NB10 Flashcards
What is the name for pain receptors
Nociceptors
What are the chemical stimuli released from damaged cells
Bradykinins
Prostaglandins
H+
ATP
What are the chemical stimuli released from platelets
Serotonin
What are the chemical stimuli released from immune cells
Cytokines
Chemokines
Cold receptor
TRP A1
TRP M8
trp - Transient Receptor Potential
Heat receptor
TRP V1
Protons receptor
ASIC
acid-sensing ion channel
Bradykinin receptor
B1/B2
Mechanical receptor
DRASIC/mDEG
dorsal root acid-sensing ion channel
mammalian degenerin
What type of fibres are there
- Aδ fibres
2. C fibres
What are Aδ fibres
- Produces sharp, localised, immediate pain
- Relay info via thalamus to cortex and trigger immediate withdrawal and allow localisation of pain
- Small, myelinated fibres
- Speed of conduction: 12-30m/s
What are C fibres
- Produces dull, diffuse pain
- Relay info to the limbic system and hypothalamus (triggering memory of stimulus and emotional response)
- Small, unmyelinated fibres
- Speed of conduction: 0.5-2m/s
Pain pathways
- Primary pain afferent to spinal cord
- Spinothalamic tract to thalamus
- Thalamus to sensory cortex
*pain from face (cranial nerve) bypasses the spinal cord
Nociceptive fibres in spinal cord dorsal horn
- On entering spinal cord, Aδ and C fibres ascend in tract of Lissauer
- They synapse with 2nd order neurones in superfiila layers of dorsal horn:
- Aδ = layers I and V (limited in II)
- C = layers II (substantia gelatinosa) - Decussation of ascending 2nd order neurones carrying pain or temperature info occurs immediately
Neurotransmitters involved in pain
afferent terminal of primary sensory neurone to dorsal horn neurone in spinal cord
Glutamate - NMDA, AMPA
Substance P - NK1
Inhibitors of pain receptor
GABA
Opiods
eCBs (endocannabinoids)
-inhibitory neurons in substanstia gelatonisa (layer II)
Where is endogenous opiods released
At sites associated with modulation of pain and act on opioid receptors
How are opioid receptors classified
- μ (heat)
- β-Endorphin and Leu-Enkephalins - δ (mechanical)
- Leu and Met-Enkephalins - κ (visceral)
- Dynorphin
Example of eCBs (endocannabinoids)
Anandamide
2-arachidonylglycerol
What are eCBs (endocannabinoids) derived from
arachidonic acid derivatives
How does eCBs (endocannabinoids) mediate their effects
Anagelsic effect mediated via activation of cannabinoid receptors:
CB1 - brain, spinal cord, dorsal root ganglion neurons
CB2 - immune cells
-reduce NT release
-reduce Ca2+ in presynaptic terminal
What are the responses to painful stimuli
- Concious perception of pain
- Spinal withdrawal reflex
- ANS changes
- Emotional response
What happens when reticular formation is activated by pain fibres
Increase alertness
raphe nuclei - increase serotonin production
What happens when pain receptors activates thalamus
Perception of pain
What happens when pain receptors which activate thalamus and reticular formation activates the hypothalamus and limbic system
Behavioral and emotional responses to pain
What happens when activated thalamus (by pain fibres) activate somatosensory cortex
Localisation of pain
What is visceral pain
Poorly localised
- felt in areas removed from site of stimulus
- referred to somatic structures
- due to convergence of visceral and somatic afferents on dorsal horn neurones and the brain interprets the signals as coming from somatic structure
Where does pain from heart referred to
Left arm
Where does pain from liver and gallbladder referred to
Right neck and shoulder
Right below the right breast
*note: both anterior and posterior
Where does pain from lung and diaphragm referred to
Left neck and shoulder
Where does pain from ureter referred to
Anterior groin area
Where does pain from colon referred to
Anterior suprapubic region
Where does pain from urinary bladder referred to
Anterior pubic region
Midline of butt
Where does pain from stomach referred to
Epigastric region
Midline of the back
What is gate theory
modulation of pain perception in dorsal horn of spinal cord
Somatic non-painful signals can inhibit transmission of pain signals in the spinal cord (analgesia)
- large diameters Aα and Aβ fibres carrying touch, pressure, vibration, temperature
- stimulate inhibitory interneurons in the substantia gelatinosa
- inhibit transmission of pain at the synapse between 1st and 2nd order neurons
- GABA and endogenous opioids are released
Descending/Analgesic pathway
- Neurons from PAG (periaqueductal gray matter) activate reticular formation and stimulate the release of endogenous opioids
- Binds to opiate receptor
- Inhibits release of substance P from afferent pain fibres
- Transmission of pain impulsese to brain blocked
- No perception of pain at thalamus
PAG - has enkephalin-producing cells which binds to opioid receptors
Neurotransmitter involved in descending control
Serotonin
Noradrenaline
Origin of descending modulating pathways
- Peri-ventricular and peri-aqueductal grey matter in midbrain
- Rostroventral medulla including raphe nuclei
Paresthesia
Pins and needles
Dysesthesia
Burning sensation
Hyperalgesia
Lower pain threshold or exaggerated pain response to noxious stimulus
Allodynia
Pain in response to a non-noxious stimulus
Deafferentation pain
Peripheral nerve lesions such as phantom limb pain
Psychogenic pain
Occuring with or without an organic cause or disproportionate to the organic cause
