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SfM topics > Nerves 4 > Flashcards

Nerves 4 Flashcards

1
Q

what is the RMP?

A

-70mV

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2
Q

what is the usual treshold needed to be reached to fire an AP?

A

-55mV

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3
Q

what is the potential at sensory neurone called?

A

generator potential

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4
Q

what is the potential at the skeletal muscle which determines whether the AP will be fired or not?

A

endplate potential

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5
Q

describe steps of the AP when stimulus is activated (4)

A
  1. stimulus causes sudden depolarisation and an overshoot to around +30 in a short space of time
  2. repolarisation then occurs (AP falls back down to below RMP)
  3. refractory period occurs
  4. cells is at RMP again
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6
Q

at rest, what is the Na and K permeability like?

A

Na permeability is low

K permeability is high (due to leaky K channels)

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7
Q

Describe ionic basis of AP when treshold is reached. (4)

A

when threshold is reached..

  1. Na channels open immediately and Na floods in depolarising the cell until its equilibrium potential is reached
  2. this causes a massive increase in permeability (decrease in resistance)
  3. K permeability slowly rises as more K channels open (voltage gated/ dependent ones NOT the leaky ones)
  4. K channels opening and Na channels closing causes repolarisation and later hyperpolarisation and then we are back to where we started at RMP
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8
Q

what is the refractory period?

A

occurs when there is no response to further stimulation (unresponsive tissue)

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9
Q

what sort of effect occurs if the Na/K pump is poisoned?

A

delayed effect (it takes time for gradients to run down)

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10
Q

what do local anaesthetics block? (procaine/ lidocaine)

A

block voltage dependent Na channels and no APs can be transported (some toxins do the same e.g. tetrodoxin)

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11
Q

what happens at depolarisation phase?

A
  • Na channels open and Na floods the cell very quickly
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12
Q

what happens at repolarising phase?

A
  • Na permeability drops
  • VOLTAGE gated K channels open (more gradual, slow and stays open for longer), making cell more negative (drop back down)
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13
Q

what are main properties of APs?

A
  1. all or none treshold
  2. can’t encode stimulus in their amplitude, only in FREQUENCY
  3. they self propagate
  4. once AP is made, they are all the same size
  5. mediated by voltage gated channels
  6. have a refractory period
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14
Q

what is meant by APs being self-propagated?

A
  • non-decremental (good for long distances)
  • depolarisation can only sweep in ONE direction (forward) along the axon
  • signal goes on until it reaches the muscle
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15
Q

what can conduction velocity be improved by?

A

myelination

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16
Q

what effect do large axons have on depolarisation?

A

-evokes a bigger AP as depolarisation evoked at one channel can spread further

17
Q

why do larger axons give a bigger AP?

A

depolarisation can happen in wider space since Na channels are more spread out and can reach their “neighbour” channels to reach treshold. The bigger the passive spread, the signal travels for longer

18
Q

what takes longer, the signal travelling or opening/closing of channels?

A

opening/closing of channels

19
Q

what is myelin sheath wrapped around?

A

the Schwann cells which wrap around axons

20
Q

in which part of the axon, do the GPs summate (integrate) which trigger an AP?

A

at the axon hillock/ initial axon segment (by reaching the treshold)

21
Q

what is saltatory conduction?

A

propagation of APs along myelinated axons from one node to the next, increasing conduction velocity of APs

22
Q

what is the site of APs on a neurone?

A

at nodes of Ranvier (AP decays as it moves along the axon)

23
Q

what glia bodies help with myelination?

A

oligodendrocytes

24
Q

why is myelination good for AP signal?

A
  • makes axon less leaky
  • increases action resistance (allows AP to spread like a local current)
  • depolarisation spreads quicker and increases velocity of conduction
25
Q

what disease is assocaited with demyelination?

A

multiple sclerosis (APs are not effectively passed as it decays quicker and leaks out, no depolarisation occurs at next node and treshold is not reached (conduction fails).

26
Q

what is a compounda action potential?

A

mammals have big and small myelinated and big and small unmyelinated axons. Therefore an extracellular recording of axons (nerve trunk) evokes a compound AP

27
Q

what is the biggest peak AP on a graph?

A

An AP that travels the fastest (smaller ones arrive slightly later)

28
Q

which type of axons give the BIGEGST peak?

A

big myelinated axons

29
Q

which type of axons give the SMALLEST peak?

A

small unmyelinated axons

30
Q

What is the order of fibres from: (Most sensitive to anoxia and least sensitive to local anaesthetics) to (Least sensitive to anoxia and most sensitive to local anaesthetics)

A
  1. proprioception, motor neurones
  2. touch, pressure receptors
  3. touch,cold, fast pain,
  4. preganglionic, autonomic fibres (unconscious actions)
  5. heat, slow pain
31
Q

which fibres are more sensitive to anaesthetics?

A

small ones are affected first by anaesthetics

32
Q

which fibres are most sensitive to absence of oxygen?

A

myelinated fibres

33
Q

Summary of graded potentials

A
  1. graded
  2. encoded by AMPLITUDE
  3. can summate
  4. no treshold
  5. no refractory period
  6. decremental
  7. de or hyper polarising
  8. ligand gated channels
  9. “decides” if cell will fire AP
  10. occurs in cell body and dendrites
  11. initiated by entry of ions through the channels
  12. usually Na,Cl and CA ions involved
  13. input signal
34
Q

Summary of Action potentials

A
  1. all or none
  2. encoded by FREQUENCY
  3. cannot summate
  4. are evoked at treshold
  5. has refractory period
  6. self-propagating
  7. depolarising
  8. voltage gated channels
  9. sends electrical signal over long distances
  10. occurs in initial/trigger segment of the axon
  11. initiated by above treshold GP at the trigger zone
  12. usually Na and K ions involved
  13. conduction signal
35
Q

what gives limits on APs?( so they happen one at a time)

A

refractory periods

36
Q

does depolarising lead towards the treshold?

A

yes

37
Q

does hyperpolarising lead away from treshold?

A

yes

SfM topics (21 decks)

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