Lecture 7 - Part 2 - Function of the nervous system, The resting neuron Flashcards
What are the 2 fundamental discoveries that allowed the elucidation of basic neural function
- Microelecrode
- Squid giant axon
What are electrochemical/nervous signals
- Changes in resting potential
What is the potential differnce between 2 axons
Difference in charge
What is resting potential
Inside of neurons negative
What is charge of negative neuron
-70mV
How can resting membrane potential change
- Hyperpolerisation - MORE NEGATIVE neuron
- Depolerisation - LESS negative neurone
What ion is on outside of nerone
Sodium ( Na + )
Cl-
What ion is inside of neurone
Potassium ( K + ) Large anions (A-)
What are the 2 types of forces acting on an ion
- Chemical force
- Electrostatic force
Chemical force
An ion will move from an area of high concentration to an area of lower concentration
CONC DIFFERENCE
Electrostatic force
An ion will be attracted to the opposite polarity/charge
ELECTRICAL CHARGE DIFFERENCE
Movement of sodium ions
Sodium attracted to inside of cell - negative
Why does sodium move into cell
- Both electrostatic and chemical forces tend to push sodium into the cell. There is therefore a strong net driving force into the cell. Strong tendency of sodium to move into cell
- Chemical force - lot of Na outside, not on inside so chemical force pushes it into neuron.
- Electrical force - Na is positive, inside is negative = pushed into neuron
How is equilibrium reached
Chemical force balanced by electrical force
What forces are acting on potassium
- 2 opposing forces act on potassium in a resting neuron. The electrostatic force holds it within the cell, while potassium tends to leave the cell down its concentration gradient. There is weak net
resultant force pushing potassium out of the cell
Potassium on inside, not outside = chemical force pushing K+ out of neuron
K+ is positive, inside of neuron negative so electrical force is holding it in = weak tendancy for K+ to leave neuron. Outside is positive = repulsion, all of it doesn’t want to leave
Where does potassium move
OUT of neuron
Why does potassium move outside
- A lot of k+ inside, not outside
- Electrical foce holding K+ in = 2 opposing forces acting on K+
What factors will determine the movement of an ion across a membrane
- The size of the electrochemical gradient
- The permeability of the membrane to ion
Why is resting potential of neurone negative
- Potassium out of neuron, down concentration
gradient - This will lead to a build up of positive charge outside of neuron and inside negative = oppose the exit of potassium - only leave out if the chemical force pushing it out is greater than electrical force holding it in.
- Eventually equilibrium is reached when chemical force driving potassium out of the cell is equalled by the electrostatic force holding it in. This occurs when the inside of the neuron is at about -75 mV, (resting potential)
Is outside positive or negative
Positive
Is inside positive or negative
Negative
At rest what is neurone permeable to
Potassium, not sodium
Proof that the resting potential of a neuron is largely determined by [K+]
- Remove the axoplasm and replace it by perfusate whose composition you control
- Alter the potassium concentration and observe the resting potential change
Sodium potassium pump
- Acts as enzyme in membrane
- For every 3 sodium ions that are removed from the cell, 2 potassium ions are pumped in
- Stop some movement of Na+ into neurone and some K out of neuron = rectifies movement
What charge are neurones
Negative
Why does Na+ have strong driving force into resting neurone and K+ weaker
Due to their electrochemical gradient
Positive potassium doesn’t want to leave negative inside neuron - electrostatic force holding it in
What did Galvani say
Electricity is actually produced, get sparks which is electricity. Nerves contain electrical charge
What to do to find out about electricity in neurons
Stick recording electron in neuron BUT….
this is hard to do cause electrodes are big and neurons are small
How does axon size affect conduction of electricity
The bigger the axon, the faster they conduct electricity
What does giant axon in squid allow
Send messages very rapidly around the body = squid can escape when in danger
What is microelectrode and what is it used for
Very small electrode
Stick it into axons
What happens when 2 electrodes are resting on surface of axon
No potential difference because they’re both in same medium
What charge is neuron and what is this called
Negative
Resting potential
Steps of movement of sodium ions through a semi - permeable membrane to establish equilibrium
- Na move left to right because there’s not that much on the right, more on the left - down conc gradient
- As it moves to the right, cause Na is positive, right side will gain positive charge = repel Na coming in. Na only move to right while chemical force driving it to right is bigger than electrical force keeping it from coming right
- Eqbm established
Can sodium move inside neuron in a resting potential
No because membrane is not permeable to Na
Why are neurons negative
At rest neurone is permeable to potassium but not to sodium = negative to -70mV = equilibrium potential for potassium is set up
