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This 4 page Class Notes was uploaded by Kelly Wetmore on Tuesday March 1, 2016. The Class Notes belongs to Bio 242 at University of Rhode Island taught by Barbara Van Sciver in Winter 2016. Since its upload, it has received 16 views.
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Date Created: 03/01/16
Thursday, May 19, y Lecture 6 Intercellular Chemical Messengers Paracrine • Binds to receptor • Secretory ———> target cell • Can only act upon nearby cells • EX: Histamine causes blood vessels to dilate • Short distance signals Neurotransmitters • Pre and post synaptic neuron • Electricity Hormones • Released into blood • Secretory cells find target cells Neurohormones Membrane Transport Solubility • ECF and ICF • Polar and Nonpolar Size • Small polar molecules can get through protein channels 1 Thursday, May 19, y • Large polar molecules in a carrier Active transport • Uphill (low concentration to high concentration) • Requires ATP • Against the concentration gradient Passive transport Carrier Mediated Transport Facilitated diffusion • Downhill (Higher to lower concentration) • With aid Na+/K+ Pump- Active Transport Pumps sodium and potassium Sodium is being pumped uphill Dephosphorated Potassium is released 3 Na+ for every 2 K+ Pump requires energy Against the concentration gradient = Uphill pump Membrane Channels Leaky • Always open 2 Thursday, May 19, y • Not regulated Ligand • Chemical messenger gated • Channels open only when it receives a receptor Voltage gated • Depends on the voltage of the channel (open or closed depending) Electrical Properties of the Membrane Anions are negative and are nondiffusible (can’t get out of the cell) in ICF Actions of the sodium/potassium pump • 2 K+ <———> Na_3 • More permeable to potassium than sodium • It requires energy to move potassium into the cell but it doesn’t require energy to get it out of the cell • Pump’s concentration gradient favors potassium movement into the cell Resting membrane potential = 70 mV • No potential energy Membrane Potential The difference in electrical voltage (potential) that exists across the membrane of most cells ———> Membrane is polarized Current Flow of electricity 3 Thursday, May 19, y Movement of Ions Excitable Tissues Neurons and muscles can undergo changes of action potentials ICF and ECF ICF • Negative charges are trapped • Potassium pumped out —> • Negative ECF • Sodium pumped in <— • Positive Charges line up at membrane Graded Potentials Short distance signals (die out very quickly) Decremental (keeps getting stronger) Strength is proportional to stimulus strength Action Potentials Long distance signals (released at axon terminal) Nondecremental Strength is not proportional to stimulus 4
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