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POSITION & SHAPEPOSITION & SHAPEIt is It is stalk likestalk like in shape . in shape .

It connects the narrow It connects the narrow spinal cord with the spinal cord with the expanded fore brainexpanded fore brain..

It occupies the It occupies the posterior cranial fossa posterior cranial fossa of the skullof the skull against the against the basal portion of the basal portion of the occipital boneoccipital bone..

It is largely It is largely covered by covered by the cerebellumthe cerebellum..

PARTSPARTS

It is made up of: It is made up of: Medulla Medulla oblongataoblongata..

PonsPons..MidbrainMidbrain..

FUNCTIONSFUNCTIONS((11)) A conduit for the A conduit for the

ascending and ascending and descending tractsdescending tracts connecting the connecting the spinal cord to the spinal cord to the higher centers in higher centers in the forebrainthe forebrain . .

((22 ) )It contains the It contains the important important cranial cranial nerve nuclei (111-nerve nuclei (111-

x11)x11)..

FUNCTIONSFUNCTIONS((33)) It contains It contains

important reflex important reflex centerscenters that control that control respiration and respiration and cardiovascular cardiovascular systemssystems . .

((44)) It controls over It controls over the the level of level of consciousness consciousness through the through the reticularreticular formationformation. .

CLINICAL CLINICAL NOMENCLATURENOMENCLATURE

It is named It is named BULBBULB..The entering fibers The entering fibers

are are Cortico BulbarCortico Bulbar..The syndromes The syndromes

associated with the associated with the medulla are medulla are pseudo pseudo Bulbar palsy Bulbar palsy and and Bulbar palsyBulbar palsy..

VENTRAL ASPECT OF THE VENTRAL ASPECT OF THE MEDULLAMEDULLA

It is divided by It is divided by the ventral the ventral median fissure median fissure into two halvesinto two halves . .

Each half has the Each half has the following following featuresfeatures::

PYRAMIDPYRAMIDIt is a longitudinal It is a longitudinal

elevation along the side elevation along the side of the fissureof the fissure..

The pyramids are The pyramids are composed of bundles of composed of bundles of nerve fibers nerve fibers ((Corticospinal)Corticospinal) that that originate from large originate from large nerve cells in the nerve cells in the cerebral cortexcerebral cortex..

PYRAMIDPYRAMIDThe pyramids taper The pyramids taper

inferiorly where the inferiorly where the majority of the majority of the descending fibers (75-descending fibers (75-90%) cross over to 90%) cross over to the opposite side the opposite side forming the forming the Decussation of the Decussation of the pyramidspyramids..

This partially obscures This partially obscures the ventral fissurethe ventral fissure..

OLIVEOLIVEIt is an oval elevation It is an oval elevation lateral to the upper lateral to the upper part of the pyramidpart of the pyramid . .

It is produced by the It is produced by the underlying underlying Inferior Inferior Olivary Nucleus (Olivary Nucleus (which which is connected to the is connected to the cerebellum)cerebellum) It is important in the It is important in the control of movementcontrol of movement..

ROOTLETS OF CRANIAL ROOTLETS OF CRANIAL NERVESNERVES

A. A. hypoglossal hypoglossal (12(12TH)TH) nerve. It emerges nerve. It emerges between the pyramid between the pyramid and oliveand olive..

B. B. GlossopharyngealGlossopharyngeal,, VagusVagus and cranial part and cranial part of the of the AcessoryAcessory (9, 10 (9, 10 and11and11TH)TH) nerves nerves . .

They emerge in the They emerge in the groove between the groove between the olive and the inferior olive and the inferior cerebellar pedunclecerebellar peduncle..

PONSPONSIt has a median groove It has a median groove

((basilar sulcusbasilar sulcus) which ) which lodges the basilar arterylodges the basilar artery..

Its anterior surface is Its anterior surface is convex from side to side convex from side to side and shows many and shows many transverse transverse PontocerebellarPontocerebellar fibers which are collected fibers which are collected laterally to form the laterally to form the Middle Middle Cerebellar PedunclesCerebellar Peduncles..

PONSPONSFourFour cranial nervescranial nerves are are

attached to its anterior attached to its anterior surfacesurface..

11 . .TrigeminalTrigeminal (5 (5thth) nerve) nerve : :It is attached to the side It is attached to the side

of the pons near its of the pons near its upper border by two upper border by two rootsroots. .

A large sensory and a A large sensory and a small motor. The motor small motor. The motor root is located antero root is located antero medial to the sensory medial to the sensory rootroot..

PONSPONS22 . .AbducentAbducent (6(6thth) nerve) nerve: :

It is located in the It is located in the groove between the groove between the lower border of the lower border of the pons and the pyramidpons and the pyramid..

PONSPONS33.. Facial Facial (7(7thth) nerve) nerve: :

It is found between the It is found between the lower border of the pons lower border of the pons and the inferior and the inferior cerebellar pedunclecerebellar peduncle . .

44 . .Vestibulo cochlearVestibulo cochlear (8 (8thth) ) nervenerve : :

It is lateral to the facial . It is lateral to the facial . The vestibular nerve is The vestibular nerve is anterior and the anterior and the cochlear nerve is cochlear nerve is posteriorposterior..

MID BRAINMID BRAINIt is formed by theIt is formed by the

MassiveMassive Basis Basis PedunculiPedunculi (Crura (Crura Cerebri)Cerebri)..

The crura are formed The crura are formed by the descending by the descending CorticobulbarCorticobulbar and and CorticospinalCorticospinal fibers fibers..

The cerebral peduncles The cerebral peduncles are separated by the are separated by the Interpeduncular FossaInterpeduncular Fossa..

InterpeduncularInterpeduncular FossaFossa..BoundariesBoundaries : :

InferiorlyInferiorly :pons :pons..AnteriorlyAnteriorly :optic :optic

chiasmachiasma . .Laterally: Laterally: optic optic

tractstracts. . Posterolaterally:Posterolaterally:

cerebral pedunclescerebral peduncles..

MID BRAINMID BRAINOculo motorOculo motor (3 (3rdrd) )

nervenerve : : Emerges through Emerges through

a groove at the a groove at the medial sides of medial sides of the cerebral the cerebral pedunclespeduncles..

DORSAL SURFACE OFDORSAL SURFACE OF THE THE MEDULLAMEDULLA

Closed medullaClosed medulla It is the It is the

continuation of the continuation of the posterior surface posterior surface of the spinal cordof the spinal cord..

It is divided by the It is divided by the posterior median posterior median sulcus into two sulcus into two halveshalves . .

Each half has the Each half has the following featuresfollowing features::

LOWER LOWER MEDULLAMEDULLAA.A. GRACILE tractGRACILE tract : :It is a longitudinal It is a longitudinal

column on both column on both sides of the sides of the median sulcusmedian sulcus . .

It expands It expands superiorly where superiorly where it ends in the it ends in the Gracile TubercleGracile Tubercle (produced by the (produced by the Gracile NucleusGracile Nucleus))..

LOWER LOWER MEDULLAMEDULLAB. B. CUNATE tract and CUNATE tract and

tubercletubercle: : Are lateral to the Are lateral to the

gracile tract and gracile tract and tubercle tubercle respectivelyrespectively . .

OPEN MEDULLAOPEN MEDULLAIt forms the lower It forms the lower

third of the floor of third of the floor of the fourth ventriclethe fourth ventricle . .

It is divided by the It is divided by the median sulcus into median sulcus into two halvestwo halves..

Each half has an Each half has an inverted (v) shaped inverted (v) shaped depression (depression (Inferior Inferior Fovea)Fovea) . .

It separates the It separates the motor motor from the from the sensory sensory nucleinuclei

OPEN MEDULLAOPEN MEDULLAMedialMedial : the : the

hypoglossal nucleushypoglossal nucleus..LateralLateral : the vestibular : the vestibular

nerve nucleusnerve nucleus..At the fovea : At the fovea : the the

nuclear complex of the nuclear complex of the glossopharyngeal and glossopharyngeal and vagus nervesvagus nerves..

PONSPONSIt is hidden by the It is hidden by the

cerebellumcerebellum..It forms the upper two It forms the upper two

thirds of the floor of the thirds of the floor of the fourth ventriclefourth ventricle..

It is It is widest at the widest at the pontomedullary junctionpontomedullary junction..

At this point, the lateral At this point, the lateral aperture (aperture (foramen offoramen of LuschkaLuschka) is found to allow ) is found to allow passage of CSF from the passage of CSF from the fourth ventricle to the fourth ventricle to the subarachnoid space subarachnoid space around the brainaround the brain..

PONSPONSThe posterior surface is The posterior surface is

limited laterally by the limited laterally by the superior cerebellar superior cerebellar peduncles and divided into peduncles and divided into symmetrical halves by the symmetrical halves by the medianmedian sulcussulcus.Lateral to the .Lateral to the sulcus is an elongated sulcus is an elongated elevation (elevation (Medial EminenceMedial Eminence)) . .

Its inferior end is expanded Its inferior end is expanded to form the to form the FaFacial Colliculuscial Colliculus produced by the fibers of produced by the fibers of the the facial nervefacial nerve winding winding around the around the nucleusnucleus of the of the abducent nerveabducent nerve..

PONSPONSLateral to the Lateral to the

medial eminence medial eminence is the is the vestibular vestibular areaarea produced produced by the by the underlying underlying vestibular nucleivestibular nuclei..

MID BRAINMID BRAINIt has fourIt has four ColliculiColliculi

((Corpora Corpora QuadregiminaQuadregimina) which ) which are rounded eminences are rounded eminences that are divided into that are divided into superior and inferior superior and inferior pairspairs..

Superior Colliculi:Superior Colliculi: centers for visual centers for visual reflexesreflexes..

Inferior Colliculi:Inferior Colliculi: lower lower auditory centersauditory centers . .

MID BRAINMID BRAINTrochlearTrochlear nerve nerve (the (the

only cranial nerve that only cranial nerve that can be identified in the can be identified in the dorsal aspect)dorsal aspect)

It emerges in the It emerges in the midline immediately midline immediately caudal to the inferior caudal to the inferior colliculicolliculi..

The The cerebral aqueductcerebral aqueduct traverses through the traverses through the length of the mid length of the mid brainbrain..

CEREBELLAR PEDUNCLESCEREBELLAR PEDUNCLESThe The superior superior andand

inferior inferior peduncles peduncles appear on the dorsal appear on the dorsal aspect of the brain aspect of the brain stemstem..

They form the They form the lateral lateral walls of the upper part walls of the upper part of the floor of the 4of the floor of the 4thth ventricleventricle..

They connect the mid They connect the mid brain and medulla to brain and medulla to the cerebellum the cerebellum respectivelyrespectively . .

LATERAL ASPECT OF THE LATERAL ASPECT OF THE BRAIN STEMBRAIN STEM

The middle The middle cerebellar cerebellar pedunclepeduncle can be can be distinguished on distinguished on the ventral, the ventral, dorsal and dorsal and lateral aspects of lateral aspects of the brain stemthe brain stem..