--to be held while making the fist. (I chose to use a round pencil sharpener, as that was what I had available). Lastly, we did nine repetitions of the initial exercise (tightening one hand into a fist). This was to gage whether fatigue would have an impact on muscle activity.







These two pictures were taken during the lab. The image on the left shows myself about to make a fist around the pencil sharpener. The image to the right is preparation for the change in temperature testing.


Effect of Temperature on Muscle Action:

Number of fists in 20 seconds
normal temp. = 21 fists
after ice = 17 (very uncomfortable!) fists

Number of fists in 20 seconds *with pencil sharpener
normal temp= 15 fists
after ice = 12 fists

Number of fists per trial
1. 16
2. 16
3. 15
4. 15
5. 15
6. 16
7. 13
8. 12
9. 13
10.13

Analysis of Data:
1. What are the three changes you observed in a muscle while it is working (contracted)? When an activity is repeated the muscle is tired and can not perform the activity at its initial rate of speed. The muscle is tight/hardened when it it working. Also, the muscle appears larger when it is flexed.

2. What effect did the cold temperature have on the action of your hand muscles? Explain. The cold was very uncomfortable for my hand muscles--I had a hard time even keeping them in the ice. The change in temperature made it more difficult to open and close my hand. It was very constricting to the muscle.

3. (graph eliminated)

4.What effect did fatigue have on the action of your hand muscles? Explain. Fatigue slowed the action of the hand muscles. As I progressed through the trials, the longer I had been doing the activity, the lower the number of fists I was able to make.



It seem the contraction of the hand muscle was an attempt to warm the hand. The muscles were contracted in order to break down ATP to regulate the sudden change in temperature. Also, due to the nature of the exercise, the muscle did not have time to relax between fists for the final testing. Calcium was not returned to the muscle and therefore the hand muscles wanted to remain contracted and the action of making a fist was slowed down.

Unit Three Ethical Issue: Exercise...is the concept working?

If Exercise Works: Why are we so FAT?

Exercise has a substancial number of benefits. Studies have shown a correlation between exercise and the improvement of cardiorespiratory endurance. Exercise helps prevent weight gain because muscles metabolize faster than other tissues. A favorable change in body composition is often coupled with exercise. Exercise seems to prevent certain kinds of cancer as well as depression. So why aren't we exercising? (she types after having spent multiple hours herself sitting in front of a computer desk).

For many, exercising is an inconvenience. Sure, some of us are within walking distance to the grocery store. With the increase of gas prices it would be sensible to walk to pick up dinner ingredients. Though in a society where we are stretched for time, one likely wouldn't have time to walk to the store and make dinner. One or the other. Most choose to drive to the store to save time. The fast-paced environment we are living in has a lot to do with our daily activities.

Also, safety and security concerns may limit a person's amount of exercise. As a woman, there are certain areas that I personally would not be comfortable working out in. Gym memberships are expensive, so while an alternative to outside exercise--it is not a practical alternative for everyone. Advances in technology have both propelled and inhibited us. Physical exercise is being replaced with mental exercise in the form of video games or television entertainment. Opportunities such as online classes encourage a degree of physical inactivity.

Lack of time, safety, and money seem to be major factors as to why people do not exercise. Taking the initiative to start community wide exercise programs would give some the incentive and support they need to begin an exercise program individually or within their family. As a society, we have gotten into a habit of increasing our mental activity and decreasing our physical activity. As a whole, we need to find time to balance the two.

Compendium Review: Movement

Unit Three, Major Topic Two

Chapters Eleven and Twelve

Muscle Cells: Contraction and Calcium (Powerpoint, web, pages 230-242)

Movement Across Joints (Powerpoint, web, page 224)

Bones, Bone Tissue, and Calcium (Powerpoint, web, pages 208-222)

Types of Muscle

(image source)

A. Smooth Muscle

1. involuntary

2. occurs in walls of internal organs

B. Cardiac Muscle

1. Involuntary

2. occurs in walls of heart

C. Skeletal Muscle

1. Voluntary

2. helps maintain posture

3. provides movement and heat

4. protects underlying organs

Muscle cells are pretty large--each containing hundreds of myofibrils. Myofibrils contain actin and myosin filaments. Muscle contraction occurs when sarcomeres shorten and actin filaments slide past myosin filaments.

Calcium Release in a Muscle

1. A motor neuron impulse arrives to axonal terminus

2. neuro-muscular junction synapse passes message along to muscle cell

3. muscle cell membrane undergoes action potential along length of cell membrane and into T-tublue system

4. voltage change causes release of calcium ions into muscle cell

5. calcium causes actin-myosin units to shorten

The shortening of actin-myosin units leads to whole muscle contraction.

Whole Muscle Contraction

A. Muscle cells all lined up in skeletal muscle

B. Contraction of many cells makes the whole muscle shorten, bringing about body movement

C. Movement happens across joints between skeletal elements

Muscle contraction as described in detail from the above web source.

Joints connect skeletal elements. Synovial joints are lubricated, mobile joints. Skeletal elements are linked by synovial joints and move when muscles pull on those skeletal elements.

The image above shows the different types of synovial joints.

Fibrous joins are immovable. (i.e. sutures of the cranium).

Cartilaginous joints are slightly moveable (such as those between the ribs and sternum and pubic symphysis).

A Bone is alive, has nerves, blood supply, and cells. Cells make bone tissue, dissolve bone tissue, and live inside bone tissue. Bone also serves as calcium storage. Calcium is needed for many aspects of cell metabolism, but especially in muscle cells.

Bones contain more calcium than any other organ. When blood calcium levels decrease below normal, calcium is released from the bones so that there will be an adequate supply for metabolic needs. When blood calcium levels are increased, the excess calcium is stored in the bone matrix. The dynamic process of releasing and storing calcium goes on almost continuously. (websource)

The image to the left is a diagram of bone cells.

The image to the right shows the bone remodeling cycle.

Bone remodeling is the renewal of bone. Some bone is recycled each year to allow the body to regulate blood calcium.

Axial Skeleton

1. skull (formed by cranium to protect brain and facial bones)

2. hyoid bone (anchors tongue)

3. vertebral column (supports head/trunk, protects spinal cord, site for muscle attachment)

4. rib cage (protects heart, lungs)

Appendicular Skeleton

1. pectoral girdles (flexibility)

2. upper limbs (flexibility)

3. pelvic girdles (supporting weight)

4. lower limbs (supporting weight)

The image to the right shows the appendicular skeleton in pink. The axial skeleton is in white.

There are two types of bone tissue: compact and spongy. The names imply that the two types of differ in density, or how tightly the tissue is packed together. There are three types of cells that contribute to bone homeostasis. Osteoblasts are bone-forming cell, osteoclasts resorb or break down bone, and osteocytes are mature bone cells. An equilibrium between osteoblasts and osteoclasts maintains bone tissue. (websource).

An interesting article on bone tissue transplantation can be found here.

The National Osteoporosis Foundation has a good website with tips for maintaining bone health.

Unit Three Compendium Review, Part One

Chapters Thirteen and Fourteen: Nervous Function

(image source)
What does a nervous system do? (page 270, web)
Diffusion and Action Potentials in Neurons-- (online lab link, Powerpoint, page 270)
rapid transmission of messages (Powerpoint)
Reflex arc (simple somatic function) (Wikipedia)
autonomic function (Powerpoint, page 270)
What can we sense? (pages 275-293)



The nervous system is divided into the central nervous system and the peripheral nervous system. The purpose of the system is to receive input, to integrate data, and to generate motor output. Nervous tissue consists of two types of cells. These are neurons and neurolgia. Neurons transmit nerve impulses, while neurolgia nourish and support them. Sensory neurons take nerves impulses from sensory neurons to the central nervous system. Motor neurons take nerve impulsed away from the central nervous system to muscles or glands.


The central nervous system consists of the spinal cord and brain.


The image to the left shows that different levels of the spinal cord control different parts of the body. The spinal cord is a column of nervous tissue that acts as a pathway to transmit information from the brain to the body.




(http://www.reeve.uci.edu/anatomy/images/scns_1b.gif)


The image to the right shows the brain and its components. The brain has three main components: the cerebrum, cerebellum, and brain stem.
The cerebrum controls sensation, reasoning, learning, memory, language, and reasoning. The cerebellum coordinates skeletal muscle contractions. The brain stem mainly controls unconscious vital signs such as breathing and heartbeat.

The Peripheral Nervous System contains only nerves and ganglia. Cranial nerves take impulses to and from the brain, while spinal nerves take impulses to and from the spinal cord.

Resting and action potential are explained in great detail in the leech lab for this unit.

Another animation of the process can be seen here.

In resting potential there is more Na+ outside the axon and more K+ inside. (This does not conduct an impulse). In action potential a nerve impulse occurs. As Na+ gates open, Na+ moves to the inside of the axon, resulting in a depolarization. When the K+ gates opens and K+ moves to outside the axon, a repolarization occurs.

Somatic System The somatic system serves the skin, skeletal muscles, and tendons. Some actions are due to reflexes which are automatic and involuntary. Others are voluntary and originate in the cerebral cortex.

"A reflex arc is an automatic reaction that allows an organism to protect itself reflexively when an imminent danger is perceived. In response to certain stimuli, such as touching a hot surface, these reflexes are 'hard wired' through the spinal cord. A reflexive impulse travels up afferent nerves, through a spinal interneuron, and back down appropriate efferent nerves". (websource: wikipedia).

Autonomic System The autonomic system is divided into two divisions: sympathetic and parasympathetic. The sympathetic division includes responses that occur during times of stress. The parasympathetic division consists of responses that occur during times of relaxation. Actions in these divisions are both automatic and involuntary. These divisions innervate internal organs. (Two neurons and one ganglion are used for each impulse).

Senses
There are four types of sensory receptors: chemoreceptors, photoreceptors, mechanoreceptors, and thermoreceptors. Sensory receptors initiate nerve impulses that are transmitted to the spinal cord/brain. Sensation occurs when nerve impulses reach the cerebral cortex. Perception is an interpretation of sensations.

A. Proprioceptors
1. mechanoreceptors involved in reflex actions
2. help maintain equilibrium and posture

B. Cutaneous Receptors
1. found in skin
2. for touch, pressure, temperature, and pain

The senses of taste and smell are due to chemoreceptors that are stimulated by molecules in the environment. This site has a really interesting article relating to the taste buds and different senses of taste. (bitter, sour, sweet, salty).



(Microvilli of taste cells have receptor proteins for molecules that cause the brain to distinguish between the tastes).

The cilia of olfactory cells have receptor proteins for molecules that cause the brain to distinguish odors.




The sense of vision depends on the eye, the optic nerves, and the visual areas of the cerebral cortex.

The eye has three layers. The sclera (or outer layer) protects and supports the eyeball.

The choroid (middle, pigmented layers) absorbs stray light rays.

The retina (inner layer) contains the rod cells (sensory receptors for dim light) and cone cells (for bright light and color).

The lens (along with cornea and humors) brings the light rays to focus on the retina. To see a close object a visual accommodation occurs as the lens rounds up.

The visual pathway begins when the light strikes photorecptors (rod cells and cone cells) in the retina. The optic nerves carry nerve impulses from the eyes to the optic chiasma, then pass through the thalamus before reaching in primary vision area. (the occipital lobe of the brain).



Hearing depends on the ear, the cochlear nerve, and the auditory areas of the cerebral cortex.




The ear has three parts. In the outer ear, the pinna and the auditory canal direct sound waves to the middle ear. In the middle ear the malleus, incus, and stapes amplify sound waves. In the inner ear, the semicircular canals detect rotational equilibrium.

The auditory pathway begins when the outer ear receives and the middle ear amplifies sound waves that then strike the oval window membrane.

The ear also contains mechanorecptors for equilibrium.