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HL Bio > 6.5 neurons and synapses > Flashcards

6.5 neurons and synapses Flashcards

1
Q

what are neurons?

A

specialised cells that transmit electrical impulses within the nervous system

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2
Q

what are the three components of neurons?

A
  1. dendrites
  2. axons
  3. soma
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3
Q

what are dendrites?

A

branched protoplasmic extensions that can convert chemical signals to electrical signals to be conducted to the cell body

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4
Q

what part of the neurons convert chemical signals to electrical signals?

A

dendrites

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5
Q

which part of the neuron conducts electrical impulse away from the cell body?

A

axons

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6
Q

what are the functions of axons

A

they transmit electrical signals to terminal regions for communication with other neurons or effectors

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7
Q

what is the axon surrounded by in some neurons?

A

the myelin sheath

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8
Q

the myelin sheath ________ the conduction speed of electrical impulses

A

improves

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9
Q

what ions are used to generate a resting potential?

A

Na+ and K+

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10
Q

what is the effect of the pumping of Na+ and K+?

A

electrical signals are generated and conducted in neurons

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11
Q

where are K+ and Na+ pumped?

A

across the neuron membrane

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12
Q

at rest the neuron cell is not ________

A

neutral

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13
Q

when the neuron is at rest, the ________(where?) of the cell is slightly more ________ charged than the _______(where?) of the cell

A

inside, negatively, outside

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14
Q

what is the resting potential of a nerve cell?

A

-70mV

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15
Q

why is there a potential difference between the inside and outside of the neuron?

A

the inside of the neuron is more negative than the outside

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16
Q

what maintains the resting potential?

A

Na+ K+ pumps

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17
Q

is ATP used to maintain the resting potential?

A

yes

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18
Q

the Na+-K+ pump is a _____________ protein

A

transmembrane

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19
Q

what type of transport protein is the Na+/K+ pump?

A

antiport

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20
Q

for every __ K+ ions admitted, __ Na+ ions are expelled

A

2, 3

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21
Q

how is an electrochemical gradient created?

A
  • for every 2 K+ ions admitted, 3 Na+ ions are expelled
  • there are more +vely charged ions outside of the cell and more -vely charged ions in the cell
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22
Q

how is a resting potential generated? (4)

A
  1. 3 Na+ ions are pumped out of the cell by active transport with the expenditure of ATP
  2. 2 K+ ions are pumped into the cell
  3. greater electrochemical gradient where cell interior is relatively negative compared to extracellular environment
  4. thus resting potential created
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23
Q

action potentials are the ______ changes across the membrane that occur when ____________________

A

rapid, a neuron is firing

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24
Q

what are the three stages of action potentials

A
  1. depolarisation
  2. repolarisation
  3. refractory period
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25
Q

depolarisation involves ___ and repolarisation involves ____ (what ions)

A

Na+, K+

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26
Q

which part of the neuron is depolarised?

A

the membrane

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27
Q

what is depolarisation?

A

it refers to a sudden change in membrane potential, usually from a relative negative to positive change

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28
Q

which part of the neuron initiates the signal?

A

the dendrite

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29
Q

what is achieved through a “wave of depolarisation”?

A

the transmission of a nerve impulse

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30
Q

during depolarisation, Na+ ions [enter/exit] the inside of the neuron

A

enter

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31
Q

what happens during depolarisation? (5)

A
  1. a signal initiated at the dendrite
  2. in response, gated Na channels open within the membrane of the axon
  3. Na ions move in -> change in membrane potential causes mass opening of voltage gated Na channels
  4. the opening of Na channels causes a passive influx of Na+
  5. this causes the membrane potential to become more +ve
32
Q

what are the two channels involved in depolarisation and repolarisation?

A

Na+ channels and K+ channels respectively

33
Q

where are Na+ and K+ channels located?

A

on the membrane of the axon

34
Q

does the opening of K channels causes K to [enter/exit] the inside of the neuron

35
Q

what is potential difference?

A

the diff in membrane potential btw the inside and outside of the neuron

36
Q

what happens during repolarisation? (5)

A
  1. Na channels close at peak of action potential -> at the same time, gated K channels open at e membrane of e axon
  2. opening K channels causes a passive efflux of K
  3. this causes the membrane potential to return to a more -ve membrane potential
  4. K channels close slowly -> brief undershoot in membrane potential
  5. Na/K pumps readjust membrane potential to back to resting potential
37
Q

what happens in an action potential? (long, 10)

A
  1. depolarisation
    - a signal initiated at the dendrite
    - in response, gated Na channels open within the membrane of the axon
    - Na ions move in -> change in membrane potential causes mass opening of voltage gated Na channels
    - the opening of Na channels causes a passive influx of Na+
    - this causes the membrane potential to become more +ve
  2. repolarisation
    - Na channels close at peak of action potential -> at the same time gated K channels open at e membrane of e axon
    - opening K channels causes a passive efflux of K
    - this causes the membrane potential to return to a more -ve diff in internal differentiation
    - K channels close slowly -> brief undershoot
    - Na/K pumps readjust membrane potential to back to resting potential
38
Q

what is the refractory period? (short)

A

the period of time following a nerve impulse before a neuron is able to fire again

39
Q

why must the resting potential be restored after the depolarisation and repolarisation? (2)

A
  • resting potential must be restored for neuron to fire again
  • the ionic distribution of more Na+ outside the neuron and and more K+ inside the neuron is reversed
40
Q

how is the resting potential restored?

A

via the antiport action of the Na+/K+ pump

41
Q

what happens during the refractory period?

A
  • after depolarisation and repolarisation -> ionic distribution is largely reversed
  • resting potential must be restored before a neuron can fire again
  • thus restored via antiport action of the Na+/K+ pump
42
Q

what are nerve impulses?

A

action potentials that move along the length of an axon as a wave of depolarisation

43
Q

what characteristic of the Na/K channels enable action potential to work as a ‘kallang wave’?

A
  • it is voltage-gated, meaning the channels open in response to changes in membrane potential
  • depolarisation at one point of e axon triggers opening of ion channels in next segment of axon
44
Q

what is the threshold potential?

A

the minimum electrical stimulus for voltage-gated ion channels to open

45
Q

what is the value of the threshold potential?

46
Q

the propagation of nerve impulses is possible as the cytoplasm is a ____________ _____________

A

continous medium

47
Q

what is the propagation of nerve impulses? (5)

A
  • majority of Na+ channels are voltage gated (VG) Na channels
    • open when membrane potential is depolarised to arnd -55 mV
  • during depolarisation of one part of the neuron -> mass movement of Na+ into cell
  • some +vely charged Na will move into more -vely charged adjacent region of the neuron -> cytoplasm is a continuous medium
  • this movement causes that part to be more +vely charged
    • triggers the opening of more VG Na channels -> initiates an action potential
  • thus this causes the propagation of nerve impulses
48
Q

label the oscilloscope

49
Q

what feature of the nerve fibres enable saltatory conduction?

A

myelination of nerve fibres

50
Q

what is the role of the myelin sheath?

A

to increase the speed of electrical transmissions via saltatory conduction

51
Q

the part of the axon membrane that is not myelinated are the ______________

A

nodes of Ranvier

52
Q

the nodes of Ranvier facilitate _________ __________

A

saltatory conduction

53
Q

what is a disadvantage of mylineation?

A

it takes up significant space within an enclosed environment

54
Q

in myelinated nerves, depolarisation occurs only at…

A

the nodes of Ranvier

55
Q

synapses are junctions found btw ______ and btw ______ and _______ or ______________

A

neurons, neurons, receptor, effector cells

56
Q

what does a synapse consist of (3, short)

A
  • synaptic cleft
  • pre-synaptic end of one neuron
  • post-synaptic end of next neuron
57
Q

how is an impulse transmitted from one neuron to another? (short)

A

it is chemically transmitted

58
Q

neurotransmitters are…

A

chemical messengers

59
Q

what is triggered when an action potential reaches the presynaptic ending? (short)

A

this triggers the opening of voltage gated Ca channels

60
Q

what is the end of a neuron called?

A

axon terminal

61
Q

what does the influx of Ca ions into the cell causes the _________ of ____________ containing neurotransmitters with the ________________ (cell part)

A

fusion, vesicles, cell membrane

62
Q

neurotransmitters are released by _______ during synapse transfer? (

A

exocytosis

63
Q

what causes special channels (in the post-synaptic neuron) to open (in the context of synapse transfer)?

A

the binding of neurotransmitters to specific receptors in the post-synaptic membrane

64
Q

when neurotransmitters bind to receptors in the post-synaptic membrane, ____________ ion channels open

A

ligand-gated

65
Q

how is an electrical impulse generated in the post-synaptic neuron? (2, short)

A
  • neurotransmitters bind to specific receptors on post-synap membrane
  • this opens ligand-gated ion channels
  • opening of ion channels generates an electrical impulse
66
Q

what happens to neurotransmitters after they synapse transfer? (short)

A
  • recycled by reuptake pumps
  • or degraded by enzymatic activity
67
Q

how are impulses transferred from neuron to neuron? (6)

A
  1. when an action potential reaches e axon terminal -> it triggers the opening of voltage gated Ca channels
  2. Ca ions diffuse into cell -> causes the fusion of vesicles containing neurotransmitters with cell membrane
  3. neurotransmitters released by exocytosis -> diffuse across synaptic cleft
  4. neurotransmitters then bind to specific receptors in post-synaptic neuron membrane -> this opens ligand-gated ion channels
  5. opening of ion channels allows Na+ to enter cell in post-synaptic neuron
  6. influx of sodium ions causes depolarisation -> generates action potential on post-synap neuron
68
Q

a neurotransmitter used by both the CNS and PNS is…

A

acetylcholine!

69
Q

why must acetylcholine be continually removed from the synapse?

A
  • otherwise overstimulation occurs
  • this may cause convulsions + paralysis
70
Q

how is acetylcholine removed? (3)

A
  • enzyme acetylcholinesterase is released into synaptic cleft by the presynaptic neuron
  • rapidly breaks down acetylcholine back into choline and an acetyl group
  • choline is reabsorbed back into the presynaptic neuron -> where it is converted back into acetylcholine in the vesicles
71
Q

acetylcholine triggers… (2)

A
  • muscular contraction
  • parasympathetic responses
72
Q

what pesticides block synaptic transmission?

A

neonicotinoid pesticides

73
Q

how does neonicotinoid pesticides kill insects?

A
  • it contains compounds that can bind irreversibly to acetylcholine receptors in postsynaptic cells
  • acetylcholinesterase cannot break them down -> continue to cause depolarisation of cell
  • leads to paralysis and death
74
Q

why are neonicotoid pesticides suitable pesticides?

A

they bind more strongly to acetylcholine receptors in insects than mammals

75
Q

neurons only fire when the potential difference reaches the __________ ________ which is at -55mV

A

threshold potential

HL Bio (53 decks)

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