anatomy of midbrain & pons

Dr. Farah RezwanaHMO,Department of

Neurology,DMCH

DEVELOPMENTDEVELOPMENT

Pons:Pons: The pons develops from the anterior part of the metencephalon, but it also receives a cellular contribution from alar part of the myelencephalon.

Midbrain: Midbrain: The midbrain develops from mesencephalon. Cells within the midbrain multiply continually and be compressed to form cerebral aqueduct.

MidbrainMidbrainConnects the pons and cerebellum with the

forebrain.It is about 0.8 inch in lengthThe midbrain is traversed by a narrow

channel called cerebral aqueduct filled with CSF.

ANTERIOR SURFACEANTERIOR SURFACEAnteriorlyAnteriorly, it

presents two large bundles of fibers, one on each side of the midline, called crus crus cerebricerebri..

The oculomotor oculomotor nervenerve emerges from the medial aspect of the crus of the same side

The crus cerebri bounds the interpeduncular interpeduncular fossa fossa on either side.

POSTERIOR SURFACEPOSTERIOR SURFACE PosteriorlyPosteriorly, the midbrain

presents four rounded swellings called colliculi- colliculi- One SuperiorOne Superior and inferior inferior colliculi one on each side.

Each colliculus is laterally related to a ridge called brachium.brachium.o   Superior and inferior Superior and inferior brachium brachium arises from respective colliculio   Superior brachium connects the superior colliculus to lateral geniculate bodylateral geniculate bodyo   Inferior brachium connects the inferior colluculus to medial geniculate bodymedial geniculate bodyo   In the midline below the inferior colliculus, the trochlear nervetrochlear nerve emerges which then winds round the side of the midbrain to reach its ventral aspectventral aspect

Lateral view

The midbrain comprises two lateral halves called- Cerebral pedunclesCerebral peduncles; which is again divided into 1. anterior part- Crus cerebri 2. posterior part -Tegmentum by a pigmented band of gray matter, substantia nigrasubstantia nigra

The central narrow cavity is called the cerebral aqueduct or aqueduct of Sylvius, which connects the 3rd and 4th ventricles.

The tectum is the part of the midbrain posterior to the cerebral aqueduct; it has four small surface swellings referred to previously; these are two superior and two inferior colliculi.

TECTUM & TEGMENTUMTECTUM & TEGMENTUM

Transverse section at the Transverse section at the levellevel of of Superior Colliculi Superior Colliculi Superior colliculiSubstantia nigraOculomotor

nucleusRed nucleusMesencephalic

nucleus of trigeminal n.

Edgnger-westphal nucleus

TractsTractsMotorMotor

CorticospinalCorticonuclearTemporopontin

eFrontopontineMedial longitudinal fasciculasDecussation of rubrospinal

tract

SensorySensoryTrigeminalSpinalMedial

TransverseTransverse Section at the level Section at the level of Inferior Colliculiof Inferior Colliculi

Substantia nigra

Troclear nucleus

Mesencephalic nucleus of

trigeminal nerve

TractsTracts

MotorMotor Corticospinal Corticonuclear Temporopontine Frontopontine Medial

longitudinal fasciculas

SensorySensory Lateral Trigeminal Spinal Medial lemnisci Decussation of

superior cerebellar peduncles

Blood SupplyBlood Supply Artery –Artery –

posterior cerebral artery

superior cerebellar

artery basilar artery

Veins –Veins – Drained by

basal or great cerebral veins

PONSPONSIt is situated anteriorly to the cerebellum

measuring about 1 inch in length.Connects the medulla oblongata to the

midbrain.Its also connects two cerebellar hemispheres

and its name comes from this bridge like appearance.

Anterior surface of PonsAnterior surface of Pons Pons has a convex anterior surface marked

by transversely running fibers which laterally form a bundle called middle cerebellar peduncle.

Main Features:Main Features: The trigeminal nerve emerges from the anterior

surface at its junction with middle cerebellar peduncle.

Presents a basilar sulcus in the midline which lodges basilar artery

In the groove between Pons and the medulla oblongata, there emerge, from medial to lateral, abducent, facial and vestibulocochlear nerves.

Posterior SurfacePosterior Surface Posterior surface

contains median sulcus which is bounded by madial eminence on both sides.

 Inferior end of medial eminence is slightly expanded to form facialfacial colliculuscolliculus, which is produced by facial nerve root.

The upper end of sulcus limitans presents a bluish-gray coloration called substantia substantia ferruginosaferruginosa..

Area vestibule liesArea vestibule lies lateral to sulcus limitans.

Structure of Pons Structure of Pons

Posterior part- Tegmentum

Anterior part- Basis pontis traversed by running fibers of Trapezoid body.

Transverse Section Through the Transverse Section Through the Cranial PartCranial Part

Motor nucleus of trigeminal n.Sensory nucleus of trigeminal n.Pontine nucleiTrapezoid nuclei

Tracts Tracts MotorMotor

CorticospinalCorticonuclearTransverse

pontine fibersMedial

longitudinal fasciculas

SensorySensoryLateralSpinalMedial

lemnisci

TransverseTransverse section through the section through the CaudalCaudal part part

Facial nucleusAbducent nucleusMedial vestibular nucleusSpinal nucleus of trigeminal nervePontine nucleiTrapezoid nuclei

TractsTracts MotorMotor

CorticospinalCorticonuclearTransverse

pontine fibersMedial

longitudinal fasciculas

SensorySensorySpinal tract of

trigemial nerveLateral Medial lemnisci

Blood SupplyBlood Supply

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