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Brain stem
External features
By
Essam eldin AbdelHady Salama
Brain stem
It is located upon the basal
portion of the occipital bone.
It is connected to and covered
by the cerebellum.
It consists of the midbrain,
pons, and medulla oblongata.
Caudally the medulla is
continuous with the spinal cord
at foramen magnum.
Rostrally the midbrain is
continuous with the
diencephalon of forebrain.
It provides a pathway for
tracts running between higher
and lower neural centers.
Each region is about an inch
in length.
Dorsal surface
Medulla oblongata and pons;
Dorsal median sulcus is
manifested in the midline of
medulla continuous with that of
the spinal cord.
 Dorsal columns in the caudal
part of the medulla are formed
by fasciculi gracilis and
cuneatus, which are continues
rostrally from spinal cord to be
terminated in gracilis and
cuneate tubercles .
Dorsal surface
The central canal of the spinal cord
is continuous in caudal part of
medulla (closed medulla).
It progresses dorsally until opens
out into the 4th ventricle, in the
medullary part (open medulla).
Dorsal surface
The floor of the 4th ventricle
forms a rhomboid depression on the
dorsal surface of rostral medulla
and the dorsal surface of pons.
It is widest laterally, forming
lateral recesses, at this point lateral
apertures (foramen of Lusaka) are
present for CSF passage to
subarachnoid space.
Its lateral walls are made up of
Superior and inferior cerebellar
peduncles which connecting the
brain stem to the cerebellum.
It becomes continuous with
cerebral aqueduct that passes
through the midbrain.
Dorsal surface (N.B)
Medullary stria ; arcuate fibers to
cerebellum dividing the floor of the 4th
ventricle into inferior medullary and
superior pontine parts.
The medullary part contains a
triangular depression on each side of the
middle lines divides the area into three
trigones hypoglossal,vagal, and
vestibular.
The pontine part contains eminentia
medialis for abducent nerve nucleus and
facial nerve fibers, the gape between the
superior cerebellar peduncles is
occupied by the superior medullary
valum.
Dorsal surface
Midbrain;
The dorsal aspect of midbrain
is marked by 4 paired elevations
(superior and inferior colliculi),
as parts of visual and auditory
systems.
The trochlear nerve lies
immediately inferior to inferior
colliculus .
Ventral surface
Medulla oblongata;
The prominent longitudinal
columns (pyramids), that contains
the pyramidal or corticospinal tract,
lie on either sides of the ventral
median fissure.
Laterally lie elongated elevations
(olive) that contain the inferior
olivary nuclei.
Inferior cerebellar peduncles lie
most laterally.
XII nerve rootlets lie in groove
between pyramid and olive.
IX, X , and XI nerve rootlets lie in
groove between olive and Inferior
cerebellar peduncles.
Ventral surface
Pons;
The transverse pontine fibers
containing pontocerebellar fibers
from pontine nuclei to cerebellum
via inferior cerebellar peduncle.
Groove for basilar artery in the
middle line.
Middle cerebellar peduncles lie
laterally.
VI, VII, and VIII emerge
between pons and medulla.
V nerve emerges midway
between upper and lower borders.
Ventral surface
Midbrain;
The massive columns of
descending fibers (crus cerebri
or bases pedunculi) on each
side.
The area in between the crus
cerebri is the inter peduncular
fossa.
the inter peduncular fossa
contains, 2 mamillary bodies,
infundibulum of hypophysis
cerebri and posterior perforated
substance.
III and IV nerves in relation
to crus cerebri.