W4 - Physiology of Nerve Cells (Lecture)

Question 1

What is the definition of membrane potential?

Answer 1

The difference in potential inside and outside the cell

Question 2

How would you generally measure the membrane potential of a cell?

Answer 2

Put the cell in a saline solution, have a recording electrode inside the cell and a reference electrode in the solution, the difference is the MP

Question 3

What is the general resting membrane potential of a cell?

Answer 3

-70mV

Question 4

What are the 2 steps of forming an equilibrium potential?

Answer 4

1. K+ flows down concentration gradient, 2. this continues until the electrical forces repel the flow of the ions

Question 5

At equilibrium, the conc of K+ and charges on either side of the membrane aren’t equal on either side of the membrane, what IS equal (due to diffusion and electrical gradients)?

Answer 5

The K+ moving from left to right will equal those moving from right to left

Question 6

What causes the repulsive electrical forces when forming a MP?

Answer 6

The inability of ions other than potassium to move across the membrane

Question 7

What did Bernstein’s Hypothesis state?

Answer 7

MP is due to unequal conc of K+ across a membrane and memb only permeable to K+

Question 8

What does the Na+/K+ pump do at rest and how?

Answer 8

Establishes gradient by moving 3Na+ out and only 2K+ in and maintains this gradient when

Question 9

What does it mean for a cell to be polarised?

Answer 9

At rest the inside and outside of a cell is different in terms of potential (inside = -ve and outside = +ve)

Question 10

What happens to the potential inside the cell when a cell undergoes hyperpolarisation and depolarisation?

Answer 10

Hyper - inside more -ve than resting, Dep - inside less -ve than resting

Question 11

What type of signal is initially perceived by neurons then what does this turn into?

Answer 11

Electrical to chemical

Question 12

Glial cells are metabolically and structurally supportive, name the four types

Answer 12

Astrocytes, ependymal, microglia and oligodendrocytes

Question 13

Where are action potentials typically initiated?

Answer 13

Axon hillock

Question 14

If concentrations of solutions on either side of a semi-perm membrane are equal, what does it mean about flow from left to right and vice/versa?

Answer 14

They will be equal

Question 15

If concentrations of solutions on either side of a semi-perm membrane aren’t equal, how would the ions flow?

Answer 15

Along a diffusion gradient from high to low

Question 16

What is the equilibrium potential determined by?

Answer 16

The difference in K+ across a membrane

Question 17

What needs to be equal for an equilibrium potential to have been reached? (what determines behaviour of ions)

Answer 17

Diffusion and electrical forces

Question 18

Why is the axoplasm of the giant squid axon so easily manually extracted?

Answer 18

It’s 100x larger than any other neuron

Question 19

What 2 things are compared when testing Bernstein’s hypothesis?

Answer 19

MEasured and theoretical potential (which is based on how much K+ is found in the axoplasm of the giant squid axon)

Question 20

The predicted potential using the giant squid axon (and only K+) was -93mV but something was making it more +ve than predicted, what was thee measured value?

Answer 20

-65mV

Question 21

What type of equilibrium potentials would the involvement of Cl- or Na+ create? (more/less -ve or +ve), and what type of reasoning was used here?

Answer 21

Cl- more -ve (-55mV) and Na+ more +ve (+55mV), deductive reasoning

Question 22

What do you add together to prove there’s not equal perm to K+ and Na+?

Answer 22

Do nernst equation for both and add them together, the answer doesn’t sum to -65mV

Question 23

There is an unequal permeability to K+, Na+ and Cl-, what equation is used to measure the MP?

Answer 23

Goldman, Hodgkin and Katz

Question 24

The pK value is 1.0, pNa is 0.04 and pCl is 0.45, what does this mean about how freely Na and Cl can move across the membrane?

Answer 24

Na moves only 4% as freely as K and Cl moves 45% as freely as K across the membrane

Question 25

If the saline solution has a conc of 10X the required K+ conc, what happens to the resting membrane potential? (reference + recording electrode exp)

Answer 25

It becomes less -ve as the diffusion gradient will flatten

Question 26

If the saline solution has a conc of 1000X the required K+ conc, what happens to the resting membrane potential? (reference + recording electrode exp)

Answer 26

It becomes positive as diffusion gradient and electrical gradient inverts

Question 27

Overton identified that Na+ on the extracellular side of the membrane are important for APs, what did he suggest happens and what experiment did he do to prove an AP cannot occur without Na+?

Answer 27

Na+ enter the cell and without Na+, put cell in solution without any Na+ at all and no matter how stimulated the cell was there was no AP

Question 28

How did Hodgkin and Huxley measure an AP?

Answer 28

Recording electrode in giant squid axon with reference in extracellular medium, axon is stimulated and AP can be measured

Question 29

What does it mean for AP to be an all or nothing event?

Answer 29

Threshold value needs to be reached, depolarisation can happen with AP if it’s not reached

Question 30

What are the 3 phases of the AP?

Answer 30

Rising (depolarisation), Falling (repolarisation), After-hyperpolarisation

Question 31

Describe the process of changing pNa and pK during an AP

Answer 31

1. pNa increases (depo) 2. pNa decreases as pK+ increases 3. perms return to resting state

Question 32

What type of ion channels do Na+ and K+ move through during APs?

Answer 32

Voltage-gated ion channels

Question 33

How would you show there is a traveling wave of APs?

Answer 33

Multiple electrodes along axon

Question 34

What is the refractory period and what does this ensure and what does it prevent?

Answer 34

The period where no new action potentials can be initiated, ensures unidirectional APs, prevents bounceback from axon terminals

Question 35

What happens to the voltage gated Na+ channels during the refractory period?

Answer 35

They are transiently inactivated by a protein ‘plug’ and then the activation gate takes over

Question 36

The AP propagates to ensure unidirectional flow, how does this generally work?

Answer 36

Current flows along activated patch to depolarise adjacent patch, historic patch repolarises and undergoes the refractory period and the adjacent patch reaches the threshold, cycle repeats along axon

Question 37

What are 3 things you can look at on the AP graphs/

Answer 37

Amplitude, frequency amd velocity

Question 38

Give a short description for amplification, frequency and velocity for neurons (+APs)

Answer 38

Amp and velocity - same every time in a neuron, can differ between neurons, freq - variable but limited by refractory period

Question 39

u = k x (sq rt of d) is used to measure the velocity of an AP, what increase do you need in d (axon diameter) to increase u by x10?

Answer 39

x100

Question 40

Other than increasing axon diameter, how else do you increase velocity of AP?

Answer 40

Myelination for saltatory conduction