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If the sinus node is blocked for some reason birth control 3 month period order cheap levlen line, the A-V node will take over as the pacemaker birth control pills 16 year old purchase levlen 0.15 mg on-line, and if the A-V node is blocked birth control lo loestrin fe purchase levlen 0.15mg without prescription, the Purkinje fibers will take over as the pacemaker of the heart taking birth control 8 hours late purchase discount levlen. D) An increase in potassium permeability causes a decrease in the membrane potential of the A-V node. Thus, it will be extremely hyperpolarized, making it much more difficult for the membrane potential to reach its threshold level for conduction, resulting in a decrease in heart rate. Increases in sodium and calcium permeability and norepinephrine levels increase the membrane potential, causing a tendency to increase the heart rate. E) Sympathetic stimulation of the heart normally causes an increased heart rate, increased rate of conduction of the cardiac impulse, and increased force of contraction in the atria and ventricles. However, it does not cause acetylcholine release at the sympathetic endings because they contain norepinephrine. The sympathetic nervous system firing increases in the permeability of the cardiac muscle fibers, the S-A node, and the A-V node to sodium and calcium. E) the contraction of the ventricles lasts almost from the beginning of the Q wave and continues to the end of the T wave. A) the heart rate can be calculated by 60 divided by the R-R interval, which is 0. A) Systemic hypertension results in a left axis deviation because of the enlargement of the left ventricle. Pulmonary valve stenosis and pulmonary valve regurgitation result in an enlarged right ventricle and right axis deviation. A rightward angulation of the heart will cause a rightward shift in the mean electrical axis. Pulmonary hypertension causes enlargement of the right heart and thus causes right axis deviation. The negative end of the resultant vector originates in the ischemic area, which is therefore the left side of the heart. In lead V2, the chest lead, the electrode is in a field of very negative potential, which occurs in patients with an anterior lesion. C) the right axis deviation in this patient has to occur because of a change in muscle mass in the right ventricle, which occurs in pulmonary valve stenosis. Aortic valve insufficiency and systemic hypertension will cause a left axis shift. A) this patient has an acute anterior infarction in the left ventricle of the heart. This diagnosis can be determined by plotting the currents of injury from the different leads (see figure below). The limb leads are used to determine whether the infarction is coming from the left or right side of the ventricle and from the base or inferior part of the ventricle. The chest leads are used to determine whether it is an anterior or posterior infarct. E) During the T-P interval in a patient with a damaged ventricle, the only area depolarized is the damaged muscle. At the J point the entire ventricle is depolarized in a patient with a damaged cardiac muscle or in a patient with a normal cardiac muscle. The area of the heart that is damaged will not repolarize but remains depolarized at all times. Pulmonary hypertension increases the ventricular mass on the right side of the heart, which gives a right axis deviation. D) In the figure below, the current of injury is plotted at the bottom of the graph. The negative end of the vector points to where the current of injury originated, which is in the apex of the ventricle. Systemic hypertension, aortic valve stenosis, and aortic valve regurgitation cause hypertrophy of the left ventricle and thus a leftward shift in the mean electrical axis. Therefore, the diagnosis that fits with these characteristics is a right bundle branch block. E) this patient has a difference in the atrial rate of 100 and in the ventricular rate of 25. The 25 rate in the ventricles is indicative of a rhythm starting in the Purkinje fibers. A-V block is occurring, but it comes and goes, which is only fulfilled by Stokes-Adams syndrome.

Induction the process through which a moving electrical current causes a voltage on a nearby wire birth control pills use purchase levlen cheap online. The interference levels depend on how your cables are routed and the type of cable used (more on cable types a little later) birth control pills 7 day break buy levlen now. Avoid routing cables near sources such as refrigerators birth control 99 percent effective order levlen 0.15mg fast delivery, copy machines birth control for women gynecology buy levlen 0.15mg line, or microwave ovens. When running past fluorescent lights, route the cable as far above the lights as possible and across, rather than with, the direction of the bulbs. In fact, it is more fragile than copper wire cables, so you need to take extra care to avoid compression or vibration. Also, fiber optic is more expensive and more difficult to work with than copper wire. Most codes require any cable routed through walls, floors, and ceilings and some require all cable, to have plenum insulation. Dielectric the plastic insulator covering the central copper wire in coaxial cable. Coaxial cable, as you can see in Figure 6-1, is constructed from one central copper wire that is covered with a plastic insulator, called a dielectric, and shielded from interference by a foil wrapping or braid. Figure 6-1 Outer cylindrical shell Second conductor Insulator Inner conductor Coaxial cable. Higher impedance means higher resistance to a changing current, which is what you have in a data signal. Recognizing Types of Coax Many types of coaxial cable are used in various applications including networking and cable television. Each type of coax has specific characteristics that meet the needs of the type of transmission being carried. Table 6-1 shows the most common types of coaxial cable, comparing their impedance in ohms, common uses, and some of their basic characteristics. Comparing Ethernet Coaxial Cables Thicknet (10Base5) was the original cabling used in Ethernet networks. The name comes from the way that the cable usually dropped from a Thicknet cable running through the ceiling to the device. Thinnet (10Base2), developed after Thicknet, is smaller in diameter than Thicknet and much easier to work with. These connectors simply have to be connected and twisted into place to ensure their connection. Vampire tap A Thicknet cable tap that pierces the dielectric to connect to the inner core. Many implementations are not grounded, giving the false sense of security and protection. Thinnet is considered antiquated by most network implementers, but its relative ease of use is appealing to some. As with coaxial cable, the shielding must be grounded to prevent the foil or braided shielding from becoming a magnet for electricity. Figure 6-3 Conductor wire Made of copper, copper treated with tin or silver, or aluminum or steel covered with copper. Dielectric Made of a nonconductive material (such as polyethylene or Teflon), which may be solid or filled with air. Jacket Made of polyvinylchloride or polyethylene for nonplenum cable; made of Teflon or Kynar for plenum cable. Braid shield Made of flexible conductive wire braided around the dielectric (and foil shield). Cross talk is the electromagnetic interference that occurs when the electrical signal on one wire changes the electrical properties of a signal on an adjacent wire. The twists in the pair provide cancellation, which is the process in which two wires are twisted together to prevent outside interference or cross talk. The structure is similar, two or more pairs of twisted wires covered in a plastic jacket, but without the shield.

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B) the taste sensation of bitter is caused by many organic substances that contain nitrogen birth control pills vs depo cheap levlen 0.15 mg with visa, as well as by alkaloids birth control pills known for weight gain buy levlen 0.15mg amex. The abducens nerve innervates the lateral rectus muscle birth control withdrawal symptoms purchase cheapest levlen and levlen, which is attached to the lateral surface of the globe of the eye birth control for excessive bleeding order 0.15 mg levlen with mastercard. Contraction of the lateral rectus muscle results in movement of the eyeball laterally away from the midline of the face in an abducting manner-thus the name abducens nerve. D) the condition of cataracts causes the lens of the eye to become opaque and resemble the look of water in a waterfall or rapids in a river, thus the name, cataract. A cataract results from the progressive coagulation of the proteins that make up the lens. One can think of this coagulation as similar to the white of an egg turning opaque as it is cooked. D) the taste sensation of sour is proportional to the logarithm of the hydrogen ion concentration caused by acids. The taste sensation of sweet is caused by a long list of chemicals, including sugars, alcohols, aldehydes, ketones, and amino acids. B) the bitter taste sense is much more sensitive than the other sensations because it provides an important protective function against many dangerous toxins in food. E) A person with presbyopia cannot accommodate for near and far vision, which means that the lenses of the eyes have lost their elasticity and thus cannot change their focal point. A child with good vision has 14 diopters of accommodation; this accommodation decreases throughout life until, at approximately 70 years, the lenses cannot change their shape and the power of accommodation is then zero. C) the malleus is attached to the tympanic membrane, and the stapes is attached to the oval window. E) Light passes through the eye to the retina in the posterior portion of the eye. The most anterior layer of the retina, through which light passes first, is the retinal ganglion layer. Light then passes through the other cell layers of the retina until it reaches the photoreceptors in the posterior region of the retina. D) Light rays from distant objects do not require as much refraction (bending) as do light rays from objects close at hand. Therefore, a thinner lens with less curvature is required for viewing distant objects. The Special Senses of the ciliary muscle thickens the lens, and relaxation causes the lens to become thinner. The high intraocular pressure causes blood vessels and axons of the optic nerve to be compressed at the optic disc, which leads to poor nutrition with possible death of the neurons. The main cause of open-angle glaucoma is reduced flow of aqueous humor through the trabecular meshwork because of tissue debris, white blood cells, deposition of fibrous material, and other factors that increase the hydraulic resistance of the meshwork. The first synapse in the visual system takes place in the lateral geniculate nucleus. Ganglion cells attached to photoreceptors on the temporal side of the retina project to the same-sided or ipsilateral lateral geniculate nucleus. Fibers from the nasal side of the retina cross over to the opposite or contralateral lateral geniculate nucleus in the optic chiasm. B) A concave lens diverges light rays; in contrast, a convex lens will converge light rays toward each other. If a convex lens has the appropriate curvature, parallel light rays will be bent so that all pass through a single point, called the focal point. Sudden closure of the iridocorneal angle prevents aqueous humor from reaching its outflow pathway in the canal of Schlemm. Intraocular pressure can increase rapidly and cause blindness without immediate treatment. C) the ampulla and saccule are part of the vestibular apparatus, not the cochlear apparatus. The cochlea has three main compartments, with fluid movement occurring in the scala vestibuli and scala media in response to sound vibrations.

C) High-frequency repetitive stimulation (indentation/ pressure) of the skin is sensed by Pacinian corpuscles birth control junel best purchase levlen. B) the process of lateral inhibition birth control pills 35 order levlen cheap, illustrated in the figure below birth control pills 5 hours late order discount levlen line, underlies the ability to discriminate two points simultaneously applied birth control for women does size levlen 0.15mg free shipping. Inhibitory postsynaptic potentials are always negative because the membrane potential is lowered to a more negative value. C) Activation of G proteins usually changes the longterm response characteristics of the neuron. D) Vasospasm and eventually ischemia in a sensory area of cortex is thought to be the basis for the prodromal symptoms experienced by patients with migraines. C) Both warm and cold receptors are able to respond to steady-state temperatures, as well as changes in temperature. A) the Pacinian corpuscle transmits a modality of sensation (vibration) that is transmitted in the dorsal column­medial lemniscal system. The first synaptic connection in this sensory pathway is in the dorsal column nuclei on the ipsilateral side of the body. B) Warm receptors mainly transmit signals along relatively slow-conducting type C fibers. A) Descending cortical modulation of somatosensation involves an increase or decrease in the perception of signal intensity. C) A facilitated neuron is one whose resting membrane potential is closer to the threshold for activation; that is, less negative or in the depolarizing direction. A) the opening of ligand-gated chloride channels and movement of chloride ions into the cell leads to hyperpolarization of the membrane. Neither increasing the extracellular sodium concentration nor the movement of potassium into the cell leads to hyperpolarization of the membrane. D) Paralysis of the contralateral arm and leg is a motor deficit, and such a deficit would not typically be observed after damage to the primary somatosensory cortex. B) In spatial summation, increasing signal strength is transmitted by using greater numbers of sensory fibers. B) A diverging neuronal pathway amplifies nerve signals; activation of a single pyramidal cell in motor cortex can stimulate as many as 10,000 muscle fibers. In a converging circuit, multiple input fibers converge upon a single postsynaptic neuron, which allows summation of information from multiple sources. An inhibitory circuit often has inhibitory interneurons that stop the spread of a nerve signal. He finds that the ants must be 10 centimeters from the convex lens to be in focus. A) Located 5 degrees lateral to the central point of vision B) the exit point of the optic nerve C) Contains only rods and thus has monochromatic vision D) Contains no blood vessels E) the area where chromatic aberration of the lens is the greatest 3. A 6-year-old boy with albinism is taken to the ophthalmologist because of difficulty seeing. Which of the following is the most likely cause of the decrease in visual acuity in this boy? A 53-year-old woman with celiac disease visits the physician because of difficulty seeing at night. A decrease in blood levels of which of the following is the most likely cause of her night blindness? A) 2-Monoglycerides B) Amino acids C) Free fatty acids D) Glucose E) Vitamin A F) Vitamin B12 5. A) Inability to move the eyes in a vertical up-anddown motion B) Inability to rotate the eyes within the eye socket C) Inability to move the eyes laterally toward the midline D) Inability to move the eyes laterally away from the midline E) Vertical strabismus 7. A) Denaturation of the proteins in the lens of the eye B) Elongated eye globe C) Unresponsive and dilated pupil D) Coagulation of the proteins in the lens of the eye E) Increase in intraocular pressure 8. Which of the following best describes the most likely vision problem in this woman? Which of the following is the middle ear ossicle that is attached to the tympanic membrane? A) Inner nuclear layer B) Outer nuclear layer C) Outer plexiform layer D) Photoreceptor layer E) Retinal ganglion layer 13.