Brainstem 1: Long Tracts

Question 1

Which cranial nerves exit medially?

Answer 1

III, IV, VI, and XII

Question 2

What do the cranial nerves that exit medially* all have in common?
*corrected from “laterally.” Sorry, that was a really bad typo.

Answer 2

All are motor only.

Question 3

Which CNs exit laterally?

Answer 3

V, VII, IX, and X.

Question 4

What is similar about CNs that exit laterally?

Answer 4

V, VII, IX and X are mixed sensory and motor.

Question 5

What’s the only CN that exits dorsally?

Answer 5

IV trochlear

Question 6

What’s in the pyramids?

Answer 6

Corticospinal tract.

Question 7

Why is the medial/lateral CN distinction clinically relevant?

Answer 7

They have different blood supplies.

Question 8

What’s the only completely crossed CN?

Answer 8

IV

Question 9

Where does IV run when it emerges from the midbrain?

Answer 9

Posterior to the inferior to the inferior coliculus.

Question 10

What separates the dorsal pons from the cerebellum?

Answer 10

The 4th ventricle.

Question 11

Where do axons that have ascended to the lower medulla synapse?

Answer 11

In the dorsal column nuclei.

Question 12

What’s the medial lemniscus? (where are things coming from / going)

Answer 12

2nd neuron axons for proprioception/mechanoreception. Came from the dorsal column nuclei, headed to the VPL in the thalamus.

Question 13

Which is more medial, the medial lemniscus or the spinothalamic tract?

Answer 13

Medial lemniscus is more medial.

Question 14

In what structure is each corticospinal tract running right before it reaches the pons? Within that structure, where does it run?

Answer 14

In the cerebral peduncle. In the middle of the ventral-ish side.

Question 15

Where do corticospinal fibers run in the brain (i.e. before the pyramidal decussation)? Dorsal/ventral, medial/lateral?

Answer 15

Ventral and medial

Question 16

Where must a vascular lesion be to mess up corticospinal fibers?

Answer 16

ventral and medial

Question 17

What would a lesion in the medial-most, ventral-most part of the basis pontis cause? (remember to specify ipsi/contralateral)

Answer 17

Contralateral spastic weakness. These are corticospinal fibers above the pyramidal decussation.

Question 18

Review: Which vertebral levels send afferent axons to the fasiculus / nucleus gracilis? Fasciculus / nucleus cuneatus?

Answer 18

T6 and below-> Gracilis

T5 and above -> Cuneatus

Question 19

What happens after afferent axons synapse in the nucleus cuneatus or gracilis?

Answer 19

Cross mid-line immediately, then travel up the medial lemniscus -> thalamus VPL nucleus

Question 20

What would a lesion to the medial lemniscus cause?

Answer 20

Contralateral loss of mechano/proprioception (in neck and below).

Question 21

How are axons within the medial lemiscus arranged with regard to their origin? Does it change?

Answer 21

Begins arranged, dorsal to ventrally, Arm-Trunk-Leg (ATL). As fibers ascend, leg and trunk fibers run laterally, so that the arrangement, from lateral to medial is Leg-Trunk-Arm (LTA).

Imagine a pair of legs (where… arm = thigh and trunk = knee, leg = foot..) that does a split as it ascends.

Question 22

Why does the spinothalamic tract give off axons as it ascends toward the VPL nucleus?

Answer 22

Gives off pain fibers to areas of the brain that suppress pain.

Question 23

What does a lesion of the spinothalamic tract in the brainstem do?

Answer 23

Contralateral loss of pain / temp sensation. (same as when it’s in the spinal cord)

Question 24

How, geographically, does the spinothalamic tract travel up the brainstem?

Answer 24

Starts lateral, stays lateral (but not all the way to the edge) until it hits the VPL nucleus.

Question 25

What fibers course right next to the spinothalamic tract (just lateral to them)?

Answer 25

Descending hypothalamic fibers controlling sympathetics.

Question 26

Where do descending sympathetics run in the brain stem? Review: In the spinal cord?

Answer 26

Way laterally in the brain stem. In the spinal cord, intermediolateral columns.

Question 27

Is Central Horner’s Syndrome ipsilateral or contralateral? How might you determine that it’s Central, not peripheral Horner’s?

Answer 27

Ipsilateral (for both central and peripheral). In central Horner’s, nearby spinothalamic tract may be lesioned, and thus may have contralateral pain / temp loss in trunk and limbs.

Question 28

What would a lateral vascular lesion in the brainstem damage (that we discused in this lecture)?

Answer 28

Spinothalamic tract and descending sympathetics.

Question 29

What does the medial longitudinal fasciculus (MLF) do?

Answer 29

Links vestibular nuclei and centers for conjugate gaze with abducens, trochlear, and occulomotor nuclei (most important for conjugate horizontal gaze).

Question 30

What two diseases is the MLF particularly susceptible to?

Answer 30

MS and neurosyphilis.

Question 31

Where does the MLF run?

Answer 31

Floor of 4th ventricle -> adjacent to central canal / cerebral aqueduct

Question 32

What 4 things will be found in every brain stem cross-section?

Answer 32

A long tract
A CN nucleus or nerve
A trigeminal nucleus
A cerebellar peduncle or fibers forming one

Question 33

Do muscles innervated by CNs typically get unilateral or bilateral innervation?

Answer 33

Bilateral

Question 34

What are the UMN axons of cranial nerves called?

Answer 34

Corticobulbar or corticonuclear axons.

Question 35

Where do LMNs of cranial nerves have their cell bodies?

Answer 35

In the corresponding CN nucleus (as covered in the following lecture).

Question 36

If you damage a whole side of CN UMNs, do you get weakness? (note that there’s an exception)

Answer 36

No, one side appears to suffice, except for some of CNVII.

Question 37

How do UMN and LMN lesions to CNVII appear differently? Why?

Answer 37

Only muscles that shut eyes and wrinkle forehead are innervated bilaterally. Thus… UMN lesion: paralysis/weakness in everything on that side except forehead wrinkling/eye-closing.
LMN lesion: weakness / paralysis of whole side of face (recall: Bell’s Palsy)

Question 38

What does a unilateral lesion to corticobulbar fibers do?

Answer 38

No CN deficits except contralateral weakness of lower face muscles. (repetition is good…)

Question 39

What does a lesion to the spinothalamic tract do? (2 thing, one less obvious)

Answer 39

Contralateral pain/temp loss.

Ipsilateral Central Horner’s Syndrome