Science Definitions
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18.5 Myelin is an insulating material and inhibits the flow of current from one point to another (Applegate, 2000, 160). Depolarization in myelinated fibers occurs only at the nodes of Ranvier, the action potential jumping from node to node. This jumping is called saltatory conduction. In unmyelinated fibers, a threshold stimulus causes a localized area to reverse polarization on the membrane, while the rest of the membrane is in a resting state (159). When part of the membrane reverses its polarity, the difference in polarity between this area and the adjacent area causes the current to flow and it depolarizes the second area. This process is continued so that the impulse flows down the nerve fiber. There is no jumping as seen in myelinated fibers: the impulse flows steadily down the entire length of the neuron.19.10 A hemorrhage in the brain on the right side causes paralysis on the left because the nerves cross over in the brain, i.e. nerves in the right side of the brain control the left side of the body (Berkow, Beers and Fletcher, 1997, 353) 19.11 The base of the brain contains the cerebellum, which controls subconscious contractions of skeletal muscle necessary for coordination, balance, and posture (Applegate, 2000, 168). It is needed for fine motor skills. The brain stem contains the medulla oblongata, which contains the cardiac center, the respiratory center, and the vasomotor center, and so is essential to life. The midbrain contains the volun
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ge (Corneal, 2004).
22.11 When light is shone onto an uncovered eye, the pupil of the covered eye also responds (Human, 2004). This is known as a consensual response. This would be a contralateral response because it occurred on the opposite side to that being tested. Such a response is important in this reflex because if the response was ipsilateral, only one eye would be protected if danger threatened, rather than both eyes.
22.12 Reflexes can be differentiated as somatic or autonomic (Human, 2004). Somatic reflexes involve the stimulation of skeletal muscles by the somatic division of the nervous system. They involve such actions as withdrawal of a hand from a painful stimulus, sneezing, and coughing. Autonomic reflexes are not subject to conscious control, and are mediated through the autonomic division of the nervous system. They usually involve the activation of smooth muscle, cardiac muscle, and glands. They control such things as blood pressure, digestion, and the secretion of glands.
22.13 Micturition: bladder; internal urethral sphincter; induce urination (Applegate, 2000, 380).
Hering-Breuer: lungs; stretch receptors; inhibit overinflation, promote exhalation (Applegate, 2000, 321).
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Some common words found in the essay are:
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Approximate Pages = 15 (250 words per page)
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