Brain stem

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