[jQuery] jQuery next() to find <select><option>

[jQuery] jQuery next() to find <select><option>


Hello I am using jQuery next() and prev() to navigate inside
<select><option> tags.
problem is I am using <optgroup> too and can't find a way to make it
work
ex:
<select>
            <optgroup label="Motion">
            <option value="/m01/" >001</option>
            <option value="/m02/" >002</option>
            <option value="/m03/" selected>003</option>
            <optgroup label="illustration">
            <option value="/illustration01/" >illustration01</option>
            <option value="/illustration02/" >illustration02</option>
</select>
    $(document).keydown (function(e) {
        if (e.keyCode == 37)
            if(n = $('select option:selected').prev().val())
                location.href = n;
        if (e.keyCode == 39)
            if(n = $('select option:selected').next().val())
                location.href = n;
    });