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Anatomy of the brain stem (external features and larger internal structures).

On the surface of the brain stem you should be able to identify the sites of attachment ("superficial origins") of the cranial nerves and also the major external landmarks of the medulla, pons and midbrain.

Drawing of lateral aspect of brain stem

Drawing of ventral aspect of brain stem

Dorsal aspect of the brain stem

Inside the brain stem the anatomy can be studied only by looking at sections. Usually these are in the transverse plane and are stained by Weigert's technique, which colours myelinated fibres black. Areas occupied by grey matter (nuclei of the brain stem) are pale in these preparations.

Many students of neuroanatomy have great difficulty relating the objects seen in sections to the external anatomy of the brain stem. Others find it easy. Try the following approach.

1.  Look at the perimeter of the section and
    associate the lumps and indentations
    with landmarks on the surface of
    a whole specimen. Pay particular
    attention to colliculi of the midbrain
    and to cerebellar peduncles.

2.  Each level of the brain stem contains one or
    two conspicuous internal objects, which
    should be committed to memory. These are:

    Closed medulla:  Pyramidal decussation
                                 (at the most caudal level)
                                Internal arcuate fibres
                                 (at a more rostral level)
    Open medulla:    Inferior olivary nucleus
    Pontomedullary junction:  Abducens nucleus
                               Fibres of facial nerve
    Mid-pontine level:   Trigeminal nerve
                               Pontine nuclei
                               Medial lemniscus
    Caudal midbrain:   Decussation of superior
                                       cerebellar peduncles

    Rostral midbrain:   Red nucleus
                                   Oculomotor nerve

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