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Unformatted text preview: Electrical Signals: • Result from o ionic concentration differences across the plasma membrane o permeability characteristics of plasma membrane Concentration Differences across Plasma Membrane: • Na/K pump moves ions by active transport (transported by a protein, uses energy, and against concentration gradient) • K moves in cell, Na out • 3 Na transported out, 2 K transported in, for each ATP molecule (outside of cell becomes more positive because more positively charged ions are pumped out of the cell than are pumped into it) • Concentrations of K and negative-charged proteins are high inside cell (attraction!); concentrations of Na and Cl are higher outside cell (again, attraction!) • Cl does not go in cell because it is repelled by the negatively-charge proteins and ions (that are previously synthesized inside cell and cannot go out of cell) Permeability of Plasma Membrane: • Ions must pass through ion channels • 2 major types of ion channels: o Leak ion channels are non-gated, always open, responsible for permeability of membrane to ions when membrane is at rest ion channels are specific to the type of ion the number of each type of leak ion channels determines permeability off resting membrane to different types of ions K ion leak channels and Cl ion leak channels > Na ion leak channels, therefore plasma membrane is more permeable to K and Cl than Na o Gated ion channels Closed until opened by specific signals Change permeability by opening and closing Gated ion channels in plasma membrane include: ⇒ Ligand-gated ion channels o A ligand is a molecule (neurotransmitter/hormone) that binds to a receptor site on a receptor (protein/glycoprotein located on plasma membrane) o These ion channels are receptors w/ extracellular receptor site and a membrane spanning part that forms a channel. When binding occurs, channel opens/closes. o These exist for Na + , K + , Ca 2+ , Cl- o Common in nerves, muscles and glands o Example: (1) Neurotransmitter acetylcholine released from presynaptic terminal of axon (this is a chemical signal) (2) Binds to ligand-gated Na channel in membrane of muscle fiber (3) Na channel opens, Na enters fiber ⇒ Voltage-gated ion channels o Open and close when small voltage changes occur in plasma membrane or when there is a charge difference o In a resting cell, inside is neg. charged relative to the outside o When cell stimulated, permeability changes because gated ion channels open and close. Movement of ions in and out the cell changes charge difference....
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This note was uploaded on 12/05/2011 for the course KINESIOLOG 1Y03/1YY3 taught by Professor Parises during the Spring '11 term at McMaster University.
- Spring '11