Biological Electricity Flashcards
What does excitable tissue allow animals to do?
It allows animals to respond more quickly to changing environmental conditions and maintain homeostasis.
Which system conveys biological electricity around the body?
The nervous system.
In addition to the nervous system, which other tissues are excitable?
Skeletal muscles, the heart and smooth muscle.
True or false? Nerve cells are passive conductors of electricity generated elsewhere, like wires.
False! Nerves cells generate (very low energy) electricity.
Neurones generate a ……………… …………….. across the membrane, creating what is, in effect, a tiny battery.
Potential difference.
If neurones store energy in a ‘battery’ by generting a potential difference across the membrane, how is this energy released?
When ions flow across the membrane.
How is charge transmitted along a neurone?
By a reversal of the electric field (polarity) as it passes along the nerve axon.
True or false? Biological materials are very poor conductors.
True. Passive electrical potentials can only spread a few millimetres before being dissipated by resistance.
Does biological electricity have a high or low voltage?
Biological electricity has a very low voltage.
What is the approximate potential difference across a neuronal membrane in millivolts? What is the frequency in Hz?
The potential difference across is approximately 70mV and the frequency is approximately 100Hz.
What is ‘the potential difference across the animal cell membrane which drives the system’.
Ressting potential.
What four factors are resting potentials derived from?
- Electrolytes in physiological fluids.
- Large, negatively charged proteins within the cell.
- Selective permeability of the cell membrane.
- The work of the Na+/K+ pump.
What do these four things create in a neurone?:
- Electrolytes in physiological fluids.
- Large, negatively charged proteins within the cell.
- Selective permeability of the cell membrane.
- The work of the Na+/K+ pump.
Resting potentials.
What are electrolytes?
Metal ions in solution.
How do the large, negatively charged molecules inside the cell contribute to generation of resting potentials?
The negatively charged proteins attract positively charged molecules from outside the cell.
The neuronal cell membrane is selectively permeable; what happens when an electrical field approaches?
Large proteins embedded in the membrane’s bilayer change shape.
True or false? The Na+/K+ pump requires very little energy input from ATP.
False! The Na+/K+ pump requires a large amount of energy, which is why a bigger brain demands enormous amounts of ATP.
Is the balance across the neuronal membrane:
a. Electrical.
b. Chemical.
c. Electrochemical.
c. Electrochemical.
What is the potential difference across the neuronal membrane at resting potential?
-70mV.
What causes the resting potential difference of -70mV?
An imbalance of potassium ions either side of the membrane.
True or false? Potassium can move freely across the cell membrane, following its chemical gradient.
True.
What attracts potassium molecules into the cell?
The large, positively charged protein molecules within the cell.
Can sodium move freely in and out of the cell (like potassium can)?
No, there are no protein molecules which will allow it through the membrane.
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?
False - the cell is ‘leaky’, so although there are no proteins to let the sodium through freely, a small amount does leak in.
Other than sodium and potassium, are any other ions present?
Yes, chloride and protein ions are present but they don’t move in or out of the cell so have no effect.
Which is the ONLY ion that can move freely across the cell membrane?
Potassium.
Why does potassium move into the cell at resting potential?
To maintain its electrochemical neutrality (Gibbs-Dannan equilibrium). It is attracted by protein anions.
Although potassium moves …………… the cell the maintain electrochemical neutrality, it will always seek to ……………….. the cell via diffusion.
Into, leave.
How does potassium leave the cell?
Via diffusion.
What is the Gibbs-Dannan equation? What has it got to do with the electrochemical neutrality of potassium?
Potassium will try and maintain its electrochemical neutrality by following its electrochemical gradient into the cell, attracted by protein anions.
What does the Nernst equation calculate?
The potential difference across the membrane, calculated from the concentration of potassium on either side of the membrane.
What can the concentration of potassium on either side of the membrane be used to calculate? What is the name for this equation?
The potential difference - this is the Nernst equation.
In a perfect system, the resting potential difference across the neuronal membrane SHOULD be -92mV. Why, in reality, is it only -70mV?
There are sodium ions leaking into the cell which increases the potential difference to -70mV.
As sodium ions move into the cell and potassium ions move out, what happens to the potential across the membrane?
It diminishes, like a battery running down.
The sodium/potassium pump move how many sodium ions out of the cell and how many potassium ions into the cell?
3Na+ are moved out for every 2K+ moved in by the sodium/potassium pump.
Does the sodium/potassium pump maintain the high concentration of K+ inside the cell directly OR indirectly?
Indirectly.
What is the ratio of Na+ to K+ ions transported by the Na+/K+ pump?
3:2.
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%.
c. 70%.
Action potentials are an ………………. biological process which regenerates a ……………… along a nerve.
Active, signal.
Can the amplitude of action potentials be changed?
No, only the frequency.
What are voltage-gated ion chnnels?
Voltage-gated ion channels are proteins which change shape in response to an approaching electric field.
Are voltage-gated channels open or closed when the membrane is depolarised?
Open.
When an action potential is generated, is the membrane polarised or depolarised?
Depolarised.
At resting potential, is the membrane polarised or depolarised?
Polarised.
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.
Selective, hydrated, hydrated.
Do the ions around the membrane have a physical size as well as a charge?
Yes, because the ions are in solution, they are hydrated so they have a physical size as well as a charge.
Which ions rapidly enter the cell to depolarise the membrane and thus generate an action potential?
Sodium ions.
When an action potential is generated, which two things draw the Na+ ions into the cell?
The concentration gradient and the negatively charged interior of the cell.
What is the potential difference across the membrane when it is depolarised?
+30mV.
When is the potential difference across the membrane +30mV?
When it is depolarised (and an action potential is generated).
At rest, the potential in the cell is……………. . When an action potential is generated, it momentarily becomes …………….. .
Negative, positive.
How is resting potential restored?
K+ channels open and K+ ions move out of the cell, restoring the resting potential.
Which ions move out of the cell to restore the resting potential (after a small undershoot)
Potassium ions.
Is the whole nerve cell wall depolarised at once?
No, only locally in a very small section.
Does the overall concentration of ions inside the cell change significantly when an action potential is generated?
No, because only a very small part of the cell wall is depolarised at any one time.
What is the refractory period?
When the proteins are changing back to their original shapes and the membrane is recovering.
Can a further action potential be generated in the absolute refractory period?
No.
Can a further action potential be generated in the relative refractory period?
Yes, but only a small action potential can be generated.
What is the difference between the relative refractory period and the absolute refractory period?
No action potentials can be generated in the absolute refractory period, whereas a small action potential can be generated during the relative refractory period.
What is saltation?
The way in which the action potential ‘jumps’ from point to point as it is regenerated along the axon.
