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Brain Stem
Brain Stem
• Brain stem:
• consists of medulla oblongata, pons, and
midbrain.
Medulla
• Medulla oblongata (Medulla)
• continues with spinal cord. The junction between spinal
cord and medulla is the upper rootlet of the first cervical
nerve. Junction between pons and medulla is an
imaginary transverse line that passes the middle
cerebellar peduncles.
• Eminences
• Anterior
– Pyramind: consists corticospinal fibers.
– Olive: oval swelling that marks the position of olivary nucleus.
• Posterior
– Gracile and Cuneate tubercles: elevations, indicates the
continued gracile and cuneate fasciculi
– Obex: apex of the V shaped boundary of fourth ventricle.
Cranial Nerves
• Abducens nerve: near the midline between the
pons and medulla
• Facial nerve: caudal border of the pons, laterally.
Has sensory and motor roots.
• Vestibulocochlear nerve: more laterally to the
facial N
• Glossopharngeal and vagus:
between olive and the tuberculum cinereum
• hypoglossal nerve: between pyramid and the
olive
Pons
• Has basal (ventral) and dorsal portions.
• Basal portion (ventral):
basilar sulcus
trigeminal nerve: has sensory and motor
(smaller) roots. Trigeminal N is terminated
by three branches:
1). Ophthalmic
2). Maxillary
3). Mandibular
Pons
• Dorsal portion:
– also called tegmentum of the pons
– Formed by the floor of fourth ventricle
Midbrain
• Ventral side:
– basis pedunculi (including corticospinal,
corticobulbar, and corticopontine fibers)
interpeduncular fossa: depression in between
these two pedunculi
– In the fossa, many blood vessels penetrate
through (posterior perfoated substance).
Oculomotor nerve also emerges from here.
• Lateral surface:
– cerebral peduncles
Midbrain
• Dorsal surface:
– superior colliculi (colliculus) part of the vision
pathway, control visual movement
– inferior colliculi (both paired), part of the auditory
pathway
– inferior brachium: connects inferior colliculi with
thalamic nuclei for hearing
– superior brachium: connects cerebral cortex and
retina with superior colliculi for vision
• trochlear nerve: emerges caudal to the inferior
colliculi
Fourth ventricle
• diamond shaped, produce CSF, median
and lateral apertures