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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
What is the chemical gradient influenced by?
By individual concentration of a particular ion
26
Movement of electrical gradient
Positive ions would flow towards areas of negative charge
27
Movement of chemical gradient
All ions move from areas of high to low concentration
28
What will the direction an ion moves depend on?
- Overall net effect of electrical and chemical (electrochemical) gradients - Permeability of membrane to ion
29
What are the only molecules and gases that can diffuse freely through the cell membrane?
Only lipophilic molecules & gases
30
What is the Na+/K+ ATPase pump?
Protein complex that spans the membrane; facilitates transport of Na+ and K+ across the plasma membrane
31
What does the Na+/K+ ATPase pump require? (dependent)
Energy-dependent process; requires ATP cellular source of energy
32
Why does the Na+/K+ ATPase pump require?
Because it is moving Na+ and K+ against their respective chemical gradients
33
How is membrane potential achieved?
Ions are moved across the plasma membrane against their concentration gradient: [Low] → [High]
34
ATP hydrolysis →
ATPases
35
What occurs to the carrier protein in the Na+/K+ ATPase pump?
Phosphorylation / de-phosphorylation
36
Sodium-Potassium pump
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
Describe the pumping action of Na+/K+ pump
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
What is the normal osmolality of all body fluid compartments?
290 mOsmol
39
Equilibrium potential
The electrical potential difference that exactly counterbalances diffusion due to the concentration difference
40
What is equilibrium potential determined by?
Nernst eqn
41
What is the function of gating of ion channels?
- 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
What is gating influenced by?
- Changes in membrane potential: Voltage-gated Channels - Extracellular ligands: Ligand-gated channels - Mechanical stimulation - Phosphorylation
43
What is the function of Goldman eqn?
Defines the membrane potential and includes permeability component
44
What is Vm typically?
-65 mV
45
Do action potentials travel faster in larger or smaller axons?
Larger
46
What do voltage-gated ions possess?
Sensors that detect change in membrane potential
47
Are voltage-gated Na+ and K+ channel open or closed in resting state?
Closed
48
Give the process of the action potential
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
Mini journey of action potential
Starts at the junction of the axon with the neurons cell body and travels down the axon to the axon terminal.
50
What is the absolute refractory period?
A period of complete resistance to stimulation
51
What is the relative refractory period?
A period of partial resistance to stimulation
52
How long does the relative refractory period last?
As long as the K channels are open
53
What can a strong stimulus in the relative refractory period trigger?
A new AP
54
What does the inactivation of Na+ channels in the absolute refractory period mean?
That after an action potential there is a brief period when no other action potential can be generated
55
What are the mutations in autosomal dominant nocturnal frontal lobe epilepsy?
CHRNA4, CHRNA2, CHRN2
56
What are the mutations in benign familial neonatal seizures ?
KCNQ2, KCNQ3
57
What is the mutation in conductane and genes in epilepsy?
Conductance: Na+ Genes: SCN1A (SCN1B)
58
What is the type of conduction of action potentials in unmyelinated axons?
Contiguous conduction
59
What is the conduction speed in unmyelinated fibres?
Nerve impulse travels 1 metre in 0.1s (100ms) = 10 metres/second
60
What in the function of C fibres?
Carry sensory information
61
Are C fibres myelinated or unmyelinated?
Unmyelinated
62
What does damage to C fibres cause?
Neuropathic pain
63
What does hot curry activate?
Unmyelinated fibres
64
What does conduction velocity speed depend on?
How local currents spread
65
What does how local currents spread depend on?
1. Resistance of the axonal membrane | 2. Internal resistance of the axon
66
What kind of resistance does a narrow axon have?
High internal resistance
67
If there were lots of channels in the membrane would there be high or low membrane resistance?
Low
68
What could you have to get fast propagation?
1. A wide axon - e.g. squid 1mm diameter | 2. Insulate the axon to increase membrane resistance
69
What produces myelin in the CNS?
Oligodendrites
70
What produces myelin in the PNS?
Schwann cells
71
What are the axon insulators?
Glial cells
72
Give a clinical consequence of demyelination.
Multiple sclerosis
73
What happens to myelin sheaths in multiple sclerosis?
Myelin sheath degenerates and forms hardened scars (sclerosis)
74
What happens to affect axons in multiple sclerosis?
They slowly degenerate
75
What does degeneration of axons in multiple sclerosis cause?
A slowing and eventual block of AP conduction
76
What type if disease is multiple sclerosis?
An autoimmmune disease – the body’s own immune system attacks the myelin sheath
77
How common is multiple sclerosis?
1 in 1000 people
78
Name a test for nerve damage
Nerve conduction velocity
79
What can NCV aid in the diagnosis of?
- Peripheral neuropathy - Nerve entrapment syndromes - Guillain-Barre syndrome
80
What might a time delay (latency) in sensory nerve conduction indicate?
Median nerve dysfunction (when testing median nerve)

Physiology (28 decks)

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