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Foundations in Neuroscience > Neurophysiology > Flashcards

Neurophysiology Flashcards

1
Q

What is electrophysiology?

A

Measuring electrical activity in biological tissue e.g. brain, spinal cord, heart, muscle, cochlea

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2
Q

What is the prerequisite for electrically excitable cells?

A

Intracellular space more negative than extracellular space

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3
Q

What does electrophysiology measure?

A

Potential difference between electrode inside the cell and outside the cell (membrane potential)

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4
Q

How is the membrane potential generated in neurons?

A

Through an imbalance of K+ ions

K+ leak channels = build up of negative charge within cell

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5
Q

What are the pros and cons of dissociated neuronal cultures?

A

Pros: cells easily accessible for intracellular recordings
Cons: no anatomical correlate, cells not in physiological environment, can early study early developmental stages

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6
Q

What are the pros and cons of acute brain slices?

A

Pros: local circuits intact, can study any developmental stage, anatomically relevant
Cons: long range inputs/outputs severed, not physiological environment

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7
Q

What are the pros and cons of using a whole animal?

A

Pros: all circuits intact, can correlate activity with behaviour
Cons: technically very challenging (esp. intracellular recordings), ethically challenging

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8
Q

What are the two types of intracellular recordings and the main differences between them?

A

Sharp pipette - high tip resistance, pokes a hole in membrane
Patch pipette - low tip resistance, perfuses cell with pipette solution

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9
Q

What are the fundamentals of patch clamp recording?

A
  1. Apply mild suction to form tight contact between pipette and membrane
  2. Strong pulse of suction breaks membrane - allows cytoplasm to become continuous with pipette interior
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10
Q

How can you record from a single ion channel?

A

Using an inside-out or outside-out patch

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11
Q

Define ionic equilibrium potential

A

The membrane potential where there is no net flow of ions.

Determined by intracellular concentration, extracellular concentration and the valence of the ion.

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12
Q

What is the Nernst equation?

A

Ex = (61.5/z)log10([x]out/[x]in)

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13
Q

What happens to the membrane potential when an ion channel opens?

A

It will tend towards the equilibrium potential of that ion

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14
Q

What are the fundamentals of voltage clamp recording

?

A
  1. Fix the voltage at a particular membrane potential
  2. Measure the current (I) required to keep the voltage (V) at that level
    E.g. amplifier must inject negative current to maintain the cell at -80mV to oppose the flow of positively charged ions
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15
Q

Define action potential

A

A short lasting event in which the electric membrane potential of a cell rapidly rises and falls

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16
Q

Describe the steps of an action potential.

A
  1. Resting membrane potential maintained by K+ leak currents
  2. When membrane reaches threshold, voltage gated Na+ channels open
  3. More Na+ channels quickly open
  4. Na+ channels inactivate and slower K+ channels activate
  5. K+ channels cause overshoot/afterhyperpolarisation
  6. Resting potential reestablished
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17
Q

What neurotransmitters do CA1 neurons and OLM interneurons use?

A

CA1 - Glutamate

OLM - GABA

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18
Q

How do you create a phase plane plot?

A

Combining AP and 1st derivative (rate of change)

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19
Q

What can you determine from a phase plane plot?

A 
Maximum rate of rise - highest peak
Maximum rate of fall - lowest trough
AP peak - x intercept
AP threshold 
Magnitude of afterhyperpolarisation
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20
Q

Differences between CA1 and OLM waveforms

A

Slower rise of AP in OLM
Lower peak in OLM
More depolarised AP threshold in OLM
Larger AHP in OLM

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21
Q

How do voltage gated Na+ channels trigger a chain reaction?

A
  1. Na+ flow into cell - results in region of positive charge across membrane
  2. Local depolarisation activates nearby Na+ channels - more Na+ flows into cell
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22
Q

How do auxillary subunits contribute to threshold differences?

A

Expression of alpha subunits with beta subunits shifts the voltage dependence of Na currents
Differential expression of beta subunits can modulate channel function

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23
Q

How does a large afterhyperpolarisation contribute to high frequency repetitive firing?

A
  1. Na+ channels exist in three states - ‘closed/available’, ‘open’ and ‘inactivated’
  2. At negative membrane potentials most are closed
  3. During depolarisation, shift to open
  4. Rapidly shift to inactivated - unavailable for opening
  5. Large AHP pushes the membrane to more hyperpolarised potentials
  6. Means Na+ channels recover faster - promotes high frequency repetitive firing
24
Q

What are the ionic mechanisms underlying large afterhyperpolarisation in GABAergic interneurons?

A
  1. Interneurons express high levels of voltage gated K+ channels (Kv3 subtype)
  2. Fast activating/deactivating channels only activated at very depolarised potentials
  3. Produce large post spike AHP
  4. Enable very fast repolarisation of AP
  5. Maximises quick recovery of resting conditions
25
What are the stages of the monosynaptic stretch reflex? (knee jerk reaction)
1. AP propagates along sensory neuron to spinal cord 2. Releases glutamate at spinal synapse 3. Spinal cord activates motor neuron whos axon extends to muscle 4. Releases ACh at neuromuscular junction
26
What are the features of synaptic vesicles?
Balls of lipid membrane | Contain membrane bound proteins for docking, release and filling
27
How are neurotransmitters transported into vesicles?
Proton antiporters Requires energy H+ pumped into vesicle then swapped out with neurotransmitter
28
What triggers migration of vesicles to the presynaptic membrane?
Depolarisation opens voltage gated Ca2+ channels | Ca2+ binds to various proteins, triggering fusion of vesicle with membrane
29
Define probability of release
Likelihood of a presynaptic bouton to release neurotransmitter Takes value between 0 and 1 Not the same in every synapse any given neuron makes
30
Can probability of release change?
Yes - Pr is dynamic not fixed, changed by physiological factors
31
How does probability of release relate to synaptic strength?
If Pr does up, synaptic strength goes up | If Pr does down, synaptic strength goes down
32
How can you lower probability of release?
Alter presynaptic Ca2+ entry by: 1. Lowering extracellular Ca2+ 2. Applying Ca2+ channel blockers 3. Activate presynaptic receptors that alter Ca2+ channel activity
33
Can neurons change probability of release by themselves?
Yes - underpins most forms of short term synaptic plasticity
34
Define short term plasticity
Short-lived changes in the strength of synaptic coupling that reflect prior experience/activity of the synapse
35
What is functional compartmentalisation at dendritic spines?
Restricting ionic and biochemical changes to the activated synapse
36
What are the 5 key facets of neurotransmitters?
1. Storage in synaptic vesicles 2. Ca2+ dependant release mechanism 3. Specific protein targets 4. Process for rapid removal of transmitter 5. Process of rapid synthesis
37
What are the differences between AMPA and NMDA receptors?
AMPA - day to day functioning, permeable to Na+ and K+ NMDA - activated under special conditions, permeable to Na+, K+ and Ca2+ (allows local biochemical changes), has Mg2+ block
38
What are the similarities between AMPA and NDMA receptors?
Bind Glutamate Ion channels - mediate fast synaptic transmission Tetrameric assemblies
39
What does postsynaptic Ca2+ do?
Can activate enzymes, regulate ion channel opening and affect gene expression Vital for LTP and LTD
40
What is the main difference between GABAa and GABAb receptors?
GABAa - ionotropic | GABAb - metabotropic
41
What are the stages of inhibitory synaptic transmission?
1. Same Ca2+ mediated release 2. Bind GABAa receptors on post synaptic membrane 3. Cl- ions flow into cell 4. Generates inhibitory post synaptic potential IPSP
42
How do IPSPs differ from EPSPs?
GABAb activates GIRK (K+ channel) | Co-activation of GABAa and GABAb produces long, biphasic IPSPs
43
What is the GABAb signalling cascade?
1. Alpha subunit exchanges GDP for GTP 2. It dissociates and inhibits adenylate cyclase 3. Beta-gamma subunit is liberated - activates K+ channel and inhibits Ca2+ channel
44
What does activation of Gi/o coupled receptors result in?
1. Inhibition of cAMP production 2. Activation of GIRK K+ channel 3. Inhibition of voltage-sensitive Ca2+ channel
45
Where are GABAb receptors commonly found?
On presynaptic terminals
46
What type of short term plasticity does GABAb mediate?
Paired pulse depression 1. Activation of presynaptic GABAb receptors - negatively coupled to Ca2+ channels 2. Restricts Ca2+ entry into cell 3. Conditioned stimuli results in reduced Ca2+ mediated exocytosis - less GABA released
47
What is Hebb's Law?
When cells A and B fire at the same time, their connection becomes stronger. Neurons that fire together, wire together
48
Define long term potentiation
The persistent strengthening of synapses based on recent activity (high frequency stimulation, 100Hz)
49
What are the 4 properties of LTP?
Input specificity - cells can change individual synapse strength Associativity and cooperativity - weak stimulus in one pathway won't elicit LTP but when paired with a strong stimulus in another pathway, LTP occurs in both Persistence - change in synaptic strength is long term
50
Does LTP satisfy Hebbs Law?
Yes
51
What is the mechanism of LTP induction?
NMDA passing Ca2+ ions vital for LTP formation Ca2+ targets calmodulin, PKC, calpain Ca2+/Calmodulin dependant protein kinase vital for LTP
52
What are the potential mechanisms of LTP expression?
All lead to greater net flow of ions 1. Change in presynaptic release properties - increase Pr, increased release sites, increase in [Glu] 2. Synaptic growth - smaller cleft = greater [Glu] 3. Change in AMPAR number - unsilencing a synapse or insertion of additional AMPARs 4. Change in AMPAR properties - increased opening time, probability of opening or size of current (gamma)
53
Define long term depression
The persistent weakening of synapses based on recent activity (low frequency stimulation)
54
What are the mechanisms of LTD induction?
NDMA activation and postsynaptic Ca2+ mAchR activation mGluR activation
55
What is an engram?
The physical location of a memory trace in the brain

Foundations in Neuroscience (6 decks)

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