Custom implementation of walkCells which only goes up and down.
function(pos, direction, e, preventWrap, verifierFn, scope) {
        if (direction == 'left') {
            direction = 'up';
        } else if (direction == 'right') {
            direction = 'down';
        }
        pos = Ext.view.Table.prototype.walkCells.call(this, pos, direction, e, preventWrap, verifierFn, scope);
        if (pos && !pos.column) {
            pos.column = 1;
        }
        return pos;
    }