Neurostimulation Flashcards

1
Q

contraction: overview

A
  • myosin can’t bond w actin (due to troponin-tropomyosin complex)
  • Ca binds to complex to expose actin
  • once bonded w actin, myosin heads pull actin filament toward centre of sarcomere
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2
Q

define: neuromuscular junction

A
  • synapse formed btw å motor neuron axon + mm fibre
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3
Q

neuromuscular junction: define motor unit

A
  • axon forming synapses w several mm fibres
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4
Q

neuromuscular junction: how to get precision of mm control?

A
  • based on motor unit size:
  • sml: precise movements of hand (fingers 1:<10)
  • lrg: leg movements (1:>300)
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5
Q

neuromuscular junction: which NT used

A
  • Ach
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6
Q

neuromuscular junction: release of Ach prod?

A
  • prod large endplate potential

- voltage changes opens Ca channels

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7
Q

neuromuscular junction: Ca entry

A
  • triggers myosin-actin interaction (rowing action)

- movement of myosin bridges shortens mm fibre

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8
Q

tension + tetany: aka

A
  • wave summation + tetany AKA freq summation
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9
Q

tension + tetany: list types (4)

A
  • twitch
  • wave summation
  • incomplete tetanus (unfused)
  • complete tetanus (fused)
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10
Q

tension + tetany: how does wave summation occur?

A
  • when set of cells repeatedly stimulated without relaxation
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11
Q

tension + tetany: define tetany

A
  • sustained contraction resulting from high freq stimulation
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12
Q

tension + tetany: eg. external source

A
  • peripheral electrical stimulation
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13
Q

reflex: H reflex

A

stimulus - dorsal root - SC - mm

  • after stimulus + M-wave
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14
Q

name types of brain stimulation (5)

A
  • transcranial magnetic stimulation (TMS)
  • transcranial electrical stimulation (TES)
  • deep brain stimulation (DBS)
  • electroconvulsive therapy (ECT)
  • direct cortical electrical stimulation (DCES)
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15
Q

DBS: involved

A
  • implantation of electrode coils w wires going deep into brain
  • for parkinsons disease
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16
Q

TES: list (4) types

A
  • transcranial direct current stimulation (tDCS)
  • transcranial alternating current stimulation (tACS)
  • transcranial random noise stimulation (tRNS)
  • sham stimulation
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17
Q

tDCS: list (2) types

A
  • anodal

- cathodal

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18
Q

tDCS: features

A
  • Aldini showed direct current stimulation improved mood of melancholy patients
  • Albert found +ve and -ve stimulation had diff effects on cortical excitability
  • recent interest in tDCS is renewed
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19
Q

tDCS: mechanism

A
  • small electric current (~1 mAmp) passed through brain
  • electrodes on scalp
  • 9 volt current source
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20
Q

tDCS: which electrode is +vely/-vely charged?

A

+ve: anodal

-ve: cathodal

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21
Q

tDCS: way current flows from electrodes?

A
  • from anode through skull + brain to cathode
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22
Q

tDCS: device features

A
  • delivers current

- controls w set current intensity and duration of stimulation

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23
Q

tDCS: general features (3)

A
  • noninvasive brain stimulation
  • electrical currents delivered to scalp
  • equivalent to voltages naturally prod by brain (1-2mA)
24
Q

tDCS: anode electrode (4)

A
  • +vely charged current
  • stimulates nearby cortical regions
  • increases +ve charge
  • neurons more likely to reach AP
25
tDCS: cathode electrode (4)
- attracts -vely charged current - inhibits nearby cortical regions - increases -ve charge - neurons less likely reach AP
26
tDCS: critical issues (3)
- tDCS is bipolar - pure anodal/cathodal stimulation impossible - NOT focal, no way to know where stimulation is occurring (be skeptical of current models)
27
tDCS: diy and foc.us gaming devices
- can diy ur own - gaming devices to 'enhance cognitive function' - 2% cost of research/clinical grade sys
28
tDCS: experimental- 3 ver
- anodal - cathodal - sham
29
tDCS: experimental- sham?
- used as control in experiments - emits brief current, remains off for remainder of time - patient doesn't know they aren't receiving prolonged stimulation
30
tDCS: pros (6)
- cortical changes even after stimulation is ended (depends on length/intensity of stimulation) - cheap - portable - relatively easy to use - safe* - bidirectional
31
tDCS: cons (3)
- poorly localised - no temporal resolution - can't elicit AP
32
tDCS: experimental- Walsh
- 'bullshit' no evidence of cognitive effects after single session - doubts of use
33
TMS: shape of wand
- using regular circle has large SA | - but 2 coils concentrate to smaller SA
34
TMS: pros- chronometry (2)
- timing the cont of focal brain activity to behaviour | - role of 'visual' cortex in tactile information processing in early blind subjects
35
TMS: virtual lesions- causal link btw
- brain activity and behaviour
36
TMS: real lesion eg.
- blind woman lost ability to read braille following bilateral occipital lesions
37
TMS: TMS lesion
- using sighted (blue) and E blind (red)
38
TMS: occipital TMS on braille reading result
- disrupts braille reading in early blind | - not control subjects
39
TMS: critical issues (3)
- online vs. offline design? - online: how are sitmuli ordered? - offline: how long experiment, r conditions dist evenly within lesion window?
40
coil localisation: find functional effect
- M1 (hand twitch- MEP) | - V5 (moving phosphenes)
41
coil localisation: find anatomical landmark
- inion/nasion - ear/ear vertex | - EEG 10/20 sys
42
coil localisation: move set dist along + across eg.
FEF = 2-4cm ant, 2-4cm lateral to hand area
43
coil localisation: but?
- not all brains are same - MRI co-registration - functional and structural scan - frameless stereotactic sys
44
coil localisation: control conditions (5)
- diff hemisphere - diff site (these have diff effect/ no effect) - real - sham (improper technique, extra padding) or interleave TMS w no TMS trials
45
coil localisation: critical issues control conditions (5)
- control nonspecific stimulation effects - control placebo/behavioural arousal etc. - control sound - control for extra physiological effects (eg. twitching) - control for task specificity
46
coil localisation: major pros summary (6)
- reversible lesions without plasticity changes - repeatable - high spatial/temporal resolution - can establish causal link btw brain activation and behaviour - can measure/modulate cortical plasticity - therapeutic benefits
47
coil localisation: major limitations summary (6)
- only regions on cortical surfaces can be stimulated - can be unpleasant for subjects - risks to subjects + esp patients - stringent ethics required (can't be used by some institutions) - localisation uncertainty - stimulation lvl uncertainty
48
safety: seizure induction-
- caused by spread of excitation - single-pulse TMS has prod seizures in patients, not normal subjects - rTMS: both - visual and/or EMG monitoring for after discharges + spreading excitation may reduce risk
49
safety: hearing loss
- TMS loud click (90-130dB) in most sensitive range (2-7kHz) - rTMS= more sustained noise - reduced alot by ear plugs
50
safety: heating of brain
- theoretical power dissaption from TMS is few mW at 1Hz, | - brain metabolic power is 13W
51
safety: engineering safety
- TMS equipment operates at lethal voltages of up to 4kV | - max energy in capacitor is 500J = dropping 100kg from 50cm on your feet
52
safety: scalp burns form EEG electrodes
- mild scalp burns in subjects w scalp electrodes | - easily avoided eg. sml low-conductivity Ag/AgCl-pellet electrodes
53
safety: effect on cognition
- slight trend toward better verbal memory, improved delayed recall and better motor reaction time
54
safety: local neck pain and headaches
- related to stimulation of local mm and nn, site and intensity dependant - particularly uncomfy over fronto-temporal regions
55
safety: effect on mood in normals
- subtle changes in mood are site, freq dependant - high freq rTMS of L frontal cortex worsens mood - high freq rTMS of R frontal cortex may improve mood
56
safety: contraindications
- metallic hardware near coil (pacemakers, medical pumps etc.) - history seizures, history epilepsy in 1st degree relative - medicines reducing seizure threshold - pregnant - history of serious head trauma - history of substance abuse - stroke - status after brain surgery - other medical/neurologic conditions assoc epilepsy/seizure will be hazardous
57
safety: critical issues (6)
- purpose of stimulation? - type of stimulation? - where is stimulation? - stimulation adequate? - control conditions? - safety?