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Pharmacy BSI > BSI Lecture 54 Basic Electrophysiology 2 > Flashcards

BSI Lecture 54 Basic Electrophysiology 2 Flashcards

1
Q

In a “resting” neuron the resting membrane potential, (RMP), is determined by _____ and _____ _____ channels, (plus a small hyperpolarizing contribution by the electrogenic Na+-K+-ATP’ase pump): these are the only channels open in the resting state

A

Na+ ;K+ ; leak

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2
Q

The Na+ equilibrium potential is _____ mV while that for K+ is _____ mV

A

~ + 60; ~ - 90

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3
Q

The RMP (~-60mV) is principally determined by the relative contributions of the two types of ______ _______

A

leak channel

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4
Q

There are actually far more ____ leak channels than ____ so the RMP is biased strongly towards the ___ equilibrium potential, (~-90mV), at around -60 mV.

A

K+ ; Na+; K+

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5
Q

Leak channels can be modulated by various ______ and ________ messengers, chemicals, etc. which can affect the _____.

A

endogenous; exogenous; RMP

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6
Q

T or F? If the neuron becomes more positive, (closer to “threshold” when voltage-gated channels will open), the neuron will be more “excitable;” if more negative, (away from threshold), the neuron will be less excitable

A

True

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7
Q

T or F? ALL neurons will stay at the RMP until “stimulated” via synaptic inputs

A

False, some neurons, (or even specialized cardiomyocytes), are “pacemakers” and need to fire spontaneously/automatically: these cells have an unstable RMP with leak channels whose conductance changes so the Em constantly decreases/depolarizes towards the threshold.

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8
Q

When depolarization occurs and does not reach threshold, does an AP occur?

A

No

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9
Q

If a neuron is already firing and depolarization occurs, what happens to the AP?

A

It’s firing rate will increase

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10
Q

T or F? Hyperpolarization will create an AP?

A

False, hyperpolarization causes a decrease in Em not increase.

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11
Q

Many neurons are rarely/never at “rest” but are always generating APs: will ________ increase the rate of AP generation while will reduce or stop it.

A

depolarizing/hyperpolarizing

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12
Q

When reaching threshold, which voltage-gated channel opens quicker, Na+ or K+?

A

Na+

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13
Q

T/F: Voltage-gated, (VG), channels have voltage sensors that open and close the pore:

A

True

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14
Q

T or F? vgNa+ channels usually have a second, inactivation gate that automatically closes to prevent excessive depolarization that can be harmful to the neuron

A

True, (positive feedback followed by negative feedback: but some vgK+ channels inactivate also).

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15
Q

T or F? Once threshold is reached vgNa+ channels open very fast causing the Em to rush towards the Na+ equilibrium potential eventually reaching Na+ equilibrium.

A

False, this rapid depolarization “overshoots” typically to around + 30 mV but never reaches the Na+ equilibrium potential because of the automatic closing of the channels by the inactivation gate.

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16
Q

The opening of vgNa+ channels is a rare example of _____ feedback: the more/faster the neuron depolarizes to and above threshold, the more vgNa+ channels open so increasing the depolarization:

A

positive; (inactivation stops this process by separate, negative feedback, (separate mechanism: see homeostasis)

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17
Q

What causes the repolarization after the vgNa+ channels have opened?

A

The opening of the vgK+ channel

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18
Q

The vgK+ channels start to close at threshold but slowly so the Em nearly reaches the K+ equilibrium potential and then slowly returns to the RMP assuming there are no further stimuli: this is the ________

A

after hyperpolarization

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19
Q

This afterhyperpolarization is essential as this removes the vgNa+ channel inactivation, why must this occur?

A

Must occur before another AP can be generated: this ensures that each AP is a complete and separate event, (the “neural code” is preserved).

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20
Q

If the depolarizing stimulus, (or even a new one), that caused the neuron to fire initially was strong and prolonged then, following the afterhyperpolarization, where would the Em be at?

A

The Em will immediately return to threshold, (after the vgK+ channels have closed), and another AP will be generated: stimulus intensity is coded by the number of APs.

21
Q

What is absolute refractory period?

A

During the period of repolarization, before the vgNa+ channels inactivation has been removed, the neuron cannot fire another AP.

22
Q

T or F? APs are “all-or-nothing” events: once threshold is reached you get a whole AP generated.

A

True

23
Q

What is the only information that neuron’s carry?

A

In a particular neuron all APs are very similar, if not identical, in amplitude, (mV), duration, (~ 1 ms), and are propagated at the same rate: therefore the only information they can carry is in the number of APs.

24
Q

The initial segment is refractory after the generation of the AP so it can only be regenerated _______ from the cell body down the axon: this is normal, orthodromic AP transmission.

A

away

25
Q

What is an antidromic transmission?

A

Stimulation, (usually artificial by applying an electric shock), of the axon terminal, will generate an AP which will regenerate back towards the cell body.

26
Q

The passive spread of current produced by an AP that brings the adjacent membrane to threshold decreases with ______, but _____ with axon diameter: a fat axon; therefore, will transmit an AP faster than a thin one, (“cable theory”).

A

distance; increases

27
Q

Oligodendrocytes are found in the _______ nervous system.

A

Central (CNS)

28
Q

Swann cells are found in the in ________ nervous system.

A

Peripheral (PNS)

29
Q

Most of our axons are _______ which is achieved by wrapping special glial cell membranes either around several axons

A

myelinated

30
Q

What is the purpose of myelination?

A

It acts as an insulator and forces the depolarizing, passive current flow to “jump” down the axon.

31
Q

What is saltatory conduction?

A

The depolarizing, passive current flow that “jump” down the axon

32
Q

What are the gaps between the myelinated sheets called?

A

Nodes of Ranvier

33
Q

T or F? Only the exposed patches of membrane at the nodes are depolarized to threshold; therefore APs are only regenerated at the nodes which speeds up transmission immensely.

A

True

34
Q

T or F? Voltage-gated Na+ channels are only expressed at the nodes: they have no function along the insulated axon.

A

True

35
Q

K+ channels may be expressed along the entire length of myelinated axons to help determine the RMP and aid AP ______

A

repolarization

36
Q

What is Multiple sclerosis (MS)?

A

the most common disease-causing demyelination, autoimmune

37
Q

_________ are a group of compounds that block vgNa+ channels and hence prevent the propagation/regeneration of APs

A

Local anesthetics (LA): their main medical use is to block the transmission of painful stimuli into the CNS.

38
Q

Cocaine enters the CNS where it causes psychotropic effects by inhibiting ______ of synaptically released dopamine and noradrenalin.

A

reuptake (most synthetic LAs cannot cross the blood-brain-barrier)

39
Q

In order to block the vgNa+ channel, the LA must either cross or at least enter the cell membrane and this requires that the LA be ________.

A

Uncharged

40
Q

To block the hydrophilic channel LA must be _____ , (R-N+)

A

Charged

41
Q

T or F? The more hydrophobic/less charged LAs probably access the pore which they plug directly from the membrane whereas other less hydrophobic LAs enter the channel from the inside.

A

True

42
Q

______ is caused by the inappropriately high-frequency firing of APs which can spread across the brain: symptoms depend on what brain areas are affected.

A

Epilepsy

43
Q

Currently, the causes of epilepsy are not well understood it seems obvious that this must be due either to abnormal electrical properties of the neurons involved, excessive excitatory stimulation or insufficient inhibitory stimulation: it is an example of uncontrolled _____ ______.

A

positive feedback

44
Q

Blocking vgNa+ channels will _____ neuronal excitability.

A

Reduce

45
Q

What type of ion channel is responsible for the RMP?

A

Leak channels

46
Q

What type of ion channel is responsible for reaching threshold?

A

Ligand-gated

47
Q

What type of ion channel is responsible for action potentials (AP)?

A

Voltage-gated

48
Q

What happens to voltage-gated Na+-channels when threshold is reached? (FULL cycle!)

A

Voltage sensing gate opens very quickly, generating an AP (more info on pre lec 54 questions)

49
Q

What happens to voltage-gated K+-channels when threshold is reached? (FULL cycle!)

A

Voltage-sensing gate opens slowly. (more info on pre lec 54 questions)

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