Brain stem
The brain stem
Consists of Midbrain Pons Medulla oblongata
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2
3
Medulla oblongataVentral surface Pyramid: contain pyramidal tr
act (corticospinal tract) Decussation of pyramid: form
ed 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
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2
3
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XXI
Medulla oblongata
Dorsal surface Lower portion
Gracile tubercle: produced by und
erlying gracile nucleus Cuneate tubercle: marks the site
of cuneate nucleus Inferior cerebellar peduncle Obex
Upper portion: forms the lower half of rhomboid fossa
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3
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Pons
Ventral surface Basilar part Basilar sulcus Bulbopontine sulcus: fr
om medial to lateral, the abducent, facial and vestibulocochlear nerves appear
Middle cerebellar peduncle
Trigeminal nerve
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2
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5VVI
VIIVIII
Pons
Dorsal surface Superior cerebellar pedu
ncle Superior medullary velu
m The upper half of rhombo
id fossa
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2
Midbrain
Ventral surface Crus cerebri Interpeduncular fossa oc
ulomotor nerves emerge from medial of crus cerebri
Posterior perforated substance
Oculomotor nerve
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VI
Midbrain
Dorsal surface Superior colliculus constitut
e centers for visual reflexes Inferior colliculus associate
d with auditory pathway Brachium of superior colliculi Brachium of inferior colliculi Trochlear nerve
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2IV
Fourth ventricle
Position Situated ventral to
cerebellum, and dorsal to pons and cranial half of medulla
Central canal →fourth ventricle →mesencephalic aqueduct→third ventricle
Boundaries Inferolateral: gracile an
d cuneate tubercles, inferior cerebellar peduncle
Superolateral: superior cerebellar peduncle
Lateral recess
FloorUpper pontine
and lower medullary separated by Striae medullares
Median sulcus divided it into righ an
dd 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
Lower part: Hypoglossal triangle: verlying hypog
lossal nucleus Lower Vestibular area Vagal triangle: overlies dorsal nucle
us of vagus nerve Inferior Fovea
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Roof Upper part: formed by su
perior 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 fo
urth ventricle