1. Brain stem

2. The brain stem
Consists of
Midbrain
Pons
Medulla oblongata 1 2 3

3. Medulla oblongata Ventral surface
Pyramid: contain pyramidal tract (corticospinal tract)
Decussation of pyramid: formed by crossing fibers of corticospinal tract
Olive: produced by underlying inferior olivary nucleus
Anterolateral sulcus: rootlets of hypoglossal nerve emerge from it
Retroolivary sulcus: rootlets of glossopharyngeal, vagus and accessory nerves emerge from it 1 IX
XII 3 X XI 4 5 2

4. Medulla oblongata Dorsal surface Lower portion
Gracile tubercle: produced by underlying gracile nucleus
Cuneate tubercle: marks the site of cuneate nucleus
Inferior cerebellar peduncle
Obex
Upper portion: forms the lower half of rhomboid fossa 3 5 2 4 1

5. Pons Ventral surface Basilar part Basilar sulcus
Bulbopontine sulcus: from medial to lateral, the abducent, facial and vestibulocochlear nerves appear
Middle cerebellar peduncle
Trigeminal nerve 1 V 5 2 VI 4
VII 3
VIII

6. Pons Dorsal surface Superior cerebellar peduncle
Superior medullary velum
The upper half of rhomboid fossa 2 1

7. Midbrain Ventral surface Crus cerebri
Interpeduncular fossa oculomotor nerves emerge from medial of crus cerebri
Posterior perforated substance
Oculomotor nerve 2 1
III 3 VI

8. Midbrain Dorsal surface
Superior colliculus constitute centers for visual reflexes
Inferior colliculus associated with auditory pathway
Brachium of superior colliculi
Brachium of inferior colliculi
Trochlear nerve 1 2 IV

9. Fourth ventricle Position
Central canal →fourth ventricle →mesencephalic aqueduct→third ventricle
Position
Situated ventral to cerebellum, and dorsal to pons and cranial half of medulla

10. Boundaries
Inferolateral: gracile and cuneate tubercles, inferior cerebellar peduncle
Superolateral: superior cerebellar peduncle
Lateral recess

11. Floor Upper part: Upper pontine
and lower medullary separated by Striae medullares
Median sulcus divided it into righ andd left halves (2Medial eminence)
Upper part:
Facial colliculus: overlies nucleus of abducent n. and fibers of facial nerve
Upper Vestibular area: overlies vestibular nuclei
Superior fovea

12. Lower part: Hypoglossal triangle: verlying hypoglossal nucleus
Lower Vestibular area
Vagal triangle: overlies dorsal nucleus of vagus nerve
Inferior Fovea 2 2

13. Roof
Upper part: formed by superior cerebellar peduncle and superior medullary velum
Lower part: formed by inferior medullary velum and choroid plexus of fourth ventricle
Three apertures
Median aperture of fourth ventricle
Two lateral apertures of fourth ventricle