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 voluntary motor tracts and the visual and auditory reflex centers, and the pons, which helps regulate breathing movements. Damage to these areas is life-threatening, whereas damage to the cortical areas may impair function, but is less likely to be life-threatening.
19.12 In the split-brain technique, the corpus callosum connecting the two hemispheres is split (Zaidel, 2004). Patients who have had this procedure can still perform many task normally, but suffer fr...