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Pharmacy BSI > BSI Lecture 53 Basic Electrophysiology 1 > Flashcards

BSI Lecture 53 Basic Electrophysiology 1 Flashcards

1
Q

Ions will flow down their _______ ________ across the membranes of excitable cells ( neurons and muscle cells)

A

Electrochemical gradients

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2
Q

What is an electrochemical gradient?

A

A concentration difference and charge separation.

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3
Q

What is the function of membrane pumps?

A

Move ions across membranes to maintain concentration gradients. (This is far too slow for normal neuronal function)

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4
Q

Ion channels are transmembrane proteins that form an _____ _____ which, when opened do allow extremely rapid ion flows.

A

Aqueous pore

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5
Q

____ ______ does not show saturations/Vmax.

A

Ion channels

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6
Q

Ion channels are composed of multiple _____ ______

A

Protein subunits

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7
Q

Ion channels can open or close by appropriate stimulus such as a _____ ____ or a _____ _____.

A

Voltage change ; chemical messenger

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8
Q

T or F? Most ion channels are specific for one or two ions only.

A

True

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9
Q

How are the specific ions determined for an ion channel?

A

Charge/polarized atoms from AA’s lining the pore; for positive ions the charges must be negative whereas for negative ions they must be positive, (“like charges” repel/”unlike charges” attract)

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10
Q

How are the “selectivity filter” of an ion channel determined?

A

By the charged side-groups, (“R” groups), of the AAs lining the pore.

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11
Q

What are the “types” of ion channels?

A

Leak
Voltage-gated
Ligand-gated (extracellular/intracellular)
Stress-gated (mechanically-gated)

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12
Q

How are voltage-gated channels opened?

A

When the membrane potential reaches a certain value.

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13
Q

How are ligand-gated channels opened?

A

By a chemical such as a neurotransmitter (ligand/agonist/primary messenger); note that some channels are opened by intracellular ligands(secondary messenger) or protein-protein interactions w/G-protein subunits

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14
Q

Leak channels are always _________.

A

Open (note: no gating but can be modulated)

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15
Q

That is the primary function of a “leak” channel?

A

They are principally responsible for generating the resting membrane potential, (RMP), which determines the overall excitability of the cell. (They can be modulated)

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16
Q

T or F? Ion channels only have 1 modulatory site.

A

False, they have multiple sites.

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17
Q

T or F? Voltage-gated channels are the channels principally involved in communication between neurons and neurons and effectors

A

False, Ligand-gated channels

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18
Q

T or F? Ionotropic receptions are ligand-gated channels with the receptor and ion channel combined: no G-proteins involved!

A

True

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19
Q

What is the potential or potential difference?

A

The voltage difference between two points

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20
Q

What is a membrane potential or transmembrane potential (Em)?

A

The voltage difference between the inside and outside of the cell

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21
Q

What is equilibrium potential (Eq. Pot)?

A

The voltage difference across a membrane that produces a flux of a given ion species that is equal but opposite to the flux due to the concentration gradient of that same ion species.

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22
Q

What is resting membrane potential or resting potential? (RMP)

A

the steady transmembrane potential of a cell that si not producing an electric signal

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23
Q

What is graded potential?

A

A potential change of variable amplitude and duration that is conducted decrementally; it has no threshold or refractory period.

24
Q

What is an action potential? (AP)

A

A brief all-or-none depolarization of the membrane, reversing polarity in neurons; it has a threshold and refractory period and is conducted without decrement

25
Q

What is a synaptic potential?

A

A graded potential change produced in the postsynaptic neuron in response to the release of a neurotransmitter by a presynaptic terminal; it may be depolarizing (an excitatory postsynaptic potential or EPSP) or hyperpolarizing (an inhibitory postsynaptic potential or IPSP)

26
Q

What is a receptor potential?

A

A graded potential produced at the peripheral endings of afferent neurons (or in separate receptor cells) in response to a stimulus

27
Q

What is a pacemaker potential?

A

A spontaneously occurring graded potential change that occurs in certain specialized cells

28
Q

What is threshold potential?

A

The membrane potential at which an action potential is initiated

29
Q

What are the driving forces that create ion flow?

A

The ions’ electrochemical gradient

30
Q

Voltage-gated (VG) channels which are responsible for ____ _____ generation and therefore propagation of signals down ____- .

A

action potential; axons

31
Q

T or F? Na+ VG channels open at a certain membrane potential, (“threshold”), very quickly and then “inactivate” very quickly.

A

True

32
Q

_______ is a separate mechanism from the gate and is necessary to prevent them, (rare), positive feedback of ↑Na+ influx which could be damaging/messes up the “neural code.”

A

Inactivation

33
Q

K+ VG channels open more slowly and often do not have an ______ mechanism

A

inactivation

34
Q

When does a K+ VG channel close?

A

They close when the membrane potential, (Em), drops below threshold.

35
Q

Voltage-gated channels open when the Em reaches a certain value, (“threshold:” a certain voltage or potential difference): these channels are responsible for action potentials and for some _____ entry.

A

Ca2+ (2ndary messenger).

36
Q

There is a huge diversity of function found in ion channels: varying ______ composition can “customize” a channel’s function to specifically suit a neuron’s function.

A

subunit

37
Q

If all is balanced in a cell, inserting a microelectrode to measure Em (Em/volts), what would the reading be and why?

A

Zero because there are no open channels so no ions flow across the membrane.

38
Q

___________ tends to balance the cations extracellularly.

A

Chloride

39
Q

What and where are the ions concentration located in relations to the cell?

A

Potassium flows inside the cell to outside the cell. Sodium, chloride, and calcium flow outside the cell to inside the cell.

40
Q

K+ leak channel: K+ leaves the cell by diffusion. Eventually, enough K+ leaves the cell that it becomes negative with respect to the ECF What balances the diffusion gradient?

A

Back attraction

41
Q

What is the cell’s eq. pot. for K+?

A

~-90mV

42
Q

Na+ leak channel: Na+ enters the cell down its gradient but eventually the cell becomes positive enough to repulse Na+ ions. What is this called?

A

Positive repulsion

43
Q

What is the cell’s eq. pot. for Na+?

A

~+ 60mV

44
Q

Cl- leak channels: Cl- enters the cell down its gradient but eventually the cell becomes _____ enough to repulse ___ ions

A

negative; Cl- (this is called negative repulsion)

45
Q

What is the cell’s eq. pot. for Cl-?

A

~-80mV

46
Q

How is the chloride gradient maintained?

A

By linking its extrusion to antiport NaHCO2 transport (so 2o active transport as this depends on ↓intracellular Na+ and therefore indirectly on the Na+-K+-ATPase)

47
Q

Ca+ leak channel: Ca2+ enters the cell down its gradient but eventually the cell becomes ______ enough to ______ Ca2+ ions.

A

positive: repulse (positive repulsion)

48
Q

What is the cells eq. pot. for Ca2+?

A

~+30mV

49
Q

T or F? Calcium levels are kept extremely low in cells (50-100nM!) by both active transport (Ca2+-ATPase) and secondary active transport by coupling to Na+

A

True

50
Q

Ca2+ entry is negligible compared to the other ions (toxic!) and so therefore is its effect on the Em: its function is as a ________ _______

A

secondary messenger

51
Q

What is the Nernst Equation?

A

The equilibrium potential is determined by the concentration of the ion inside and outside the cell, temperature, valence of the ion, (amount of charge), and the amount of “work” required to separate a given quantity of charge.

52
Q

What can lead to ion channel dysfunction?

A
  • Mutation of an ion channel gene
  • Defective regulation/modulation
  • Bacteria and our own immune system inserting ion channels
53
Q

T or F? An ion channel contains a hydrophobic pore.

A

False; hydrophilic

54
Q

T or F? All ion channels are specific for only one ion.

A

false: many cation channels conduct Na+ and Ca2+

55
Q

T or F? All ion channels have gates.

A

false: (leak channels are always open)

56
Q

Why do ions not follow simple rules of diffusion?

A

Because they are charged and when you let just a cation or anion cross a membrane you are separating charges (+ & -)

57
Q

What kind of disease is MS?

A

Autoimmune

Pharmacy BSI (58 decks)

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