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INTS > INTS8 - Membrane Potentials > Flashcards

INTS8 - Membrane Potentials Flashcards

1
Q

What are the four types of channels in membranes.

A

Voltage gated. Ligand gated. Mechanically regulated. Thermally gated.

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2
Q

Define chemical gradient.

A

Difference in concentration across a membrane.

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3
Q

Define electrical gradient.

A

Difference in charge across the membrane.

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4
Q

What are the common ions that membranes have channels for.

A

Calcium. Potassium. Sodium. Chloride.

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5
Q

Define diffusion.

A

Movement of molecules or ions down their concentration gradient until equilibrium is reached.

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6
Q

Define electrochemical gradient.

A

Electrochemical potential difference for ions that can move across the membrane comprising of chemical gradient and electrical gradient.

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7
Q

What are the three electrical properties and their explanations, relative to plasma membranes.

A

Potential difference - differences in charge across the membrane.
Current - movement of ions due to potential difference.
Resistance - barrier preventing movement of ions.

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8
Q

How do membrane potentials arise.

A

Differences in concentration of ions on either side of a membrane. Membrane potentials are expressed as the charge inside, relative to the outside.

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9
Q

Define passive diffusion.

A

Movement of molecules down a concentration gradient that does not require energy.

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10
Q

How is membrane potential altered.

A

Flow of ions through channels.

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11
Q

Define threshold potential.

A

The level that membrane potential needs to release in order to generate an action potential.

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12
Q

What are the relative concentrations of sodium and potassium inside and outside the cell.

A

Greater concentration of sodium ions outside the cell. Greater concentration of potassium ions inside the cell.

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13
Q

Define diffusion potential.

A

Movement of ions across the membrane creates a driving force which is the diffusion potential.

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14
Q

Define electrochemical equilibrium.

A

A state reached when concentration gradient is balanced by the electrical gradient across the membrane,

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15
Q

Define equilibirum potential.

A

Potential difference that is unique to each ion and is determined by a set of ion concentrations on either side of the membrane. Potential difference at which there is no movement of ions across the membrane.

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16
Q

How can Nernst equation be used. What factors does it include.

A

Used to calculate the potential at which an ion would stop moving across the membrane.
Factors - temperature, faraday constant, gas constant, concentration of ions intracellularLy and extracellularly

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17
Q

Discuss the process by which the equilibrium potential for K+ is determined.

A

K+ ions move down their concentration gradient passively from inside the cell to the outside. Their associated anions do not move through the K+ ion channel. Ratio of anions to cations becomes unbalanced, resulting in a negative charge on the inside of the cell. Negative electrical force pulls K+ back into cell through ion channel. When concentration gradient and electrical force are balanced - membrane potential for that ion has been established.

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18
Q

What is the membrane potential for sodium and potassium.

A

ENa - +73mV

EK - -92mV

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19
Q

Discuss what determines resting potential.

A

Takes into consideration a mixture of equilibrium potentials present for different ions.

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20
Q

Discuss resting potential relationship to membrane potentials for sodium and potassium and what can be implied.

A

Resting potential is -70mV. Membrane potential for sodium is +73mV. Membrane potential for potassium is -92mV. Resting potential is closer to membrane potential for potassium indicating that that membrane is more permeable to K+ than Na+.

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21
Q

What is the purpose of the Goldman-Hodgkin-Katz equation.

A

Allows determination of resting membrane potential taking into account probability of movement of various ions intracellularLy and extracellularly.

22
Q

Define action potentials.

A

Nerve impulses that travel along the surface of the neuron due to changes in permeability to different ions.

23
Q

Speed of an action potential.

A

Approx 4 milliseconds.

24
Q

Discuss process by which an action potential occurs.

A

Stimulus occurs which changes permeability of membrane to Na+. Some sodium ions initially move into cell bringing potential from -70mV to threshold of -55mV. More Sodium ions move into cell, making the interior more positive and so depolarises the membrane to +40mV. Sodium ion channels close preventing further influx of Na+
K+ ion channels become opened, causing them to shoot out of the cell, depolarising the membrane. Overshoot of K+ ions results in hyperpolarisation around -90mV, as K+ ion channels are slow to close. Membrane potential eventually restored when sodium and potassium levels go back to normal.

25
Q

What are the five stages of an action potential.

A 
Depolarisation - rising phase. 
Action potential - peak phase. 
Depolarisation - falling phase. 
Hyperpolarisation. 
Resting potential - refractory period.
26
Q

What are the two refractory periods and define each.

A

Absolute - Na+ channels inactivated meaning depolarisation cannot occur.
Relative - larger stimulus require to induce a further action potential as the speed at which voltage gated K+ ion channels close is slower.

27
Q

What are the three distinct stages of voltage gated Na+ channels. Describe each.

A

Closed, open and inactivated.
Closed - membrane at resting potential.
Open - during depolarisation stage.
Inactivated - after initial opening, channels rapidly adopt inactive conformation meaning that cannot open even though membrane is still depolarised.

28
Q

Discuss sodium ion channel state at resting potential.

A

Sodium ion channel closed meaning no sodium can flow through,

29
Q

Discuss sodium ion channel state at depolarisation.

A

Sodium ion channel opens however inactivated state is more stable.

30
Q

How is the backwards spread of depolarisation ensured.

A

Sodium ion channels become inactivated.

31
Q

Why does hyperpolarisation occur.

A

Potassium ion channels are slow to close meaning there is an overshoot of potassium ions.

32
Q

What is the purpose of the axon hillock.

A

Ensures summation of the signal which must be strong enough to result in an action potential. Commonly referred to as the trigger zone.

33
Q

What increases the speed of action potential propagation.

A

Presence of myelin. Increase in temperature. Larger axon diameters..

34
Q

Which glial cells produce myelin and where from.

A

Peripheral nervous system - Schwann cells.

Central nervous system - oligodendrocytes.

35
Q

What are the Nodes of Ranvier.

A

Areas along an axon where myelin is not present.

36
Q

Where along an axon are voltage gated channels presented.

A

Nodes of Ranvier.

37
Q

Is conduction faster in unmyelinated or myelinated axons.

A

Myelinated axons conduction speed is 120m/s.

Unmyelinated axons conduction speed is 5m/s.

38
Q

Define axolemma and axoplasm.

A

Cytoplasm of axon is axoplasm.

Plasma membrane of axon is axolemma.

39
Q

Why is the speed of conduction faster with larger axon diameters.

A

Less resistance for ion flow.

40
Q

Which types of fibres are the fastest.

A

Group I fibres.

41
Q

What factors slow conduction velocity.

A 
Reduced axon diameter e.g. injury. 
Reduced myelination e.g. some neurodegenerative diseases degrade myelin. 
Absence of oxygen, 
Reduced temperature. 
Drugs.
42
Q

What are the two methods of classifying nerve fibres.

A

Letters - conduction velocity.

Roman numerals - axon diameter.

43
Q

What are the three letters used to describe nerve fibres in terms of conduction velocity. Give description for each.

A

A - fast, 4 types.
B - preganglioninc autonomic fibres.
C - postganglioninc autonomic fibres.

44
Q

Give the different types of type A nerve fibres. What do the letters represent.

A

Alpha - motor to skeletal muscle
Beta - sensory from Golgi tendon organs
Lambda - motor to intrafusal muscle fibres
Delta - sensory from free nerve endings for pIn and temperature and hair follicles.
A type nerve fibres are differentiated by conduction velocity.

45
Q

What are the numbers used to classify nerve fibres by axon diameter.

A

Roman numbers I-IV.
I - large
II - sensory from skin receptors
III - sensory from free nerve endings for pain and temperature and hair follicles
IV - small, post ganglionic autonomic fibres, sensory from free nerve endings for pain and temperature

46
Q

What is acetylcholine.

A

Neurotransmitter released at neuromuscular junction.

47
Q

What can determine whether a post synaptic potential is excitatory or inhibitory.

A

Type of ion channel.

48
Q

Discuss what happens at excitatory post synaptic potentials.

A

Post synaptic potentials bring membrane potential closer to the firing threshold by making it less polarised. Increases the likelihood of action potentials being generated. Mediated by influxes of sodium ion channels.

49
Q

Discuss what happens at inhibitory post synaptic potentials.

A

Post synaptic potentials take membrane potential further away from finishing reshoot by making it more polarised. Decrease the likelihood of an action potential being generated. Mediated by influx of chloride ions.

50
Q

Discuss cumulative effect/temporospatial summation.

A

Combines the effect of many axons in order to summate the effects.

51
Q

Give examples of excitatory neurotransmitters.

A

Acetylcholine. Dopamine via D1 receptor. Noradrenaline. Serotonin. Histamines.

52
Q

Give examples of inhibitory neurotransmitters.

A

Glycine. Dopamine via D2 receptors. Opioids.

INTS (11 decks)

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