7 neurons 118 - Biology 118 7. NEURONS AND NERVOUS SYSTEMS...

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Biology 118 7. NEURONS AND NERVOUS SYSTEMS Overall, the nervous system can be divided into the central and peripheral portions, the CNS and the PNS, respectively. Nervous systems are made of neurons and neuroglia. Neurons specialize in using membrane electricity to function. THE RESTING POTENTIAL : In any cell: The phospholipid bilayer can separate charges (ions) on either side of the membrane. There are leaky channels in the membrane. The Na + -K + pump helps maintain higher Na + concentrations outside the cell, higher K + inside the cell. Cytosolic proteins are trapped inside the cell, and have negative charges. All this makes for an uneven distribution of charge across the membrane, making it slightly more positive outside compared to inside. This is the resting membrane potential, an electrical voltage that every cell possesses. It represents stored potential energy – energy that can be put to work. Membrane potentials are measured by noting the charge difference on the inner membrane surface (i.e. the side facing the interior of the cell). At rest, this side is negative compared to the outside, so resting membrane potentials are negative. NEURONS: Neurons are specialized to receive, integrate and transmit information – their specialized structures include the dendrites, the cell body, the axon and the axon terminals. Neurons, like all other cells, have the membrane components described above, and thus also have a resting potential. It measures around –70mV. Unlike most other cells, neurons are excitable – they have additional membrane proteins that can alter membrane voltage drastically: voltage-gated ion channels – these are closed most of the time (i.e. the ‘gate’ is closed), and are sensitive to membrane voltage – they open and close depending on the membrane voltage: V-Na + channels V-K + channels THE ACTION POTENTIAL : The action potential is a rapid, drastic change in membrane voltage – it’s the electrical signal neurons use to transmit information. It occurs in eight easy steps: 1. The membrane starts at rest, -70mV. 2. A stimulus starts raising the membrane voltage towards threshold. 3. The membrane voltage reaches the threshold potential, -55mV. At this point, the V-Na + open. 4.
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This note was uploaded on 02/24/2011 for the course BIO 118 taught by Professor Bilgen during the Spring '08 term at University of Washington.

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7 neurons 118 - Biology 118 7. NEURONS AND NERVOUS SYSTEMS...

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