discendere = scendere
ascendere = salire
Only in the meaning.
The context of usage is quite different!
/Ascendere/ is used in a religious or mythological contexts,
while /discendere/ is used in religious or mythological contexts,
and also in expressions like:
-- l'aereo e` disceso a mille metri di quota.
In simple contexts salire, and scendere are far better choices!