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BDS2 BAMS - Oral biology > LA symposium - 1 action potentials mechanisms > Flashcards

LA symposium - 1 action potentials mechanisms Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What cells have membrane potentials

A

all

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2
Q

what is more negative ICF or ECF

A

ICF is negative with respect to the ECF

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3
Q

There are equal numbers of +ve and -ve charges in ECF and ICF, so why is ICF negative with respect to ECF

A

ion/charge distribution is ‘polarised’

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4
Q

What are the rough concentrations of ions (Na, K and Cl) in ECF and ICF

A
  • Na+ (ECF = 145mM, ICF = 15mM)
  • K+ (ECF = 4mM, ICF = 150mM)
  • Cl- (ECF=110mM, ICF=10mM)
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5
Q

if the ion concentrations of Na and K are such that Na wants to come in and K wants to come out why don’t they?

A

the membrane doesn’t let them because they are not lipophilic

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6
Q

Is the resting membrane potential permeable to Na

A

no

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7
Q

is the resting membrane potential permeable to K

A

yes

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8
Q

what ion’s diffusion gradient results in an excess -ve charge inside the cell (the resting membrane potential)

A

the diffusion of potassium from cell interior through potassium channels

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9
Q

what happens to the small amount of Na that leaks into the cell (at resting membrane potential)

A

it is expelled by the Na/K pump

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10
Q

What creates the resting membrane potential

A
  1. mainly diffusion of K from cell interior

2. also Na/K pump exchanging unequal numbers of Na and K

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11
Q

How does the Na/K pump work

A 
3 Na outwards
2 K inwards
ADP --> ATP
(active transport)
The Na/K pump is electrogenic
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12
Q

What is the action potential threshold

A

-55mV

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13
Q

What is the resting membrane potential value

A

-70mV

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14
Q

what is the rising phase of the action potential due to

A

Na influx via voltage gated Na channels

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15
Q

what is the highest value the action potential reaches

A

+35mV

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16
Q

what is the falling phase of the action potential due to

A

K efflux via voltage gated K channels

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17
Q

What ion channel has more than 1 gate

A

sodium

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18
Q

what are the gates in the sodium channel called

A
  • M gate

- H gate

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19
Q

When the voltage gated sodium channel is closed (not in refactory period), are m and h gates open or closed

A

m gate - closed

h gate - open

20
Q

When the voltage gated sodium channel is closed during the refactory period, are the m and h gates open or closed

A

m gate - open

h gate - closed

21
Q

when is the h gate open only

…closed???

A

during the refactory period

22
Q

what happens at 35mV to the voltage gated sodium channel

A

h gate closes first, then m gate

23
Q

how many gates does the voltage gated potassium channel have

A

1

24
Q

Describe the stages of an action potential

A
  1. Stimulus applied
    - depolarisation
    - MP moves towards ‘threshold’
    - gated ion channels closed
  2. MP reaches ‘threshold’ (-55mV)
    - Na channels start opening
    - Na influx
    - more depolarisation
    - K channels remain closed
    • all Na channels open
    • max Na influx
    • MP overshoots 0mV
  4. When MP reaches +35mV
    - Na channels shut (h gate closes)
    - K channels open
    - K efflux begins
  5. AP down stroke
    - recovery phase
    - Na channels shut (-> refactory period)
    - K channels open
    - K efflux continues
  6. MP returns to ‘resting’ level
    - ion channels return to resting state
    - excitability restored
25
Q

What would happen if there was no refactory period

A
  • signal could move in direction not allowed

- wouldn’t have control

26
Q

Summarize action potentials

A
  • all or nothing events
  • amplitude independent of stimulus
  • At ‘threshold’:
    voltage-gated Na+ channels open, Na diffuse in, further depolarisation, positive feedback involved here
  • at ‘peak’
    Na channels close, voltage gated K channels open, K diffuse out, repolarisation
  • return to resting membrane potential
27
Q

What is the refactory period

A
  • after an AP is initiated, the neuron cannot generate another AP until the first one has ended
  • this period of inexcitability is called the refactory period
28
Q

what is responsible for the refactory period

A
  • inactivation of voltage gated sodium channels

- the inactivation (h) gates shut, and so Na cannot diffuse into the neuron

29
Q

what are the consequences of refractory period

A
  • limits max firing frequency of ap’s in axons
  • ensures unidirectional propagation of action potentials
  • prevents summation of action potentials
  • prevents summation of contractions in cardiac muscle - the cardiac AP lasts as long as the ventricular contraction
30
Q

if you were going to block sodium channels where would you need to block them from and why

A

from the inside of the cell as gates are positioned intracellularly

31
Q

Describe action potential propagation

A
  • an AP in one section of axon sets up longitudinal current flow
  • this depolarises adjacent ‘resting’ parts of the axon
  • the AP is regenerated further along the axon
  • more current flows, and the next region of axon is activated
  • action potentials travel along the axon as waves of depolarisation
32
Q

in what direction does action potential propagation move along the length of the axon

A
  • current flows in ICF and ECF from +ve to -ve regions
  • this current flow alters the membrane potential in adjacent regions, and the AP ‘creeps’ along the axon

(in this way the AP travels along the length of the axon)

33
Q

Does the speed of AP propagation increase or decrease with the axon diameter

A

increase

34
Q

Do large or small axons conduct impulses more rapidly than the other

A

large is more rapid

35
Q

what greatly increases the speed of AP propagation

A

myelin

36
Q

What does myelin do to AP propagation

A

increases speed

37
Q

how does myelin arrange on an axon

A

many layers of cell membranes wrapped round the axon

38
Q

what cells lay myelin down

A

glial (schwann) cells

39
Q

how does myelin speed up AP propagation

A

forms an insulating layer, reducing leakage of current from axon

40
Q

what are the intervals which interupt myelin

A

nodes of ranvier

41
Q

what happens at the nodes of ranvier

A

the axon membrane is exposed to the ECF, and ion flow can occur

42
Q

describe saltatory conduction

A
  • in myelinated nerve, the passive currents spread further along the axon
  • there are fewer regeneration steps per unit length of axon
  • thus, the AP propagates more rapidly than in unmyelinated axons
43
Q

apart from axons, what do we have high concentrations of in peripheral nerves

A
  • lipid
  • fat pads
  • blood vessels
  • mix of myelinated and unmyelinated axons
44
Q

how do axons within peripheral nerves differ

A

Size

  • axon diameter
  • conduction velocity

Function

  • sensory
  • motor
45
Q

What axon types are prevent in ‘cutaneous’ nerves and what are their functions

A 
A beta (myelinated)
- mechanoreceptors

A delta (myelinated)

  • mechanoreceptors
  • thermoreceptors (cold)
  • nocieptors
  • chemoreceptors (taste)

C (unmyelinated)

  • mechanoreceptors
  • thermoreceptors (hot (and cold?))
  • nocieptors
46
Q

Of the mental and canine nerve, which has less myelination and why

A

less myelination in canine nerve

  • as nerve enters the tooth they loose myelination
  • has an affect on how LA works

Mental is near tooth
Canine nerve inside pulp

47
Q

explain the last slide of the lecture

A

find out what he said

BDS2 BAMS - Oral biology (9 decks)

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