Diffusion:Solution=solvent(water) and solute (dissolved molecules)Due to random movement (thermal energy), solute molecules will show net movement from region of high concentration to a region of low concentration; solute moves down the concentration gradientRate of diffusion:Increases with temperatureIncreases with concentration gradientIncreases with surface area of membraneDecreases with distanceIf solute molecules can penetrate the membrane then diffusion can occur across the membraneLipids, small gas molecules, ions through protein channels in membrane, nonpolar moleculesOsmosis:Diffusion of water across a semipermeable membrane; through aquaporin channels in plasma membraneWater moves from low solute concentration solution to high solute concentration solution( water diffuses from high water concentration to low water concentration)Water will diffuse by osmosis across the membrane until solute concentration is the same on both sides of the membraneOsmotic pressure: how strongly a concentrated solution pulls water by osmosis across the membranePure water=0Equal osmotic concentration=isotonicLess concentrated=hypotonicMore concentrated=hypertonicIf pure water moves into the cell, it will cause the cell to swell and burst (lyse)Osmolality vs molalityMolality is the number of compound molecules per liter of waterOsmolality is the number of solute particles per literCarrier-Mediated Transport Mechanisms:Mediated by carrier proteins that span the plasma membraneProperties:Specificity for a specific moleculeLimited number of transporters can be saturated, with a max transport rateClosely related molecules can compete to transporters on the cell surfaceFacilitated diffusion:Transported molecule is moved down its concentration gradientDoesn’t require extra energy from the cellBecause facilitated diffusion requires using a limited number of transporters, transport can be regulated by increasing or decreasing the number of transportersPrimary active transport:Membrane carrier protein is an ATPase that breaks down ATP to release energyEnergy is used to transport molecule against its concentration gradient(up the gradient will require energy)Ca2+ ATPase pump: hydrolysis of ATP and release of ADP causes conformational change in transporter, releasing Ca2+ outside the cell (moves calcium from low to high)If you run out of ATP the transport will no longer take placeCoupled active transport:Cell uses energy to establish steep concentration gradient for molecule 1Co-transporter allows molecule 1 to move down concentration gradientCouples energy of first molecule to co-transport molecule 2 up its gradientMost cells maintain a steep Na+ and K+ gradient across their membranesNa+/K+ ATPase pump:3 Na+ ions bind to inside of carrier proteinATP is hydrolyzedRelease of ADP moves 3 Na+ to outside of cellRelease of Pi moves 2 K+ to inside of cellCotransport/ symport: both molecules move in the same directionCountertransport/ antiport: molecules move in opposite directionsResting Membrane potential:VmCells have an unequal distribution of charge across their membrane: more positive charges on the outside and more negative charges on the insideCharge separation is caused by movement of ions in and out of the cellIons are moved by chemical diffusion down concentration gradients and by electrical attraction and by active transportConcentration of ions inside and outside reaches equilibrium due to equilibrium potentialEach ion species feels two forces pulling on it through open ion channels:1. Chemical driving force: depends on concentration gradient across membrane2. Electrical driving force: depends on electrical potential difference across membraneThese forces can act in same direction or opposite directions across the membraneExample: K+ has chemical driving force out of cell, but electrical driving force into cell.Example: Na+ ions has both chemical driving force and electrical driving force into cell.The electrical potential that balances the concentration gradient is called the equilibrium potential.If there are open channels for an ion, the electrical and chemical driving forces will try to force the ions to move across the membrane.The ion will move across the membrane until the change in electrical charge causes the cell’s Vm to reach the ion’s equilibrium potential.2 forces on ions:diffusion down concentration gradientelectrical attraction toward opposite charge: Positive ions will be pulled by electrical force from the outside to the inside no matter whatfor K+, chemical and electrical forces are in opposite directionfor Na+, chemical and electrical forces are in the same directionNernst Equation:Eion = 61 / charge • log ([ion]out / [ion]in)Membrane potential (Vm) or RMPThe cell’s overall membrane potential (Vm) is a combination of the Eion of all the ions that can permeate the membrane, with a greater contribution for the ions with the greatest permeability (i.e. with the most open ion channels).Vm approaches the Equilibrium Potential of the most permeable ion.For neurons and most cells, the most permeable ion is K+.So, the membrane potential Vm at -70 mV is close to EK+ at -90 mV.Goldman Equation finds the compromise membrane potential accounting for each permeant ion.Structure of Vertebrates:Peripheral compartment:Everything outside of the brain and spinal cord (heart, lungs, gastrointestinal tract, liver, kidneys, skeletal muscle, skin etc.)Neurons and nerve fibers outside the brain and spinal cordCentral nervous system:Brain at front of bodySpinal cord running down the backProtected by skull and vertebraSensory receptors clustered in head (vision, hearing, taste, smell)Functions of Nervous SystemSensory motor integration: detect changes in the environment or in the body via sensory receptors; coordinate responses across the body. Initiate response via skeletal muscle (somatic nerves for voluntary movement) or via smooth muscle and glands (autonomic nervous system)Neurons (nerve cells): point to point communication across the body to coordinate responses; integrate electrical and chemical signals at dendrites and cell body; depending on inputs, neuron sends electrical and chemical signals down axon to synapse on target cellSensory neurons (afferents): carry sensory information into the CNSMotor Neurons (efferents): carry impulses out of CNS to make muscles move or effect target organsAssociation neurons: neurons within the CNS that process informationAnatomy of NeuronsCell body:
View Full Document
Unlocking...