Brainstem
 COMPONENTS:
 Midbrain: most rostal part
 Pons
 Medulla oblongata: most
caudal part
 EMBRYOLOGICAL ORIGIN:
 Midbrain: arises from
mesencephalon
 Pons & medulla: arise from
rhombencephalon or
hindbrain (together with
cerebellum)
Brainstem
 COMPONENTS:
 Midbrain: most rostal part
 Pons
 Medulla oblongata: most
caudal part
 EMBRYOLOGICAL ORIGIN:
 Midbrain: arises from
mesencephalon
 Pons & medulla: arise from
rhombencephalon or
hindbrain (together with
cerebellum)
Brainstem
 COMPONENTS:
 Midbrain: most rostal part
 Pons
 Medulla oblongata: most
caudal part
 EMBRYOLOGICAL ORIGIN:
 Midbrain: arises from
mesencephalon
 Pons & medulla: arise from
rhombencephalon or
hindbrain (together with
cerebellum)
Anterior view
Brainstem
 COMPONENTS:
 Midbrain: most rostal part
 Pons
 Medulla oblongata: most
caudal part
 EMBRYOLOGICAL ORIGIN:
 Midbrain: arises from
mesencephalon
 Pons & medulla: arise from
rhombencephalon or
hindbrain (together with
cerebellum)
Posterior view
Brainstem
Brainstem
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.
Brainstem
 CONNECTION TO CEREBELLUM:
 Midbrain: by superior cerebellar
peduncle
 Pons: by middle cerebellar
peduncle
 Medulla oblongata: by inferior
cerebellar peduncle
Brainstem
 IMPORTANCE:
 Pathway of tracts between cerebral
cortex & spinal cord
 Site of origin of nuclei of cranial
nerves (from 3rd to 12th)
 Site of emergence of cranial nerves
(from 3rd to 12th)
 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
Brainstem
 Ventral surface
•
MEDULLA:
Ventral median fissure:
•
• It divides the medulla into 2
halves.
• Its lower part is masked by
decussation of pyramidal
(corticospinal) fibers.
•
Pyramid:
• It lies on either side of ventral
median fissure.
• It is an elevation produced by
corticospinal tract.
Anterior view
Brainstem- Ventral Surface of Medulla
• MEDULLA:
• Olive:
• It lies lateral to the pyramid &
separated from it by the ventrolateral
sulcus.
• It is an elevation produced by inferior
olivary nucleus.
• Nerves emerging from Medulla (4
nerves):
• Hypoglossal (12 ): between
th
pyramid & olive
• Glossopharyngeal (9
th),
vagus
(10th) & cranial part of accessory
(11th): dorsolateral to olive (from
above downwards)
Brainstem - Ventral Surface of Pons
PONS:
•
•
Basilar sulcus
It divides the pons into 2 halves.
•
• It is occupied by basilar artery.
Transverse pontine (pontocerebellar) fibers:
Originate from pontine nuclei.
•
• Cross midline & pass through contralateral
middle cerebellar peduncle to enter the
opposite cerebellar hemisphere.
Brainstem - Ventral Surface of Pons
PONS:
•
Nerves emerging from Pons (4 nerves):
Trigeminal (5th): from the middle of
ventrolateral aspect of pons, as 2 roots: a
small medial motor root & a large lateral
sensory root
•
• Abducent (6
th):
at junction between pons
& pyramid
• Facial (7
th)
& 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
Brainstem - Ventral Surface of Midbrain
• 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 (3
rd):
From medial
aspect of crus cerebri
Brainstem - Dorsal Surface of Medulla
• Divided into 2 parts:
• Caudal 2/3: Closed medulla
• Rostral 1/3: Open medulla
Brainstem - Dorsal Surface of Medulla
•
•
•
CLOSED MEDULLA
Contains the rostral continuation of central
canal.
Composed of:
•
•
•
•
•
Dorsal median sulcus: divides 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.
Brainstem - Dorsal Surface of Medulla
• OPEN MEDULLA
• Forms the lower part of floor of 4
th
ventricle.
• On either side, an inverted V-shaped
sulcus divides the area into 3 parts
(from medial to lateral):
• Hypoglossal triangle: overlies
hypoglossal nucleus
• Vagal triangle: overlies dorsal
vagal nucleus
• Vestibular area: overlies
vestibular nuclei
Brainstem - Dorsal Surface of Medulla
• PONS
• Forms the upper part of floor of 4
th
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):
Medial eminence: overlies
abducent nucleus.
•
• Vestibular area: overlies
vestibular nuclei.
Brainstem - Dorsal Surface of Medulla
• MIDBRAIN:
• Marked by 4 elevations:
• Two superior colliculi:
concerned with visual reflexes.
• Two inferior colliculi: forms
part of auditory pathway.
• Nerve emerging from midbrain
(one):
• Trochlear
(4 ): just caudal to
inferior colliculus (the only
th
cranial nerve emerging from
dorsal surface of brain stem)
Fourth Ventricle
Fourth Ventricle
•
•
•
•
•
Cavity of hindbrain
Diamond (rhomboid) in shape
Triangular in cross section
Communications:
Rostrally: with cerebral acqueduct
(cavity of midbrain)
Caudally with central canal (cavity of
spinal cord)
•
•
Lateral walls (boundaries): superior &
inferior cerebellar peduncles
Fourth Ventricle
•
Roof:
Upper part: superior cerebellar
peduncle & superior medullary
velum (a layer of pia & ependyma
bridging the space between the 2
peduncles)
•
• Middle part: cerebellum
• 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:
•
•
•
Whole dorsal surface of pons
Open medulla (dorsal surface of rostral
1/3 medulla)
Apertures: provide communication
between 4th ventricle & subarachnoid
space for circulation of CSF
• One median aperture (Foramen of
Magendi): in the roof of 4th ventricle
• Two lateral apertures (Foramena of
Luschka): at cerebellopontine angle
Fourth Ventricle
Brainstem - Ventral Surface
Brainstem - Ventral Surface
Brainstem - Medulla
Cross-section through the medulla at the level of the sensory decussation.
Brainstem - Medulla
Cross-section through the medulla at the level of the caudal part of
the 4th ventricle.
Brainstem - Pons
The pons: level of the right VI nerve nucleus and the intrapontine course of
the facial nerve and, on the left, of the nuclei of V.
Brainstem - Midbrain
The midbrain: level of the inferior colliculus and decussation of the
superior cerebellar peduncle.
Brainstem - Midbrain
The midbrain: level of the superior colliculus and the red nucleus.
Lamina tecti
(quadrigemina)
Brainstem - Dorsal Surface of Medulla