140 Neuroanatomy: Draw It to Know It
Know-It Points
Brainstem Composite — Axial View
■ Th e axial plane of the brainstem divides from anterior
to posterior into a basis, tegmentum, and tectum.
■ Within the basis lie the corticopontine,
corticonuclear, and corticospinal tracts, and most of
the supplementary motor nuclei.
■ In the anterior tegmentum lie the medial lemniscus,
anterolateral system, and trigeminothalamic tracts.
■ In the posterior tegmentum lie the cranial nerve
nuclei and neurobehavioral cells.
■ Additional tegmental structures are the reticular
formation, supplementary motor and sensory tracts,
and the brainstem auditory components.
■ Th e tectum is the roof of the brainstem and includes
the superior and inferior colliculi.The Midbrain
■ Th e substantia nigra contains dopaminergic nuclei; it
lies within the basis just posterior to the white matter
pathways.
■ Th e superior cerebellar peduncle decussates in the
central midbrain tegmentum in the inferior midbrain.
■ Th e periaqueductal gray area contains opioids, which
function in pain suppression.
■ Th e reticular formation divides into lateral, medial,
and median zones.
■ Th e raphe nuclei populate the median zone of the
reticular formation and are primarily serotinergic.
■ Th e central tegmental tract carries ascending reticular
fi bers to the rostral intralaminar nuclei of the
thalamus as part of the ascending arousal system and
descending fi bers from the red nucleus to the inferior
olive as part of the triangle of Guillain-Mollaret.
■ Th e superior colliculi lie in the upper midbrain and
are involved in visual function.
■ Th e inferior colliculi lie in the lower midbrain and
are involved in auditory function.The Pons
■ Th e pontine nuclei send pontocerebellar tracts into
the cerebellum via the middle cerebellar peduncle as
part of the corticopontocerebellar pathway.
■ Corticospinal tract fi bers descend through the
pontine basis.
■ Th e cerebrospinal fl uid space of the pons is the fourth
ventricle and the central gray area surrounds it.
■ Locus coeruleus nuclei are most heavily concentrated
in the pons and they are nearly entirely
noradrenergic.The Medulla
■ Th e descending corticospinal tract fi bers populate the
medullary pyramids.
■ In the lower medulla, internal arcuate fi bers originate
from the gracile and cuneate nuclei and form the
great sensory decussation.
■ Th e inferior olive receives tracts from the spinal cord
(from below) and from the red nucleus (from above).
■ Th e olivary nuclei send climbing fi bers to the
contralateral dentate nucleus of the cerebellum,
which projects back to the contralateral red nucleus
to complete the triangle of Guillain-Mollaret.
■ Along the anterior border of the fourth ventricle
(in its inferior fl oor) lies the area postrema.