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Biology 317 > Calculating Tau and Lambda > Flashcards

Calculating Tau and Lambda Flashcards

1
Q

What is the equation to calculate the length constant (original and simplified)

A

I = square root|(Rm/[Ri+Ro])

I = Square root| (Rm/ Ri)

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2
Q

Define Length constant (Lambda λ)

A

Distance at which the Vm decays to 37% of its original value

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3
Q

How are Rm and Ri related

A

They are related to diameter of the cell or axon

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4
Q

Rm is inversely related to what
and inversely proportional to what

A

membrane surface area
inversely proportional to the radius

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5
Q

what is geometry of a cylinder

A

As= 2prh

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6
Q

Ri is inversely related to what
and inversely proportional to what

A

The volume of the cytoplasm
inversely proportional to the square of the radius

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7
Q

Geometry of a circle

A

Ax= pr2

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8
Q

an increase in diameter will decrease what, Which will decrease faster

What will an increase of diameter increase

A

decrease both Rm & Ri, Ri will decrease faster

Increase in diameter increases lambda λ
(ie. the distance of electronic spread)

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9
Q

More channels = more what

A

= more depolarization

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10
Q

relatively small changes in diameter results in a fairly large change in what

A

large changes in the length constant

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11
Q

Tau and Lambda result from…
Also called what?

A

passive electrical potentials

Also called cable properties

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12
Q

what 3 are inherent features of membrane

A

resistance (Rm and Ri)
Capacitance
geometry

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13
Q

Example: If you have an extension cord and you try to plug your car in in the winter, so you take a couple extension cords and put them together to make one long extension cord, then it seems your car didn’t get enough juice from the extension cord. You should get a thicker cord because the diameter of the cord doesn’t allow for the flow of the charge to reach your car.

A
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14
Q

EPSP
IPSP

A

Excitatory post-synaptic potential
Inhibitory post-synaptic potential

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15
Q

EPSPs move Vm towards the threshold voltage; if threshold is reached…

A

an AP is generated at the axon hillock

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16
Q

IPSPs move Vm away from threshold, makes it harder to…

A

Harder to generate an AP

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17
Q

AP results from change in Rm

A

changing resistance through membranes, by opening channels

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18
Q

What are the 5 main characteristics of an AP?

A
  1. Exhibits a threshold voltage (all or nothing)
  2. Displays a rapid change in Rm
  3. Has sequential opening and closing of voltage-gated channels (depolarization, repolarization)
  4. Once generated, is actively propagated (unchanged & in one direction) along axonal membrane
  5. is a discrete signal; transient with quick return to RMP
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19
Q

Three types of Vm in a neuron

A
  1. Resting membrane potential (RMP) - all areas of membrane ie. K+ leak channels
  2. graded (electrotonic) potential (GP) - used in dendrites and axons ie. no channels (electrotonic)
  3. Action potentials (AP) - used in axon & terminals ie. voltage-regulated Na+ and K+ channels
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20
Q

Describe a dendrite

A

short axons, therefore small resistance and small diameter,

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21
Q

Electrical properties of a cell membrane are either…

A

Passive- do not change over time or
active - change over time (voltage-gated channels

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22
Q

what are the two passive electrical properties of cell membrane are…

A

resistance (R)
capacitance (C)

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23
Q

Passive membrane properties determine:

A
  • magnitude of electrical current travelling on membrane surface
  • time course (shape) of any Vm change
  • Distance an electrical current will travel on membrane surface
  • speed of action potential propagation along axon (conduction velocity)
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24
Q

biomembranes act as…
where is potential stored?

A

capacitors (nonconductors that store charge
- opposite charges line-up along membrane surfaces

  • potential is stored along the membrane surfaces
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25
bioelectricity would not be possible without...
capacitance
26
because of capacitance, only a few....
few ions are needed to generate a transmembrane potential (Vm)
27
Rm is lowered due to...
K+ leak channels
28
Cm holds charges where
at membrane surfaces
29
RMP is the result of?
Resting membrane potential is a result of the passive electrical properties interacting with a transmembrane I(k)
30
measuring Vm over time
RMP stays unchanged over time just as long as nothing disturbs the equilibrium established by the I(k) through its leak channels
31
what is the change in Vm due to a surface current called?
electrotonic potential - flow of current along surface
32
where are electrotonic potentials used
used in dendrites and along axons of neurons & in t-tubules of skeletal muscles: - to propagate an electrical signal along membrane surfaces
33
How do passive properties influence currents along membrane surface?
over time - measured as a time constant Tau over distance - measured as length constant lambda
34
what do tau and lambda affect?
the electrical propagation in neurons and muscles
35
time constant tau:
time required for Vm to reach 63% of its maximum the longer the tau the longer it takes to reach polarization
36
what is the equation for Tau
tau = RmCm
37
where is there more tau in, neurons or muscle?
less in neurons more in muscle
38
Which variable (Rm or Cm) could easily change to decrease tau (ie. to reach maximum Vm faster)?
Resistance is the easiest to change - by adding or increasing or opening channels - having a shorter tau makes a faster capacitance
39
measuring the length constant lambda...
injected current flows along surface due to opposites attract, like repel - but size of Vm due to injected current decays over distance
40
Injected current "escapes" along..
the path of least resistance
41
what are the two paths for current to follow...
through the membrane Rm and the Cytoplasm Ri
42
which is bigger Rm or Ri
Rm
43
which is the only group of animals without specific neurons or muscle cells?
sponges
44
from the top down list what is in an axon nerve
dendrites (short branches) | Nucleus | Soma | Axon hillock | Axon initial segment | Axon | Schwann cells & myelin sheath | Terminal branches | Presynaptic terminal branches (release chemical signal from pre to post)
45
Neurons use electrical potential to...
communicate with other cells
46
what is a nerve
a collection of axons from several neurons
47
Neurons are signalling cells with four functional regions:
1. Reception & integration of signals - dendrites, cell body - receives signals from environment (pressure, temp, sight, sound etc) 2. Generation of signal - axon hillock 3. Conduction of signal - axon 4. Transmission of signal - terminals, synapses
48
membrane potentials in a neuron are due to...
- passive electrical properties (RMP & GP) - active electrical properties (AP ) - results from changes in RMP - channels open or close
49
In RMP what establishes the ion gradient
Na+ K+ ATPase Na out K in
50
Neurons and muscle cells have K+ leak channels
- the Rm to K+ is very low - allows a large outward K+ current I(k) - I(k) establishes a large equilibrium potential
51
lambda is easily adjusted by changes in what
diameter
52
dendrites - small diameter means what type of tau or lambda?
a smaller diameter means a short lambda
53
a longer axon =
bigger diameter = higher Rm
54
How do we know the RMP is due to the outward I(k)
by comparing the actual and theoretical potentials
55
example for nernst equation: K+ out = 20 K+ in = 400 Ek = ?
Ek = RT/zF ln [Ko]/[Ki] = 58 mV log10 (20mM/400mM) = -76mV
56
At rest (in a non-excited state), a neuron/muscle cell:
- is electrically polarized - remains in a steady-state (equilibrium) as long as cell has ATP
57
Depolarized Hyperpolarized Repolarized
Depolarized - Vm moves towards zero Hyperpolarized - Vm is larger than the RMP - further from zero Repolarized - Vm moves back towards the RMP
58
What two ways can membrane polarity be moved away from RMP?
- by graded (electrotonic) potentials (GP) [due to passive electrotonic spread] and - by an action potential (AP) [due to an electrical property that changes and interacts with the passive electrical properties] * changing the polarity of neurons*
59
Where do GP commonly occur?
- commonly occur along membrane of dendrites/cell body - Dendrites receive input from other neurons via SYNAPSES
60
few ion channels in dendrites are opened by...
neurotransmitters from other neurons
61
channel opens > ions _____ > moves_______
channel opens > ions move in > moves along membrane (electrotonically)
62
RMP conditions in a dendrite:
Axon terminal from presynaptic neuron with neurotransmitter (nt) *membrane capacitor is holding charge* - neurotransmitter released into synapse - neurotransmitter causes channel to open - cation flows through open channel - opposites attract, like repel - change in transmembrane potential - channel closes, is a small depolarization in Vm adjacent to channel - depolarization spreads away from channels - distance travelled by electrotonic spread depends on lambda
63
the change in Vm decreases in size as .... is a type of graded potential called...
it spreads along membrane synaptic potential
64
answer depolarize or hyperpolarize Opening a K+ channel in the synapse will ____ Opening a Na+ channel in the synapse will ______ Opening a Cl- channel in the synapse will ________
1. hyperpolarize 2. Depolarize 3. Hyperpolarize (repolarize?)
65
why does decay of Vm happen?
it happens over distance due to leakage through cytoplasm/K+ leak channels

Biology 317 (6 decks)

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