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.
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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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