Pain / Nociception

Pathways :

where does crossing over of touch / motor sensation?

at the midbrain

Pathways :

where does crossing of of nociception occur?

at the spinal cord segment

What type of receptors sense pain?

free nerve endings

How are free nerve endings different to others?

less myelination, thin, different Na channels

Why are the properties of FNEs significant in veterinary medicine?

they are accessible for drugs - analgesics.

Give a brief overview of the pain pathway.

FNEs → spinal cord, dorsal horn / dorsal root ganglion → spinothalamic tract → brain

What is the significance of the ‘substantia gelatinosa’ of the grey matter in spinal cord?

layer (laminae) of grey matter

This is where pain fibres cross over?? / cell bodies live…?

How do a2 agonists work in the brain?

inhibit NAd release from the presynaptic neurone, stops pain message from continuing

neuromodulation - reduce pain perception in brain

How do a-2 agonists work in the spinal cord?

pain is processed in dorsal horn of spinal cord

inhibits SP release from the presynaptic neurone that is sending pain signal.

stops signal at spinal cord - no perception of pain from brain.

What two pathways are included in the ventrolateral ascending pathways?

What senses are / aren’t included?

spinothalamic

spinoreticular

all except proprioception, especially pain

Describe the spinothalamic tract

direct from spine → thalamus (via medial lemniscus)

sends pinprick and thermal stimuli

Describe the spinoreticular tract

from spine → reticular formation → thalamus

‘true pain’ sense

Where is the reticular formation located (brain)

caudal medulla

What are the different pathways that can trigger vomiting?

dopamine → chemoreceptor trigger zone → vomit centre

Pain → histamines → vomit centre

vestibular apparatus → ACh → vomit centre

Where is ‘true pain’ perceived in the brain?

cerebellum

primary sensory area

What is the pain gate theory?

phenomenon where pain can be ‘switched off’

under high stress situations, areas of the brain stem send descending fibres to dorsal horn that trigger enkephalin receptors - inhibit pain sensation from traveling up from dorsal horn.

Describe the concept of referred pain

visceral pain receptors are not super sensitive / there are fewer - hard to sense location

OR

Primary afferent sensory receptors synapse onto the same ascending fibre. Confuses signals of origin of pain.

Explain phantom limb pain

Primary afferent sensory receptors of remaining limb / lost limb synapse onto the same ascending fibre. Confuses signals of origin of pain.

What is the ‘Lewis triple response’?

AP from inflammatory triggers doesn’t just got to brain, spreads out.

causes :

• vasodilation - oedema

• flare

• itch / pain

These are the three parts of response

Describe the spinocervicular tract (not found in humans)

sensations of : touch, pinprick, fleas

tract ascends in lateral funiculus

at C2 moves to other side?

goes through the midbrain/cerebellum to the thalamus

not a fucking clue