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Physiology > Action potential > Flashcards

Action potential Flashcards

1
Q

What are all activities in amoeba coordinated by?

A

Nucleus

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2
Q

What type of cell is amoeba?

A

Simple unicellular protist

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3
Q

What sub kingdom is amoeba in?

A

Phylum Protozoa

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4
Q

What is the unit of structure of CNS?

A

Neuron

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5
Q

What is the neuron doctrine proposed by?

A

Cajal

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6
Q

What do neurons need to do?

A

Need to send signals rapidly over long distances (e.g. Sciatic nerve)

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7
Q

What do nerves generate?

A

Generate electrical signals - the nerve impulse or action potential

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8
Q

Plasma membrane structure diameter

A

6-10 nm

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9
Q

What is the plasma membrane (layer)

A

Lipid bilayer

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10
Q

What is the bilayer composed of?

A
  • Phospholipids
  • Glycolipids
  • Cholesterol
  • Membrane proteins
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11
Q

Diffusion

A

high [solute] → low [solute]

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12
Q

Osmosis

A

high [H2O] → low [H2O]

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13
Q

What do osmosis and diffusion depend on?

A 
Concentration gradient (Δc)
Membrane permeability (P)
Substance properties
Particle size
Lipid solubility
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14
Q

What is the rate of diffusion governed by? (law)

A

Fick’s law

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15
Q

What are the two types of substance transport?

A
  • Facilitated diffusion (Passive)

- Active transport

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16
Q

Describe facilitated diffusion

A

Channels - water filled pores that allow for ion movements along their gradients. Their openings can be regulated (gating), have ion-selectivity (e.g. Na+, K+, Cl-, Ca2+, cations etc.

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17
Q

What are the two active transport processes?

A
  • ATPases

- Exchangers

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18
Q

Describe exchangers in active transport

A

Movement of 1 substance along its gradient is coupled to movement of another against its gradient (Na+-Ca2+ exchanger, Na+ Glucose co-transporter

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19
Q

How can neurons respond to various stimuli?

A

By altering electrical charge across their membrane

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20
Q

What are the main ions in membrane potential?

A
  • K+
  • Na+
  • Ca2+
  • Cl-
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21
Q

What type of charge does the interior of a cell have in comparison to outside and why?

A

A relative negative net charge in comparison to outside of the cell due to ionic composition of cytoplasm

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22
Q

What type of charge does the interior of a cell have in comparison to outside and why?

A

A relative negative net charge in comparison to outside due to ionic composition of cytoplasm

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23
Q

Electrical potential

A

Difference in charge between inside and outside

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24
Q

What is the electrical gradient influenced by?

A

By overall electrical charge

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25
Q

What is the chemical gradient influenced by?

A

By individual concentration of a particular ion

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26
Q

Movement of electrical gradient

A

Positive ions would flow towards areas of negative charge

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27
Q

Movement of chemical gradient

A

All ions move from areas of high to low concentration

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28
Q

What will the direction an ion moves depend on?

A
  • Overall net effect of electrical and chemical (electrochemical) gradients
  • Permeability of membrane to ion
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29
Q

What are the only molecules and gases that can diffuse freely through the cell membrane?

A

Only lipophilic molecules & gases

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30
Q

What is the Na+/K+ ATPase pump?

A

Protein complex that spans the membrane; facilitates transport of Na+ and K+ across the plasma membrane

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31
Q

What does the Na+/K+ ATPase pump require? (dependent)

A

Energy-dependent process; requires ATP cellular source of energy

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32
Q

Why does the Na+/K+ ATPase pump require?

A

Because it is moving Na+ and K+ against their respective chemical gradients

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33
Q

How is membrane potential achieved?

A

Ions are moved across the plasma membrane against their concentration gradient: [Low] → [High]

34
Q

ATP hydrolysis →

A

ATPases

35
Q

What occurs to the carrier protein in the Na+/K+ ATPase pump?

A

Phosphorylation / de-phosphorylation

36
Q

Sodium-Potassium pump

A
  1. Binding of cytoplasmic Na+ to the pump protein stimulates phosphorylation by ATP.
  2. Phosphorylation causes the protein to change its shape.
  3. This shape change expels Na+ to the outside, and extracellular K+ binds.
  4. K+ binding triggers release of the phosphate group.
  5. Loss of phosphate restores the original conformation of pump protein.
  6. K+ is released and Na+ sites are ready to bind Na+ again
37
Q

Describe the pumping action of Na+/K+ pump

A
  1. Pump, bound to ATP, binds Na+
  2. ATP is hydrolysed and the pump is phosphorylated
  3. Conformational change occurs exposing Na+ to extracellular side - phosphorylated form has little affinity for Na+ so ions are released
  4. Pump then binds K+ which cause it’s dephosphorylation reverting to it’s previous conformation and transporting K+ to the interior
  5. Unphosphorylated pump has higher affinity for Na so K is released
38
Q

What is the normal osmolality of all body fluid compartments?

A

290 mOsmol

39
Q

Equilibrium potential

A

The electrical potential difference that exactly counterbalances diffusion due to the concentration difference

40
Q

What is equilibrium potential determined by?

A

Nernst eqn

41
Q

What is the function of gating of ion channels?

A
  • Have conducting and non-conducting states e.g. open or closed
  • Transition between states is called ‘gating’
  • Ion selectivity: Na+ ,K+ ,Ca2+ ,Cl- or cations.
42
Q

What is gating influenced by?

A
  • Changes in membrane potential: Voltage-gated
    Channels
  • Extracellular ligands: Ligand-gated channels
  • Mechanical stimulation
  • Phosphorylation
43
Q

What is the function of Goldman eqn?

A

Defines the membrane potential and includes permeability component

44
Q

What is Vm typically?

A

-65 mV

45
Q

Do action potentials travel faster in larger or smaller axons?

A

Larger

46
Q

What do voltage-gated ions possess?

A

Sensors that detect change in membrane potential

47
Q

Are voltage-gated Na+ and K+ channel open or closed in resting state?

A

Closed

48
Q

Give the process of the action potential

A
  1. Voltage-gated Na+ and K+ channels are closed in resting state.
  2. A stimulus opens activation gate of some Na+ channels depolarizing membrane potential. If threshold potential is reached , more Na+ channels open, triggering an action potential
  3. Above threshold potential activation gates of all Na+ channels are open. K+ channels are mostly closed but begin to slowly open.
  4. Na+ channel inactivation gates close and K+ channels are fully open.
    Efflux of K+ from the cell drops membrane potential back to and below resting potential.
  5. Continued efflux of K+ keeps potential below resting level.
  6. K+ channels finally close and Na+ channel inactivation gates open to return to resting state.
49
Q

Mini journey of action potential

A

Starts at the junction of the axon with the neurons cell body and travels down the axon to the axon terminal.

50
Q

What is the absolute refractory period?

A

A period of complete resistance to stimulation

51
Q

What is the relative refractory period?

A

A period of partial resistance to stimulation

52
Q

How long does the relative refractory period last?

A

As long as the K channels are open

53
Q

What can a strong stimulus in the relative refractory period trigger?

A

A new AP

54
Q

What does the inactivation of Na+ channels in the absolute refractory period mean?

A

That after an action potential there is a brief period when no other action potential can be generated

55
Q

What are the mutations in autosomal dominant nocturnal frontal lobe epilepsy?

A

CHRNA4, CHRNA2, CHRN2

56
Q

What are the mutations in benign familial neonatal seizures ?

A

KCNQ2, KCNQ3

57
Q

What is the mutation in conductane and genes in epilepsy?

A

Conductance: Na+
Genes: SCN1A (SCN1B)

58
Q

What is the type of conduction of action potentials in unmyelinated axons?

A

Contiguous conduction

59
Q

What is the conduction speed in unmyelinated fibres?

A

Nerve impulse travels 1 metre in 0.1s (100ms) = 10 metres/second

60
Q

What in the function of C fibres?

A

Carry sensory information

61
Q

Are C fibres myelinated or unmyelinated?

A

Unmyelinated

62
Q

What does damage to C fibres cause?

A

Neuropathic pain

63
Q

What does hot curry activate?

A

Unmyelinated fibres

64
Q

What does conduction velocity speed depend on?

A

How local currents spread

65
Q

What does how local currents spread depend on?

A
  1. Resistance of the axonal membrane

2. Internal resistance of the axon

66
Q

What kind of resistance does a narrow axon have?

A

High internal resistance

67
Q

If there were lots of channels in the membrane would there be high or low membrane resistance?

A

Low

68
Q

What could you have to get fast propagation?

A
  1. A wide axon - e.g. squid 1mm diameter

2. Insulate the axon to increase membrane resistance

69
Q

What produces myelin in the CNS?

A

Oligodendrites

70
Q

What produces myelin in the PNS?

A

Schwann cells

71
Q

What are the axon insulators?

A

Glial cells

72
Q

Give a clinical consequence of demyelination.

A

Multiple sclerosis

73
Q

What happens to myelin sheaths in multiple sclerosis?

A

Myelin sheath degenerates and forms hardened scars (sclerosis)

74
Q

What happens to affect axons in multiple sclerosis?

A

They slowly degenerate

75
Q

What does degeneration of axons in multiple sclerosis cause?

A

A slowing and eventual block of AP conduction

76
Q

What type if disease is multiple sclerosis?

A

An autoimmmune disease – the body’s own immune system attacks the myelin sheath

77
Q

How common is multiple sclerosis?

A

1 in 1000 people

78
Q

Name a test for nerve damage

A

Nerve conduction velocity

79
Q

What can NCV aid in the diagnosis of?

A
  • Peripheral neuropathy
  • Nerve entrapment syndromes
  • Guillain-Barre syndrome
80
Q

What might a time delay (latency) in sensory nerve conduction indicate?

A

Median nerve dysfunction (when testing median nerve)

Physiology (28 decks)

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