deck_533571 Flashcards

1
Q

What is a membrane potential?

A

An electrical potential difference across a cell membrane

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2
Q

What is used to measure membrane potential?Give the characteristics for the unique component of the measuring device/

A

Microelectrode with a micropipette– one electrode measures the extracellular fluid & a micropipette measures voltage inside the cell membrane– teh micropipette has a diameter of >1micrometres and is filled with a conducting solution (KCl/solution which is a s similar as possible to intracellular fluid to prevent excess disruption)

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3
Q

How is a membrane potential expressed?

A

A value which is relative to the outside of the cell

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4
Q

What is the range for membrane potential for animal cells?

A

-20mV to -90mV

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5
Q

What is the membrane potential range for cardiac muscle?

A

-80mV to -90mV

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6
Q

What is the membrane potential range for nerve cells?

A

-50mV to -75mV

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7
Q

Why do membrane potentials occur?

A

The membrane is selectively permeable to different ions due to transmembranous channel proteins.

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8
Q

What are the charactersitics of ion channels?

A
  1. Are specific to one/ a few ion species2. Gating – teh channel can be opened or closde by a conformational change in the protein molecule3. Ion flow always occurs down the electrochemical gradient
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9
Q

What is specific about potassium channels?What movement of K+ ions occur at rest?

A

They are voltage insenstive and tend to open at resting potential – Increased K+ inside cell so ions move out down chemical gradient– Negative charge on the inside of the cell so ions are attracted bck into the cell down an electrical gradient

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10
Q

How is a membrane potential generated?

A

K+ channels are open so K+ can diffuse out down a conc. gradientAnions cannot follow (cant diffuse through the membrane) so negative anions build up in cell. Negative charge is present on inside in comparison to the outside. Membrane potential opposes K+ outward diffusion so equilibrium arises.

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11
Q

What is an equilibrium potential?

A

The membrane potential where the electrical and diffusion forces balance each oter so there is no further net movement of an ion

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12
Q

What equation crayon use to calculate the potassium equilibrium potential?

A

Nernst equation

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13
Q

What are the two terms which can be used to describe changes of the membrane potential from its resting level and describe them.

A

HYPERPOLARISATION – an increase in the membrane potential so the inside becomes less negativeDEPOLARISATION – a decrease in the membrane potential so the inside becomes more negative

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14
Q

What will cause depolarisation of cells?

A

Opening Ca2+ or Na+ channels

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15
Q

What will causes hyperpolarisation of cells?

A

Opening K+ or Cl- channels

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16
Q

How can you determine how important each ion is to determining the membrane potential?

A

It depends upon how easily the ion can diffuse through the membrane relative to other ions — depends on: the number of channels and how easily they let the ion through

17
Q

How is ion channel opening determined?

A

Gating mechanisms which open and close the cells

18
Q

What are the two main forms of hating mechanisms?

A

Ligand gating – channel is opened/closed by binding of a chemical ligand (can be extracellular transmitter or and intracellularly messenger) Voltage gating – channel opens or closes in response to changes in membrane potential

19
Q

What is a specific characteristic of a receptor in a fast synaptic transmission?

A

The receptor is also a ligand gated ion channel

20
Q

What type of channels do depolarising transmitters open?

A

Channels with positive reversal potentials– channels for Na+, Ca2+ or cations

21
Q

What type of potential change do depolarising transmitters cause?

A

Excitatory postsynaptic potential – causes excitation of cells

22
Q

What type of channels do hyper polarising transmitters open?

A

Negative reversal potentials– channels for K+ or Cl-

23
Q

What type of change in potential do hyperpolarising transmitters cause?

A

Inhibitory postsynaptic potential– lead to inhibition

24
Q

What happens in slow synaptic transmission?

A

The receptor is not an ion channelIt signals to the channel in one of two ways:1. Within the membrane2. By an intracellularly messenger— both involve GTP-binding protein

25
Q

What are the characteristics of channels signalling within the membrane?

A

Is localisedVery rapid

26
Q

What are the benefits of signalling the ion channel by an intracellularly messenger?

A

It occurs throughout the cellIs amplified by a cascade

27
Q

What is responsible for the distribution of ions between the intra and extra cellular fluid?

A

The selective permeability of the membrane

28
Q

Why is the value calculated for a resting membrane potential not often the value measured?

A

The membrane is not permeable to one ion only. Other ions ar Beale to diffuse in and out which has an effect on the actual resting potential value.

29
Q

What contribution does Na+-K+-ATPase make to the maintainance of the resting membrane potential?

A

It generates the potential by removing Na+ bringing K+ into the membrane.It helps to maintain the ion gradient.