different receptors (eg pain, temperature, touch) have different axon fibres which have different speeds of transmission towards the CNS which means some modalities are slower to be transmitted than others.
the diagram below outlines
Group I and Alpha a fibres are the same fibre type but they are known by different names because Aa is axons from skin and Group I is axons from muscles
generally you can tell if a pathway has begun in the CNS or the PNS based on its name
for examples spinocerebellar suggests it began outwith the CNS and is then travelling up the spinal cord and into the brain.
whereas
Cerebellar’’…’’ suggests it starts in the brain and descends
The white matter of the spinal cord is divided up into tracts of axons carrying typified information - fasciculus Gracilis and fasciculus Cuneatus are important tracts for the carriage of information.
carries information from the lower body extremities
carries information from the upper body extremities