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biological sciences > Lecture 8 - Part 1 - Neural Transmission > Flashcards

Lecture 8 - Part 1 - Neural Transmission Flashcards

1
Q

What is an action potential

A

Response to neurone to depolerisation of 15mV - all or nothing

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2
Q

What happens if threshold is reached

A

Action potential transmitted along neurone = depolerisation

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3
Q

What is the 1st positive shape of action potential due to

A

Influx of sodium into neuron

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4
Q

What is charge outside neuron

A

Positive

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5
Q

What is charge inside

A

Negative

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6
Q

How does neuron become negative after being positive by Na entering

A

Potassium moves out of neuron by opening potassium ion channels

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7
Q

How is resting potential restored

A

Sodium potassium pump - pumps K+ back in neurone and Na+ back out

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8
Q

What forces are acting on K+ when the neuron is depolarised during the action potential?

A

Both the electrical and chemical forces are acting to push potassium
out of the neuron.
Electrical force is pushing it out as inside has become positive and K is positive
Chemical force - a lot of K inside, not outside

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9
Q

What act as ion channels

A

Proteins inside plasma membrane of a cell which change shape to let ion through

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10
Q

Examples of ion channels

A

Sodium and potassium ion channels - open and close depending on voltage

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11
Q

What happens to ion channels when membrane is depolerised

A

Changes shape
open Na channels = Na into neuron
Then Na channel shuts
K channel opens - K out of neuron

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12
Q

What happens when sodium conductance increases

A

Na+ channel open

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13
Q

What happens when potassium conductance increases

A

K+ channel open

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14
Q

What happens when sodium conductance decreases

A

Na+ channel closes

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15
Q

What happens when K+ rises much later

A

Fall of action potential

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16
Q

What do Na+/k+ channels form

A

Alpha helices

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17
Q

What are alpha helices

A

Long chains of proteins that change shape to open/close - pore/hole in middle = ion goes through

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18
Q

How do channels open/close

A

Due to charge = repulsion/attraction within amino acids makes repulsion

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19
Q

What happens to channels during negative resting neuron and why

A

Close

Negative attract the positive

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20
Q

What happens to channels during action potential and how is triggered

A

Inside becomes + = opens Na+ channel

Positive charge inside neuron repels positive bit of protein = molecule flip = open channel = Na move

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21
Q

What property does axoplasm have

A

High resistance to current spread

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22
Q

What happens as a result of axoplasm having high resistance to current spread

A

Local (electrotonic) potentials will therefore diminish in size and not be propagated along (longer) neurons = die out
Small potential at one end of neuron will never get to far end of neuron

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23
Q

Do action potentials diminish in size as they travel along neuron

A

No

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24
Q

What happens to action potentials as they go along nueron

A

Regenerated

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25
Q

How is action potential transmitted - moved

A

Inside = positive = Na channel opens = Na pushes in = positive inside = action potential

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26
Q

What happens to action potential when neuron positive

A

It freezes

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27
Q

What are local circuits

A

Action potential triggers next bit of axon to produce new action potential

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28
Q

How are local circuits trasnmitted

A

Positive ions surrounding axoplasm attracted forward to part of neuron that is not stimulated ( opposites attract ) = action potential triggers next bit of axon to produce new action potential
Na+ moves in = attracted to next bit of neuron = opens more Na+ channels = another action potential

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29
Q

How is the speed of impulse propagation increased

A
  • Increasing the diameter of the axon

- Myelinisation

30
Q

How does myelinisation increase speed of impulse propagation

A

Action potentials are only regenerated at the nodes of Ranvier – saltatory conduction

31
Q

How does Increasing the diameter of

the axon increase speed of impulse propagation

A

Faster conduction of action potential

32
Q

What is saltatory conduction

A

Action potentials jump from node to node

33
Q

What are nodes of ranvier and what happens here

A

Gaps = no myelin

Action potential is regenerated = opens Na channels

34
Q

Where do sodium ion channels open

A

At nodes of ranvier

35
Q

What wrap around axon

A

Schwann cells

36
Q

What is myelin sheath

A

Insulator -no current flows across membrane

37
Q

What happens when sodium enters in

A

Axon potential regenerated at nodes of ranvier

38
Q

What does myelination do

A

Save a lot of space - can’t have big neurons like squids

39
Q

What happens at unmyelinated axon

A

Regenerated whole way, Na+ goes to next node of ranvier = opens channels = another action potential

40
Q

What is Refractory period

A

The interval after an action potential during which a second action potential absolutely cannot be initiated no matter how intense the stimulus
Can’t keep firing action potentials in neuron - need to rest between action potentials

41
Q

How is threshold stimulus strength and axon diameter related

A 
The threshold stimulus strength needed 
to activate a neuron is inversely 
proportional to its axon diameter
(i.e. larger axons are more easily 
stimulated)
42
Q

What size axons are more easily stimulated

A

Larger axons - decrease threshold - increase sensitivity - conduct faster - easier to stimulate
Big axons need less voltage to stimulate action potentials

43
Q

What are types of neural transmission

A

Action potential

Electrotonic current spread - common in short neurons

44
Q

Action potentials using calcium

A

Use Ca2+ rather than Na+ for initial depolarisation - coming into neuron

45
Q

Example of action potentials using calcium

A

Slow jelly fish swimming

Action potential due to Ca coming in = small action potential

46
Q

What is all or nothing principle?

A

Either an action potential is produced, or it is not.

47
Q

What is first part of action potential

A

Threshold reached = depolarisation = sodium ion channels opened = sodium rushes into neuron until eqbm reached

48
Q

Proof of sodium rushing into neuron

A

Alter sodium concentration outside neuron experimentally

49
Q

How does amount of sodium affect size of action potential and what does that tell you

A

Less Na outside neuron = smaller action potential = 1st phase of action potential is definitely due to Na rushing into neuron

50
Q

What happens once sodium reaches equilibrium potential

A

Neuron becomes negative again

51
Q

What is second part of action potential

A

Potassium leaves inside of neuron, goes out due to electrical and chemical force pushing it out. This is by potassium ion channels opening

52
Q

What happens when potassium is pushed out

A

Inside becomes negative again

53
Q

When will potassium stop moving

A

Until it reaches equilibrium potential

54
Q

Summary of action potential

A
  • Resting neuron negative inside
  • Threshold reached = depolarisation
  • Opens Na channels = Na rushes in until equilibrium reached
  • Closes Na channels
  • Opens K channels = it leaves neuron
  • Na/K pump restores resting potential
55
Q

What are sodium/potassium ion channels

A

Long chain of amino acids which when go through neuron form alpha helices - go in/out membrane - bunch together

56
Q

What is each alpha helix and what does it have

A

A tube

It has a pore/hole in the middle

57
Q

What causes channels to open and shut

A

Due to charge because of repulsion of attraction within amino acids that make up protein that makes up channel

58
Q

Do local potentials die out

A

Yes - diminish in size and not propogated along neuron

59
Q

What moves action potential

A

By local circuits

60
Q

What happens in local circuit

A 
Sodium goes into neuron at start of action potential
Sodium attracted to next bit of neuron 
That opens more Na channels
Another action potential...
All the way down the neuron
61
Q

Giant squid axon - diameter

A
  • Giant axon = axon that runs down side of squid = conducts action potential quickly = squid contract mantle to escape
  • 1mm across - conduct it at 20ms-1 approx
62
Q

Why can squid axon get away with having neurone 1mm in diameter

A

It doesn’t have many neurons

63
Q

How many neurons does human brain have

A

10^12

64
Q

Why can’t human brain have a 1mm wide axon

A

Brain would be too big

65
Q

What causes refractory period

A

Sodium potassium pump restoring and sorting the ions out back to resting level

66
Q

What do you need to depolarise axon by to trigger action potential

A

15mV

67
Q

What does threshold depend on

A

Size of axon

68
Q

Which neurons conduct slower and why

A

Tiny neurons
Less sensitive
Conduct slower

69
Q

Which neurons faster slower and why

A

Bigger neurons
More sensitive
Conduct faster

70
Q

What does sodium potassium pump do

A

Restores negative resting potential by pumping potassium back in and sodium back out

biological sciences (27 decks)

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