بسم الله الرحمن الرحیم

The Brainstem

The Brainstem

Consists of • Midbrain • Pons • Medulla oblongata

The brainstem has three broad functions:

(1) it serves as a conduit for the ascending tracts and descending tracts connecting the spinal cord to the different parts of thehigher centers in the forebrain

(2) it contains important reflex centers associated with the control of respiration and the cardiovascular system and with the control of consciousness

(3) it contains the important nuclei of cranial nerves lll through Xll.

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

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

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

Pons

Dorsal surface• Superior cerebellar peduncle • Superior medullary velum • Trochlear nerve

Midbrain Ventral surface• Crus cerebri • Interpeduncular fossa

oculomotor nerves emerge from medial of crus cerebri

• Posterior perforated substance

Midbrain

Dorsal surface• Superior colliculus

constitute centers for visual reflexes

• Inferior colliculus associated with auditory pathway

• Brachium of superior colliculi

• Brachium of inferior colliculi

Fourth ventricle

Position • Situated ventral to

cerebellum, and dorsal to pons and cranial half of medulla

Central canal →fourth ventricle →mesencephalic aqueduct→third ventricle

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Boundaries• Inferolateral: gracile and

cuneate tubercles, inferior cerebellar peduncle

• Superolateral: superior cerebellar peduncle

• Lateral recess

Features • Median sulcus • Sulcus limitans• Vestibular area overlies vestibular

nuclei

• Acoustic tubercle• overlying dorsal cochlear nucleus

• Medial eminence• Striae medullares

• Facial colliculus: overlies nucleus of abducent n. and genu of facial nerve

• Hypoglossal triangle : overlying hypoglossal nucleus

• Vagal triangle: overlies dorsal nucleus of vagus nerve

• Area postrema • Locus ceruleus

Roof • Anterior part: formed by

superior cerebellar peduncle and superior medullary velum

• Posterior 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

Tela choroidea and choroid plexus

The characters of internal structure of brainstem

Medulla oblongataLower part (closed part)• Two decussations–

– Decussations of medial lemniscus – Decussations of pyramid

V nucleuos

Cuneatus n

Medulla oblongata

Upper part (open part) • Appearance of inferior

olivary nuculeus and inferior cerebellar peduncle

• Enlargement of central canal to form the fourth ventricle floor

• Spinoolivary accessory olivary• Cortico olivary inf. Olivary n.• Central tegmental tract inf. Olivary n.• Olivocerebellar fibers• Inf. Olivary = center of coordination of

afferents of cerebellum

Internal structures

Gray matter• Cranial nerve nuclei• Relay nuclei

Relay nuclei• Gracile nucleus• Cuneate nucleus• Inferior olivary nucleus • Superior olivery nucleus• Pontine nucleus• Nucleus of inferior colliculus• Gray matter layers of superior

colliculus• Red nucleus • Substantia nigra • Pretectal area

Non-cranial nerve nuclei Nucleus Site

Gracile nucleus Medulla (underneath gracile tubercle)

Cuneate nucleus Medulla (underneath cuneate tubercle)

Superior olivery nucleus Pons

Pontine nucleus pons

Nucleus of inferior colliculus Midbrain

Gray matter layers of superior colliculus

Midbrain

Red nucleus Midbrain

Substantia nigra Midbrain

Pretectal area Midbrain

White matterAscending tracts• Medial lemniscus • Spinal lemniscus• Trigeminal lemniscus • Lateral lemniscus

Medial lemniscus

Spinal lemniscus

Trigeminal lemniscus

Descending tracts

• Corticospinal tract • Rubrospinal tract • Tectospinal tract • Vestibulospinal tract • Reticulospinal tract

Lateral lemniscus

Reticular formation of brainstem

• Ascending reticular activating system (ARAS)

• Motor central and vital centres– Reticulospinal tract– Cardiovascular center and

respiratory center

• Serotonergic rapheal nuclei

• Medial longitudinal fasciculus= medial vestibolospinal tract

• Dorsal n of vagus =parasympathic part• Solitarious n= gustatory• Central tegmental tract