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CST - BIOSCI107 > ET : N - Action Potentials > Flashcards

ET : N - Action Potentials Flashcards

1
Q

is potential inside neurons constant

A

no

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2
Q

when does potential inside neurons change

A

when ion concs or membrane permeability changes

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3
Q

hyperpolarisation occurs when it becomes more

A

negative

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4
Q

in hyperpolarisation, the potential inside the cell moves closer to the EP of

A

potassium

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5
Q

depolarisation occurs when it becomes more

A

positive

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6
Q

in depolarisation, the potential inside the cell moves closer to the EP of

A

sodium

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7
Q

what is an action potential (technically speaking)

A

a brief fluctuation in membrane potential caused by a transient opening of voltage-gated ion channels, which spreads, like a wave, along an axon

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8
Q

when does an action potential occur

A

when the membrane has been depolarsied to threshold

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9
Q

information is coded in the…

A

frequency of action potentials

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10
Q

what are action potentials a key element of

A

the process of signal transmission along axons

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11
Q

look at diagram of three stages of action potentials: what is the * representing

A

a slow and graded depolarisation evoked by a stimulus

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12
Q

look at diagram of three stages of action potentials: what is the 1 representing

A

after the MP reaches threshold: fast depolarisation to approx 30mV (overshoot)

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13
Q

look at diagram of three stages of action potentials: what is the 2 representing

A

repolarisation

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14
Q

look at diagram of three stages of action potentials: what is the 3 representing (and what happens in this)

A

after-hyperpolarisation (AHP) (becomes slightly more negative than RMP before returning to RMP)

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15
Q

look at diagram of three stages of action potentials: 1+2 together represent what period

or

what period does stimulus evoking and rapid depolarisation represent

A

absolute refractory period

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16
Q

look at diagram of three stages of action potentials: what period is 3

A

relative refractory period

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17
Q

in the refractory period the neuron is not ________. if you applied a second stimulus what would happen?

A

excitable

nothing (usually)

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18
Q

absoulte refractory period means (and compare to relative)

A

even if you introduced a second stimulus which was powerful and strong, no action potential will be evoked where as in stage three (relative) it will regain its excitability but a much stronger stimulus is required to depolarise it to threshold

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19
Q

when MP reaches threshold, there is a sudden activation (opening) of…

A

voltage-gated Na+ channels

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20
Q

when MP reaches threshold and voltage gated Na+ channels are activated what is the Pk:PNa+ (used to be 40:1)

A

1:20

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21
Q

thus in overshoot the MP shifts towards…

A

E(Na)

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22
Q

do the voltage gated Na channels open for long

A

no it is short lasting as these channels inactivate quickly

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23
Q

what happens when the Na+ channels are inactivated

A

followed by transient opening of voltage-gated K+ channels, leading to repolarisation and AHP

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24
Q

when K+ channels are opened what happens to MP and Pk:PNa

A

shifts towards E(K) and 100:1

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25
when the voltage threshold is reached... (sodium channels and Na+ ions)
sodium channels open and Na+ ions move into the cell along both the conc and electrical gradient
26
influx of Na+ slows down and stops when..
1) the inside potential becomes positive (moves towards E(Na)) and thus attracts Na+ ions less 2) Na+ channels inactivate
27
if the activation gate is closed, is the channel permeable
no
28
why is the first phase of action potential so fast
because when threshold is met, Na+ channels open and due to conc grad, sodium ions rush into the cell, thus rapidly bringing positive charge into the cell
29
permeability is solely determined by
leak channels
30
inactivation gate sense depolarisation and
changes conformation to block etc
31
briefly state the steps of how voltage-gated Na+ channels activate and inactivate
RMP = gate closed Depolarisation = gate opens After fraction of a second = inactivation gate blocks the channel back to initial state when membrane repolarises (gate closed, inactivation gate no longer blocking channel)
32
each action potential is an all or none event, which contrasts...... which are .....
contrasts small (sub threshold) depolarisations or hyperpolarisations which are graded
33
the amplitude of action potentials is usually ___________ and does not depend on the ________ _________ (provided that this ________ is _________)
constant stimulus intensity stimulus suprathreshold
34
what does suprathreshold mean
stimulus causes depolarisation which just crosses the threshold
35
what does graded mean
the amplitude depends on the amplitude of the stimulus while the amplitude of the whole action potential does not depend on the stimulus intensity (provided that the stimulus causes depolarisation to threshold)
36
what is one way to induce an action potential
applying an electrical stimuli
37
when switch is closed, one electrode becomes _____ and one electrode becomes _____, this causes a _________ ___________
positive negative potential difference
38
current follows the path of
least resistance
39
what are the two main paths that current follows
1) outside from + to - | 2) across membrane and inside axon
40
which path can change RMP
the second path, across membrane and inside axon
41
What happens when the current generated by an outside source flows through the cell membrane from outside to inside
hyperpolarisation (MP becomes more negative)
42
what happens when the current generated by an outside source flows through the cell membrane from inside to outside
depolarisation (MP becomes less negative)
43
flow goes from
positive to negative
44
in electrolytes current is carried by
ions
45
what is the largest component
the movement of cations (positively charged ions)
46
what affects excitability and the potential inside
the smaller component of the current where current goes across cell membrane, along cytoplasm and back to cathode (negative charged electrode)
47
along this path, current flows outside > inside which causes
accumulation of negative charge along this path
48
due to accumulation of negative charge, anode expects to see
increase in negativity of MP, known as local hyperpolarisation
49
under cathode (negative electrode) we have accumulation of
cations
50
if postivie charge shifted to this area, this would cause
local depolarisation
51
if the local depolarisation reaches threshold, the next event would be
activation of the voltage gated sodium channels and initiation of action potential
52
where are AP's first generated
in the axon initial segment
53
why do AP's generate in the axon initial segment
because it has the lowest threshold and thus serves as the 'trigger zone' for APs
54
what is depolarisation to threshold evoked by
excitatory postsynaptic potentials (EPSPs) which spread mainly passively from dendrites
55
what happens to APs once generated
APs are transmitted actively along the axon away from the cell body
56
what EPSPs evoked by
synaptic transmission from presynaptic axons to dendrites and, to a smaller degree, cell bodies
57
the current loop flows through the cell membranes in the axon initial segment region from ______ to ________
inside to outside
58
once generated, APs also spread from axon initial segment back to the
cell body
59
what are the two types of axons
unmyelinated axons and myelinated axons
60
diameter difference in unmyelinated axons and myelinated axons
``` unmyelinated = small diameter myelinated = larger diameter ```
61
difference in transmission of APs in unmyelinated axons and myelinated axons
``` unmyelinated = slow, continuous myelinated = fast, saltatory (in large steps) ```
62
what are the two stages of action potential transmission in both types of axons
1) passive spread | 2) generation of action potentials
63
what are the three steps of passive spread of current
1) (subthreshold) depolarisation at one region of the membrane 2) passive current flow (inside and outside the axon) 3) depolarization of adjacent parts of membrane
64
what is subthreshold
hasn't reached threshold at which voltage gated sodium channels kick in
65
when one section is depolarised it has
higher potential than the regions next to it
66
potential difference always leads to
flow of current
67
will there be flow of current in the extracellular space through the interstitial fluid? why?
yes because depolarisation is normally associated with loss of positive charges outside, there will also be a potential graident outside the axon, thus a potential difference and a flow of current in the extracellular space through the interstitial fluid
68
how can current move through the membrane
through the leak potassium channels as current is carried by ions
69
current can spread passively only over...
short distances
70
current quickly _________ as it flows along the axon
dissipates
71
when the circuit is enabled, you have highest potential at the _____ compared to the _______ and due to this ___________ ___________ current will flow
+ ground potential difference
72
what are the five specific steps of action potential transmission in unmyelinated axons
1) action potential 2) passive current flow 3) depolarisation of adjacent parts of membrane to threshold 4) activation of voltage-gated Na+ channels 5) new (full size) action potentials generated in adjacent parts of membrane
73
if current is strong enough we expect hyperpolarisation under the ________ and depolarisation under the _______ which can cause action potential / opening of voltage gated sodium channels
anode | cathode
74
can passive current generated by action potential depolarise other adjacent parts of membrane to threshold
yes
75
in myelinated axons, action potential conduction velocity is
increased
76
how does myleination increase speed of action potential conduction
by increasing the effciency of passive spread
77
myelinated: where are APs generated
at nodes of ranvier
78
myelinated: current flows passively between _______
nodes
79
in myelinated axons, do AP need to be regenerated at every part of the axonal membrane
no
80
why is speed of AP transmission in unmyelinated axons slower than in myelinated axons
passive current flow between two adajcent points is fast, however AP must be regenerated at every point on the membrane in unmyelinated, where as it doesn't in myelinated. This takes time and therefore conduction is slow
81
AP propogate in which axon faster
myelinated
82
in myelinated axons, what is the myelin sheath formed by in CNS and PNS
oligodendrocytes in CNS and schwann cells in PNS
83
what types of cells are oligodendrocytes and schwann cells
glia cells
84
in myelinated axons, myelination is ________________; interrupted at _________ ____ _____________
discontinuous | nodes of ranvier
85
myelination increases...
passive spread of current
86
how does myelination increase passive spread of current
due to the insulating properties of myelin, there is less current dissipation as it flows across the axon
87
what direction does passive conduction occur
in both directions
88
if myelinated fibres are much more effcient, why do we still have unmyelinated fibres
because unmyelinated fibres have a much smaller diameter and we have limited space in CNS due to skull, so by using unmyelinated, even though slower, yu can have more of them.
89
axons are able to conduct AP in both directions except...
under physiological conditions (ap one direction but passive conduction still goes both ways)
90
why does AP conduct in only one direction under physiological conditions
due to the absolute refractory period - by the time the absolute refracty period is over, AP has already moved down the axon
91
PNS contains axons of ___________ _______ as well as axons of _______________ and the '______________ ____________ ____________'
sensory neurons motorneurons Autonomic Nervous System
92
explain the process of AP generation in sensory neurons
- When stimulus acts on receptors in sensriy neurons, it does not immediately evoke APs - first it evokes a graded depolarisation, known as the receptor potential - the receptor potential spreads passively to more distally located trigger zone, where APs are generated - APs then spread along the axon (myelinated or unmyelinated) towards the CNS
93
where is information about the strength of the stimulus coded (in sensory neurons?)
in the amplitude of the receptor potential and the frequency of APs
94
go to page 231 of course guide, label the bottom diagram
okay

CST - BIOSCI107 (13 decks)

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