Trigger 9 Flashcards by Anna Parker

what is the pain pathway

injury - nociceptive, inflammatory mediators
peripheral nerve - afferent neurone, excitatory (glutamate and ATP release)
spinal cord - receptor binding, AMPA (fast), NMPA (slower, release block of prolonged depolarisation)
thalamus
cortex

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what are the two types of pain conduction

fast response - A delta fibres

slow response - C fibres

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describe the A delta fibres

fast
large myelinated
up to 10m/sec
sharp stabbing pain

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describe the C fibres

slow
small unmylinated
1.2m/sec
aching burning pain

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How does an agonist of nAChR lead to block?

IV injection of suxamethonium

Depolarisation effect lasts sufficient time to make motor endplate inexcitable
AChE (in situ at motor end plate) does not hydrolyse suxamethonium

Endogenous ACh released in brief spurts & rapidly hydrolysed at the motor endplate by AChE
ACh never causes prolonged depolarisation required for block, unless AChE inhibited

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depolarzing muscle relaxant

Structurally two joined ACh
Agonist of nAChR

Metabolised by plasma cholinesterase
- quickly hydrolysed.
Action lasts a few minutes

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layers of the eye

Outer fibrous layer (cornea, conjunctiva & sclera)
Middle vascular layer (iris & choroid)
Inner neural layer (retina)

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non-depolarzing muscle relaxant

competeive reversible antagonist of nAChR

curare deravitive
prevent Ach binding to receptors

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cones

colour vision
high details

activated by
Higher acuity
Higher light threshold
Hundreds off photons

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rods

sight in low light

activated by
Low intensity
light (single photon)

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steps of photoreception

GPCR and light sensor convalent coupled 
II cis retinal - light causes it to change to ..
all trans retinal 
metarhodopsin 
activation of transducin 
activation of phophodiesterase
decreased cyclic GMP 
closure of Na2+ channels 
hyperpolarisation of photoreceptor membrane 
decreased release of glutamate

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retina structure

epethilail membrane
photoreceptors
- rods
- cons

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what is the effect of decreased release of glutamate

decreased excitatory glutamate response (ionotropoic receptor)
hyperpolarisation of bioplar and horizontal cells

decreased inhibitory glutamate response (metabotrophic receptor)
depolarisation of bioplar and horizontal cells

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glutamate iontrophic receptors

NMDA - Ca2+ (blocked by Mg2+)
AMPA - Na
kainate - Na

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glutamate metabotrophic receptors

mGlu - Group II/III Presynaptic
Gi/Go
Inhibits VOCCs & opens K+ channels

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what is the mian inhibitory neurotransmitter in the brain

glutamate

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what are the GABA pathways

both are inhibitory
GABAa - ligand gated chloride channel
hyperpolarisation reduces excitabilty

GABAb - Gi/Go
Inhibits VOCCs & opens K+ channels
= reduces excitability

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what is a receptive field

every cell has one
Area of retina that, when stimulated with light, changes cell’s membrane potential

Usually excitatory centre,
inhibitory surround

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describe the direct pathway when there is no light

no light 
photoreceptor depolarised
glutamate signals 
depolarises OFF centre of bipolar cell
off centre of ganglion cell more likely to reach threshold 
action potential more likely

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describe the indirect pathway when there is no light

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no light
- horizontal cell (from surronding photoreceptors) signal via GABA
hyperpolarises on centre of bipolar cell
- amacrine cell ( from surronding bipolar cell)
on centre ganglion cell less likely to reach threshold
action potentail less likely

describe the direct pathway when there is light

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light
photoreceptor hyperpolarised
less glutamate signals hyperpolarises OFF centre of bipolar cell
ON centre ganglion cell less likely to reach threshold
action potentail less likely

describe the indirect pathway when there is light

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light
horizontal cells and amacrine cells release less GABA
depolarises ON centre of bipolar cell - release more glutamate
ON centre of ganglion cell more likely to reach threshold
action potential more likely

sound recognition

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Vibration of oval window generates fluid wave down scala vestibuli then back through the scala tympani to round window.
Wave conducted to scala media, leading to displacement of basilar membrane.

mechanism of auidtory transduction

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sound waves
vibration of organ of corti
bending of cilia on hair cells
change in K+ conductance of hair cell membrane
osciliating receptor potential
intermittent glutamate release
intermittent action potentials in afferent cochlear nerves

how is pitch determined

PITCH is determined by the FREQUENCY of the signal - these are detected at different positions along the cochlea: higher frequencies closer to the oval window lower frequencies nearer the helicotrema

how is loudness determined

LOUDNESS is identified by the AMPLITUDE of deflection at a given part of the cochlea

basic response to surgery

``` peripheral nociceptor stimulation travel vis afferent neurone synapse in dorsal horn +/- modulation lateral STT (contralateral) transmitted to thalamus post-central gyrus ```

aims of anaesthesia

``` muscle relaxation immobility hypnosis amnesia analgesia control of stress response ```

Iv agents benefits

rapid onset and recovery

IV agents disadvanatage

unpredicitable dosing | over dose potential

inhalation agents advantage

reasonably rapid onset and recovery predicitable dosing difficult to overdose

factors increasing reticuar activating system

surgery - opiodids, NSAIDs, LAs | stimulatory system - glutamate/NMDA mediated

factors decreasing reticuar activating system

inhibitory system - GABAa/Cl- mediated

opoid receptors

sites - brain, spinal cord, GI tract G protein linked - cellular hyper-polarization - inhibits synaptic transmission of pain

opioid effects

``` analgesia constipation sadation respiratory depression mood alterations ```

examples of opioids

morphate | codeine

what are muscle relaxants used for

allow intra-cavity surgery facilitate intubation/ventilation paralysis only - no anaesthesia

major compliaction of anaesthesia

failed intubation or ventialtion pulmonary aspiration of gastric contents intra-operative awareness drug error/mishap

what is pain

an unpleasant sensory and emotinal experience assocaited with actual or potentail tissue damage or described in terms of such damage

factors affecting pain

``` expectation injury infection inflammation stress anxitey gender age culture ```

positive affect of pain

``` danger alert - withdrawal protection - rest injury prevention - learning ```

negative affect of pain

``` suffering impaired function - motor - respiratory - CVS ```

nociceptors

bare nerve endings respond to mechanical, thermal or chemical injury sensitivity altered by inflammatory mediators - bradykinin, histamin, prostaglandins

visceral pain

iniated by distesion, inflammation and ischaemia pathways generally via automatic NS poorly localized may be perceived in the relevant dermatome - refferred pain

neuroptahic pain

``` results from nerve damage - trauma - infection often becomes chronic difficult to treat ```

sites of local anaesthetic

spinal epidural peripheral nerve site of injury

how do local anaesthetcis work

administered extracellulary in ionzed form LA becomes unionized to corss membrane (H+ dissociates) LA works intracellularly in ionzed form to prevent Na+ channels from opening

what are prostagplandins

part of the eicosaniod system - local ell signalling - derivatives of eicosanoic acid short lived - systhesized and released almost instantly involved in peripheral pain sensitization

Trigger 9 Flashcards

(48 cards)