Biological Electricity

Question 1

What does excitable tissue allow animals to do?

Answer 1

It allows animals to respond more quickly to changing environmental conditions and maintain homeostasis.

Question 2

Which system conveys biological electricity around the body?

Answer 2

The nervous system.

Question 3

In addition to the nervous system, which other tissues are excitable?

Answer 3

Skeletal muscles, the heart and smooth muscle.

Question 4

True or false? Nerve cells are passive conductors of electricity generated elsewhere, like wires.

Answer 4

False! Nerves cells generate (very low energy) electricity.

Question 5

Neurones generate a ……………… …………….. across the membrane, creating what is, in effect, a tiny battery.

Answer 5

Potential difference.

Question 6

If neurones store energy in a ‘battery’ by generting a potential difference across the membrane, how is this energy released?

Answer 6

When ions flow across the membrane.

Question 7

How is charge transmitted along a neurone?

Answer 7

By a reversal of the electric field (polarity) as it passes along the nerve axon.

Question 8

True or false? Biological materials are very poor conductors.

Answer 8

True. Passive electrical potentials can only spread a few millimetres before being dissipated by resistance.

Question 9

Does biological electricity have a high or low voltage?

Answer 9

Biological electricity has a very low voltage.

Question 10

What is the approximate potential difference across a neuronal membrane in millivolts? What is the frequency in Hz?

Answer 10

The potential difference across is approximately 70mV and the frequency is approximately 100Hz.

Question 11

What is ‘the potential difference across the animal cell membrane which drives the system’.

Answer 11

Ressting potential.

Question 12

What four factors are resting potentials derived from?

Answer 12

1. Electrolytes in physiological fluids.
2. Large, negatively charged proteins within the cell.
3. Selective permeability of the cell membrane.
4. The work of the Na+/K+ pump.

Question 13

What do these four things create in a neurone?:

1. Electrolytes in physiological fluids.
2. Large, negatively charged proteins within the cell.
3. Selective permeability of the cell membrane.
4. The work of the Na+/K+ pump.

Answer 13

Resting potentials.

Question 14

What are electrolytes?

Answer 14

Metal ions in solution.

Question 15

How do the large, negatively charged molecules inside the cell contribute to generation of resting potentials?

Answer 15

The negatively charged proteins attract positively charged molecules from outside the cell.

Question 16

The neuronal cell membrane is selectively permeable; what happens when an electrical field approaches?

Answer 16

Large proteins embedded in the membrane’s bilayer change shape.

Question 17

True or false? The Na+/K+ pump requires very little energy input from ATP.

Answer 17

False! The Na+/K+ pump requires a large amount of energy, which is why a bigger brain demands enormous amounts of ATP.

Question 18

Is the balance across the neuronal membrane:

a. Electrical.
b. Chemical.
c. Electrochemical.

Answer 18

c. Electrochemical.

Question 19

What is the potential difference across the neuronal membrane at resting potential?

Answer 19

-70mV.

Question 20

What causes the resting potential difference of -70mV?

Answer 20

An imbalance of potassium ions either side of the membrane.

Question 21

True or false? Potassium can move freely across the cell membrane, following its chemical gradient.

Answer 21

True.

Question 22

What attracts potassium molecules into the cell?

Answer 22

The large, positively charged protein molecules within the cell.

Question 23

Can sodium move freely in and out of the cell (like potassium can)?

Answer 23

No, there are no protein molecules which will allow it through the membrane.

Question 24

No sodium at all can get into the cell at resting potential, because of the absence of proteins in the membrane which will allow it through - true or false?

Answer 24

False - the cell is ‘leaky’, so although there are no proteins to let the sodium through freely, a small amount does leak in.

Question 25

Other than sodium and potassium, are any other ions present?

Answer 25

Yes, chloride and protein ions are present but they don't move in or out of the cell so have no effect.

Question 26

Which is the ONLY ion that can move freely across the cell membrane?

Answer 26

Potassium.

Question 27

Why does potassium move into the cell at resting potential?

Answer 27

To maintain its electrochemical neutrality (Gibbs-Dannan equilibrium). It is attracted by protein anions.

Question 28

Although potassium moves ............... the cell the maintain electrochemical neutrality, it will always seek to .................... the cell via diffusion.

Answer 28

Into, leave.

Question 29

How does potassium leave the cell?

Answer 29

Via diffusion.

Question 30

What is the Gibbs-Dannan equation? What has it got to do with the electrochemical neutrality of potassium?

Answer 30

Potassium will try and maintain its electrochemical neutrality by following its electrochemical gradient into the cell, attracted by protein anions.

Question 31

What does the Nernst equation calculate?

Answer 31

The potential difference across the membrane, calculated from the concentration of potassium on either side of the membrane.

Question 32

What can the concentration of potassium on either side of the membrane be used to calculate? What is the name for this equation?

Answer 32

The potential difference - this is the Nernst equation.

Question 33

In a perfect system, the resting potential difference across the neuronal membrane SHOULD be -92mV. Why, in reality, is it only -70mV?

Answer 33

There are sodium ions leaking into the cell which increases the potential difference to -70mV.

Question 34

As sodium ions move into the cell and potassium ions move out, what happens to the potential across the membrane?

Answer 34

It diminishes, like a battery running down.

Question 35

The sodium/potassium pump move how many sodium ions out of the cell and how many potassium ions into the cell?

Answer 35

3Na+ are moved out for every 2K+ moved in by the sodium/potassium pump.

Question 36

Does the sodium/potassium pump maintain the high concentration of K+ inside the cell directly OR indirectly?

Answer 36

Indirectly.

Question 37

What is the ratio of Na+ to K+ ions transported by the Na+/K+ pump?

Answer 37

3:2.

Question 38

It has been suggested that the Na+/K+ pump uses how much of the ATP generated in the body? a. 55%. b. 29%. c. 70%.

Answer 38

c. 70%.

Question 39

Action potentials are an ................... biological process which regenerates a .................. along a nerve.

Answer 39

Active, signal.

Question 40

Can the amplitude of action potentials be changed?

Answer 40

No, only the frequency.

Question 41

What are voltage-gated ion chnnels?

Answer 41

Voltage-gated ion channels are proteins which change shape in response to an approaching electric field.

Question 42

Are voltage-gated channels open or closed when the membrane is depolarised?

Answer 42

Open.

Question 43

When an action potential is generated, is the membrane polarised or depolarised?

Answer 43

Depolarised.

Question 44

At resting potential, is the membrane polarised or depolarised?

Answer 44

Polarised.

Question 45

Voltage-gated ion channels present in the membrane are ................... for certain ions. They only allow some ...................... ions through. The ions are ................... because they are in solution.

Answer 45

Selective, hydrated, hydrated.

Question 46

Do the ions around the membrane have a physical size as well as a charge?

Answer 46

Yes, because the ions are in solution, they are hydrated so they have a physical size as well as a charge.

Question 47

Which ions rapidly enter the cell to depolarise the membrane and thus generate an action potential?

Answer 47

Sodium ions.

Question 48

When an action potential is generated, which two things draw the Na+ ions into the cell?

Answer 48

The concentration gradient and the negatively charged interior of the cell.

Question 49

What is the potential difference across the membrane when it is depolarised?

Answer 49

+30mV.

Question 50

When is the potential difference across the membrane +30mV?

Answer 50

When it is depolarised (and an action potential is generated).

Question 51

At rest, the potential in the cell is................ . When an action potential is generated, it momentarily becomes ................. .

Answer 51

Negative, positive.

Question 52

How is resting potential restored?

Answer 52

K+ channels open and K+ ions move out of the cell, restoring the resting potential.

Question 53

Which ions move out of the cell to restore the resting potential (after a small undershoot)

Answer 53

Potassium ions.

Question 54

Is the whole nerve cell wall depolarised at once?

Answer 54

No, only locally in a very small section.

Question 55

Does the overall concentration of ions inside the cell change significantly when an action potential is generated?

Answer 55

No, because only a very small part of the cell wall is depolarised at any one time.

Question 56

What is the refractory period?

Answer 56

When the proteins are changing back to their original shapes and the membrane is recovering.

Question 57

Can a further action potential be generated in the absolute refractory period?

Answer 57

No.

Question 58

Can a further action potential be generated in the relative refractory period?

Answer 58

Yes, but only a small action potential can be generated.

Question 59

What is the difference between the relative refractory period and the absolute refractory period?

Answer 59

No action potentials can be generated in the absolute refractory period, whereas a small action potential can be generated during the relative refractory period.

Question 60

What is saltation?

Answer 60

The way in which the action potential 'jumps' from point to point as it is regenerated along the axon.