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FINAL EXAM REVIEW Covers all the material in BIOL 273. Excellent source to study for the final exam.

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BIOL 273
Bruce Wolff

BIOL 273: Module 1 The methods of communicating through the cell: 1. Nervous system 2. Endocrine system The resting membrane potential The cytoplasm of the nerve cells has a negative charge in comparison to the extracellular fluid (ECF) ++ + - Ions concentrated in ECF (Plasma, Interstitial Fluid): Ca , Na , Cl Ions concentrated in cytoplasm of nerve cells (Intracellular Fluid): K and organic metabolites Maintained by two factors: o Na+ and K+ are actively transported across the cell membrane o Ca++, Cl-, K+ can cross the membrane o Harder for proteins and large organic molecules to cross (large, negatively charged) In neurons the resting membrane potential (RMP) is -70mV K+ can cross the membrane o K+ leaks out of cell because of higher levels of concentration in the cell, goes down concentration gradient o Inside of cell becomes negatively charged -70mV to -90mV o Draws back the K+ into the cell, until it reaches equilibrium Na+ can cross the membrane o Na+ leaks into the cell because of higher concentration outside of the cell. Moves down electrical gradient o Inside of cell goes from -70mv to +60mV, no more Na+ can enter the cell Cl- can cross the membrane o Diffuse into the cell, down concentration gradient, until equilibrium has been reached, -70mV K+, Na+, and Cl- cross the membrane, but not at equal rates o K+ ions are the fastest- easily move out, -70mv to -90mV o Na+ ions are about forty times more slower- move into cell, -70mV to +60mV o Cl- is at resting potential at the equilibrium potential, so there is no movement Hypothetically it would move into the cell to equilibriate the cell at -70mV Goldman Equation o Ions that dont cross the membrane make no contribution to the RMP (Ca++) o Ion with the highest permeability (K+) has the greatest influence on the voltage across the membrane RMP is the closest toKE (-90mV) than tNaE Active transport o The leakage of K+ (out) and Na+ (in) down their chemical gradient are balanced by active transport, in the opposite direction o ATPase, 3Na+ out and 2K+ in The Graded Potential Anatomy of Neuron o Cell body= nucleus and most of organelles o Dendrites= receive incoming signals o Axons= carry electrical signals to other cells, can be up to one meter long Change in Electrical potential o Membrane of neuron contains chanlles for K+, Na+, Cl-, and Ca++ o The open-close or close-open of a channel changes the distribution of the ions o The electrical potential that is measured across the membrane is the RMP o 2 types of electrical signals that are carried by neurons are: Graded potential Action potential Characteristics of Graded Potential o Depolarizing (-70mV to (+)) o Hyperpolarizing (-70mV to (-)) This depends on which ion channel changes o The amplitude of graded potential is dependent on the number of ion channels that change This depends on the intensity of the even that causes the change Greater amplitude- a lot of channels open- greater potential of binding between ligand Depolarizing Graded Potential (-70mV to+60mV) o At resting state the Na+ ligand gated are commonly closed o So when the ligand is dissolved into solution, this opens the channels o The ligands binds to the channel and open it o Increases the amplitude o Binding of the ligand is what initiates the Na+ channel to open There is a temporary increase in the rate of flow through the membrane o The number of Na+ that enters the neuron is dependent on the amount of ligand that is bound to the channel o The wave of depolarization decreases in amplitude as it moves further away The further the point from the Na+ the smaller the amplitude of graded potential would be Its like standing infront of a pond and skipping rocks, where the rock lands the wave would be bigger, the further the rock goes the wave size decreases and slowly dies down Hyperpolarizing Graded potential (-70mV to -90mV) o Ligand gated channels for K+, K+ floods out of the cell, making the inside of the cell more negative o The further the point is from the K+ channel the smaller the hyperpolarizing curve will be Graded potentials are created on the dendrites or the cell body of the neuron Action Potential Are different than graded potential because: o The amplitude is not graded, but always the same can go for a very long time -70mV to +30mV the change in membrane potential is 100mV o The amplitude does not decrease as they travel across a neurons membrane Suitable for long distance signal transmission o Voltage gated channels of Na+ and K+ are responsible for action potentials Open when resting membrane is depolarized to a threshold of -55mV o Graded arise from ligand and Action arise from Voltage Voltage Gated Channels o Both Na+ and K+ open in response to depolarizing supra threshold K+ and Na+ channels open at different times The Na+ channels open first and after a bit of a delay the K+ channels are opened (half a millisecond) Na+ has two gates: activation gate and inactivation gate Activation gate is closed at rest and opens when threshold is -55mV Inactivation gate is open at rest, it closes about half a millisecond after activation gate opens Cannot be reopened until a few milliseconds have passed an membrane is repolarized Sequence of events in the initiation of an action potential 1. At rest, -70mV, both Na+ and K+ channels are closed 2. The graded potential depolarizes the membrane 3. When the threshold value of -55mV is reached, the voltage gated Na+ activation channel opens and Na+ floods into the cell 4. The inward movement of Na+ ions causes a large, rapid depolarization of membrane (- to +) 5. At peak the membrane potential is +30mV, the Na+ channels become inactivated, inactivation gate closes (no Na+ can pass through K+ channels simultaneously open 6. K+ flows out of the cell, causing the cell to repolarize 7. The cell repolarizes slightly more negative than -70mV, the K+ voltage gates close (hyperpolarization) 8. Over the next few milliseconds the membrane potential returns to resting value (-70mV Propagation of the Action Potential o The activation potential travels in only one direction, because of refactory period Moves to the right Refactory Period o Makes the neuronal membrane less responsive to a stimulus directly after an action potential o No new action potential can be started during the absolute refactory period, no matter how strong the stimulus is o This is the interval where the Na+ channels are maximally open- 3(between the threshold and the peak) or inactivated- 7 The rate of influx of Na+ ions into the cell cannot be increased, so no new potential can start o Relative refactory period occurs right after absolute refactory period An action potential can be initiated, but only a stimulus that is stronger than normal This is the period at which Na+ channels return to their resting conditions, but some K+ are open A larger number of Na+ channels must be open in order for enough positive charges to enter, this requires a larger depolarization then the threshold After step 7-9 Static event o An action potential travels from the place where it begins in all directions o When Na+ floods into the cell (4), the depolarization causes the surrounded membrane to surpass the threshold- which open the voltage gated Na+ channels and spread the action potential o In a single neuron the amplitude of action potential is the same everywhere Amplitude does not depend on the size of the initiating event (as long as it passes threshold) but depends on two factors The resting membrane potential (constant) The length of time that Na+ channels are open- 0.5ms Trigger zone o Action potentials are created in the trigger zone Some neurons at the base of the axon where it joins the cell body In other the base of dendrites o It is the centre of integration o Only a graded potential that depolarized the membrane to the threshold (-55mV) can produce an action potential o If the graded potential is below the threshold when it reaches the trigger zone it will not produce an action potential Summation of Graded Potential o 2 separated graded potentials, neither that exceed the threshold value can summate and draw an action potential o Temporal summation- when th
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