I'm stuck with .parents()

I'm stuck with .parents()

Hi,

I have a list of input field in my table, i need it to bold the header when user focus on the input field, i've tried many ways but it is not working.

<style tyle="text/css">
  .f_row { }
  .f_row_focus { background-color: #CCC; }
  .f_header { }
  .f_header_focus { font-weight: bold; }
</style>

<script language="javascript">
  // I can highlight the row , but  I dont' know how to bold the header
  // I have no idea how to select f_header in f_row
  $(document).ready(function() {
    $("input").focus(function() {
      $(this).parents('f_row').addClass('f_row_focus');
    }).blur(function() {
      $(this).parents('f_row').removeClass('f_row_focus');
    });
  });
</script>

<table>
  <tr class="f_row">
    <td class="f_header">Name</td>
    <td><input type="text" id="cust_name"></td>
  </tr>
    <tr class="f_row">
    <td class="f_header">Email</td>
    <td><input type="text" id="cust_email"></td>
  </tr>
</table>


Anyone can help me ? Thanks.