Anatomy of the brainstem

Question 1

midbrain = (travel) + the 2 parts it’s divided into: (slide 34-35 for pic)

Answer 1

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

Question 2

midbrain = (size)

Answer 2

smallest part of the cerebral aqueduct

Question 3

cerebellum = (connection)

Answer 3

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

Question 4

4th ventricle = (size) in a junction

Answer 4

the widest at the ponto-medullary junction

Question 5

pons = (size) in brainstem:

Answer 5

the largest part of the brainstem

Question 6

optic tract (location):

Answer 6

around the superior border of the midbrain

Question 7

what do we find inf to colliculi?

Answer 7

trochlear nerve that emerges before sweeping across the anterior surface
= only nerve to have a dorsal exit from the brainstem

Question 8

cerebral peduncles (separations):

Answer 8

• separated anteriorly by the interpeduncular fossa
• extend from the hemispheres to converge as they meet the pons

Question 9

Nerves originating from the ventral surface of the pons:

Answer 9

• 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)

Question 10

In cerebellopontine angle: (what do we find)

Answer 10

• cerebellar focculus
• choroid plexus
• CN VII + CN VIII
• surrounding the lateral aperture of the 4th ventricle: the foramen of Lushka

Question 11

olive (how is it made + function):

Answer 11

• produced by inferior olivary nucleus
• essential to the development of fine motor control and coordination

Question 12

the running tracts of the brainstem (+ their functions):

Answer 12

• 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)

Question 13

the midbrain = (size):

Answer 13

the most superior + widest part of the brainstem

Question 14

the medulla oblongata (size):

Answer 14

most distal + middle child

Question 15

junction of pons + medulla + cerebellum =

Answer 15

cerebellopontine

Question 16

nerves emerging from medulla:

Answer 16

• 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

Question 17

emergence of cranial nerves:

Answer 17

❖ 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)

Question 18

brainstem = formed by:

Answer 18

➢the myelencephalon (fifth vesicle)
➢the metencephalon (fourth
vesicle)
➢the mesencephalon (third
vesicle).

Question 19

brainstem location: (truc de fossa et tt)

Answer 19

It lies at the cerebral posterior fossa, on the basilar part of occipital bone (clivus) under the tentorium of the cerebellum

Question 20

brainstem relationships:

Answer 20

➢ Above: diencephalon by transverse
fissure of BICHAT
➢ backward: cerebellum by cerebellar
peduncles
➢ Downward: spinal cord by foramen of magnum

Question 21

tectum:

Answer 21

• 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.

Question 22

the cerebral peduncles: (limits + separation + the nerves related (chemin)):

Answer 22

• 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.

Question 23

function of the pons:

Answer 23

group of nerves that function
as a connection between the cerebrum and cerebellum

Question 24

anterior surface of the pons: (what is the bulging formed by + basilar groove and its artery + pontomedullary junction):

Answer 24

• 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.

Question 25

cranial nerves originating from the ventral surface of the pons:

Answer 25

* 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.

Question 26

Posterior surface of the pons: (what separates the cerebellum and the pons + what would be revealed if you removed the cerebellum)

Answer 26

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

Question 27

posterior surface of the midbrain:

Answer 27

* 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).

Question 28

nerves emerging from medulla:

Answer 28

➢Hypoglossal(12th): from sulcus between pyramid & olive ➢Glossopharyngeal(9th) ➢vagus(10th) ➢cranial part of accessory(11th): from sulcusdorsolateralto olive (from above downwards)

Question 29

in the brainstem:

Answer 29

* Ependymal cavity : ➢ Fourth ventricle ➢ Sylvius Aqueduct * The gray matter: ➢ Nuclei of origin of cranial nerves ➢ Reticular formation

Question 30

The Reticular formation:

Answer 30

* 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.

Question 31

descending motor pathway tracts:

Answer 31

- corticospinal and corticobulbar tracts - It controls the voluntary skeletal muscle activity of the body and face

Question 32

ascending tracts:

Answer 32

➢Conscious tracts : comprised of the dorsal column-medial lemniscal pathway and the anterolateral (spinothalamic) system. ➢Unconscious tracts : comprised of the spinocerebellar tracts.

Question 33

fourth ventricle: (relationships):

Answer 33

* 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.

Question 34

vascularisation of the brainstem:

Answer 34

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.

Question 35

Functions of the brainstem: (origin of nuclei of cranial nerves + control)

Answer 35

* 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

Question 36

brainstem function:

Answer 36

breathing, consciousness, blood pressure, heart rate, and sleep

Question 37

Ten of the twelve?

Answer 37

cranial nerves arise from their cranial nerve nuclei in the brainstem.

Question 38

what is the cerebral aqueduct

Answer 38

a narrow channel connecting the third and fourth brain ventricles

Question 39

what nerve emerges inferior to the colliculi before sweeping to the anterior face:

Answer 39

the trochlear nerve (IV)

Question 40

which nerve exits from the cerebral peduncles and which one surrounds the superior border part of the midbrain?

Answer 40

The oculomotor nerve (CNIII) is seen exiting from between the peduncles while the optic tract runs around the superior border of the midbrain

Question 41

what surrounds the foramen of Luscshka at the cerebellopontine junction?

Answer 41

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).

Question 42

what are the medulla ventral surface, the pyramid and olive (+ where they lie):

Answer 42

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).

Question 43

small, narrow tube connecting the third and fourth ventricles of the brain:

Answer 43

cerebral sylvius aqueduct