PARACETAMOL:

Central action via COX 3 inhibition which is associated with decreased brain PGE2 levels. It also modulates endogenous cannabinoid system

MORPHINE:

Morphine work by stimulating presynaptic Gi-protein-coupled MOP and KOP opioid receptors. Binding of the ligand causes the following events:

> Closure of voltage-gated Ca2+ channels

> Decreased cAMP production

> Stimulation of K+ efflux from the cell

> Hyperpolarisation of the cell membrane.

> This leads to decreased excitability of the cell and therefore decreased neurotransmitter release and pain transmission