Notes on Chapter 4

Notes on Chapter 4 - NOTES ON CHAPTER 4 Here we take a look...

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NOTES ON CHAPTER 4 Here we take a look at what kind of activity is really happening in the brain. The brain is full of electrical events including changes in membrane potentials and nerve impulses, or action potential, which can rip along at over 100 mph. The electrical activity has been long known, but only later did we find that the brain is functioning with little squirts of chemicals known as neurotransmitters. The interconnections of neurons in the brain is very, very extensive. Understanding all this can be very difficult when you first approach it so I have tried to break activity down into rather simple events to try to make it more understandable. You see in the book that ions are very important for our story. An ion is a particle which has either a positive or negative charge. If we look at molecules of salt, NaCl, we find that there is no electrical charge, but put NaCl in the water and a very strange thing happens. The atoms of sodium (Na+) breaks away from the chlorine (Cl-) atoms and we have ions with a charge. Similarly if we take potassium chloride it dissociates into K+ and Cl-. If we look at a typical neuron we find that the sodium is mostly outside the cell and the potassium is largely in the cell along with the chloride ion. The cell also contains amino acids with a negative charge. The inside is 70 mV negative to the outside in the resting state. There are a few simple rules about ions. When we have lots of one ion in one place and few of these ions in another place the ions try to run “down their concentration gradient” until concentrations are the same everywhere. Secondly opposites attract. Positive ions tend to move toward negative ions. Thirdly positive ions tend to be repulsed by other positive ions and negative ions repulse negative ions. Now consider this. Sodium ions are in high concentrations outside the neuron and we expect they should move down their concentration gradient into the neuron and also they should be attracted by the negatively charged interior of the neuron. At rest they don’t do this because they cannot penetrate the cell wall. Potassium and chlorine move across the membrane much more easily. If the neuron’s membrane is depolarized (the membrane potential moves toward zero) by only about 5 mV something remarkable happens. Sodium is allowed to enter the cell so fast and so much that the neuron becomes totally depolarized (membrane potential = zero) and actually becomes positively polarized by about 50mV. Then the membrane potential goes back to -70
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Notes on Chapter 4 - NOTES ON CHAPTER 4 Here we take a look...

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