Dr. Ahmed Fathalla Ibrahim
BRAIN
PROSENCEPHALON (FOREBRAIN):
1. TELENCEPHALON: Cerebral hemispheres
(cavities: 2 lateral ventricles)
2. DIENCEPHALON: thalamus, hypothalamus,
epithalamus & subthalamus (cavity: 3rd
ventricle)
MESENCEPHALON (MIDBRAIN)
•
Cavity: cerebral aqueduct
RHOMBENCEPHALON (HINDBRAIN)
1. METENCEPHALON: Pons & cerebellum
2. MYELENCEPHALON: Medulla
• Cavity: 4th ventricle
BRAIN STEM
COMPONENTS:
1. Midbrain: most rostal part
2. Pons
3. Medulla oblongata: most caudal part
EMBRYOLOGICAL ORIGIN:
• Midbrain: arises from
mesencephalon
• Pons & medulla: arise from
rhombencephalon or hindbrain
(together with cerebellum)
BRAIN STEM
SITE:
• 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
peduncle
2. Pons: by middle cerebellar peduncle
3. Medulla oblongata: by inferior
cerebellar peduncle
BRAIN STEM
IMPORTANCE:
1. Pathway of tracts between cerebral
cortex & spinal cord
2. 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 STEM
VENTRAL SURFACE
BRAIN STEM
VENTRAL SURFACE
BRAIN STEM
VENTRAL 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 STEM
VENTRAL SURFACE
MEDULLA:
• Olive:
1. It lies lateral to the pyramid & separated
from it by the ventrolateral sulcus
2. It is an elevation produced by inferior
olivary nucleus
Nerves emerging from Medulla (4 nerves):
1. Hypoglossal (12th): between pyramid &
olive
2. Glossopharyngeal (9th), vagus (10th) &
cranial part of accessory (11th): dorsolateral
to olive (from above downwards)
BRAIN STEM
VENTRAL SURFACE
BRAIN STEM
VENTRAL SURFACE
PONS:
•
1.
2.
•
Basilar sulcus:
It divides the pons into 2 halves
It is occupied by basilar artery
Transverse pontine (pontocerebellar)
fibers:
1. Originate from pontine nuclei
2. Cross midline & pass through contralateral
middle cerebellar peduncle to enter the
opposite cerebellar hemisphere
BRAIN STEM
VENTRAL 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 STEM
VENTRAL SURFACE
BRAIN STEM
VENTRAL 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 STEM
DORSAL SURFACE
BRAIN STEM
DORSAL SURFACE
MEDULLA
• Divided into 2 portions:
1. Caudal 2/3: Closed Medulla:
2. Rostral 1/3: Open Medulla
BRAIN STEM
DORSAL SURFACE
CLOSED MEDULLA
•
•
1.
2.
3.
4.
5.
Contains the rostral continuation of central canal
Composed of:
Dorsal median sulcus: divdes the closed medulla
into 2 halves
Fasciculus gracilis: on either side of dorsal median
sulcus
Gracile tubercle: an elevation produced at the
upper part of fasciculus gracilis, marks the site of
gracile nucleus
Fasciculus cuneatus: on either side of fasciculus
gracilis
Cuneate tubercle: an elevation produced at the
upper part of fasciculus cuneatus, marks the site
of cuneate nucleus
BRAIN STEM
DORSAL 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 STEM
DORSAL SURFACE
BRAIN STEM
DORSAL 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 STEM
DORSAL SURFACE
BRAIN STEM
DORSAL SURFACE
MIDBRAIN:
• Marked by 4 elevations:
1. Two superior colliculi: concerned with
visual reflexes
2. Two inferior colliculi: forms part of
auditory pathway
Nerve 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
•
•
•
•
1.
Cavity of hindbrain
Diamond (rhomboid) in shape
Triangular in cross section
Communications:
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: cerebellum
3. 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 pons
2. 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