Dr. Ahmed Fathalla Ibrahim
BRAINPROSENCEPHALON (FOREBRAIN):1. TELENCEPHALON: Cerebral hemispheres (cavities:
2 lateral ventricles)2. DIENCEPHALON: thalamus, hypothalamus,
epithalamus & subthalamus (cavity: 3rd ventricle)MESENCEPHALON (MIDBRAIN)• Cavity: cerebral aqueductRHOMBENCEPHALON (HINDBRAIN)1. METENCEPHALON: Pons & cerebellum2. MYELENCEPHALON: Medulla• Cavity: 4th ventricle
BRAIN STEMCOMPONENTS: 1. Midbrain: most rostal part2. Pons3. Medulla oblongata: most caudal partEMBRYOLOGICAL ORIGIN:• Midbrain: arises from mesencephalon• Pons & medulla: arise from
rhombencephalon or hindbrain (together with cerebellum)
BRAIN STEMSITE: • It lies on the basilar part of occipital bone
(clivus)• The midbrain is continuous rostrally with
diencephalon of forebrain• The pons is continous rostrally with
midbrain & caudally with medulla• The medulla is continuous caudally with
spinal cord at the margin of foramen magnum
BRAIN STEM
CONNECTION TO CEREBELLUM:1. Midbrain: by superior cerebellar
peduncle2. Pons: by middle cerebellar peduncle3. Medulla oblongata: by inferior
cerebellar peduncle
BRAIN STEMIMPORTANCE:1. Pathway of tracts between cerebral cortex &
spinal cord2. Site of origin of nuclei of cranial nerves
(from 3rd to 12th)3. Site of emergence of cranial nerves (from 3rd
to 12th)4. Contains groups of nuclei & related fibers
known as reticular formation responsible for: control of level of consciousness, perception of pain, regulation of cardiovascular & respiratory systems
BRAIN STEMVENTRAL SURFACE
BRAIN STEMVENTRAL SURFACE
BRAIN STEMVENTRAL SURFACE
MEDULLA:• Ventral median fissure: 1. It divides the medulla into 2 halves 2. Its lower part is masked by decussation of
pyramidal (corticospinal) fibers• Pyramid: 1. It lies on either side of ventral median
fissure 2. It is an elevation produced by corticospinal
tract
BRAIN STEMVENTRAL SURFACE
MEDULLA:• Olive: 1. It lies lateral to the pyramid & separated from it
by the ventrolateral sulcus2. It is an elevation produced by inferior olivary
nucleusNerves emerging from Medulla (4 nerves):1. Hypoglossal (12th): between pyramid & olive2. Glossopharyngeal (9th), vagus (10th) & cranial
part of accessory (11th): dorsolateral to olive (from above downwards)
BRAIN STEMVENTRAL SURFACE
BRAIN STEMVENTRAL SURFACE
PONS:• Basilar sulcus:1. It divides the pons into 2 halves2. It is occupied by basilar artery• Transverse pontine (pontocerebellar)
fibers:1. Originate from pontine nuclei2. Cross midline & pass through contralateral
middle cerebellar peduncle to enter the opposite cerebellar hemisphere
BRAIN STEMVENTRAL SURFACE
PONS:Nerves emerging from Pons (4 nerves):1. Trigeminal (5th): from the middle of ventrolateral
aspect of pons, as 2 roots: a small medial motor root & a large lateral sensory root
2. Abducent (6th): at junction between pons & pyramid
3. Facial (7th) & vestibulocochlear (8th): at cerebellopontine angle (junction between medulla, pons & cerebellum). Both nerves emerge as 2 roots: from medial to lateral: motor root of 7th , sensory root of 7th , vestibular part of 8th & cochlear part of 8th
BRAIN STEMVENTRAL SURFACE
BRAIN STEMVENTRAL SURFACE
MIDBRAIN:• It is formed of a large column of
descending fibers (crus cerebri or basis pedunculi), on either side
• The 2 crura cerebri are separated by a depression (interpeduncular fossa)
Nerve emerging from Midbrain (one):• Occulomotor (3rd): from medial aspect
of crus cerebri
BRAIN STEMDORSAL SURFACE
BRAIN STEMDORSAL SURFACE
MEDULLA• Divided into 2 portions:1. Caudal 2/3: Closed Medulla:2. Rostral 1/3: Open Medulla
BRAIN STEMDORSAL SURFACE
CLOSED MEDULLA• Contains the rostral continuation of central canal• Composed of:1. Dorsal median sulcus: divdes the closed medulla into 2
halves2. Fasciculus gracilis: on either side of dorsal median
sulcus3. Gracile tubercle: an elevation produced at the upper part
of fasciculus gracilis, marks the site of gracile nucleus4. Fasciculus cuneatus: on either side of fasciculus
gracilis5. Cuneate tubercle: an elevation produced at the upper
part of fasciculus cuneatus, marks the site of cuneate nucleus
BRAIN STEMDORSAL SURFACE
OPEN MEDULLA• Forms the lower part of floor of 4th ventricle• On either side, an inverted V-shaped sulcus
divides the area into 3 parts (from medial to lateral):
1. Hypoglossal triangle: overlies hypoglossal nucleus
2. Vagal triangle: overlies dorsal vagal nucleus
3. Vestibular area: overlies vestibular nuclei
BRAIN STEMDORSAL SURFACE
BRAIN STEMDORSAL SURFACE
PONS• Forms the upper part of floor of 4th ventricle• Separated from the medulla by an imaginary
line passing between the caudal margins of middle cerebellar peduncle
• On either side, a sulcus divides the area into 2 parts (from medial to lateral):
1. Medial eminence: overlies abducent nucleus
2. Vestibular area: overlies vestibular nuclei
BRAIN STEMDORSAL SURFACE
BRAIN STEMDORSAL SURFACE
MIDBRAIN:• Marked by 4 elevations:1. Two superior colliculi: concerned with
visual reflexes2. Two inferior colliculi: forms part of
auditory pathwayNerve emerging from Midbrain (one):• Trochlear (4th): just caudal to inferior
colliculus (The only cranial nerve emerging from dorsal surface of brain stem)
FOURTH VENTRICLE
FOURTH VENTRICLE
FOURTH VENTRICLE
FOURTH VENTRICLE
FOURTH VENTRICLE• Cavity of hindbrain• Diamond (rhomboid) in shape• Triangular in cross section• Communications:1. Rostrally: with cerebral acqueduct
(cavity of midbrain)2. Caudally with central canal (cavity of
spinal cord)• Lateral walls (boundaries): superior &
inferior cerebellar peduncles
FOURTH VENTRICLE• Roof:1. Upper part: superior cerebellar peduncle
& superior medullary velum (a layer of pia & ependyma bridging the space between the 2 peduncles)
2. Middle part: cerebellum3. Lower part: inferior medullary velum (a
layer of pia & ependyma), has a central defect that forms the median aperture of 4th ventricle
FOURTH VENTRICLE• Floor (rhomboid fossa): formed of:1. Whole dorsal surface of pons2. Open medulla (dorsal surface of rostral 1/3
medulla)• Apertures: provide communication
between 4th ventricle & subarachnoid space for circulation of CSF
1. One median aperture (Foramen of Magendi): in the roof of 4th ventricle
2. Two lateral apertures (Foramena of Luschka): at cerebellopontine angle