Your parameters will be part of the computational graph if you used them to compute the [loss] variable you start backpropagation from. There are some special cases when backpropagation is not being performed in some sub-graph. You can read more in the docs 169.
But parameters do not get updated during backpropagation. Only their gradients are being changed (the new gradients are added to the existing values) when calling backward(). Parameters are usually updated afterwards by an optimizer based on the gradients computed during backpropagation.