Anatomy of the brainstem Flashcards
midbrain = (travel) + the 2 parts it’s divided into: (slide 34-35 for pic)
travels through the opening in tentorium (foramen of BICHAT)
* It can be divided into two main parts:
➢Tectum: located posterior to the cerebral
aqueduct
➢Paired cerebral peduncles: located
anteriorly and laterally
midbrain = (size)
smallest part of the cerebral aqueduct
cerebellum = (connection)
connected with brainstem by 3 peduncles (inferior, medial, superior)
➢Superior peduncle
connects midbrain with
cerebellum
➢Middle peduncle connects
pons with cerebellum
➢ Inferior peduncle
connects medulla oblongata with cerebellum
4th ventricle = (size) in a junction
the widest at the ponto-medullary junction
pons = (size) in brainstem:
the largest part of the brainstem
optic tract (location):
around the superior border of the midbrain
what do we find inf to colliculi?
trochlear nerve that emerges before sweeping across the anterior surface
= only nerve to have a dorsal exit from the brainstem
cerebral peduncles (separations):
- separated anteriorly by the interpeduncular fossa
- extend from the hemispheres to converge as they meet the pons
Nerves originating from the ventral surface of the pons:
- CN V (lateral mid pons) (tri-geminal)
- CN VI (pontomedullary junction) (abducens)
- CN VII (cerebellopontine + lateral aspect of pontomedullary junction) (facial)
- CN VIII (vestibulochlear nerve)
In cerebellopontine angle: (what do we find)
- cerebellar focculus
- choroid plexus
- CN VII + CN VIII
- surrounding the lateral aperture of the 4th ventricle: the foramen of Lushka
olive (how is it made + function):
- produced by inferior olivary nucleus
- essential to the development of fine motor control and coordination
the running tracts of the brainstem (+ their functions):
- Descending: motor pathway = corticospinal tract + corticobulbar tract = control of skeletal muscles of body + face
- Ascending: sensation (periphery to cortex) =
- conscious tracts: dorsal column-medial lemniscal (mediate tactile discrimination and proprioception) + anterolateral (spinothalamic) system (pain and temperature sensation)
- unconscious tracts: spinocerebellar tracts (carry unconscious proprioceptive information gleaned from muscle spindles, Golgi tendon organs, and joint capsules to the cerebellum)
the midbrain = (size):
the most superior + widest part of the brainstem
the medulla oblongata (size):
most distal + middle child
junction of pons + medulla + cerebellum =
cerebellopontine
nerves emerging from medulla:
- Hypoglossal (12th) = from sulcus between pyramid + olive
- Glossopharyngeal(9th)
- Vagus
- Cranial part of accessory(11th): from sulcusdorsolateralto olive (from above
downwards) - Ependymal cavity: 4th ventricle + sylvius aqueduct
emergence of cranial nerves:
❖ Anterior surface:
➢ At the level of the midbrain, between the cerebral peduncles, the:
* III the common occulomotor nerve (ocular motor)
➢ At the level of pons: trigerminal nerve V
➢ At the level of the bulbopontine groove, we have a series of nerves, from inside to outside:
* VI abducens, nerve VII the facial nerve ,VII bis Wrisberg intermediate
* VIII cochleo-vestibular
➢ at the level of the Ant collateral groove opposite the bulbar olive: XII
❖ Lateral surface of the BR
➢ at the level of the posterior collateral
groove (The bundle of mixed nerves):
* IX the glossopharyngeal nerve
* X the vagus nerve
* XI the spinal accessory nerve
❖ Posterior surface:
➢ at midbrain: Nerve IV (pathetic nerve: the only one that emerges on the posterior surface of the
brainstem innervates the major oblique muscle of the eye: ensures upward gaze)
brainstem = formed by:
➢the myelencephalon (fifth vesicle)
➢the metencephalon (fourth
vesicle)
➢the mesencephalon (third
vesicle).
brainstem location: (truc de fossa et tt)
It lies at the cerebral posterior fossa, on the basilar part of occipital bone (clivus) under the tentorium of the cerebellum
brainstem relationships:
➢ Above: diencephalon by transverse
fissure of BICHAT
➢ backward: cerebellum by cerebellar
peduncles
➢ Downward: spinal cord by foramen of magnum
tectum:
- The tectum houses four rounded
prominences named colliculi which sit
directly inferior to the pineal gland. there are two superior and two inferior colliculi. - Extending laterally from each colliculi are the quadrigeminal brachium:
➢ Superior quadrigeminal brachium forms a pathway between the superior colliculus and the retina of the eye( vision).
➢ Inferior quadrigeminal brachium conveys
fibres from the lateral lemniscus and inferior colliculus to the medial geniculate body
(hearing). - Inferior to the colliculi, the trochlear
nerve (CN IV) emerges before sweeping
across to the anterior surface.
the cerebral peduncles: (limits + separation + the nerves related (chemin)):
- The paired cerebral peduncles extend
from the cerebral hemispheres to
converge as they meet the pons.
They are separated anteriorly in the
midline by the interpeduncular fossa. - The oculomotor nerve (CNIII) is seen
exiting from between the peduncles
while the optic tract runs around the
superior border of the midbrain.
function of the pons:
group of nerves that function
as a connection between the cerebrum and cerebellum
anterior surface of the pons: (what is the bulging formed by + basilar groove and its artery + pontomedullary junction):
- The anterior or ventral surface of the pons is marked by a bulging formed by the transverse pontocerebellar fibres.
It measures around 2.5 cm in adults. - The basilar groove demarcates the midline of the ventral surface and is where the basilar artery is located.
- The pontomedullary junction is an important anatomical landmark defined by the angle between the lower border of the pons and the superior border of the medulla.
cranial nerves originating from the ventral surface of the pons:
- Several cranial nerves originate from the ventral surface of the pons:
➢ Cranial nerve V: trigeminal – originates from the lateral aspect of mid pons
➢ Cranial nerve VI: abducens – originates from the pontomedullary junction, close to the midline
➢ Cranial nerve VII: facial – originates from the cerebellopontine angle, the more lateral aspect of the pontomedullary junction.
➢ Cranial nerve VIII: vestibulocochlear – originates laterally to the facial nerve.
Posterior surface of the pons: (what separates the cerebellum and the pons + what would be revealed if you removed the cerebellum)
The pons is intimately related to
the cerebellum and is connected
to it by the middle cerebellar peduncles. Removal of the
cerebellum will reveal the
underlying fourth ventricle
posterior surface of the midbrain:
- The floor of the fourth ventricle is composed of the dorsal
surface of the pons and the medulla. There are some
important anatomical landmarks here: - The medial eminence marks the midline of the floor.
- The facial colliculus is a bulging formed by the fibres of the
facial nerve looping around the abducens nucleus. - The stria medullaris of the fourth ventricle is a bundle of nerve fibres crossing transversely from the lateral aspect into the midline. They mark the posterior border between
the pons and the medulla. - The angle formed at the junction of the pons, medulla, and
cerebellum is another anatomical landmark and is named cerebellopontine angle. Here, the cerebellar flocculus, the ventricular choroid plexus and the
emerging CNs VII and VIII surround the lateral apertures of
the fourth ventricle (the foramen of Luschka).
nerves emerging from medulla:
➢Hypoglossal(12th): from sulcus between pyramid & olive
➢Glossopharyngeal(9th)
➢vagus(10th)
➢cranial part of accessory(11th): from sulcusdorsolateralto olive (from above
downwards)
in the brainstem:
- Ependymal cavity :
➢ Fourth ventricle
➢ Sylvius Aqueduct - The gray matter:
➢ Nuclei of origin of
cranial nerves
➢ Reticular formation
The Reticular formation:
- It is like a network extending from the spinal cord through the medulla, the pons, the midbrain, the subthalamus, hypothalamus and the thalamus
- serve as a major integration and relay center for many vital brain systems to coordinate functions necessary for survival: arousal, consciousness,
circadian rhythm, sleep-wake cycles, coordination of somatic motor movements, cardiovascular and
respiratory control, pain modulation, and habituation.
descending motor pathway tracts:
- corticospinal and corticobulbar tracts
- It controls the voluntary skeletal muscle activity of the body and face
ascending tracts:
➢Conscious tracts : comprised of the dorsal column-medial lemniscal pathway and the anterolateral (spinothalamic) system.
➢Unconscious tracts : comprised of the spinocerebellar tracts.
fourth ventricle: (relationships):
- The roof, located dorsally is formed by
the superior medullary velum and inferior medullary velum overlying the cerebellum. - The floor, located ventrally, is formed by the rhomboid fossa, a diamond-shaped depression on the dorsal surface of the pons and upper half of the medulla.
- The sidewalls are formed by the vela
and cerebellar peduncles. The peak of the fourth ventricle within the cerebellum is the fastigium and it underlies the fastigial nucleus. It is widest at the level of the pontomedullary junction. - The obex is the most caudal tip of the fourth ventricle.
- The fourth ventricle contains choroid plexus along its roof along the tela choroidea which may protrude out the median foramina of Magendi and 2 lateral foraminas of Luschka.
vascularisation of the brainstem:
The brainstem receives vascular
supply from the basilar artery and
its branches. The major vessels
are:
* Posterior cerebral artery and its
peduncular branch
* Superior cerebellar artery
* Posterior choroidal artery
* Interpeduncular branches of the
basilar artery.
Functions of the brainstem: (origin of nuclei of cranial nerves + control)
- Pathway of tracts between cerebral cortex & spinal cord (ascending and descending tracts).
- Site of emergence of cranial nerves (from 3rd to 12th).
- Contains groups of nuclei & related fibres known as reticular formation responsible for: control of
level of consciousness, perception of pain, regulation of cardiovascular& respiratorysystems
brainstem function:
breathing, consciousness, blood pressure, heart rate, and sleep
Ten of the twelve?
cranial nerves arise from their cranial nerve nuclei in the brainstem.
what is the cerebral aqueduct
a narrow channel connecting the third and fourth brain ventricles
what nerve emerges inferior to the colliculi before sweeping to the anterior face:
the trochlear nerve (IV)
which nerve exits from the cerebral peduncles and which one surrounds the superior border part of the midbrain?
The oculomotor nerve (CNIII) is seen
exiting from between the peduncles
while the optic tract runs around the
superior border of the midbrain
what surrounds the foramen of Luscshka at the cerebellopontine junction?
The angle formed at the junction of the pons, medulla, and
cerebellum is another anatomical landmark and is
named cerebellopontine angle. Here, the cerebellar flocculus, the ventricular choroid plexus and the emerging CNs VII and VIII surround the lateral apertures of the fourth ventricle (the foramen of Luschka).
what are the medulla ventral surface, the pyramid and olive (+ where they lie):
Medulla Ventral Surface:
➢Ventral median fissure:
➢Continuation of ventral median fissure of spinal cord.
➢Divides the medulla into 2 halves
➢Its lower part is marked by decussation of most of pyramidal(corticospinal) fibers (75%-
90%).
* Pyramid:
➢An elevation, lies on either (lateral)side of ventral median fissure
➢Produced by corticospinal tract.
* Olive:
➢An elevation, lies lateral to the pyramid.
➢Produced by inferior olivary nucleus
(important in control of movement).
small, narrow tube connecting the third and fourth ventricles of the brain:
cerebral sylvius aqueduct
