organelles
Chapter 12 1 MRI uses the relative amount of water in tissue to distinguish different areas, so gray and white matter in the nervous system can be seen clearly in these images. 3 Neurons enable thought, perception, and movement. Plants do not move, so they do not need this type of tissue. Microorganisms are too small to have a nervous system. Many are single-celled, and therefore have organelles for perception and movement. 5 Sodium is moving into the cell because of the immense concentration gradient, whereas potassium is moving out because of the depolarization that sodium causes. However, they both move down their respective gradients, toward equilibrium. 7 A second signal from a separate presynaptic neuron can arrive slightly later, as long as it arrives before the first one dies off, or dissipates. 9 C 11 D 13 B 15 B 17 A 19 C 21 C 23 A 25 B 27 D 29 B 31 D 33 A 34 Running on a treadmill involves contraction of the skeletal muscles in the legs, increase in contraction of the cardiac muscle of the heart, and the production and secretion of sweat in the skin to stay cool. 36 The disease would target oligodendrocytes. In the CNS, oligodendrocytes provide the myelin for axons. 38 Afferent means toward, as in sensory information traveling from the periphery into the CNS. Efferent means away from, as in motor commands that travel from the brain down the spinal cord and out into the periphery. 40 The cell membrane must reach threshold before voltage-gated Na+ channels open. If threshold is not reached, those channels do not open, and the depolarizing phase of the action potential does not occur, the cell membrane will just go back to its resting state. 42 EPSP1 = +5 mV, EPSP2 = +7 mV, EPSP 3 = +10 mV, IPSP1 = -4 mV, IPSP2 = -3 mV. 5 + 7 + 10 4 3 = +15 mV.