Excitable Membranes Flashcards

1
Q

what is an excitable cell or membrane?

A

any membrane that can hold a charge or propagate and electrical signal

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2
Q

2 types of excitable tissues and what they do?

A
  1. neurons: transmit electrical impulses

2. muscles: contract to produce a pulling force

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3
Q

diffusion

A

net movement of molecules from an area of high concentration to an area of low concentration

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4
Q

osmotic gradient

A

the difference in concentration b/w 2 solutions on either side of a semi-permeable membrane and is used to tell the difference in percentages of the concentration of a specific particle dissolved in a solution

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5
Q

what is a gradient?

A

difference in concentration of any parameter across a distance

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6
Q

what are the 4 types of gradients?

A
  1. ion gradient (osmotic gradient)
  2. energy gradient
  3. temperature gradient
  4. pressure gradient
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7
Q

what is net flux and what equation do we use?

A

(Jnet) occurs from high concentration to low concentration until the gradient disappears; Fick’s law of diffusion

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8
Q

when does diffusion work best?

A

over small areas

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9
Q

what do we mean by resting membrane potential?

A

all excitable cells maintain a non-zero membrane potential; the cell is inactive but ions are still diffusing/maintaining a negative voltage

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10
Q

what is the resting membrane potential for neurons?

A

-70 mV

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11
Q

what is the resting membrane potential for muscles?

A

-85 mV

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12
Q

what kinds of ions are inside/outside the cell during resting membrane potential?

A
  1. high concentration of K+ and proteins inside (low concentrations outside cell)
  2. high concentration of Cl- and Na+ outside (low concentrations inside cell)
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13
Q

what is the Nernst Equation used for?

A

calculate electrical potential from concentration gradients but dose NOT consider permeability of the membrane

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14
Q

what affects membrane permeability?

A

membrane channels

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15
Q

what 3 things are happening at resting membrane potential?

A
  1. lots of K+ leaking out of cell through leak channels
  2. little Na+ leaking in cell through membrane
  3. Cl- leaking through leak channels
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16
Q

membrane potential only exists because?

A

ions are flowing through the membrane

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17
Q

What does the Goldman-Hodgkin-Katz Equation tell us?

A

it determines the reversal potential across a cell’s membrane, taking into account all of the ions that are permeant through that membrane

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18
Q

what prevents the concentration gradient from approaching zero?

A

maintenance of gradients requires an active process which require ATP to pump ions against their concentration gradient (Na+K+ATPase pump)

19
Q

for every 1 ATP hydrolyed–>

A

3 Na+ move OUT

2 K+ move in

20
Q

is the Na+K+ pump working while the cell is at rest?/why?

A

YES; the pump maintains the resting membrane potential

21
Q

3 parts of an action potential

A
  1. depolarization
  2. repolarization
  3. hyperpolarization
22
Q

what happens during depolarization?

A

there is a positive change in voltage due to activation of voltage-gated channels

23
Q

voltage-gated channels control permeability of what ion?

A

Na+ and K+

24
Q

when does Na+ flow into the cell?

A

only when both the activation gate and inactivation gates are open

25
when the cell is at rest, the activation/inactivation gates are open/closed?
activation gate is closed and inactivation gate is open
26
at depolarization, which gates open/close? what happens?
activation gate opens, inactivation gate is open, Na+ flows into cell
27
what occurs when the cell is at rest?
threshold has not been met. RMP is still at -70 mV. K+ flows out of cell through leak channels, activation gate of Na+ channel is closed so Na+ doesn't flow in, voltage-gated K+ channels are closed
28
what occurs during depolarization?
threshold stimulus is met and cell becomes more positive and approaches zero. K+ leaking out of cell through leak channels, activation gate for Na+ channels opens and Na+ flows in to cell, activation gate of K+ channels opens slowly
29
what occurs at the peak of an AP?
the AP reaches its highest point and becomes the most positive. K+ leaking out of cell through leak channels, inactivation gate of Na+ channels is closing, activation gate of K+ channels continues to open and more K+ flows out of cell
30
what occurs during repolarization?
cell becomes more negative again.K+ leaking out of cell through leak channels, inactivation gate is closed for Na+ channels, activation gate of K+ channels is fully open and more K+ flows out of cell
31
what occurs during hyperpolarization?
cell undershoots -70 mV. K+ still leaking out through leak channels, inactivation gate reopens and activation gate closes of Na+ channels. activation gate of K+ closes slowly
32
what is the refractory phase?
period of time where we cannot re-stimulate the membrane
33
what is the absolute refractory period?
activation gate of Na+ channels is open and insensitive to any additional voltage, inactivation gate is closed and insensitive to any voltage altogether
34
what is the relative refractory period?
voltage-gated Na+ channels activation gate closes and inactivation gate reopens and both gates can be re-stimulated, need a supra-threshold stimulus
35
what happens when 1 voltage-gated Na+ channel opens?
it creates a cascade of continuous conduction, voltage-gated Na+ channels open in sequences along the length of the cell
36
structure of neurons?
1. dendrites- receiving end 2. axon- AP travels down it 3. cell body w/ soma- houses nucleus 4. terminal- sends out signal to postsynaptic cell
37
what is continuous conduction?
voltage-gated Na+ channels open in sequences along the length of the cell, propagates AP at ~2 m/s; very slow
38
what is saltatory conduction?
requires myelin sheath that insulates the axon: oligodendrocytes in CNS and schwann cells in PNS, rich in cholesterol, insulates axon from ion leakage, voltage-gated Na+ and K+ channels are located in nodes b/w myelinated regions of axon, propagates AP at ~ 100 m/s; very fast
39
what are the steps that occur at the end of an A.P.?
1. AP propagates down axon 2. AP stimulates voltage-gated Ca2+ channels to open 3. Influx of Ca2+ 4. Ca2+ signals vesicles to fuse with membrane and exocytose their neurotransmitter contents into synapse (transduce electrical signal into a chemical signal 5. neurotransmitters bind to ligand-gated channels on postsynaptic cell
40
what are ligand-gated channels?
chemically-gated channels on the postsynaptic cell that receive the neurotransmitter from the presynaptic cell
41
what is the effect of Na+ ligand-gated channels?
make the cell more positive
42
what is the effect of K+ ligand-gated channels?
make the cell more negative
43
what is the effect of Cl- ligand-gated channels?
make the cell more negative