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Chapter 3 Neurophysiology

Chapter 3 Neurophysiology - Chapter 3 Neurophysiology The...

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Chapter 3 Neurophysiology: The Generation, Transmission, and Integration of Neural Signals Electrical Signals Are the Vocabulary of the Nervous System o All living cells posses an electrical charge—they are more negative on the inside than the outside. o A balance of electrochemical forces produces the resting membrane potential of neurons Neuron at rest. Consist of many ions (electrically charged molecules that a neuron contains), a majority are anions (negatively charged ions), especially large protein anions that cannot exit the cell. Neurons contain relatively fewer cations (positively charged ions). All of these ions are dissolved in an intracellular fluid (aka cytoplasm. The water solution found within cells), which is separated from the extracellular fluid (the fluid in the spaces between the cells and in the vascular system) by a cell membrane (the lipid bilayer that unsheathes a cell.) When inserting a microelectrode (small electrode used to record electrical potentials from living cells) into the interior of a neuron and compare it to the extracellular fluid, we find that the neuron is more negative inside than out the outside. Specifically, a neuron at rest exhibits a characteristic resting membrane potential (an electrical- potential difference across membrane) of about -50 too -80 millivolts (mV); the negative sign indicates the negative polarity. Cell membranes are made up of a lipid bilayer—two layers of linked fatty molecules—within which many sorts of specialized proteins “float”. The ion channel (a tube-like pore that allows ions of a specific type to pass through the membrane) where some are gated and can open and close rapidly in response to changed in voltage, to the presence of certain chemicals, or to mechanical deflection of the cell membrane. Some ion channels stay open all the time like the potassium ions (K+), a potassium atom that carries a positive charge, to cross the membrane. Since it is studded with these K+ channels, the cell membrane of a neuron exhibits selective permeability to potassium; that is K+ ions (but not other types of ions) can enter or exit the cell fairly freely, unimpeded by the cell membrane. The resting potential of the neuron reflects a balancing act between two opposing forces that drive ions in and out of the neuron 1) Diffusion, which is the force that cause molecules of a substance to diffuse from regions of high concentration to low concentration. Molecules tend to move down their concentration gradient until they are evenly distributed. 2) Electrostatic pressure, which carries from the distribution of
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electrical charges rather than the distribution of molecules. Positively charged cations are thus attracted to the negatively
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Chapter 3 Neurophysiology - Chapter 3 Neurophysiology The...

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