In the Senate, any Senator may appeal the ruling of the chair. The Senate then decides the point of order, usually by majority vote, when it votes on the appeal; occasionally the ruling of the chair is overturned. The chair also has the option of submitting a point of order to the Senate for a decision without first ruling on it, but is only required to do so when constitutional questions or certain Senate rules are involved.
In the House, appeals to overturn the chair's ruling are also possible, but they are rarely demanded and almost never succeed.