Biological Electricity

Question 1

What is excitable tissue allow for ?

Answer 1

it allows an individual animal to respond more rapidly to changingg environmental conditions and maintain homeostasis

Question 2

What medium is used to convey information rapidly around the body ?

Answer 2

Electricity is the medium that evolution has chosen to convey information rapidly around the body via the nervous system

Question 3

Other than the nervous system what else in the body are excitable tissues ?

Answer 3

The skeletal muscles, the heart and smooth muscle are all excitable tissues

Question 4

Do nerve cells generate electricity ?

Answer 4

Nerve cells are not simply a medium for the conduction of electricity generated elsewhere. They are not just passive conductors as they so GENERATE ELECTRICITY, although at a very low energy

Question 5

How do nerve cells generate electricity ?

Answer 5

1. They generate a p.d across the membrane and thus create in effect a tiny battery
2. Energy stored by the electrochemical gradient is released when ions flows across the membrane

Question 6

How do nerve cells transmit changes ?

Answer 6

By a reversal of the local electric field which passes along the nerve axon

Question 7

How re biological materials has conductors and why ?

Answer 7

Biological materials are very poor conductors, their “cable properties “ are disappointing
This is because passive electric potentials can only spread by a few mm before they are dissipated by the resistance.

Question 8

What is the voltage like of biological electricity ?

Answer 8

Is very low voltage

Question 9

What are 4 point where the resting potential derives from ?

Answer 9

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

Question 10

What is the resting potential caused by ?

Answer 10

In nerve cells the P.D across the membrane is approx 70mV inside negative, labelled as a -70 mV difference.
Essentially it is caused by the imbalance of potassium ions on either side of the membrane.

Question 11

How come the relative concentration of movable ions determines the final potential ?

Answer 11

There are several charged ions on either side of the membrane generating potentials.
Only those ions that can move can affect the aggregate potential, because of this the relative conc of these movable ions determines the final potential.

Question 12

What makes the cell electrically negative ?

Answer 12

Large protein ions with multiple negative charges make the inside of the cell electrically negative. - they are not able to move because of the selective permeability of the cell membrane.

Question 13

How come Na+ and cl- ions cannot cross the membrane to any great extent ?

Answer 13

As the membrane is in resting state

Question 14

How come potassium is the only ion able to move freely across the membrane ?

Answer 14

It moves into the cell, to maintain electrochemical neutrality, attracted by the protein anions by can only balance the forces to an extent

Question 15

How can the p.d across the membrane be calculated by ?

Answer 15

Can be calculated from the k+ concentration on either side of the membrane.

Question 16

What occurs as Na+ moves in and K+ leaks out and what is this process known as ?

Answer 16

As Na+ moves in and k+ leaks out, the potential across the membrane tends to diminish and thus the excitable ability of the cell is compromised.
This is the sodium/potassium pump
Considerable energy is required to indirectly maintain the gradient by moving 3 Na+ out in exchange for 2k+

Question 17

What is an action potential ?

Answer 17

The action potential overcomes the limitations of the passive electrical properties of the neurone. It is an active biological process that regenerates an initial signal along the length of the nerve. It is also referred to as an electric impulse or spike.
Action potentials often occurs in bursts and these groups of signals vary frequency. Individuals do not convey information by change in amplitude.

Question 18

What occurs as the axon hillock ?

Answer 18

Nerve axons from other neurones contact the cell body or dendrites of another nerve cell. They transmit signal from nerve to nerve and thus generate changes in the local electrical field at the root of the axon
Here, at the axon hillock the action potential is generated.

Question 19

What are the ion channels in the membrane sensitive to electric fields called ?

Answer 19

they are called voltage gated ion channels

Question 20

What are voltage gated ion channels and how do they allow the passage of ions ?

Answer 20

They are proteins that form pores of specific size and are thereby selective for certain hydrated ions. In the presence of electric fields they change shape slightly, sufficient to allow the passage of ions.

Question 21

What is depolarisation ?

Answer 21

Is when an action potential occurs as a result of sodium ions entering the cell very rapidly, drawn by the concentration gradient and the negatively charged interior. This rapid influx of positively charged ions changes the polarity of the local electric field
The change is referred to as depolarisation.

Question 22

What occurs when the inside negative potential at rest becomes momentarily positive inside ?

Answer 22

Sodium rushes in. This movement ceases at +30 mV as electrochemical forces diminish
Potassium channels then open and k+ moves out restoring the resting potential following a small undershoot.

Question 23

Where do these changes occur in a cell ?

Answer 23

in a restricted volume in one section of the nerve cell wall.

Question 24

What occurs to the overall conc of ions in the cell during these changes ?

Answer 24

They do not change significantly and the movement of ions is actually very small, despite the profound change in the electrical behaviour of the cell.

Question 25

When can an action potential occur again after one has already occurred?

Answer 25

The action potential cannot occur again until the membrane has RECOVERED.

Question 26

How does an action potential move across an axon ?

Answer 26

The localised change in the electric field moves in one direction along the axon in a wavelike motion, progressively causing these local alterations in ionic balance across the membrane.

Question 27

What occurs to the signals in nerve axons which are electrically insulated by fat cells?

Answer 27

The signal will jump down the axon between the Nodes of Ranvier