Physiological Basis of Behavior

09/26/2016

The Iconic basis of the resting membrane potential:

Use a miniature voltmeter (check electrical potential between any two points, checking absence of electrostatic equilibrium), use an electrode inside the neuron and another in the fluid outside the neuron (you would get a reading). A segregation of charge between outside and inside of a membrane is present and there is potential of current flow on both sides of the membrane. It is always negative inside (approx. -65mV or -70mV) [similar within and across species].

*this reading is called the resting membrane potential.

Eg. Began with the testing of the giant squid (studies about electrical potentials across membranes were based on this)- followed through in mice, rats and humans.

Electrical transmission (communication) lead to change in these readings; more negative-decreasing likelihood of other neurons being able to fire an impulse.

Resting Membrane Potential

OUTSIDE: Extracellular fluid (similar composition to sea water)

      Na+  K+  Cl-

Membrane

INSIDE: Cytoplasm

1.  Na+  K+  Cl-

*neural membranes have ion channels for all the, Na, K & Cl

*Large A- proteins (anions) live in the cytoplasm (unless) aren’t able to diffuse outside in the extracellular fluid; no channels for this particular one.

Putting one probe inside and one probe outside would give rise to the -70mV reading.

*this reading of a membrane resting potential that the membrane is polarized and that there are more negatively charged ions that positively charged ions

-this imbalance suggests that there is a barrier, some force is disrupting the movements.

-concentration gradient (ion moving from a region of high concentration to low concentration in order to achieve electrostatic homeostasis is achieved).

Movement of ions:

Objective is to achieve concentration equilibrium.

- If there is balance, no diffusion.

-If no, the ions would diffuse towards the empty chamber or the one with the lower charge.

Iconic Basis of the Resting Membrane

There are 4 ion players, that have some charge.

The resting potential is a consequence of the way the ions display themselves in resting potentials.

*Equation: always you to calculate the exact expected value for the equilibrium potential of a system (membrane resting potential); assuming that the membrane is permeable for the ion, assuming that there are no other mysterious forces acting on the ion, and that the membrane is actually in a resting state.

-some compromise that ions give in to some extent to the concentration and electrostatic gradients to achieve electrostatic potential.

-the compromise that has been achieved is tested by ##

*Nernst Equation: The equilibrium potential (membrane resting potential) = Z is the valence of indivudal ions (K+,Na+,Cl-)

E=Z58log [(C)o/(C)i]

There is an electrostatic force in the system that is driving the ion away from the concentration equilibrium (and this amount can be predicted by the electrostatic force that defines the system).

*uses the individual valences using the table of Distribution of Ions across the Membranes

^Check E (Cl): Solve:

There is something repelling electronically charged chlorine to move inside.

^Check E (K)

No concentration equilibrium because the inside of the neuron is electronegative charge and is drawing all the potassium in. (there is more potassium inside than explained the the -70 electromagnetic force)

^Check E (Na)

Positive and abundant in the extracellular and less in the cytoplasm, interior of the cell must be electro positive and must be repelling the sodium.

Since there no balance in the equations, there must be something wrong with the assumptions:

There are certain drugs that work as metabolic poisons (block extraction of ATP), if they exert some in the extracellular fluid (eg. cyanide), the concentration of sodium inside rises slowly as compared to outside indicating a energy dependent mechanism {led to the discovery of ion pump}.

This pump only operates when ATP is present, it is  sodium-potatssium pump.

When it is inward facing, picks up NA ions into the cytoplasm, picks them up and carriers them across outside the cell. (check).

Under resting conditions, membrane has low permeability to sedum, even though it can pass through, it gives pump advantage, it rapidly and effectively throws sodium out.

Potassium has a moderate permeability, it is still at a disadvantage

*Ion pumps are throwing it out faster (Na, K)

*Membrane is at low permeability.

-if there is a dramatic increase due to switch of Na+ channels from close to open, Na ions will take advantage and ions would rush in.

-At resting potential, K would rush out (exit); positive charged K ions rush out, would again lead to imbalance.

Membrane would become moe negative than before. Membrane would become more polarized than it was when at rest.

^Another ion, positively charged Ca ion, none inside the neuron but they exist in the extracellular fluid. At the terminal boutons of axons, there are voltage When chemical signals arrive there, there are electrical charges and make it briefly open. Ca ions flow inwards as the channels open slowly, and this influx is responsible for neurotransmitter release [there are vesicles filled with neurotransmitters in the boutons].

-the amount of neurotransmitters is directly proportional to concentration of calcium in extracellular.

##

Process (nerve signal, neurons)

Electrical signal (arrives in nerve button)

Open

Propels nt filled chan

Membrane depolarization: changing of the concentration state: excitatory post synaptic potential (EPSP); rising and slow decaying.

-It rises and decays with time, it also decays with distance from the synapse; as the cytoplasm isn’t a very good conductor (EPSP measure)

*opposite effect by opening other channels.