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Anatomy 403 > Changes in Membrane Potential > Flashcards

Changes in Membrane Potential Flashcards

1
Q

electrically excitable

A
  • nerve and muscle cells are specialized to use rapid changes in their electrical properties for signaling or mechanical work
  • due to presence of gated ion channels
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2
Q

dendrites

A
  • numerous
  • receive input
  • generate local potentials
  • LGIC (can also be mechano-gated)
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3
Q

cell body

A
  • integrates local potentials
  • contains cell body and organelles
  • LGIC
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4
Q

axon hillock

A
  • site of AP generation
  • VG Na+
  • VG K+
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5
Q

axon

A
  • send information one way via action potential
  • one per neuron
  • VG Na+
  • VG K+
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6
Q

axon terminal

A
  • release of neurotransmitter
  • VG Na+
  • VG K+
  • VG Ca+2
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7
Q

ligand receptor

A
  1. neuron stimulated by chemical
  2. ion channel opens
  3. ionic current flow
  4. local change in membrane potential
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8
Q

depolarizing

A

toward zero

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9
Q

overshoot

A

polarity reversed (inside positive, outside negative)

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10
Q

repolarizing

A

towards resting membrane potential

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11
Q

resting membrane potential

A

-70 mV

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12
Q

hyperpolarizing

A

more negative than resting membrane potential

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13
Q

types of potentials

A
  • local (graded) potential

- action potential

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14
Q

local (graded) potential

A

small change in membrane potential confined to small region of membrane

  • small distance signals
  • produced by non-voltage gated channels
  • primary at dendrites and cell body
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15
Q

local potential use:

A
  • LGIC (nerve / muscle)

- mechano (sensory receptors)

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16
Q

local potential characteristics

A
  • “graded”
  • decremental
  • depolarizing or hyperpolarizing
  • can summate
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17
Q

“graded”

A

proportional to size of stimulus

  • magnitude of potential can vary
  • strong stimulus = more channels will open
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18
Q

decremental

A

decay with distance from stimulus because charge leaks through membrane
- flow of charge decreases as the distance from the site of the potential increases

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19
Q

characteristic: depolarizing

A

Na+ in

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20
Q

characteristic: hyperpolarizing

A

Cl- in, inside is more positive or K+ out, inside is more negative

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21
Q

summate

A

add together

- if threshold is reached (-55mV) neuron will generate action potential

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22
Q

excitatory

A

depolarizing

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23
Q

inhibitory

A

hyperpolarizng

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24
Q

action potential

A

large and rapid change in membrane potential that propagates over long distances

  • use voltage gated channels
  • only excitable membranes (nerve, muscle cells)
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25
action potential characteristics
- all or none - not graded by stimulus size - not decremental (self-propagating) - cannot summate (refectory period)
26
action potential step #1
steady state RMP P k > P Na due to leak channels
27
action potential step #2
threshold reached due to local potentials
28
action potential step #3
VG Na+ channels open rapidly depolarizing membrane --> Na+ in (positive feedback - depolarization
29
action potential step #4
inactivation of Na+ channels and delayed opening of K+ channels stop depolarization
30
action potential step #5
open VG K+ channels depolarize to negative potential (K+ out) - repolarization
31
action potential step #6
slow closing K+ channels hyperpolarize membrane closer to EKj Na+ channels return to closed state - hyperpolarization
32
action potential step #7
Na+ / K+ ATPase establishes RMP
33
local anesthetics (novocaine, lidocaine)
- VG Na+ channel blockers - pain receptors can't send signals to brain - NO action potential
34
tetrodotoxin (TTX)
VG Na+ channel blocker
35
saxitoxin
- produced by algae | - VG Na+ channel blocker
36
scorpion toxin mechanism of action
- prevents Na+ channel in activation | - blocks neural transmission
37
tetraethylammonium (TEA) mechanism of action
blocks VG K+ channels
38
absolute refractory period
- no amount of stimulation will produce another action potential - because Na+ channels already open or inactivated
39
relative refractory period
- only a very strong stimulus will produce another action potential - hyperpolarization because K+ channels open drives Vm more negative
40
refractory period
- contributes to the separation of action potentials so that individual electrical signals pass down axon - as V, approaches RMP, threshold stimulus strength decreases
41
propagation
one produces the next
42
unmyelinated fibers
- local current from the opening of LGIC in dendrites and cell body causes an action potential to be insulated in region 1 - local current depolarizes in region 2 - will not propate backwards because of refractory period - region 1 is refractory (Na+ channels inactive) --> repolarizing - ex: digestive system
43
myelination
protein and lipid (80%) insulation
44
PNS myelination
Schwann cells
45
CNS myelination
oligodendrocytes
46
nodes of ranvier
not a continuous sheet of insulation in the central nervous system (CNS)
47
myelinated fibers
- VG Na+ channels concentrated at nodes - current flows thru axon to next node - action potentials 'jump' from node to node - Na+ ions can't flow in/out where there is myelin - ex: pain receptors
48
conduction velocity increases with:
- axon diameter | - myelination
49
Cm
membrane capacitance, electrostatic forces acting through bilayer
50
Rm
membrane resistance | - how many leak channels are open
51
Ri
current path provided in axoplasm
52
length
how far current will flow
53
time
time to change Vm | - T is proportional to Cm
54
larger axons
- more cross sectional area - more charge carriers - - leads to lower Ri - local current decay less over a given distance - larger local current - increases conduction velocity
55
internal regions
where there is myelin
56
saltatory conduction
larger local currents are available to depolarize axon form node to node
57
myelin covering
no flow of ions
58
pathogenesis
- increased B and T cell sin CNS - increased astrocyte and microglia activity - inflammation - demyelination and neurotoxicity in CNS - current is lost through exposed membrane --> conduction block may occur - myelin replaced with scar tissue due to increased astrocyte activity = sclerosis
59
conduction block in MS
disrupts ability of neurons to communicate
60
symptoms of MS
life expectancy: 5-10 years less than unaffected

Anatomy 403 (13 decks)

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