Chapter 4 Flashcards

The action potential

1
Q

Cytosol relative to extracellular space

A

(-ve) charge

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2
Q

Generating an action potential (cause)

A

caused by depolarization of membrane beyond threshold (-40mV)

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3
Q

Chain reaction example

A

puncture foot-stretch membrane of nerve fibers-opens Na+permeable channels-Na+ influx-depolarized membrane-reaches threshold-Action potential

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4
Q

Generation of multiple action potentials

A

Firing frequency reflects the magnitude of the depolarizing current

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5
Q

Depolarization

A

influx of Na+

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6
Q

repolarization

A

efflux of K+

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7
Q

Membrane current

A

the net movement of K+ across membrane

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8
Q

Potassium channel number

A

proportional to electrical conductances

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9
Q

membrane potassium current

A

flow and driving force

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10
Q

Rising phase

A

influx of Na+ (inward sodium current)

transient increase in g(Na)

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11
Q

falling phase

A

efflux of K+ (outward potassium current)

transient increase in g(K)

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12
Q

hodgekin and Huxley

A

Voltage clamp creators: clamped the membrane at a chosen potential value.

discovered existence of sodium “gates) in the axonal membrane

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13
Q

Voltage-gated sodium channel

A

transmembrane, 6 subunits, one pore loop, a selectivity filter, voltage sensor and gate. selective to size of partially hydrated Na+ ion, as K+ is too big to fit. Opens at -40mV

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14
Q

patch clamp method

A

(erwin Neher) for sodium gated channels

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15
Q

functional properties of Voltage-gated sodium channel

A
  1. open with little delay
  2. Stay open for about 1ms
  3. Cannot be opened again by depolarization
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16
Q

Absolute refractory period

A

Channels are inactivated

17
Q

generalized epilepsy with febrile seizures

A

a channelopathic genetic disease

18
Q

tetrodotoxin

A

clogs Na+ permeable pore

19
Q

red tide (saxitoxin)

A

is a Na+ channel-blocking toxin

20
Q

Batrachotoxin

A

(frog) blocks inactivation so channels remain open

21
Q

Veratridine

A

(lillies) inactivates channels

22
Q

Aconitine

A

(buttercups) inactivates channels

23
Q

clues about 3D structure of channels

A

due to differential toxin binding sites and result it has on the Voltage-gated sodium channels

24
Q

Potassium vs Sodium gates similarities

A

both are open in response to depolarization

25
Potassium vs Sodium gates dissimilarities
potassium gates open later than sodium gates.
26
delayed rectifier
Potassium conductance (g(K)) serves to rectify/ reset membrane potential
27
Voltage-gated potassium channels
four separate polypeptide subunits join to form a pore
28
relative refractory period
the period after an action potential by which it takes more to depolarize and reach the threshold to create another action potential
29
Orthodromic
action potential travels in one direction: down the acon terminal
30
Antidromic
backwards propagation
31
conduction velocity (typical)/length of action potential
10m/s 2ms
32
factors influencing concudction velocity in an action potential
1. spread of action potential along membrane (dependent upon axon structure) 2. Path of +ve charge (inside of the axon=faster, across the axonal membrane=slower) 3. Axonal excitability (axonal diameter: bigger=faster, number of voltage-gated channels) 4. Myelin (layers of myelin sheath facilitate current flow)
33
saltatory conduction
at nodes of ranvier (in myelinating cells), voltage gated sodium channels are concentrated at the nodes and travel to another node quicker
34
spike initiation zone
membrane with high density of voltage-gated sodium channels, either at sensory nerve endings or the axon hillock
35
Neuronal signal transmits
as the generation and regeneration of action potentials