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Biology A level > 6.2 Nervous transmission > Flashcards

6.2 Nervous transmission Flashcards

1
Q

What are the 2 types of cells of the NS?

A

neurones and neuroglia

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2
Q

What is the role of neuroglia?

A

cells that provide structural and/or metabolic support for the neuron

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3
Q

What are neuroglia?

A

single layer of myelin sheath wrapped around the axon
it has a nucleus

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4
Q

Name all the structures of a neurone

A

nucleus
dendrites
cell body
axon
myelin sheath
schwann cells
node of ranvier
axon terminal
synaptic knob

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5
Q

What is the role of dendrites?

A

transmits impulses towards the cell body

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6
Q

What is the role of the axon?

A

transmits impulses away from the cell body

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7
Q

Where does the motor neuron transmit impulses from and to?

A

from = CNS
to = effector

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8
Q

Where does the sensory neurone transmit impulses to and from?

A

from = receptor
to = CNS

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9
Q

Where does the relay neurone transmit impulses to and from?

A

from = sensory neurone
to = motor neurone

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10
Q

How can you identify a motor neurone?

A

cell body is at the end of the axon

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11
Q

How can you identify a sensory neurone?

A

cell body on the side of the axon

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12
Q

How can you identify a sensory neurone?

A

cell body in the middle of the axon

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13
Q

What equipment is used to measure potential difference changes over time?

A

a cathode ray oscilloscope

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14
Q

What part of the CRO measures the potential difference?

A

microelectrodes - one inside and one outside of the axon

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15
Q

What does it mean that the neurone is myelinated?

A

schwann cells are wrapped around them

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16
Q

What is the role of myelin?

A

provides electrical insulations = ions cannot move in and out of the areas of the axon that are myelinated, so they cannot be depolarised here

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17
Q

At what structure of the neurone is the axon depolarised?

A

the node of ranvier

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18
Q

What is a nerve impulse?

A

it is produced by a difference in charge across the axon membrane

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19
Q

What is the potential difference measured in?

A

milivolts - mV

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20
Q

How is a potential difference caused?

A

by the disturbance of ions

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21
Q

What are the 2 ions involved in creating a potential difference?

A

Na+ and K+

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22
Q

What does it mean that the axon membrane is polarised?

A

there are fewer ions on the inside of the membrane therefore the inside is more negative relative to the outside
the membrane is at resting potential

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23
Q

What does it mean that the axon membrane is depolarised?

A

there are more ions in the inside of the membrane so the inside is positive relative to the outside
the membrane is at action potential

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24
Q

What does it mean when the SAN sends waves of depolarisation?

A

it pushes ions into the cardiac cells

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25
Q

What is the potential difference value at resting potential?

A

-70 mV

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26
Q

What is the potential difference value at action potential?

A

+40 mV

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27
Q

What does the straight line at -70 mV show on the PD vs T graph?

A

resting potential = majority of ions outside of the membrane, it is polarised

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28
Q

What does a steep line upwards towards +40mV on the PD v T graph show?

A

depolarisation = ions are moving into the cell

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29
Q

What does the top of the PD v T graph at +40 mV show?

A

action potential - the cell is depolarised and the majority of ions are inside the cell

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30
Q

What does the steep line downwards on the PD v T graph towards -70mV show?

A

repolarising = ions are moving out of the cell

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31
Q

What are all the proteins in the membrane of the node of ranvier?

A

voltage-gated Na+ channel
Na+ / K+ pump
K+ leakage channel
voltage-gated K+ channel

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32
Q

What are voltage-gated channels?

A

channel proteins that open and close at a certain value of potential difference is reached

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33
Q

How many Na+ and K+ does the Na+ / K+ pump transport per 1 ATP? and in what direction?

A

3Na+ out
2K+ in

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34
Q

Explain the events in establishing a resting potential

A
  1. Na+/ K+ pump actively transports 3 sodium ions out of the axon and 2 K+ ions into the axon
  2. The membrane of the axon is more permeable to potassium ions because there are more K+ leakage channels - K+ diffuses out
  3. The membrane is polarised as the axon is negative relative to the outside
35
Q

Explain the events causing action potential

A
  1. voltage-gated Na+ channels open at the potential diff value of about -50mV
  2. Na+ diffuse rapidly into the axon, depolarising the axon
  3. K+ voltage-gated channels remain closed and the K+ moves in by the Na+ /K+ pump
36
Q

Explain the events of repolarisation

A
  1. Na+ voltage-gated channels close at +40mV
  2. K+ voltage-gated channels open at +40mV
  3. K+ rapidly diffuses out of the membrane
  4. the Na+/K+ pump is responsible for returning the membrane to resting potential
  5. hyperpolarisation - PD falls below -70mV = the V-gated channels are not sensitive so too many K+ moves out of the membrane
37
Q

Explain the events in generating an action potential

A
  1. a stimulus causes some voltage-gated Na channels to open
  2. Na+ diffuse into axon
  3. depolarises membrane as more voltage-gated Na channels open and influx of Na into membrane - they move towards the part of the axon that is in resting potential - attracted to negative area
  4. action potential reaches approx +40mV, Na channels close and potassium gates open
  5. influx of sodium ions out of the axon = membrane is repolarised
  6. RP reached and possium gates close slowly
  7. refractory period = PD falls below -70mV temporarily as more potassium ions are diffusing out, axon is hyperpolarised
38
Q

What is saltatory conduction?

A

the jumping of action potential between one node of ravier to the next

39
Q

What is the refractory period?

A

a period of time when the membrane cannot be depolarised

40
Q

What are the 2 benefits of the refractory period?

A

separtes impulses and action potential so they do not merge and 1 impulse is received at a time

ensures unidirectional transmission

41
Q

What is the absolute refractory period?

A

it is not possible at all to generate an action potential at this point of time regardless how strong the stimulus is

42
Q

What causes the absolute refractory period?

A

inactivated Na+ channels

43
Q

What is the relative refractory period?

A

it is highly unlikely for an action potential to be generated but it is still possible, the stimulus must be very strong for more Na+ to be released and the membrane to reach -70mV

44
Q

Where is the absolute refractory period located on the potential diff graph?

A

the time the PD is above -70mV and when it returns to -70mV

45
Q

Where is the relative refractory period located on the potential diff graph?

A

the time frame when the PD is lower than -70mV to when it returns to -70mV

46
Q

What is the all or nothing principle?

A

a stimulus must cause the threshold to be reached to cause an action potential to occur

47
Q

What are failed initiations?

A

attempts to reach the threshold but failed as the stimulus is not strong enough

48
Q

What is the threshold value?

A

-55Mv

49
Q

What is a generator potential?

A

the first action potential when the threshold is reached - there are enough Na+ moving into the axon

50
Q

How does a strong stimulus cause a strong response?

A

there is an increase frequency of action potentials
the refractory period limits how frequent the action potentials are

51
Q

What are the 3 factors affecting conduction velocity?

A

myelination
temperature
axon diameter

52
Q

How does myelination increase conduction velocity?

A

saltatory conduction = depolarisation can only occur at the nodes of ranvier so Na+ have to move a further distance
action potentials move faster

53
Q

How are action potentials transmitted in unmyelinated neurons?

A

step-by-step conduction = every section of the axonal membrane is depolarised

54
Q

How does a larger axon diameter increase conduction velocity?

A

less resistance from the axon plasm so Na+ channels are more spread out and depolarisation occurs over further sections of the axon

55
Q

How does an increased temperature increase conduction velocity?

A

increased Ke of ions

56
Q

Explain how action potentials pass along unmyelinated neurones

A
  1. Na+ ions diffuse into the axon to begin action potential, it is only in 1 section of the axon
  2. the adjacent section is still in resting potential
  3. Na+ diffuse to the next section of the axon
  4. this raises the PD to threshold and starts an action potential in the next part of the axon
57
Q

What are nodes of ranvier?

A

gaps along the axon in between shcwann cells

58
Q

Why is step-by-step conduction slower than saltatory conduction?

A

step-by step = the whole membrane must become depolarised when there is no myelination

59
Q

Describe the process of synaptic transmission of acetylcholine

A
  1. action potential arrives at the axon terminal of presynaptic neurone, depolarisation of pre-synap
  2. Ca2+ gated channels open and Ca2+ diffuses into presynpa terminal
  3. synaptic vesicles contain neurotransmitter - acetylcholine, move toward and fuse with presynap membrane to release acetylcholine into synaptic cleft by exocytosis
  4. acetylcholine diffuses across the synaptic cleft
  5. it binds to protein receptors on the postsynap membrane
  6. this causes Na+ gated channels to open and Na+ goes into post synap neuron - depolarisation
  7. if depolarisation reaches threshold potential, an action potential is propagated in the post synap neurone
60
Q

What is the main function of a synapse?

A

transmit impulses between neurones

61
Q

Why is there unidirectional movement of neurotransmitter across the synapses?

A

the vesicles containign neurotransmitter are found in the pre-synaptic neurone
and the receptors complementary to the neurotransmitter are only found on the post-synaptic neurone
Ca channels are only located on the presynaptic terminal to transport neurotransmitter

62
Q

What happens to excess neurotransmitter at the synaptic cleft?

A
  1. broken down by enzymes
  2. transported back into the presynaptic neuron where it is recycled for when another stimulus triggers an action potential
63
Q

What is the synapse that transports acetylcholine called?

A

cholinergic synapse

64
Q

What enzyme breaks down acetylcholine?

A

acetylecholinesterase

65
Q

What is acetylcholine broken down into by acetyl CoA

A

acetate and choline

66
Q

What are all the functions of a synapse?

A
  1. ensures unidirectional transmission of an impulse
  2. filters out background/ low level stimuli
  3. protects against overstimulation of effectors by synaptic fatigue
  4. prevents the merging of action potential
  5. acts as a junction
67
Q

How do synapses filter out background stimuli?

A

low frequency action potentials cause little release of neurotransmitter, so there is not enough to open Na+ channels to reach threshold for AP

68
Q

How do synapses protect against overstimulation of effectors by synaptic fatigue?

A

synaptic fatigue is when neurotransmitter has ran out
there is a slower regeneration rate than the release rate of neurotransmitter

69
Q

How do synapses prevent the merging of action potentials?

A

This all requires time:
- Ca to actively transport out of the pre-synaptic neuron
- regeneration of neurotransmitter
- endocytosis
- action of enzyme

70
Q

How do synapses act as a junction?

A

multiple neurons converge at 1 synapse = summation

71
Q

What is temporal summation?

A

post-synaptic neuron is stimulated by multiple high frequency action potentials in short succession from 1 pre-synaptic neuron

72
Q

What is spatial summation?

A

mulitple low frequency action potentials from multiple pre-synaptic neurons, collectively cause an action potential in the post-synaptic neuron

73
Q

What is an example of spatial summation?

A

rod cells = multiple connected to 1 bipolar neuron - retinal convergence

74
Q

What is an excitatory synapse?

A

makes it more likely for an action potential to continue in post synaptic neurone

75
Q

What is an inhibitory synapse?

A

makes it less likely for an action potential to continue in post-synaptic neurone

76
Q

How does an excitatory synapses cause depolarisation of the post-synaptic neurone?

A
  1. neurotransmitter causes opening of Na+ channels
  2. depolarisation in the postsynaptic membrane to exceed threshold potential
  3. generates action potential in postsynaptic neuron
77
Q

How does an inhibitory synapses cause hyperpolarisation of the post-synaptic neurone?

A
  1. neurotransmitter causes opening of K+/ Cl- channels
  2. hyperpolarisation in the postsynaptic membrane - more difficult to exceed threshold potential
  3. No action potential generated in postsynaptic neurone
78
Q

What do drugs that inhibit transmission lead to?

A

it leads to muscle paralysis

79
Q

How can a drug be made to inhibit transmission?

A
  1. similar shape to neurotransmitter
  2. prevents release of neurotransmitter
  3. prevent reformation of neurotransmitter
  4. cause hyperpolarisation of post-synaptic membrane
80
Q

What happens if a drug is a similar shape to a neurotransmitter?

A

blocks recptor proteins so neurotransmitters cannot bind and Na+ channels remain closed = the post-synaptic neurone is not depolarised

81
Q

How does an inhibitory drug prevent the release of neurotransmitter?

A

prevents Ca2+ entry into the presynaptic terminal

82
Q

What do drugs that amplify transmission lead to?

A

leads to tetany = muscle spasm

83
Q

How can a drug be made to amplify transmission?

A
  1. the drug increases the number of Na channels/ protein receptors
  2. drug is a non-competitive inhibitor of Acetylcholinesterase
  3. mimics the normal neurotransmitter
  4. blocks endocytosis in the presynaptic neurone
84
Q

What happens if the drug is an non-competitive inhibitor of acetylcholinesterase?

A

inhibits the breakdown of acetylcholine = keeps the neurotransmitter in the receptor and Na channels remain open

Biology A level (33 decks)

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