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Neuro > Excitable cell > Flashcards

Excitable cell Flashcards

1
Q

3 mains roles of neurons

A

Collect
Integrate
Output

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2
Q

Role of the nervous system

A

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

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3
Q

What are the 2 mechanisms of the nervous system?

A

Electrical activity for rapid speed
Chemical messengers for flexibility

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4
Q

What are 2 subsections of electrical signals?

A

Grading potential
Action potentials

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5
Q

Define an action potential

A

A fixed size, all or nothing signal that propagates an axon

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6
Q

Define a grading potential

A

A variable size, local signal which can pass both ways along neuronal membranes

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7
Q

How are APs coded?

A

By frequency

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8
Q

How are GPs coded?

A

By size

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9
Q

When can neurons transmit action potentials?

A

When they reach a depolarisation threshold

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10
Q

What causes neurons to have a resting potential?

A

Selectively permeable membrane
Unequal distribution of charged molecules/ions
Physical forces

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11
Q

What happens to the membrane potential if the membrane becomes non-selective?

A

Membrane potential becomes 0

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12
Q

What is the difference between a membrane channel and a membrane pump?

A

A channel confers selectivity
A pump assists unequal charge distribution

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13
Q

What 2 forces control the flow of ions in an aqueous solution?

A

Diffusion
Electrical field

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14
Q

Why does a membrane have to have a potential difference and channels?

A

Bilayers provide a barrier to ion movement
So, if no channel/potential difference, conductance is 0

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15
Q

What is current flow dependent on?

A

Electrical potential (voltage)
Electrical conductance
Electrical resistance

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16
Q

What would not occur without ion pumps?

A

Resting membrane potential

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17
Q

In which direction does the Na+/K+ ATPase work?

A

Against the conc gradient
Internal sodium for extracellular potassium
(High Na+ outside membrane, high K+ inside membrane)

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18
Q

Why is a low intracellular Ca+ important?

A

High Ca+ is toxic and can kill neurons
Ca is a signalling ion

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19
Q

When does Equilibrium potential occur?

A

When electrostatic force exactly counteracts the diffusional force

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20
Q

What determines the rate at which ions are driven across the membrane ?

A

Rate proportional to the diff between membrane and equilibrium potential

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21
Q

What is the Nernst equation?

A

Eion = 2.303 x (RT/zF) x log (ion o/ion i)

R = gas constant
T = temperature in K
z = charge of ion
F = faraday constant
i = intracellular
o = extracellular

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22
Q

Which ion is the neuronal membrane permeable to at rest?

A

K+

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23
Q

What does increasing the extracellular K+ do to membrane potential?

A

The membrane potential will increase and the membrane will become depolarised

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24
Q

What is the goldman equation used for?

A

To estimate the real Vm (membrane potential) when the membrane is permeable to other ions

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25
Q

What is the goldman equation?

A

Vm = 61.54 mV x log Pk(K+)o + PNa(Na+)o /
PK(K+)i + PNa(Na+)i

26
Q

How do ionic gradients influence membrane potentials?

A

They determine the membrane potential that would have to be achieved in a neurone if the membrane was selectively permeable to the ion

27
Q

What is ion movement rate proportional to ?

A

IDF proportional to Vm -Eion

28
Q

What are the 4 features of an action potential?

A

Rising phase
Overshoot
Falling phase
Undershoot

29
Q

Describe the rising phase

A

Rapid depolarisation of the membrane

30
Q

Describe the overshoot

A

Membrane potential is above 0

31
Q

Describe the falling phase

A

Rapid repolarisation of the membrane (more -ve than the starting resting membrane potential)

32
Q

Describe the undershoot

A

After hyperpolarisation
- gradual decline so the membrane potential comes back to resting level

33
Q

Does amplitude change if you change the holding membrane potential?

A

No it doesn’t change

34
Q

When does a neurone depolarise?

A

When the permeability to Na is increased

35
Q

Describe the change in sodium channels with an action potential

A

At rest - most sodium channels ar closed
Depolarisation - sodium channels open, selective permeability increases for sodium
Repolarisation - sodium channels close, a decrease in membrane potential causes the channels to close again fully at rest

36
Q

What is the structure of the voltage-gated Na+ channels?

A

Several transmembrane domains,
Domain 4 has lots of positively charged amino acids

37
Q

Describe the conformational change of a voltage-gated Na+ channel

A

Due to small ion movements
Lipid part of the protein tries to move from one side of channel to the other
Minimal opening of the pore allows selectivity

38
Q

How fast is Na+ channel inactivation?

A

1ms

39
Q

When does the relative refractory period occur?

A

Whilst voltage gated K channels remain open

40
Q

When does the undershoot ware off?

A

As voltage gated K+ channels close

41
Q

How does an action potential conduct down the axon?

A

Spread of charged particles (Na+)

42
Q

Why does an action potential only travel in one direction?

A

As the ap travels down the axon, Na channels behind the ap close, therefore Na+ cannot move retrospectively.

43
Q

What happens to membrane potential after ap?

A

The membrane potential rises due to depolarisation

44
Q

What factors affect conduction velocity?

A

Diameter
Myelination
Permeability of the membrane

45
Q

How does diameter affect conduction velocity?

A

Resistance to current flow increases as the cross sectional diameter decreases

46
Q

How does myelination affect convection velocity?

A

Prevents membrane from leaking
Allows ap to ‘jump’ from node to node (saltatory conduction)

47
Q

Why may some small axons not be myelinated?

A

Myelination costs lots of energy
Benefit of high membrane resistance is reduced by the high internal resistance

48
Q

Why does a myelin sheath not wrap the whole axon?

A

Space is needed for the voltage gated channels

49
Q

What is the difference between an axon and a dendrite?

A

Dendrites have voltage sensitive channels but rarely produce action potentials

50
Q

How do action potentials carry electrical signals?

A

In a non-decremental manner (amplitude remains the same)

51
Q

What is action potential frequency dependent on?

A

The size of the depolarising stimulus

52
Q

What is the absolute refractory period?

A

1 ms
- the neuron is incapable of generating another ap

53
Q

What is the relative refractory period?

A

A few ms
- you can fire another ap but a stronger stimulus is required due to threshold being raised

54
Q

What is stimulus intensity controlled by?

A

The action potential frequency in the nervous system

55
Q

What are the 2 types of graded potential?

A

Inhibitory (hyperpolarizing)
Excitatory (depolarizing)

56
Q

What are graded potentials caused by?

A

Opening of neurotransmitter gated ion channels or
Opening/closing of potassium channels

57
Q

What is an EPSP?

A

Excitatory post synaptic potential

58
Q

What is an IPSP?

A

Inhibitory post synaptic potential

59
Q

What is summation?

A

The act of integrating multiple neuronal inputs together to reach a threshold

60
Q

What is spatial summation?

A

When progressively larger numbers of primary afferent neurons are activated simultaneously

61
Q

What is shunting?

A

Making the membrane leaky to dissipate the shunting effect caused by the opening of non-selective cation channels in axon membrane

62
Q

How do ions travel through the membrane?

A

Through GAP junctions

Neuro (25 decks)

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