How to create postgresql triggers to calculate geometry from x,y and vice versa at the same time

I have a postgis table with point geometry which looks like this

CREATE TABLE mypoints 
 (
  gid serial NOT NULL,
  coordid integer,
  geom geometry(Point,4326)
 );

And a table with coordinates like this

CREATE TABLE mycoords
 (
  coordid serial NOT NULL, 
  x numeric(10,4),
  y numeric(10,4)
 );

I want to create several triggers, that update or insert mypoints.geom value with MakePoint(mycoords.x, mycoords.y) function, taking values from joined mycoords table, and at the same time vice versa - when mypoints.geom is updated or inserted, correlated mycoords.x and mycoords.y values should be calculated with ST_X(mypoints.geom) and ST_Y(mypoints.geom) respectively.

How can I do that?