gistfile1.rb

# app/models/consult.rb

class Consult < ActiveRecord::Base

  attrs_accesible :nota_ingreso_attributes
  has_one :nota_ingreso

  accepts_nested_attributes_for :nota_ingreso

end

# app/view/.. 

<%= form_for(@consult) do |f| %>
<%= link_to "Listado", :action => "list"%>
<%= f.submit "Actualizar" %>
<fieldset>
<legend align="left">Datos Personales</legend>
  <td align="right"><label for="notaingreso">motivo de ingreso:</label></td>
  <% f.fields_for :nota_ingreso do |ni| %>
    <%= ni.text_area "motivo_ingreso", :class => "textinput_width", :size => "100x6" %>
  <% end
</table>
   </div>
 </tr>
 <% end %>
</table>
</fieldset>
</div>

# app/controllers/consults_controller.rb

class ConsultsController < ApplicationController

  def update
    @consult = Consult.find(params[:id])
    @consult.update_attributes(params[:consult])
    redirect_to "/"
  end

end