Case 2 - Back pain and addiction Flashcards
what is neuropathic pain?
pain arising as a direct consequence of a lesion or disease affecting the somatosensory system
what is allodynia?
pain triggered by non-noxious stimuli
what is hyperalgesia?
increased pain from a noxious stimuli
what is central pain?
damage to modulation of ascending pathways within brain or spinal cord. traumatic or degenerative injury to spinothalamic pathways
common causes of central pain?
stroke MS Cancer Epilepsy Parkinsons
symptoms of neuropathic pain?
spontaneous pain - shooting, burning, numbness, pins and needles
allodynia
hyperalgesia
what is paraesthesia?
an abnormal sensation: e.g. numbness, pins and needles, crawling ants etc. can be evokes or constant
what are some of the mechanisms of central neuropathic pain?
enhancement of facilitatory pathways diminished inhibitory pathway central sensitisation neuronal plasticity genetic
what sensory modalities does the dorsal column pathway carry?
proprioception
fine touch
vibration
spinothalamic tract has two divisions - what are they and what sensory modalities do they carry?
lateral - pain and temperature
anterior - crude touch and pressure
the faciculus gracilis transmits information coming from where?
proprioception, fine touch and vibration from lower limbs - inferior to T6
the faciculus cuneatus
transmits information coming from above T6 - upper limbs
what are the three pairs of corticospinal tracts?
lateral, anterior and corticobulbar
where do corticospinal fibres decussate?
at the pyramids in the medulla - most decussate and form the lateral tract - some remain and are called the anterior tract
what are the 4 subconscious motor tracts?
vestibulospinal tract
tectospinal tract
reticulospinal tract
rubrospinal tract
what is the role of the vestibulospinal tracts?
- information is sent from the inner ear to monitor position of the head
- vestibular nuclei respond by altering muscle tone, neck muscle contraction and limbs for posture and balance
what is the role of tectospinal tract?
- sends information to the head, neck and upper limbs in response to bright and sudden movements and loud noises
- the tectum area consists of the superior and inferior colliculi
- -superior colliculi - receives visual information
- -inferior colliculi receives auditory information
what structures modify and coordinate movements so that they are performed in a smooth manner?
basal nuclei and cerebellum
what are some of the treatments of neuropathic pain?
- antidepressants - TCA e.g. amitriptyline, amoxapine trimipramine
- anticonvulsants - gabapentin or pregabalin
- opiate painkillers - morphine, tramadol
what is the MOA of TCAs?
blockage of sertonin and noradrenalin reuptake transporters (SERT) increasing levels of seratonin and noradrenalin available in the synaptic cleft
what are some of the side effects of TCAs?
dry mouth blurred vision weight gain constipation cardiotoxicity and neurotoxicity are related to overdose
what receptor do opiates act on?
agonists of Mu opioid receptors in the CNS
influx of which ions causes the depolarisation of neurons during an action potential?
Na+ influx depolarises neruone
K+ efflux causes repolarisation
Na/K co transporter restores membrane potential
what are the two main types of receptor?
Ionotropic
metabotropic
how is dopamine synthesised?
tyrosine –tyrosine hydroxylase–> L-DOPA –dopa decarboxylase (DDC) –> dopamine
what is the rate determining step in the synthesis of dopamine?
tyrosine hydroxylase is the rate determining step in DA synthesis - it is usually saturated by a substrate
what are the Dopamine receptor subtypes?
D1 family - D1 and D5 - excitatory
D2 - D2,3,4 - inhibitory
what two enzymes metabolise catecholamines?
COMT -catechol-O-methyl transferase
MAO (A and B) - Monoamine oxidase
what are the 4 steps for acute pain?
- Transduction
- Transmission
- Perception
- Modulation
for each or the mechanoreceptors of somatosensation state what stimuli they transduce:
- free nerve endings
- mechanoreceptors (merkel’s disc)
- Raffini’s corpuscle
- Meissner’s corpuscle
- Pacinian corpuscle
- muscle spindle
- golgi tendon organ
- pain, temperature, mechanical deformation
- low frequency vibration
- stretch (joint, skin)
- light touch
- deep pressure
- muscle contraction and stretch
- stretch of tendons
what is peripheral sensitisation?
reduction in threshold and an increase in responsiveness of the peripheral ends of nociceptors
what is central sensitisation?
increase in the excitability of the neurones within the CNS - normal inputs begin causing abnormal responses
what is an example of central sensitisation?
hyperalgeasia
What is a pain management programme?
a psychologically based rehabilitation programme delivered in a group setting by an interdisciplinary team.
What neurotransmitter is central to the neurochemistry of reward? and where are increases in levels noted?
Dopamine
nucleus accumbans
how to stimulants like cocaine work?
directly increase dopamine by blocking DA reuptake transporter
Opiates increase dopamine by…
acting on Mu receptors on GABAergic neurons inhibiting GABA release onto DA neurones
what are two main pathways to addiction?
Self medication - negative reinforcement to negative reinforcement
sensation seeking - positive reinforcement to negative reinforcement
drug abuse is…
taking of a substance in a manner that does not conform to social norms
drug dependance (physical) is…
an individual depends on a drug for normal physiological functioning - abstinence produces withdrawal symptoms
drug dependance (psychological) is…
compulsive use of a drug
Drug addiction is…
not a clinical diagnosis - typically used to emphasise psychological dependance
describe the cell body, myelination, nerve conduction and function of:
- Aalpha/Abeta
- Adelta
- C fibres
- large cell body, myelinated, fast conduction, proprioception and low threshold mechanoreception
- small/medium cell body, thinly myelinated, medium conduction, high threshold mechanoreception
- small, unmyelinated, slow, pain and temperature, high threshold mechanoreception
what primary afferent receptor does heat and capsaicin activate?
TRPV1
TRPM8 is activated by what?
cold and mint
what causes secondary hyperalgesia?
mast cell activation and degranulation
what are nociceptors?
pain sensing nerve cells A delta (sharp pain) and C fibres (dull pain)
what is substance P?
pain neurotransmitter - from 1st to 2nd order neurone
what substances are produced in response to injury which initiates the ascending pain pathway
prostaglandins
descending pain pathway arises from?
anterior cingulate gyrus, amygdala and hypothalamus and are relayed to the spinal cord
what are the inhibitory neurotransmitters involved in the descending modulation of pain?
noradrenalin, seratonin and opioids (enkephalin, endorphins)
where is sympathetic outflow along the spinal cord?
T1-L2
where are sympathetic nerve cell bodies of the preganglionic neurones located?
lateral horn of grey matter
what is the MOA of ibuprofen?
non-selective COX-inhibitor
what is the MOA of lidocaine?
blockage of Na+ channels prevent depolarisation along axons - prevent propagation of pain signals
what is the gate control theory of pain?
- A synaptic gate lies between peripheral nerves and neurons of the spinal cord
- Pain signals from peripheral nerves compete with other neural signals to get through the gate
- The gate may be opened or closed by physical factors, (e.g. counter stimulation of other peripheral nerves, endogenous opioids) or by psychological factors, (e.g. attention, downward stimulation from the brain, moods)
- The theory provides a basis on which to understand the interplay between physical and psychological factors in pain
- Also accounts for the phenomenon of pain being reduced through touch
- Can help people understand that their mental attitudes and behaviour can influence their pain
