Neuroscience Week 5: The Medulla

Question 1

THE MEDULLA

Answer 1

From a clinician’s broad perspective, the medulla is the center for the most basic generators of life.

Question 2

THE MEDULLA Key features

Answer 2

• The medullary pyramids: contain descending motor fibers.
• The inferior olive: an important motor relay center.
• The gracile and cuneate nuclei: receive large, proprioceptive sensory fibers from the spinal cord.

Question 3

Medulla Key Clinical Stroke Correlation

Answer 3

• Wallenberg’s Syndrome -Dorsolateral Medullary Infarct
• Dejerine’s Syndrome - Medial Medullary Infarct

Question 4

Medulla General Anatomy

Answer 4

• There is a relatively small basis (compared to the pons, which has a large basis from the pontine nuclei and pontocerebellar tracts) and a large tegmentum, and no formal tectum.
• The basis comprises corticospinal tract fibers, which decussate at the cervico-medullary junction.
• They form the medullary pyramids.
• Importantly, the corticonuclear and corticopontine fibers synapse either above or at the level of the medulla.
• The only major cortical motor pathway to descend through the medulla is the corticospinal tract.

Question 5

THE INFERIOR OLIVE location

Answer 5

Lies in the anterior tegmentum.

Question 6

THE INFERIOR OLIVE contains

Answer 6

• It contains climbing fibers, which project to the contralateral dentate nucleus of the cerebellum as part of the triangle of Guillain-Mollaret.
• The dentate nucleus of the cerebellum projects back to the contralateral red nucleus, and then down to the inferior olive of origin via the central tegmental tract.
• The inferior olive (aka inferior olivary complex) comprises: the main inferior olivary nucleus and the accessory olivary nuclei.
• The inferior olive receives many different fiber pathways, including tracts from the spinal cord (from below) and from the red nucleus (from above).

Question 7

THE LARGE FIBER SENSORY NUCLEI location

Answer 7

In the dorsal medulla, medially, lies the gracile nucleus.
-It receives lower body sensory fibers from the gracile posterior column tract.

Then, laterally, lies the cuneate nucleus.
-It receives upper body sensory fibers from the cuneate posterior column tract.

In the lower medulla, internal arcuate fibers decussate from the gracile and cuneate nuclei to the opposite side of the medulla (called the great sensory decussation).
-The internal arcuate fibers form the medial lemniscus pathway in midline.

Lateral to the medial lemniscus, lies the anterior trigeminothalamic tract.

Question 8

Along the lateral wall of the medulla, lies the

Answer 8

spinothalamic tract (of the anterolateral system).

Question 9

Posterior trigeminothalamic tracts originate

Answer 9

and ascend from the principal sensory nucleus in the pons, so no posterior trigeminothalamic tract fibers are evident within the medulla.

Question 10

Lateral to the medial lemniscus, lies the

Answer 10

anterior trigeminothalamic tract.

Question 11

In the lower medulla, internal arcuate fibers decussate from the

Answer 11

• gracile and cuneate nuclei to the opposite side of the medulla (called the great sensory decussation).
• The internal arcuate fibers form the medial lemniscus pathway in midline.

Question 12

laterally from the dorsal medulla lies the

Answer 12

cuneate nucleus.
-It receives upper body sensory fibers from the cuneate posterior column tract.

Question 13

At the medullary level, the anterolateral system contains

Answer 13

many different ascending sensory pathways in addition to the spinothalamic fibers.

Question 14

Posterior to the spinothalamic tract, lies the

Answer 14

anterior and posterior spinocerebellar tracts.

Question 15

The rubrospinal tract provides

Answer 15

upper extremity flexion.

Question 16

In posterior midline, lies the

Answer 16

medial longitudinal fasciculus.

Question 17

Anterior to The rubrospinal tract lies the

Answer 17

tectospinal tract

Question 18

The antero-posterior and medial-lateral positions of these pathways remain

Answer 18

roughly unchanged throughout their course through the brainstem).

Question 19

The inferior cerebellar peduncle lies in the

Answer 19

medulla

Question 20

superior and middle cerebellar peduncles in the medulla

Answer 20

, but here we do not find the superior and middle cerebellar peduncles in the medulla, as we did in the pons.

Question 21

Along the anterior border of fourth ventricle, lies the

Answer 21

• area postrema
• Indicate that it is an important chemoreceptor trigger zone for vomiting, especially in obstructive hydrocephalus (or, less commonly, in a 4th ventricular tumor)

Question 22

In the ventral tegmentum, lies the

Answer 22

reticular formation. It serves numerous functions; the most notable one is wakefulness.

Question 23

The reticular formation divides into

Answer 23

• lateral, medial, and median zones. Indicate that the raphe nuclei populate the median zone. They are primarily serotinergic and are modulated by psychotropic medications.
• Next, let’s include the cranial nerve nuclei in an axial view of the medulla; they’re in opposite orientation of our prior radiographic diagram.

Question 24

CRANIAL NERVES

The motor nuclei

in the medulla

Answer 24

CN 12

CN 10 (the dorsal motor nucleus)

CN 9 (the inferior salivatory nucleus)

CNs 9 and 10 (nucleus ambiguous).

Question 25

CRANIAL NERVES

The sensory nuclei

in the medulla

Answer 25

CNs 7, 9, and 10 (the solitary tract nucleus)

CN 8

CN 5 (the spinal trigeminal nucleus).