Lecture 4- Neurophysiology

Question 1

How do i figure out if the neuron has a positive or negative nernst potential

Answer 1

1. where is the SPECIFIC ION most concentrated?
2. therefore, will the ion flow IN or OUT of the neuron?
3. Given the ions charge, and where they go, will it make the inside more or less positive

Question 2

A calcium Nernst step by step

Answer 2

1. Calcium is most concentrated outside the cell
2. therefore it will flow into the neuron
3. this makes the inside of the neuron more positive

THEREFORE… calcium has a positive nernst potential

Question 3

what is the Nernst equation and when can it be used?

Answer 3

It can be used to calculate the voltage at EQUILIBRIUM of ONE ION at a time

Question 3

Resting voltage of a neuron?

what factors affect it

Answer 3

-65mV

Primarily permeable to K+ leak channels
K+ is more concentrated on inside
therefore E(k) is similar to that of resting potential

Question 4

Nernst equation of 4 molecules in brain

and values of voltage

Answer 4

E(K)= -84mV
E(Na) = 67mV.
E(Cl) = -67mV
E(Ca) = 116mV

Question 5

action potentials

Answer 5

1. all voltage channels are closed, they are at rest. apart from K+ leak channels

then a nerve impulse comes along the neuron and disturbs the charge to reach the threshold(-50mV)

2. DEPOLARIZATION: A small amount of Na+ enters neurons thru ligand or mechanically gated Na+ channels. Causes membrane potential to get more positive
   more voltage leads to more Na+ channels opening

inside of the cell gets more postitive than the outside

3. ACTION POTENTIAL: Na+ channels deactivate and K+ channels open. K+ flows out dropping the charge inside of the cell
4. REPOLARIZATION: most voltage-gated channels are closed but leak channels are open.
   so K+ is more permeable than at rest during this period making voltage more negative. The loss of K+ ions is the repolarization
5. HYPERPOLARIZATION:
   overshoots resting potential and can’t conduct an impulse during that time. Returning Na+ to the outside and K+ inside to return to resting potential which is -65mV

Question 5

Goldman equation

Answer 5

Vm = -65mV

includes all 3 ions

Question 5

what happens during action potential in terms of molecules

Answer 5

K+ is permeable and always flowing in

First step of action potential Na+ rushes in and resting potential moves closer to Na+ Nernst potential