SQL & PL/SQL

Hi
I have created a trigger on a table on a insert after every row event. Trigger will update three different table let say "b","c","d" once a record is inserted into table say "a". Now this tables b,c,d will also be updated from application running. Now i am afraid that whether trigger running and application accessing same tables may causes any deadlock.
Can anyone help to say is there is possibility of any deadlock and also how the trigger aquires lock on tables used. Is trigger applys lock on all three table before starts running its action or it will aquire lock on the table on the fly when it fire update statement on a table.