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Neuroscience (BMS109) > The excitable cell > Flashcards

The excitable cell Flashcards

1
Q

What is Eion?

A
  • The equilibrium potential of a particular ion

- The membrane potential that would be achieved if the membrane was selectively permeable to that ion

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2
Q

How is resistance affected by cross sectional area?

A

Resistance is inversely proportional to CSA

R = 1/ CSA

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3
Q

What is temporal summation?

A
  • Multiple inputs from the same neuron in a very short space of time
  • Increases the chance of an action potential occurring
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4
Q

What happens during to falling phase of an action potential?

A
  • Voltage gated K+ channels open
  • K+ out of membrane via electrochemical gradient
  • Na+ voltage gated channels close
  • Vm –> Ek
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5
Q

What is IDF?

A
  • Ionic driving force
  • Rate at which ions travel from one side of the membrane to the other
  • Proportional to Vm - Eion
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6
Q

What is the ‘space constant’?

A
  • Distance from the site of depolaristion where the strength of depolarisaion is 37%
  • Is proportional to membrane resistance / internal resistance
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7
Q

Where are Na+ channels localised?

A
  • More concentrated at the nodes of Ranvier
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8
Q

How does the Na+ channel become inactivated?

A

~1ms after activation

  • Globular portion swings up and occludes the pore
  • Must be ‘reset’ to resting potential -65mV before another action potential can occur
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9
Q

What is undershoot?

A

Vm lower than normal

  • Vm ~ Ek
  • Due to delayed and rectifying voltage gated K+ channel
  • Harder to fire action potential again
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10
Q

What is conduction velocity?

A

The speed of action potential propagation

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11
Q

Describe the properties of graded potentials

A
  • LOCALISED changes in the membrane potential
  • Any variable size
  • Coded for by amplitude, which varies depending upon the stimulus
  • Usually occur in the dendrites
  • Pass both ways along the axon, fading from the site of origin
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12
Q

What is the Eion of K+?

A

-80mV

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13
Q

What 2 things is conduction velocity affected by?

A
  • Diameter

- Myelination

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14
Q

What is the ‘equilibrium potential’?

A
  • When diffusion = electrical force

- No net movement of ions

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15
Q

What is needed for a functioning nervous system?

A
  • A negative membrane potential (-65mV)
  • Negative inside (less Na/more K)
  • Positive outside (more Na/less K)
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16
Q

Describe the properties of action potentials

A
  • All or nothing
  • Has ‘spikes’ which are FIXED in size and duration
  • Doesn’t change when propagated
  • Travels down the axon of a neuron
  • In one direction
  • Coded for by frequency
17
Q

What does the Goldmann equation calculate?

A
  • True Vm

Vm is not the same as the Eion of K+ as the membrane is selectively permeable to other ions, which change the Vm

18
Q

What is the Eion of Na+?

A

+62mV

19
Q

What can’t action potentials occur in dendrites?

A

Not a high enough number of Na+ channels

20
Q

What are the costs of myelination?

A
  • Metabolic cost

- Volume cost

21
Q

What is the structure of the Na+ voltage gated channel?

A
  • 4 domains, each with 6 transmembrane domains

- S4 domain has a voltage sensor, where a change in voltage causes a confirmational change activating the channel

22
Q

What is the threshold of Na+ channels opening?

A

-40mV

23
Q

What is the Nerst equation?

A

Eion = 61.54 x log ([K+]o / [K+]i)

24
Q

What threshold is reached, what happens to the permeability of Na+ and K+

A
  • They are switched

- Condunctance of Na+ is higher than K+

25
Q

What 2 things does the movement of ions through their channels depend upon?

A
  • Concentration gradient

- Difference in electrical potential

26
Q

What does myelination acheive?

A
  • Increases the resistance of the membrane, preventing current loss
  • Increases space constant
27
Q

What is spatial summation?

A
  • Multiple potentials are received onto the post synaptic membrane at the same time
  • From different areas of the body
  • Increases chance of action potential occurring at higher EPSP felt
28
Q

What is the Goldmann equation?

A

Vm = 61.54 x log ( (Pk[K+]o + Pna [Na+]o) / (Pk[K+]i + Pna[Na+]i) )

Where P is the permeability of that ion

29
Q

Where do action potentials occur?

A
  • At the axon initial segment (where the highest density of Na+ channels are)
  • In pyrimidal, cells this is at the cell body
  • In sensory neurons, this is at the nerve ending
30
Q

What is an electrical synapse?

A
  • Gap junctions
  • Excitation can spread from one neuron to the other without a neurotransmitter
  • Works both ways
  • Rapid
  • Rare
31
Q

What happens during to rising phase of an action potential?

A

Vm –> Ena

- Rapid depolarisation

32
Q

What does the Nerst equation calculate?

A

Eion

Neuroscience (BMS109) (23 decks)

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