Mark Corson

By P. Ramon. University of La Vernee. 2018.

He conducted a series of experiments in which cheap flagyl 500mg visa, over a number of trials buy discount flagyl 250 mg, dogs were exposed to a sound immediately before receiving food purchase flagyl 200mg without prescription. He systematically controlled the onset of the sound and the timing of the delivery of the food, and recorded the amount of the dogs‘ salivation. Initially the dogs salivated only when they saw or smelled the food, but after several pairings of the sound and the food, the dogs began to salivate as soon as they heard the sound. Pavlov had identified a fundamental associative learning process called classical conditioning. After the association is learned, the previously neutral stimulus is sufficient to produce the behavior. Top right: Before conditioning, the neutral stimulus (the whistle) does not produce the salivation response. Conditioning is evolutionarily beneficial because it allows organisms to develop expectations that help them prepare for both good and bad events. Imagine, for instance, that an animal first smells a new food, eats it, and then gets sick. The Persistence and Extinction of Conditioning After he had demonstrated that learning could occur through association, Pavlov moved on to study the variables that influenced the strength and the persistence of conditioning. Extinctionrefers to the reduction in responding that occurs when the conditioned stimulus is presented repeatedly without the unconditioned stimulus. Pavlov found that, after a pause, sounding the tone again elicited salivation, although to a lesser extent than before extinction took place. If conditioning is again attempted, the animal will learn the new associations much faster than it did the first time. Pavlov also experimented with presenting new stimuli that were similar, but not identical to, the original conditioned stimulus. For instance, if the dog had been conditioned to being scratched before the food arrived, the stimulus would be changed to being rubbed rather than scratched. He found that the dogs also salivated upon experiencing the similar stimulus, a process known as generalization. Generalization refers to the tendency to respond to stimuli that resemble the original conditioned stimulus. If we eat some red berries and they make us sick, it would be a good idea to think twice before we eat some purple berries. Although the berries are not exactly the same, they nevertheless are similar and may have the same negative properties. In his experiment, high school students first had a brief interaction with a female experimenter who had short hair and glasses. The study was set up so that the students had to ask the experimenter a question, and (according to random assignment) the experimenter responded either in a negative way or a neutral way toward the students. Then the students were told to go into a second room in which two experimenters were present, and to approach either one of them. However, the researchers arranged it so that one of the two experimenters looked a lot like the original experimenter, while the other one did not (she had longer hair and no glasses). The students were significantly more likely to avoid the experimenter who looked like the earlier experimenter when that experimenter had been negative Attributed to Charles Stangor Saylor. The participants showed stimulus generalization such that the new, similar-looking experimenter created the same negative response in the participants as had the experimenter in the prior session. The flip side of generalization is discrimination—the tendency to respond differently to stimuli that are similar but not identical. Pavlov‘s dogs quickly learned, for example, to salivate when they heard the specific tone that had preceded food, but not upon hearing similar tones that had never been associated with food. Discrimination is also useful—if we do try the purple berries, and if they do not make us sick, we will be able to make the distinction in the future. And we can learn that although the two people in our class, Courtney and Sarah, may look a lot alike, they are nevertheless different people with different personalities. In some cases, an existing conditioned stimulus can serve as an unconditioned stimulus for a pairing with a new conditioned stimulus—a process known as second-order conditioning. Eventually he found that the dogs would salivate at the sight of the black square alone, even though it had never been directly associated with the food. Secondary conditioners in everyday life include our attractions to things that stand for or remind us of something else, such as when we feel good on a Friday because it has become associated with the paycheck that we receive on that day, which itself is a conditioned stimulus for the pleasures that the paycheck buys us. The Role of Nature in Classical Conditioning As we have seen in Chapter 1 "Introducing Psychology", scientists associated with the behavioralist school argued that all learning is driven by experience, and that nature plays no role. Classical conditioning, which is based on learning through experience, represents an example of the importance of the environment. Nature also plays a part, as our evolutionary history has made us better able to learn some associations than others. For example, driving a car is a neutral event that would not normally elicit a fear response in most people. But if a person were to experience a panic attack in which he suddenly experienced strong negative emotions while driving, he may learn to associate driving with the panic response. Psychologists have also discovered that people do not develop phobias to just anything. Although people may in some cases develop a driving phobia, they are more likely to develop phobias toward objects (such as snakes, spiders, heights, and open spaces) that have been dangerous to people in the past. In modern life, it is rare for humans to be bitten by spiders or snakes, to fall from trees or buildings, or to be attacked by a predator in an open area.

But it’s more than just bones; it’s also ligaments and cartilage and the joints that make the whole assembly useful order flagyl 200 mg with visa. In this chapter flagyl 250 mg discount, you get lots of practice exploring the skeletal functions and how the joints work together purchase flagyl 500mg with mastercard. Understanding Dem Bones The skeletal system as a whole serves five key functions: Protection: The skeleton encases and shields delicate internal organs that might other- wise be damaged during motion or crushed by the weight of the body itself. For exam- ple, the skull’s cranium houses the brain, and the ribs and sternum of the thoracic cage protect organs in the central body cavity. Movement: By providing anchor sites and a scaffold against which muscles can con- tract, the skeleton makes motion possible. The bones act as levers, the joints are the fulcrums, and the muscles apply the force. For instance, when the biceps muscle con- tracts, the radius and ulna bones of the forearm are lifted toward the humerus bone of the upper arm. Support: The vertebral column’s curvatures play a key role in supporting the entire body’s weight, as do the arches formed by the bones of the feet. Upper body support flows from the clavicle, or collarbone, which is the only bone that attaches the upper extremities to the axial skeleton and the only horizontal long bone in the human body. Mineral storage: Calcium, phosphorous, and other minerals like magnesium must be maintained in the bloodstream at a constant level, so they’re “banked” in the bones in case the dietary intake of those minerals drops. The bones’ mineral content is con- stantly renewed, refreshing entirely about every nine months. Blood cell formation: Called hemopoiesis or hematopoiesis, most blood cell formation takes place within the red marrow inside the ends of long bones as well as within the ver- tebrae, ribs, sternum, and cranial bones. Marrow produces three types of blood cells: erythrocytes (red cells), leukocytes (white cells), and thrombocytes (platelets). Most of these are formed in red bone marrow, although some types of white blood cells are pro- duced in fat-rich yellow bone marrow. In cases of severe blood loss, the body can convert yellow marrow back to red marrow in order to increase blood cell production. If you hesitated to choose “all of hemostasis, which is the stoppage the above,” ask yourself this: If you of bleeding or blood flow. Besides support and protection, the skeleton serves other important functions, including a. Divide different body areas Chapter 5: A Scaffold to Build On: The Skeleton 63 Boning Up on Classifications, Structures, and Ossification Adult bones are composed of 30 percent protein (called ossein), 45 percent minerals (including calcium, phosphorus, and magnesium), and 25 percent water. Mineral in the bones increases with age, causing them to become more brittle and easily fractured. Various types of bone make up the human skeleton, but fortunately for memorization purposes, bone type names match what the bones look like. They are as follows: Long bones, like those found in the arms and legs, form the weight-bearing part of the skeleton. Short bones, such as those in the wrists (carpals) and ankles (tarsals), have a blocky structure and allow for a greater range of motion. Flat bones, such as the skull, sternum, scapulae, and pelvic bones, shield soft tissues. Irregular bones, such as the mandible (jawbone) and vertebrae, come in a vari- ety of shapes and sizes suited for attachment to muscles, tendons, and ligaments. Irregular bones include seed-shaped sesamoid bones found in joints such as the patella, or kneecap. Unfortunately for students of bone structures, there’s no easy way to memorize them. So brace yourself for a rapid summary of what your textbook probably goes into in much greater detail. Compact bone is a dense layer made up of structural units, or lacunae, arranged in concentric circles called Haversian systems (also referred to in short as osteons), each of which has a central, microscopic Haversian canal. A perpendicular system of canals, called Volkmann’s canals, penetrate and cross between the Haversian systems. Compact bone tissue is thick in the shaft and tapers to paper thinness at the ends of the bones. The bulbous ends of each long bone, known as the epiphyses (or singularly as an epiphy- sis), are made up of spongy bone or cancellous bone tissue covered by a thin layer of compact bone. The diaphysis, or shaft, contains the medullary cavity and blood cell–producing marrow. A membrane called the periosteum covers the outer bone to provide nutrients and oxygen, remove waste, and connect with ligaments and tendons. Bones grow through the cellular activities of osteoblasts on the surface of the bone, which produce layers of mature bone cells called osteocytes. Osteoclasts are cells that function in the developing fetus to absorb cartilage as ossification occurs and function in adult bone to break down and remove spent bone tissue. There are two types of ossification, which is the process by which softer tissues harden into bone. Both types rely on a peptide hormone produced by the thyroid gland, calci- tonin, which regulates metabolism of calcium, the body’s most abundant mineral. The two types of ossification are Endochondral or intracartilaginous ossification: Occurs when mineral salts, particularly calcium and phosphorus, calcify along the scaffolding of cartilage formed in the developing fetus beginning about the fifth week after conception. The absence of any one of these sub- stances causes a child to have soft bone, called rickets. Next, the blood supply entering the cartilage brings osteoblasts that attach themselves to the cartilage.

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Halogens can stabilize the transition states leading to reaction at the ortho and para positions order flagyl 250 mg amex. On the other hand flagyl 200mg visa, the electron-withdrawing inductive effect of halogens influences the reactivity of halobenzenes buy flagyl 250mg mastercard. Cl, donates an unshared pair of electrons, which give rise to relatively stable resonance structures contributing to the hybrids for the ortho- and para- substituted arenium ions. The resonance contributors formed from ortho, meta and para attacks on the chlorobenzene are shown below. Toluene, like benzene, undergoes electrophilic substitutions, where the substitutions take place in ortho and para positions. For example, the nitration of toluene produces ortho-nitro- toluene (61%) and para-nitrotoluene (39%). Oxidation of toluene Regardless of the length of the alkyl substituent in any alkylbenzene, it can be oxidized to a carboxylic acid provided that it has a hydrogen atom, bonded to the benzylic carbon. Hydroxybenzene, the simplest member of the phenols, is generally referred to as phenol. Numbering is often used to denote the position(s) of the substituent(s) on a phenol skeleton, e. Phenol itself is somewhat soluble in water (9 g per 100 g of water) because of hydrogen bonding with water. Physical properties of nitrophenols Physical properties of o-, m- and p- nitrophenols differ considerably. Intermolecular hydrogen bonding Intermolecular hydrogen bonding in ortho-nitrophenol in meta-nitrophenol 4. This intramolecular hydrogen bonding takes the place of intermolecular hydro- gen bonding with other phenol molecules or water molecules. Although weaker than carboxylic a acids, phenols are more acidic than alcohols (K values around 10À16 to a 10À18). Hydrolysis of diazonium salts Diazonium salts react with water in the presence of mineral acids to yield phenols. For example, the bromination of phenol produces ortho-bromophenol (12%) and para-bromophenol (88%). For example, phenol reacts with benzoylchloride to yield phenylbenzoate, and bromophenol reacts with toluenethionyl chloride to produce bromophenyltoluene sulphonate. This reaction is applied in the conversion of phenol itself into ortho-hydroxybenzoic acid, known as salicylic acid. Acetylation of salicylic acid produces acetylsalicylic acid (aspirin), which is the most popular painkiller in use today. A substituted benzalchloride is initially formed, but is hydrolysed by the alkaline medium. Again, salicylaldehyde could be oxidized to salicylic acid, which could be acetylated to aspirin. H H H H :O H N H N H Intermolecular hydrogen bonding Intermolecular hydrogen bonding in aniline of aniline with water Basicity of aniline Aniline, like all other amines, is a basic compound À10 (Kb¼ 4. Arylamines are stabilized relative to alkylamines because of the five resonance structures as shown below. Resonance stabilization is lost on protonation, because only two resonance structures are possible for the arylammonium ion. The group (phenyl) attached to the carbonyl carbon in the amide (benza- mide) is found joined to nitrogen in the product (aniline). The final stage of this reaction involves the formation of a quaternary ammonium salt where four organic groups are covalently bonded to nitrogen, and the positive charge of this ion is balanced by the negative chloride (ClÀ) ion. Formation of amide Aniline reacts with acid chloride to form corre- sponding amide. For example, when aniline is treated with benzoylchloride in the presence of pyridine, it produces benzanilide. For example, when aniline is treated with benzenesulphonylchloride in the presence of a base, it produces the sulphonamide N-phenylbenzenesulphonamide. Alkylamines also react with nitrous acid, but the alkanediazonium salts are so reactive that they cannot be isolated. The reaction of an arene diazonium salt with cuprous salt is known as a Sandmeyer reaction. Arenediazonium salts are extremely important in synthetic chemistry, because the diazonio group (N N) can be replaced by a nucleophile in a radical substitution reaction, e. Under proper conditions, arenediazonium salts react with certain aromatic compounds to yield products of the general formula Ar–NÀÀN–Ar ,0 called azo compounds. Sulphanilamide, the first of the sulpha drugs, acts by inhibiting the bacterial enzyme that incorporates para-aminobenzoic acid into folic acid. The lower layer (aqueous) contains the salt of aniline, and the ether layer has the neutral compound. Ether is evaporated from the ether layer using a rotary evaporator to obtain purified neutral compound. To the aqueous layer, sodium hydroxide and ether are added, and the resulting solution is shaken in a separating funnel. The ether layer (top layer) contains free aniline, and the aqueous layer (bottom layer) has the salt, sodium chloride. Ether is evaporated from the ether layer using a rotary evaporator to obtain purified aniline. In addition to the usual electrophilic substitutions, naphthalene can also undergo oxidation and reduction reactions under specific conditions as outlined below. Oxidation Oxidation of naphthalene by oxygen in the presence of vanadium pentoxide (V2O5) destroys one ring and yields phthalic anhydride (an important industrial process). N, O or S (hetero-atoms), in their rings are called heterocyclic compounds or heterocycles, e.