Mayo Clinic I - 10 - Brainstem And Cranial Nerves: The Midbrain

Front 1

Regarding the anatomy of the midbrain, where does it extend from and to?

Back 1

From the level of the trochlear nucleus to the imaginary line drawn between the mammillary bodies and the posterior commissure

Front 2

Important structures of the midbrain? (6)

Back 2

1. Cerebral peduncles

2. Superior and inferior colliculi

3. The red nucleus

4. Substantia nigra

5. Decussation of the middle cerebellar peduncle

6. CN III and IV

Front 3

Blood supply of the midbrain?

Back 3

Depends on the level; lower - perforators from the basilar artery and the superior cerebellar artery; middle and upper - predominantly by the posterior cerebral artery P2 segment

Front 4

Which structures traverse the crus cerebri?

Back 4

1. Corticospinal

2. Corticobulbar

3. Corticopontine fibers

It is located ventrally

Front 5

Where does the superior colliculus lie?

Back 5

In the rostral midbrain dorsal to the cerebral aqueduct (3)

Front 6

What is the role of the superior colliculus?

Back 6

It is a visual reflex center, receiving afferent input from the retina, visual cortex and other sensory modalities; also an integral part of the efferent output to burst neurons involved in saccadic eye movements

Front 7

Where is the inferior colliculus located?

Back 7

In the caudal midbrain (3)

Front 8

Role of the inferior colliculus?

Back 8

Obligatory synapses in the auditory pathway

Front 9

Where is the red nucleus located?

Back 9

In the ventral tegmentum ofthemidbrain

Front 10

Main role of rubrospinal fibers?

Back 10

Flexion of upper extremity muscles

Front 11

Where is the substantia nigra found?

Back 11

Midbrain tegmentum, just dorsal to the corticospinal tracts

Front 12

Which muscles act to widen the palpebral fissure?

Back 12

Müller muscle receives sympathetic innervation and the levator of the lid, innervated by cranial nerve III, plays the greater role

Front 13

What is the role of the Edinger-Westphal nucleus?

Back 13

Functions in pupillary constriction

Front 14

Compressive lesions of the third nerve complex often result in a pupil-involving third-nerve palsy. Why? And what is the pupil-involvement you see?

Back 14

Pupillomotor fibers travel in the outer bundle of the third nerve complex, and that's why you often see pupillary dilation due to impaired parasympathetic component

Front 15

Primary and secondary positions of superior oblique?

Back 15

Intorsion and depression

Front 16

Primary and secondary positions of lateral rectus?

Back 16

Only primary: abduction

Front 17

Primary and secondary positions of inferior oblique?

Back 17

Extorsion and elevation

Front 18

Cranial nerve III has two components. What are they?

Back 18

GSE - oculomotor nucleus

GVE - Edinger-Westphal nucleus

Front 19

Role of the GSE component of CN III?

Back 19

Innervate medial, superior, and inferior recti, and inferior oblique and levator palpebrae

Front 20

Role of the GVE component of CN III?

Back 20

Pupillary constriction and accommodation of the lens

Front 21

Where is the trochlear nucleus located?

Back 21

At the level of the inferior colliculus

Front 22

The trochlear nerve pathway

Back 22

The nerve fascicles course posteroinferiorly around the aqueduct to decussate in the dorsal midbrain in the anterior medullary velum; they den tmerge from the brainstem near the dorsal midline. After traveling on the undersurface of the tentorial edge, the nerve pierces the dura into the cavernous sinus along the lateral aspect. It then enters the orbit through the superior orbital fissure

Front 23

Dysfunction of CN IV may result in?

Back 23

1. Hypertropia

2. Excyclotropia

3. Diplopia

4. Head tilt

Note that head tilt toward the abnormal side makes symptoms of diplopia worse, recall that a lesion of the nucleus results in contralatreral dysfunction

Front 24

A unilateral oculomotor nerve palsy may result in?

Back 24

1. Ptosis

2. Dilated pupil

3. Down (siperior oblique, cranial nerve IV intact) and out (lateral rectus, CN VI intact) eye position

Front 25

A unilateral oculomotor nucleus palsy will result in?

Back 25

The same findings as in oculomotor nerve palsy, but will also result in contralateral ptosis and superior rectus dysfunction

Front 26

If there is a lesion at the level above the red nucleus, a patient may have what type of posturing?

Back 26

Decorticate due to the influences of the rubrospinal tract (input to flexors of the upperextremity), reticulospinal (predominantly extensor influence of upper and lower extremities), and vestibulospinal tracts (predominantly extensor influence of the upper and lower extremities)

Front 27

If there is a lesion between the red nucleus and the medulla, the patient may have what type of posturing?

Back 27

Decerebrate; this results because the input to flexors is removed and the patient mainly has input from the pontine reticulospinal tract and the vestibulospinal tracts

Front 28

Examples of diseases resulting in parkinsonism?

Back 28

1. Progressive supranuclear palsy (pallor of substantia nigra and locus ceruleus)

2. Corticobasal-ganglionic-degeneration (intraneuronal inclusions in the substantia nigra)

3. Multiple systems atrophy (neuronal loss in substantia nigra)