BIOC32H3 Study Guide - Midterm Guide: Potassium Channel Blocker, Walther Nernst, Nernst Equation

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Published on 23 Nov 2017
Hypothesis = to assume based on the logic available and should be testable.
1)How to Test a Hypothesis.
-Have Subject, divide into control and experimental groups.
-Identify dependant and independent variables.
-Hypothesis should not include any subjective statements.
2)Experimental Design
-Determines the validity of the results.
-Have to account for cost, time required to carry out experiment.
-Ethical Issues are mandatory to Account for.
- Always take baseline tests because beginning an experiment, all participants should
start from equal points.
- Always have Variability between the subjects being tested. (Sex, Life-Styles, Weight, Race... etc.)
-Psychological Bias;
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2) Double-Blid, hee eithe the patiipats o the Epeiete do’t ko hih group is
being tested or not.
-Ethically soundness is of utmost importance.
Thalidomide (1954), was medication given to pregnant women who were undergoing morning sickness.
This was then seen to induce birth of children with malformations and was withdrawn from the public.
-Its is now used as a means of therapy for cancer.
History behind the dynamics of the membranes of the body.
-Neurophysiologists, use anatomically connections and rules of cellular responses.
-Biophysicists, use rules of cellular responses using physical, chemistry and electricity.
Julius Bernstein came up with the Membrane Theory or Potassium Electrode Hypothesis.
(Neurobiologist and Neurophysiologist).
-Potassium is one of the major components in the living cell.
-At Rest= there is a pre-existing electrical difference between the membranes (INSIDE AND OUTSIDE)
-Suggested that intercellular concentration was higher than extracellular concentration of Potassium.
-The gradient is formed as a result of the properties of the plasma membrane which is relatively
impermeable to many molecules.
Difference between;
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1) Resting Membrane Potential- Potential or electrical charge/difference between the inside and
outside of cell (biological system and permeable to various ions). GOLDMAN HODGKINS-KATZ
2) Equilibrium Potential- the difference in electrical potential within an artificial cell (only
permeable to one specific ion). We look at specifically potassium and sodium as they are
important ions that govern the properties of excitable cells. NERNST EQ.
Why is the membrane more permeable to potassium at rest?
Due to the leak channels that allow slight movement of potassium.
Main method through which NA+ or K+ moves in and out of the cell. If front it would just be a solid
impermeable membrane regarding the two ions.
Components of body fluids:
- ionic composition of IC and EC solutions differs
- high [K+] IC
- high [Na+] EC
- high [Cl-] EC
Membrane dynamics governed by
- permeability of the plasma membrane
- voltage-gated ion channels
- Na / K ATPase pump
- chemical gradient, electrical gradient, electrochemical gradient
- equilibrium potential / potential difference
- Eion derived using the Nernst equation
Resting membrane potential:
- Generated by leak K+ channels, Na/K pump
- Goldman-Hodgkin-Katz equation to derive Vm
The influence of Julius Bernstein and Walther Nernst
Action Potential I
What governs the excitability of cells?
1) The number of channels (distribution of potassium to cells through the channels)
2) Concentration of ions between the two compartments.
The opening and closing of the voltage gated ion channels are what allow changes in the membrane
Membrane potential baseline is (-70Mv), any changes can be regarded as;
1) Hyperpolarizing, which means its increases above (-70mv), away from 0 (more negative)
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2) Depolarizing, which means it decreases below (-70mv), towards 0 (less negative)
-Repolarizing, it the state at which the cell comes back to -70mv from a depolarization of a less negative
Graded potentials= momentary changes in excitability.
Depolarization is mainly due to sodium channels.
They have two gates to get out. They can never however, be closed at the same time.
-At rest (RMP/-70mv), at the sodium channel, there is one gate known as the activation gate that is
closed and the inactivation gate that is open. This is when the sodium channel is in a state where It can
be opened/activated, and sodium can come into the cell.
-At Depolarization, the activation gate opens and the Inactivation gate stays open (It has to reach a
voltage of -55mv, which is the standard threshold for depolarization to occur) at which point Sodium
rushes into the cell. After approximately 0.5ms the inactivation gate closes and terminates the sodium
from coming in. after another approximate 2ms, the default position of the closed activation channel
and open inactivation channel is regained.
-During an action potential, the configuration of a sodium channel changes throughout the course of the
action potential such that the gates change in their position and this stands as a crucial point for
governing the stages of the action potential. All channels regardless of ions and governed by proteins
structure of that channel. In the sodium channel, it does’t have gates but its rather the structure that
changes in a way to prevent or allow the movement through the channel.
There are two sub-types of potassium channels; they have a high similarity in the nucleotide sequence
and channel function. A family of voltage gated proteins.
1)Leak Potassium Channels- contribute to RMP(-70mv), the direction of the potassium flux depends on
the IC AND EC. They stay open during RMP allowing potassium to move out of the cell.
2) Voltage Gated Potassium Channels- Respond to changes in voltage, they open in response to
membrane depolarization (-55mv/threshold), this causes a small amount of potassium efflux(less
potassium goes out than amount of sodium that comes in). Sodium activation gate closes and at this
point the potassium gate stays open as their react much slower and thus potassium continues to move
out of the cell reaching (-90mv). This contributes to repolarization and soon following hyperpolarization
because it takes long for the potassium gates to close and prevent efflux of pottasium. Only have a
single gate that opens and closes.
Changes in membrane potential do not cause dramatic changes in homeostasis. The IC and EC
composition is relatively stable.
The Neuron.
Glial cells and Neurons. (STRUCTURES)
Electrical Signalling in Neurons: Graded Potentials, GPs.
-Amplitude of a GP is directly proportional to the strength of the triggering signal.
-GPs decrease in amplitude as they move away from stimulus through the cell body.
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