When does the brain stem appear in humans? When does the brain stem appear in humans?

The following article states:


  Once the neural tube closes, at around week 6 or week 7 of pregnancy,
  it curves and bulges into three sections, commonly known as the
  forebrain, midbrain and hindbrain. Just to the rear of the hindbrain
  sits the part that will soon turn into your baby's spinal cord. Soon,
  these areas bubble into those five different regions of the brain that
  we're most familiar with: the cerebrum, cerebellum, brain stem,
  pituitary gland and the hypothalamus.


How "soon" after 6 - 7 weeks is this soon the article talks about? When does the brain stem appear in humans?

Fetal Brain Development
I'm not sure this question is answerable at that specificity. There isn't a discrete point in time where the cells are definitively a brain stem rather than a precursor structure such the bulge mentioned above. One could identify a set of a cells in earlier structures that eventually are located in the adult area we call the brain stem, but that doesn't mean at the point those cells are identifiable that they are IN the brain stem during development.