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 sulcustrigeminal nerve: has sensory and motor (smaller) roots. Trigeminal N is terminated by three branches: 1). Ophthalmic 2). Maxillary3). 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