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Brainstem( Pons,Medulla,

Midbrain)

Lecture 3

Dr. Maria

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Brainstem

The brainstem is made up of themedulla oblongata, the pons, and themidbrain and occupies the posteriorcranial fossa of the skull.

t is stalklike in shape and connectsthe narro! spinal cord !ith the

e"panded forebrain.

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Functions:

#. t ser$es as a conduit for the ascending tractsand descending tracts connecting the spinal

cord to the di%erent parts of the higher centersin the forebrain

&. t contains important refex centersassociated !ith the control of respiration and

the cardio$ascular s'stem and !ith the controlof consciousness

3. t contains the important nuclei o cranialnerves through .

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ross *ppearance of the Medulla

+blongata

The medulla oblongata connects the pons superiorl'!ith the spinal cord inferiorl'.

The unction of the medulla and spinal cord is at theorigin of the anterior and posterior roots of the -rst

cer$ical spinal ner$e, !hich correspondsappro"imatel' to the le$el of the foramen magnum.

The medulla oblongata is conical in shape, its broade"tremit' being directed superiorl'.

The central canal of the spinal cord continuesup!ard into the lo!er half of the medulla in theupper half of the medulla, it e"pands as the ca$it' ofthe fourth $entricle.

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*nterior /urface of Medulla

+blongata

Anterior median ssure

Pyramid

Decussation o the pyramids

Anterior external arcuate bers

Olives n the groo$e bet!een the p'ramid and the oli$e emerge

the rootlets of the hypoglossal nerve.

Posterior to the oli$es are the inerior cerebellarpeduncles.

n the groo$e bet!een the oli$e and the inferior cerebellarpeduncle emerge the roots of the glossopharyngeal andvagus nerves and the cranial roots o the accessorynervs

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Posterior /urface of Medulla

+blongata

/uperior half forms the lo!er part ofthe 0oor of the fourth $entricle.

nferior half is continuous !ith theposterior aspect of the spinal cordand possesses a posterior mediansulcus.

racile tubercle

1uneate tubercle

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ross *ppearance of thePons

The pons is anterior to thecerebellum and connectsthemedulla oblongata to the midbrain. t

is about inch (&.2 cm) long ando!es its name to the appearancepresented on the anterior surface,

!hich is that of a bridgeconnectingthe right and left cerebellarhemispheres

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*nterior /urface of Pons

1on$e" from side to side

Trans$erse -bers that con$erge on each side to form themiddle cerebellar peduncle.

!asilar groove, !hich lodges the basilar arter'.

+n the anterolateral surace of the pons, thetrigeminal ner$e emerges on eachside(smallermedialmotor)(largelateralsensor')

n the groove bet"een the pons and the medullaoblongata# there emerge, from medial to lateral

*bducent

4acial

5estibulocochlear ner$es

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posterior surface of thepons

6idden

t forms the upper half of the 0oor of the fourth$entricle and is triangular in shape.

/uperior cerebellar peduncles Median sulcus

Medial eminence

/ulcus limitans

4acial colliculus

/ubstantia ferruginea

*rea $estibuli

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ross *ppearance of theMidbrain

The midbrain measures about 7.8 inch(& cm) in length and connects the ponsand cerebellum !ith the forebrain.

ts long a"is inclines anteriorl' as itascends through the opening in thetentorium cerebelli.

The midbrain is tra$ersed b' a narro!channel, the cerebral a9ueduct, !hichis -lled !ith cerebrospinal 0uid

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Posterior /urface ofMidbrain

4our colliculi (corpora 9uadrigemina)

/uperior colliculi are centers for $isualre0e"es

nferior colliculi are lo!er auditor' centers n the midline belo! the inferior colliculi,

the trochlear ner$es emerge.

These are small:diameter ner$es that !indaround the lateral aspect of the midbrain toenter the lateral !all of the ca$ernous sinus

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Lateral *spect of theMidbrain

The superior and inerior brachiaascend in an anterolateral direction.

The superior brachium passesfrom the superior colliculus to thelateral geniculate body and theoptic tract.

The inerior brachium connects theinferior colliculus to the medialgeniculate body

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The *nterior *spect +f The Midbrain

nterpeduncular fossa

1rus cerebri

Posterior perforated substance The oculomotor nerve emerges

from a groo$e on the medial side ofthe crus cerebri and passes for!ardin the lateral !all of the ca$ernoussinus.

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