Grid view- updating error

Server Error in '/GridView_7' Application.

Must declare the scalar variable "@emp_name".

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.Data.SqlClient.SqlException: Must declare the scalar variable "@emp_name".

Line 62: 
Line 63:         con.Open();
Line 64:         cmd.ExecuteNonQuery();
Line 65:         con.Close();
Line 66:         

Source File: f:\Prasad Guduri\GridView_7\Default2.aspx.cs    Line: 64 

protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {
        GridViewRow row = GridView1.Rows[e.RowIndex] as GridViewRow;



        var emp_name = row.FindControl("TextBox1") as TextBox;
        var emp_id = row.FindControl("TextBox2") as TextBox;
        var emp_dept = row.FindControl("TextBox3") as TextBox;
        var emp_location = row.FindControl("TextBox4") as TextBox;
        var emp_salary = row.FindControl("TextBox5") as TextBox;

        SqlCommand cmd = new SqlCommand();
        cmd.CommandText=" update Employee set ename=@emp_name,eid=@emp_id,department=@emp_dept,elocation=@emp_location,esal=@emp_salary";
        cmd.CommandType = CommandType.Text;

        cmd.Connection = con;
        cmd.Parameters.AddWithValue("@ename", emp_name.Text);
        cmd.Parameters.AddWithValue("@eid", emp_id.Text);
        cmd.Parameters.AddWithValue("@department", emp_dept.Text);
        cmd.Parameters.AddWithValue("@elocation", emp_location.Text);
        cmd.Parameters.AddWithValue("@esal", emp_salary.Text);

        con.Open();
        cmd.ExecuteNonQuery();
        con.Close();
        

        GridView1.EditIndex = -1;          
    }