Lecture 7 - Part 2 - Function of the nervous system, The resting neuron

Question 1

What are the 2 fundamental discoveries that allowed the elucidation of basic neural function

Answer 1

• Microelecrode

- Squid giant axon

Question 2

What are electrochemical/nervous signals

Answer 2

• Changes in resting potential

Question 3

What is the potential differnce between 2 axons

Answer 3

Difference in charge

Question 4

What is resting potential

Answer 4

Inside of neurons negative

Question 5

What is charge of negative neuron

Answer 5

-70mV

Question 6

How can resting membrane potential change

Answer 6

• Hyperpolerisation - MORE NEGATIVE neuron

- Depolerisation - LESS negative neurone

Question 7

What ion is on outside of nerone

Answer 7

Sodium ( Na + )

Cl-

Question 8

What ion is inside of neurone

Answer 8

Potassium ( K + )
Large anions (A-)

Question 9

What are the 2 types of forces acting on an ion

Answer 9

• Chemical force

- Electrostatic force

Question 10

Chemical force

Answer 10

An ion will move from an area of high concentration to an area of lower concentration
CONC DIFFERENCE

Question 11

Electrostatic force

Answer 11

An ion will be attracted to the opposite polarity/charge

ELECTRICAL CHARGE DIFFERENCE

Question 12

Movement of sodium ions

Answer 12

Sodium attracted to inside of cell - negative

Question 13

Why does sodium move into cell

Answer 13

• 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

Question 14

How is equilibrium reached

Answer 14

Chemical force balanced by electrical force

Question 15

What forces are acting on potassium

Answer 15

• 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

Question 16

Where does potassium move

Answer 16

OUT of neuron

Question 17

Why does potassium move outside

Answer 17

• A lot of k+ inside, not outside

- Electrical foce holding K+ in = 2 opposing forces acting on K+

Question 18

What factors will determine the movement of an ion across a membrane

Answer 18

• The size of the electrochemical gradient

- The permeability of the membrane to ion

Question 19

Why is resting potential of neurone negative

Answer 19

• 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)

Question 20

Is outside positive or negative

Answer 20

Positive

Question 21

Is inside positive or negative

Answer 21

Negative

Question 22

At rest what is neurone permeable to

Answer 22

Potassium, not sodium

Question 23

Proof that the resting potential of a neuron is largely determined by [K+]

Answer 23

• Remove the axoplasm and replace it by perfusate whose composition you control
• Alter the potassium concentration and observe the resting potential change

Question 24

Sodium potassium pump

Answer 24

• 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

Question 25

What charge are neurones

Answer 25

Negative

Question 26

Why does Na+ have strong driving force into resting neurone and K+ weaker

Answer 26

Due to their electrochemical gradient

Positive potassium doesn’t want to leave negative inside neuron - electrostatic force holding it in

Question 27

What did Galvani say

Answer 27

Electricity is actually produced, get sparks which is electricity. Nerves contain electrical charge

Question 28

What to do to find out about electricity in neurons

Answer 28

Stick recording electron in neuron BUT….

this is hard to do cause electrodes are big and neurons are small

Question 29

How does axon size affect conduction of electricity

Answer 29

The bigger the axon, the faster they conduct electricity

Question 30

What does giant axon in squid allow

Answer 30

Send messages very rapidly around the body = squid can escape when in danger

Question 31

What is microelectrode and what is it used for

Answer 31

Very small electrode

Stick it into axons

Question 32

What happens when 2 electrodes are resting on surface of axon

Answer 32

No potential difference because they’re both in same medium

Question 33

What charge is neuron and what is this called

Answer 33

Negative

Resting potential

Question 34

Steps of movement of sodium ions through a semi - permeable membrane to establish equilibrium

Answer 34

• 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

Question 35

Can sodium move inside neuron in a resting potential

Answer 35

No because membrane is not permeable to Na

Question 36

Why are neurons negative

Answer 36

At rest neurone is permeable to potassium but not to sodium = negative to -70mV = equilibrium potential for potassium is set up