Reproduction Lab

There are many stages to the fetal development. Some are minute and some are monumental, depending on how one sees things. Even so, it is an ongoing process and changes are not sudden. There are landmarks that can tell you what and when certain developments happen. Here are some that I find very interesting.

1. At 4 weeks the embryo is just two layers of cells, the epiblast and the hypoblast.
2. A lot happens in just the "first month" (beginning at about 4 weeks after conception) by week six, just two weeks after the embryo was but two layers of cells, the embryo is forming vocal chords and a tongue. It already has fingers and will begin to move its arms and legs in this week. The heart is apparent by this time, too.
3. At 8 weeks the brain has begun to connect nerve paths to other parts of the body. The baby has knee joints and definitive, flexed wrists. The baby also has formed eyelids that virtually cover the eyes.
4. By 11 weeks the baby has developed bones. This week the bones will have begun to harden. Teeth buds will also have formed beneath the gums.
5. By 13 weeks the baby will have a unique set of fingerprints. It will also have the abilityto urinate, as it begins to expel amniotic fluid it has swallowed.
6. By 16 weeks the circulatory system is developed and the baby's heart is busy pumping.
7. By 18 weeks the baby has begun to move about regularly.
8. At 24 weeks the baby started to develop taste buds and what would life be like without those? Also thelungs have developed more and the bronchial tree is noticeable.
9. Because a baby's lungs are fully developed at this point, baby's born at 34 weeks have a 99% survival rate!10. In the 40th and 41st weeks the baby is as developed as it will be before birth. It is ready to make the trip into the outside world. Its skull plates have separated to make it easier for the head to go through the birth canal.

Self Evaluation

Which Unit did you like best and why? Unit two was probably my favorite, but 3 was close. These are both very interesting units.My favorite parts to study have been the circulatory system and the central nervous system. The brain and the heart are fascinating.

Which Unit did you like least and why? Unit 1, simply because it wasn't as focused as the others, but I do think it was and is necessary to cover all that information quickly so the studies can become more focused.
Is there some major area of Human Biology that you feel was neglected and should be included in the course? Not that I can think of, but then again, I'm not the human biology expert.
MAJOR TOPICS
-Cells
-Genetics
-Oxygen/Blood/Immunity
-Food and Nutrition
-Nervous Function
-Movement
-Reproduction
-Human Ecology
Which two Major Topics stand out as particularly well presented?Oxygen/Blood/Immunity and Cells. Why? The topics were thorough but not overwhelmed with information.
Which two Major Topics stand out as having been confusing or difficult to understand? I can't really think of any. Why? Well, they all have been well presented so far.

Your Own Personal Functioning Limb

I have constructed a model working arm with an elbow joint. I created this model using: cardboard, wire hanger, acrylic paints and paper.




The bicep and tricep are a muscle pair that work together to either bend the arm at the elbow or extend it. The origin of each is on the humerus. The insertion of the tricep is on the ulna and the insertion of the bicep is on the radius (at least on the elbow side.) The elbow itself is a hinge joint, where ligaments, cartilage and synovial cavities with fluid make the "hinge" movable. The reason it is a hinge joint is because it moves in only one direction. Motor neurons stimulate the contraction of muscles making movement possible. In the upper arm, most of these neurons come off of three nerves: the radial, the ulnar and the median nerves.



Muscle fibers are very unique cells. They contain tons of myofibrils. These segments are what makes a muscle fiber contract.


The Myofibrils are bundles of myofilaments. These strands of protein are the cause of contraction. The thick myofilaments (made of mosin protein) and the thin filaments (actin) slide past each other to make a muscle contract. This happens in the area between two "Z bands" in a myobril. This section is called a sarcomere. The filaments themselves do not shorten but the sarcomere does as the filaments slide and become more compact.


The cause of this is function is motor neurons on a muscle fiber. When the impulse for contraction reaches a axon terminal on the fiber the neurotransmitter ACh is released. These Ach molecules are carried in vesicles out of the axon terminal and into the synaptic cleft. There they are picked up by receptors on the sarcolemma (plasma membrane of a muscle fiber.)


This stimulates the myofilaments to slide which contracts the sarcomeres in a muscle fiber. As a muscle contracts, it pulls on the bone (in this case the ulna and the radius) to draw the forearm upward. This is how a joint is moved.

Muscle Fatigue

# of fists in 20 seconds

NORMAL: 50

ICE WATER: 43

For this section I used a pair of muscle grips, which I would imagine was more straining than the suggested actions.
# of Squeezes in 20 seconds

1 54


2 42


3 39


4 34


5 30


6 23



7 16


8 14


9 10


10 6







ANALYSIS OF DATA:

1. What are the three changes you observed in a muscle while it is working (contracted)?
The muscle Hardened and since it contracted it moved into a smaller area. It also bulged up, or outward.
2. What effect did the cold temperature have on the action of your hand muscles? Explain.
It made reaction slightly slower. I was not able to contract the muscles in my hand and forearm as quickly.
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.







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

The action became slower, harder and more painful.

Leech Lab

This is was a very fun little project, a dissection nix the squirting organism juices. I can smell the anesthesia now!

Here is a picture of the oscillator saying, "You've poked him where he feels it, Billy!"
Here is the dyed nerve cell under Ultra Violet:



1.An electrode measures a nerve impulse
2.Leeches are a great specimen for this experiment, because it is very simple. Simple organisms can give us clues as to how more complex systems operate. No one will be to sad at the loss of a leech, save for the crazy (but caring) people at PETA, and can you really trust people who protest wearing only cellophane? (JUST KIDDING!!, for all you PETA people, more power to you.)
3. Sensory neurons detect stimulus whether internally or externally, these are the neurons that "sense." Motor neurons are the reaction sent by the brain or other interneurons as a reply to the sensory impulse.
4. I think leeches experience pain (not in the sense that his girlfriend left him, that's not even why she sucks.hahaha) Pain is simply impulses sent from chemoreceptors to tell the body of damage done.
5. The two most interesting things about this lab were the uses of the probe for oscillation reception and UV dying. It was very interesting, something that would be fun to do for real someday.
6. Off of the bat it was confusing that they were identifying cells that were specific to leeches that weren't explained.

From Concept to Practice

We have all seen the commercials (and me since I was quite young,) "Play a game." "Real Reality." "30 minutes a day." There have been and continue to be a number of adds that target children (as our future) to get fit through just plain "getting out." What was the result? Kids were commanded by less-than-perfect physical role models, called parents to "get out." Or the parents would drive them to the park with chips and soda as a snack.
The concept is great, and to some extent it works, but the practice is flawed. Our society is not built to promote physical fitness. It has been organized around convenience and, of course, monetary gain. Our drive-through society clearly caters to a slothful approach to bodily maintenance.
There are, certainly, other environments that do nurture a physical mindset. When I lived on Kauai, there was certainly a very physical environment. Though there were common examples of so-called "anti-physical" catering, like highways and McDonald's the atmosphere was different. Sidewalks were everywhere. The county had a project to build a side walk along the entire eastern coastline. It was a beautiful ride...or walk. There were a lot of hiking trails and none were "no bikes" trails, which is very important to someone like me. Now, of course, pacific islands are a great place to find less common activities, like diving, sea-kayaking and surfing, but hiking, swimming, running and cycling/mountain biking can be done most anywhere.
The problem is in the profit. The people who live in places like Hawaii, go there not just because it is beautiful but they enjoy the outdoor activities provided there. There is little to no immediate profit in converting an enviroment to pro-physical. This is what prevents such a conscious effort to change a population's plans to enhance a fit lifestyle. I think the eventual benefits would be great, but hardly are economic issues looked at for the long-term benefit.

Unit Three: Compendium II

I. Skeletal System

A. Overview

B. Bone: Growth and Repair

C. Axial Skeleton

D. Appendicular Skeleton

E. Articulations.

II. Muscular System

A. Overview

B. Skeletal Muscle Fiber Contraction

C. Whole Muscle Contraction

D. Muscular Disotrophy

E. Homeostasis

I. Skeletal System

A. Overview

The skeletal system consists of bone, cartilage and connective tissue in the ligaments and joints. Its functions are body support, protection, blood cell production, mineral and fat storage and assists in flexible movement. The shaft of a long bone is the diaphysis. The medullary cavity of the diaphysis is filled with yellow bone marrow. This marrow stores fat. The bone fans on the end into the epiphysis. This bone is spongy and contains red bone marrow, which makes blood cells. The bone is covered in periosteum, which contains blood vessels, lymphatic vessels and nerves. This continues right into ligaments and tendons. Compact bone is made of tube-like sections called osteons. Osteocytes are bone cells of the osteon the lie in lacunae (circular chambers around a canal, for vessels and nerves.)Osteocytes nearest the center of the osteon exchange nutrients and wastes with blood vcssels. Spongy bone lies within and looks less organized than compact bone, but its brace-like structure is for strength. Its spaces are filled with red bone marrow. Cartilage is a flexible tissue, not as strong as bone. It has many collagenous and elastic fibers. Cartilage contains no nerves which is ideal for the stress placed on it from flexible movement. It heals slowly, though, as it has no blood vessels. The three types of cartilage are: hyaline (firm fairly flexible), fibrocartilage (stronger than hyaline, found in disks between vertabrae.), elastic cartilage is the most flexible. Ligaments and tendons are made up of fibrous connective tissue. They connect bone to bone and muscle to bone.

B. Bone: growth and repair

Boes first appear at six weeks in an embryo . They continue to grow until as late as age 25. They change shape and size and strength to deal with stress. Bones can repair when fractured. Some different types of bone cells are: osteoblasts (bone forming cells), osteocytes (maintain structure), osteoclasts (breakdown bone.) Ossification is the formation of cone. The two types of ossification are: intramembranous and endochondral. Flat bones, like the skull, are results of intramembranous ossification which develops bone between sheets of fibrous connective tissue. Endochondral ossification happens in most bones of the body where cartilag models are replaced by bone construction. THe cartilage model literally becomes the bone!. The epiphyseal plates close at about age 20 which ends bone legth growth. Vitamin D is vital to bone growth and strength in that it plays a great role in calcuim absorbtion. As much as 18% of bone is recycled each year and renewed in bone remodeling. This helps keep bones strong. Bones are the storage sight for calcium and regulates the amount of calcium in the blood. Two hormones are integral to this process: parathyroid and calcitonin. Osteoperosis is a condition in which osteoclasts are more active than osteoblasts causing bone mass decrease. Bone repair is very important to functioning structure. If a break occurs bood will clot in the break. Thn fibrocartilage will form in the break.Then osteoblasts convert the fibrocartilaginous callus into a bony callus. It is lastly filled in with compact bone and repair is complete.

Normally, a fracture like this will heal through

bone remodeling.

C. Axial skeleton

The axial skeleton refers to the skull, hyoid, vetebral column and rib cage. The skull is the cranium and facial bones. The cranium protects the brain. It is actually eight bones fused together. The sphenoid bone extends across the floor of the cranium. It completes the sides of the cranium and formsthe eye sockets. The ethmoid bone forms the nasal septum. The facial bones are: the mandible, maxillae, zygomatic and nasal. The Hyoid bone is the only bone that does not articulate with other bones. It is attatched to the larynx and anchors the tongue. The vertebral column contains 33 vertebrae (the spine.)There are five types of vertebrae (from the top down): cervical, thoracic, lumbar, sacrum and coccyx. There are fibrocartilagous disks called intervertebral disks that absorb shock and protect the vertebrae. The rib cage is protective and flexible. It is made up of the ribs and the sternum.

skeleton 1 shows the axial skeleton

while skeleton 2 shows the appendicular

skeleton.

D. Appendicular skeleton

The appendicular skeleton makes up every other bone of the body. There are the pectoral girdles on either side that make up the shoulder. They contain the scapulas and the clavicle. The muscles of the arm and chest attach to the scapula. The rotator cup is made of tendons connecting the scapula to the humerus. It is the single long bone of the upper arm. This connects at the elbow to the radius and the ulna. The hand has many bones for increased flexibility. There are the carpal bones, the metacarpal bones and the phalanges. At the waste is the pelvic girdle. The pelvis is made up of two heavy coxal bones, the ilium, the pubis, and the ischium. This connects at a joint, to the femur: the single long bone of the upper leg. This is connected to the tibia and fibula by the patella (kneecap) and ligaments and tendons. There are many bones in the feet, like the hands, for flexibility. The ankle area is made of tarsals then there are five metatarsals and then phpalanges in the toes.

E. Articulations

Bones join at the joints. There are three types of joints: fibrous, cartilaginous and synovial. Fibrous joints are virtually immovable. Cartilaginous joints are slightly movable. Synovial joints are freely movable. The synovial joints are joint cavities that are filled with synovial fluid. Bursae are sacs of this fluid that lubricate bones and overlapping muscle and ease friction. Then areas of hyaline cartilage fill in a C-shaped area for shock absorbtion. The synovial joints in the shoulders and hips are ball joints and permit movement in any direction. Th elbows and knees are hinge joints and only allow single-directional movement.

The joints are capable of impressive articulations.

II. Muscular System

A. Overview

All muscles contract and this causes movement. There are three types of muscle tissue: smoothe, cardiac and skeletal. These are made of muscle fibers. Smooth muscle fibers have a spindle shape. Smooth muscle is found in the walls of hollow organs which causes the contractions in them. These tend to contract without conscious control. Cardiac muscle has inuncleated fibers that are striated and is found in the heart wall. It's formation facillitates quick contractions throughout the heart wall. Cardiac muscle contracts involuntarily. Skeletal muscles have many functions. It supports the body. It makes the skeleton move. They maintain body temperature. The contractions of skeletal muscles help move blood and lymph through their respective vessels. Skeletal muscles also help protect internal organs. Skeletal muscles are made of fascicles. Fascicles are covered with fascia which connects muscles to tendons. When a skeletal muscle contracts its tendons pull on the bone to move it. It takes groups of muscles to move a particular area, but one muscle will take the bulk of the movement. Since muscles work in pairs one must reflex as one contracts in order for the bone to move. Skeletal muscles are named according to one of these seven factors: size, shape, location, direction of fibers, attachment, number of attachments and/or action.

B. Skeletal muscle fiber contractions

The striations in skeletal muscles is dues to the arrangement of myofilaments in the muscle fiber. There are different names for kthe cellular components of muscle fiber. THe plasma membrane is called the sarcolemma, the sarcoplasm is the cytoplasm. Muscle fiber contains sarcoplasmic reticulum. The sarcolemma forms transvers (T) tubules that dip into that make contact with the sarcoplamic reticulum. These sights of contact store calcium which is vital to muscle contraction. The myofibrils are the contracting parts of the muscle fibers. Other organelles are found between the myofibrils. Glycogen in the sarcoplasmacts as stored energy for contraction. Myofibrils are cylindrical. Units that make up the are sarcomeres. There are two types of protein in the myofibrils called myosin and actin. There are thick and thin myofilaments. The thick filaments are made of hundreds of myosin molecules. Thin filaments are made mostly of actin and there are also tropomyosin and troponin proteins in them. As an impulse travels down a T tubules, calcium is released. This causes the myofilaments to shorten, thereby contracting the muscle. The sliding of thin filaments past the thick filament is called the sliding filament model. Motor neurons attached to one or a few muscle fibers stimulate contractions by releasing ACh into the synaptic vesicles. Botox blocks the release of ACh into the symaptic cleft. This can be used to stop wrinkling. Rigor mortis probably sets in because ACh is not inhibited from flowing into the muscles.

C. Whole Muscle Contraction

A motor unit is the combination of the nerve axon as well as all the muscle fibers it stimulates. A muscle twitch is caused by infrequent electrical impulses. The three periods of this are the latent (between relaxation and contraction), contraction and relaxation. When this occurs rapidly without relaxation, the energy is dpleted in a state called tetanus, not to be confused with the infection, tetanus. THe four possible energy sources of contraction are: muscle triglycerides, plasma fatty acids, blood glucose and muscle glyfogen. Which one is used depends of the type of exercise and its intensity. Muscle fibers metabolize aerobically and anaerobically. Fast twitch muscle fibers use the anaerobic methods of producing ATP. They can fatigue very quicly because they dpend on lactate. Slow twitch fibers have more endurance. They are good for running, biking, jogging and swimming. They do not fatigue easilly because they have a more abundant fuel supply.

Cycling uses slow-twitch fibers.

D. Muscular disorders

There are many different muscular conditions. Spasms are involuntary muscle contraction. When this happens in multiple muscles it is called a convulsion. Cramps are strong spasms. Facial tics are spasms in the face that can be controlled with great effort. Strain is a stretching or tearing of the muscle. Sprains are twisting of joints that swell the muscle and the ligaments, tendons, nerves and blood vessels. Tendinitis is an inflamed tendon that does not glide properly. Myalgia is a condition of achy muscles. Fibromyalgia refers to a chronic condition where muscles are sore, stiff and tender. It may be due to an infection. Muscular dystrophy refers to a number of disorders in which the muscles weaken and degenerate. A lack of the protein dystrophin causes the Duchenne muscular dystrophy, a common type. Myasthenia gravis is a disease in which muscle contraction is impared because the body produces antibodies that mistakenly destroy ACh receptors. Lou Gehrig's disease is characterized by the loss of all muscle related abilities, though mental function stays intact.

Mike Neufeldt suffers from Muscular Dystrophy.

E. Homeostasis

Movements is integral to homeostasis. The skeletal and muscular systems work together for movement. Movement helps us respond to changes in the environment. Muscle contraction at the mouth allows us to mechanically breakdown food. Peristasis moves food through the digestive system. Muscle movement is important to breathing and venous return for blood circulation. Bones and muscles work together. They both protect organs. Bones release calcium which is used by muscles. Blood cells are made in the bone marrow, while muscles aid in body temperature homeostasis.

Unit III: Compendium 1

I. The Nervous System

A. Overview

B. Central Nervous system

C. Limbic System

D. Peripheral System

E. Drug Abuse

II. Senses

A. Sensory Receptors

B. Proprioceptors and Cutaneous Receptors

C. Taste and Smell

D. Vision

E. Hearing

F. Equilibrium


I. The Nervous System

A. Overview

There are two major parts of the nervous system: the central nervous system and t he peripheral system. The central nervous system encompasses the brain and the spinal cord. The peripheral consists of nerves. Those these systems are labeled separately, they work together as one system. The functions of the nervous system are: receiving sensory input, integrates the input and generates reactions through motor response. Nervous tissue is made up of nuerons which send nerve impulses to the different parts of the system. Neuroglia support the neurons.
There are three different types of neurons. Sensory neurons take impulses from receptors to the central nervous system (CNS). Interneurons, in the CNS, take in all the impulses from sensory neurons and other internuerons. Then motor neurons take a reactionary impulse to an effector, which can be muscles or glands. Neurons have three parts: the cell body, dendrites and an axon. Axons generate impulses while dendrites receive them. Myelin sheaths are a protective lipid-containing substance that are found around some axons. These protect and help in the regeneration of damaged axons.
Nervous information is conveyed in nerve impulses. Measuring these is done using a voltmeter on an axon. When an impulse is not being conducted the voltmeter reads the resting potential of an axon. The charge of the inside of the neuron is more negative than positive at this point. The action potential is the measurement of a neuron when an impulse is being conducted. The change of polarity is very quick. Conduction in myelinated axons is much quicker than in axons without myelin during an impulse. Action potential is always the same in an axon. Intensity depends on how many impulses are fired, because the action potential is the same every time. After an impulse is conducted the sodium gates on an impulse stay shut, called the refractory period, ensuring that the impulse travels in one direction and never backward.
The synapse is the small space between a sending axon and the receiving neuron. The transmission must be carried out by neurotransmitters. These molecules are release when an impulse reaches the axon terminal at the end of an axon. They diffuse through the synaptic cleft and bind to receptors on the receiving neuron or dendrite. Neurotransmitters are then either reabsorbed or destroyed. A neuron then receives either an excitatory or an inhibitory signal. These signals tell a neuron whether to move toward active potential or to move from it.

B. The central nervous system

Sensory information is received and motor response is conducted in the CNS. The brain and the spinal cord make up the CNS. They are both protected my bone and by membrane called meninges. Cerebrospinal fluid fills in the membrane which protects the CNS. There are four ventricles that hold cerebrospinal fluid in the brain. Excesses fluid drains into the cardiovascular system. There are two types of nervous tissue in the CNS. Gray matter is made up of nonmyelinated fibers. Whiter matter is made up of myelinated axons running in tracts.
The spinal cord starts at the base of the brain and runs through the vertebrae. The spinal cord is made up of a central canal, gray matter and white matter. The central canal has cerebrospinal fluid. Sensory and motor neurons are found somewhat in the the gray matter. The white matter contains ascending tracts to the brain and descending tracts from the brain. The spinal cord transmits information between the brain and the peripheral system. Sensory messages are sent to the brain from receptors to the brain. These can be blocked by endorphins. Reflex actions are caused as motor neurons send a response after being stimulated by interneurons who have processed an impulse from sensory neurons.
The brain contains four major parts: the cerebrum, the diencephalon, the cerebellum and the brain stem. The cerebrum is the largest part of the brain. There are two hemispheres of the cerebrum. Sulci are shallow grooves that divide the hemisphere into lobes. The lobes are: the frontal, the parietal, the occipital and the temporal. each lobe has different functional control. The cerebral cortex is a thin, dense layer that covers the lobes. It contains the functions of sensation, voluntary movement, and conscious thought. Most motor sensory is contained within the frontal lobe. Sensory information from the skin and muscles goes to the parietal lobe. Vision is processed in the occipital lobe. Hearing is processed in the temporal lobe.
Homeostasis is in part maintained by the hypothalamus in the diencephalon. It regulates things like sleep, hunger, thirst, body temperature and water balance. The thalamus first receives all sensory input except for smell. It integrates the input and then sends it out to the correct area of the brain. The cerebellum is found directly below the occipital lobe. The cerebellum receives sensory input and motor output from the cerebral cortex. It then sends motor impulses to skeletal muscles. It maintains posture in balance in one regard. The brain stem contains the midbrain, the pons and the medulla oblongata. The midbrain receives input from the tracts and also sends out reflexes. The pons contains axons that bridge the cerebellum and the rest of the CNS. It also works in conjunction with the medulla oblongata. The medulla oblongata contains many reflex centers for involuntary actions, such as breathing and heartbeat.

The central nervous system consists of the brain

and spinal cord.

C. Limbic system
The limbic system contains much including primitive emotion and higher mental function. It blends and integrates these systems. The hippocampus, contained in the limbic system is thought to be very much integral to the learning process. It determines which information should be stored as memory and how to encode it. It most likely communicates with the frontal lobe. Memory is one function of learning. There are different types of learning. Short term memory is associated with the prefrontal area of the brain. Long term memory is a mixture of semantic memory and episodic memory. This is why we easily associate a phone number with a person, place and/or event. Skill memory is the memory of motor ability. Long term memory is apparently stored throughout the cerebral cortex. It appears as though the different hemispheres process the same information differently. Whereas it was believed that the left side of the brain was more rational and logical and the right was more creative and intuitive, it is now believed that the left side is more global and the right side is more specific.

A view of the deep-lying limbic system.

D. Peripheral System

The peripheral system(PNS) contains all the nerves. All nerves take impulses to and from the CNS. Nerves that come from the brain are cranial and those from the spinal cord are spinal. There are 12 pairs of cranial nerves in humans. Cranial nerves are, for the most part, used for the face, head and neck. There are 31 pairs of spinal nerves on either side of the spine. All spinal nerves are "mixed" in that they have sensory and motor fibers. The somatic system is a division of the PNS that tends to the skeletal system, skin and tendons. This system contains the receptors that sense outer stimulus. Reflexes are automatic responses to certain stimuli. When reflexes occur much is involved. Outer stimulus is received by a receptor. The sensory neuron sends the information to interneurons in the spinal cord. These send a response impulse through motor neurons that react quickly. The interneurons also send an impulse to the brain. So the reflex is automatic, but also conducts brain activity. The pain is only felt after the brain processes the impulses. The autonomic system is the other major division of the PNS> This controls smooth muscles, breathing and glands. There are two types of autonomic division: sympathetic (urgent) and parasympathetic (relaxed.)

E. Drug Abuse

Drugs, whether natural or synthetic affect the nervous system to either increase the likelihood of excitation (stimulants) or decrease the likelihood of excitation (depressants) of neurons. Drugs artificially stimulate the reward circuit (collection of neurons that promote healthy pleasurable activities, like eating.) Drug abuse is characterized by a physical or psychological dependence and use that is potentially harmful. Alcohol is the most readily available and socially acceptable drug. It can be very harmful when abused. It causes damage to the liver and extensive damage to the brain. It can cause death or coma when used heavily at one time. Nicotine is also highly accepted. Addiction rate in American smokers is about 70%. Cocaine is highly addictive and is pleasurable to users because it keeps dopamine in "rotation" in the system without reabsorbing it quickly. It is a very dangerous drug with many side effects. Methamphetamine works similarly to cocaine in the way that it binds to dopamine keeping it in the system longer. Its characteristics as well as its side effects are incredibly dangerous. Heroin is a depressant that is incredibly strong. It is pleasurable to users because it is converted to morphine which blocks pain and stimulates the reward circuit. It is highly addictive and its intravenous popularity can lead to hepatitis, HIV and bacterial infection. Marijuana is the most commonly used illegal drug. Its mild euphoria and depressant affects make it very popular. It affects the areas of the brain that maintain memory, balance, coordination and perception.Though not physically addictive, frequent use can make one psychologically dependant.

The popularity of "shooting up" (intravenous injection)

has caused many cases of Hepatitis and HIV in heroin users.

II. Senses

A. Sensory receptors

Dendrites that detect specific stimuli are called sensory receptors. When they detect outer sensations they are called exteroceptors. When they detect inner changes they are called interoceptors. Interoceptors are integral to homeostasis. Exteroceptors are integral to detecting environmental changes. Chemoreceptors respond to chemicals nearby. These can be either interoceptors or exteroceptors. Pain receptors, which are protective, sense chemicals that have been released by damaged tissue, to alert the body to damage. Photoreceptors respond to light giving us a sense of vision. Mechanoreceptors respond to pressure. This gives us hearing as well as equilibrium. Thermoreceptors respond to changes of temperature respectively. Sensation is the perception of stimuli. Some sensory receptors are just nerve endings. Others contain specialized cells. Still others have receptor proteins that reacts to chemicals. Perception of stimuli happens in the cerebral cortex. No sensation is felt until the impulse has made it to the cerebral cortex. Integration, however, occurs in sensory receptors. This can cause sensory adaptation, which can cause a stimuli to either be ignored or filtered out.

B. Proprioceptors and cutaneous receptors

The three types of receptors found in the muscles, joints, tendons, skin and some internal organs. These are the proprioreceptors, cutaneous receptors and pain receptors. As reflexive mechanoreceptors, proprioreceptors help maintain poster and balance. They sense the amount of tension in a muscle and the stretch of tendons to pinpoint the location of a limb. Cutaneous receptors are many different types of receptors in the skin that determine touch, size, temperature and texture of an objects.Meissner corpuscles, Merkel disks and root hair plexuses are the "touch sensitive." Pacinian corpuscles and Ruffini endings are pressure sensitive. There are are many pain receptors, or nociceptors that detect chemical release at the sight of damage.

meissner corpuscles.

C. Taste and Smell

Taste and smell are chemical senses. They respond to molecules in the food we eat as well as those in the air. Olfactory cells (smell) act from a distance and taste cells act directly. In humans taste buds are found on the tongue, the hard palate, the pharynx and the epiglottis. Taste buds open at a taste pore. These lead to supporting cells which eventually lead down into the sensory nerve. They are then carried to the gustatory cortex where they are interpereted. 80-90% of what is perceived as taste is actually smell. which is sensed by olfactory cells. Certain odor molecules bind to certain smell receptors which is what determines the interpretation of the smell. Smell is very connected to the limbic system and can, therefore, trigger memory.

an illustration of a taste bud.

D. Vision

There is a very complex process to sight that involves the brain and the eye. There are three layers to the eye: the sclera, the choroid, and the retina. The cornea is the only transparent part of the sclera, the rest is fiberous and white. The iris is found at the front of the choroid. This determines the size of the pupil, which is the center of the iris and allows in light for vision process. The ciliary body of the choroid determines the shape of the lense for distance of viewing. The retina contains photo receptors. There are two types: rod and cone. Rods are very sensitive to light but only perceive black and white. Cones perceive colors but need much more light and that is why it is much easier to detect color the more light there is. The optic nerve runs from the retina to the visual cortex. An image is focused, through the lens, on the retina. Photoreceptors in the retina recieve light and break down the refraction chemically. The signals are passed to ganglion cells and then to the optic nerve where they are carried to the optic chiasma. The image is crossed and split. Then it goes on to be processed in the visual cortex. Color blindness and distance vision are the most common eye problems.

E. Hearing

The inner ear has to sensory jobs: balance and hearing. There are three parts to the ear. The outer ear contains the pinna and the auditory canal. The middle ear contains the tympanic membrane (eardrum) It ends at a bony wall with two small openings called the oval and round windows. It also contains the auditory tube, which runs to the nasopharynx. This is mimportant to air balance and equilibrium. The inner ear is filled with fluid. There are three areas: the semicircular canals, the vestibule and the cochlea. The first two are important to equilibrium and the last to hearing. When sound waves hit the tympanic membrane it vibrates. The pressure is multiplied by the maleus and sent to the stapes. The pressure strikes the oval window. This makes the vibration pressure to pass into the fluid in the inner ear. This stimulates the cochlear nerve which sends the signal to the auditory cortex and is interpreted as sound. Different parts of the nerve are sensitive to different frequencies. Volume is determined by the amount of pressure wsound waves place upon the inner fluid.

The inner ear senses hearing and contributes to equilibrium.

F. Equilibrium

Also within the ear are the parts that maintain equilibrium. The vestibular nerve carries pressure signals from the semicircular canals, saccule and utricle to the brain stem and cerebellum. The mechanoreceptors in the semicircular canals are responsible for detecting rotational movement. The reaction of the cupula on the end of vestibular nerve sends a signal of pressure that tells position. Dizziness occurs when the cupula gets used to rotational movement and when the movement stops the cupula slowly comes back to normal throwing off our true rotational balance. Mechanoreceptors in the utricle and saccule dtect movement in the horizontal/vertical planes. These membranous sacs contain little hair cells which are stimulated by the movement of the otolithic membrane they are suspended in. This gel moves with the movement of the head. Impulses are increased or decreased dpending on the direction of the flow. When this data reaches the brain it determine the correct motor output for the gravitational positioning.