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Neuroscience > The Excitable Cell > Flashcards

The Excitable Cell Flashcards

1
Q

What is the nervous system and what does it allow?

A

System of communication that allows an organism to react rapidly and modifiable to changes in its environment

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2
Q

Neurones need to:

A
  • Collect
  • Integrate
  • Output
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3
Q

Why might chemical activity be used instead of electrical activity?

A

Provides more flexibility between and within cells i.e. inhibition

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4
Q

How can electrical signals be divided?

A

Action potentials and graded potentials

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5
Q

Action potentials

A
  • Fixed size (all-or-nothing)
  • Propagate along axon
  • Usually one way
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6
Q

Graded potentials

A
  • Variable size
  • Not propagated over long distances - usually generated in the dendrites
  • Can pass both ways
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7
Q

Information Coding

A

Action potentials are coded by frequency as they are of unit size
Graded potentials are coded by size and vary according to the strength of the stimulus

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8
Q

How do action potentials differ with a stronger stimulus?

A

Increased frequency

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9
Q

How do graded potential differ with stronger stimuli?

A

Bigger size

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10
Q

What is the resting potential?

A

-70mV

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11
Q

Why is there a resting potential?

A
  • Selectively permeable membrane
  • Unequal distribution of charged molecules/ions
  • Physical forces e.g. diffusion, electrostatic
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12
Q

Why is the membrane selective and unequal?

A
  • Channels are highly selective for specific ions

- Pumps assist unequal distribution

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13
Q

Equilibrium potential (E ion)

A

The membrane potential that would be achieved if the neurones membrane were selectively permeable to that ion

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14
Q

What equation can be used to calculate the equilibrium potential for an ion?

A

Nernst equation

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15
Q

What is the resting membrane potential for K+?

A

No voltage

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16
Q

How would you estimate the real membrane potential for K+?

A

Use the Goldman equation as it takes other ions into account, not just K+

17
Q

How would you derive the Nernst equation from the Goldman equation?

A

Make permeability of Na = 0 in Goldman equation

18
Q

What is the ionic driving force?

A

The ion movement rate

19
Q

What is the ionic driving force proportional to?

A

Membrane potential to equilibrium potential to an ion

20
Q

Action potential steps

A

DEPOLARISATION - Stimulus causes Na+ channels to open. Once threshold is released, voltage-gated Na+ channels open. Influx of Na+ down electrochemical gradient
Na+ channels close at +40mV and K+ channels open
REPOLARISATION - K+ diffuses out of cell down the concentration gradient
HYPERPOLARISATION - K+ channels reamin open and Na+ channels inactivated
Some K+ channels open so diffuses out and Na+/K+ pump restores resting potential

21
Q

How is the action potential propagated?

A

The Na+ diffuses out although in both direction Na+ channels behind are inactivated as they are in the refractory period so only Na+ channels ahead can open

22
Q

What are some factors affecting conduction velocity?

A
  • Axon diameter
  • Temperature
  • Permeability of membrane
  • Myelination
23
Q

How does myelination alter the conduction velocity?

A

Myelin is an electrical insulator so no depolarisation of the membrane can occur where it is wrapped around the axon. There are regular breaks in the myelin called nodes of Ranvier in which depolarisation can occur. So this means longer local circuits and the impulse jumps from node to node which is called saltatory conduction and increases conduction velocity of an action potenetial

24
Q

2 reasons for why are there so many unmyelinated, small axons?

A
  • The benefit of a high membrane resistance is reduced by the high internal resistance
  • Metabolic and volume costs of myelination
25
Q

Which channels are blocked by tetraethylammonium?

A

K+ channels

26
Q

K+ channels can be blocked by which poison?

A

Tetraethylammonium

27
Q

Which poisons can block Na+ channels?

A

Tetrodotoxin and saxitoxin

28
Q

Where are saxitoxins from?

A

Shellfish

29
Q

Which poison is present in puffer fish?

A

Tetrodotoxin

30
Q

Why do axons produce action potentials whereas dendrites don’t?

A

Axons contain a lot more voltage-gated Na+ channels

31
Q

What kind of channels double as a GABA receptor?

A

Cl- channels

32
Q

The nerve action potential involves a very large amount of Na+ ions moving into the axon: true or false?

A

False, although ion flow is rapid. The actual amount is very little

33
Q

Are synaptic potentials graded potentials?

A

Yes

34
Q

Where are action potentials generated in neurones?

A

Axon hillock

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