Neurology Of Pain Flashcards
What are the three forms of nociceptor stimuli?
Chemical
Mechanical
Thermal
Which forms of stimuli can be classified as fast, sharp pain?
Mechanical
Thermal
Which forms of stimuli can be classified as slow, dull pain?
Chemical
Mechanical
Thermal
How many types of nociceptors are there?
4
Thermal, mechanical, chemical AND poly modal
What types of fibres are found in thermal nociceptors?
A delta and C fibres
What types of fibres are found in mechanical nociceptors?
A delta and C fibres
What types of fibres are found in chemical nociceptors?
C fibres
Describe what the capsaicin receptor is.
A heat activated ion channel in the pain pathway.
A non-selective cation channel that is structurally related to members of the transient receptor potential family of ion channels.
Describe the action of capsaicin.
It elicits a sensation of burning pain by selectively activating sensory neurons that convey information about noxious stimuli to the CNS.
How are mechanical nociceptors activated?
Many ion channels are activated by membrane stretch (swelling)
Give some example of mechano-sensitive TRP channels.
TRPV1
TRPV 2
TRPV 4
What are the basic steps in unipolar conduction of pain?
Noxious stimulus
Transduction
Conduction
Transmission
Modulation
Describe acute pain.
Nociceptive and inflammatory
Sudden onset in response to discreet event
Recedes during healing
Describe chronic pain.
Neuropathic
Persists long after recovery (>3 months)
Often difficult to tie to a certain event
Often unresponsive to analgesics
What is neuropathic pain caused by?
A lesion or disease in the P/CNS
Change in the neurone not the tissue
What is neuropathic pain?
Can present as burning or tickling or dull aches
May be associated with allodynia or hyperalgesia
Describe what allodynia is.
Sensation of pain in response to something not normally painful in nature
Describe what hyperalgesia is.
Increased intensity of pain sensation for a given nociceptive stimulus.
More painful than it should be
What is peripheral sensitisation?
Increased sensitivity of C and A delta fibres due to prostaglandins release
Increased voltage dependant Na+ channel expression
Describe phantom limb pain.
It’s a peripheral mechanism
Proximal portion of the severed nerve sprouts to form neuromas
Increased Na+ channel expression
Hyper-excitability and spontaneous discharges
Doesn’t explain the presence of congenital phantom limb pain
Which fibres are for fast pain?
Myelinated neurone
A delta fibres
Which fibres are for slow pain?
Unmyelinated neurones
C fibres
What are conduction velocities of fast vs slow pain?
Fast - 6-30 m/s
Slow - 0.5-2 m/s
What responses are seen due to effects of the sympathetic nervous system?
Fear
Pupillary dilation
Pallor
Sweating
What responses are seen due to the parasympathetic nervous system?
Bradycardia
Syncope
Hypotension
Urination
Nausea
Which areas are involved in the natural analgesic pathway?
Periventricular nuclei (PVN)
Periaqueductal gray (PAG)
Raphe Magnus (RMN)
What are the steps of the natural analgesic pathway?
PVN - PAG (enkephalins) RAM - serotonin releases - inhibitory interneurones - enkephalin / GABA release - (GABA)DHN Cl- channels activated - hyperpolarisation - reduced DHN firing - (enkephalin) opioid receptors activated
How do enkephalins inhibit DHN firing?
Opens k+ ion channels
Hyperpolarises the DHN
What other ion channels can enkephalins affect?
They can act presynaptically to inhibit the opening of Ca2+ channels
Less Ca2+ means less transmitter is released and there will be less firing
