Brainstem morphology lecture

Question 1

How many ascending/descending tracks in the brainstem?

Answer 1

7, all run parallel to the vertical neuroaxis

Question 2

spinal lemniscus: what it conveys and its location

Answer 2

conveys fast pain and temp from contra-lateral 1/2 of the body. either lateral to medial lemniscus or posterolateral to medial lemniscus

Question 3

medial lemniscus

Answer 3

conveys proprioceptive, vibratory, and 2 pt tactile discrim from contra-lateral 1/2 of body (posterior columns)

@ level of upper pons and medullar, contains fibers for taste sensation from ipsilateral 1/2 of tongue+pharynx.

Question 4

Trigeminal Lemniscus

Answer 4

conveys pain, temperature, crude tactile sensations from opposite 1/2 of face. located between medial lemniscus + spinal lemniscus

Question 5

lateral lemniscus

Answer 5

conveys bilateral auditory information, predominantly information from opposite ear. located in the lateral aspect of the brainstem

Question 6

medial longitudinal fasciculus (MLF)

Answer 6

MLF conveys vestibular influences to cranial nerves III, IV, VI ; oculomotor fibers located 1) next to the midline and anterior to the central gray 2) in medulla+lower pons @ lower lip of the medial lemniscus

Question 7

lesions of MLF (basic description, not the clinical observations)

Answer 7

intranuclear ophthalmoplegia syndrome patients have abnormal response to horizontal gaze in direction opposite the side of the lesion

Question 8

lesions of the MLF (clinical observations)

Answer 8

unilateral lesions of the MLF result in an impairment of the or loss of adduction of ipsilateral eye, nystagmus of the abducting eye

Question 9

Corticospinal tract

Answer 9

conveys descending motor information from cortex.

Question 10

corticospinal tract in the midbrain

Answer 10

comprises middle 3/5’s of crus cerebri

Question 11

corticospinal tract in the pons

Answer 11

splits into numberous tracks by pontine nucleu and pnotocerebellar fibers

Question 12

corticopsinal tract in the medulla

Answer 12

forms the pyramids, 75-80% decussate in lower medulla

Question 13

lesion in the corticospinal track described as

Answer 13

spastic hemiplegia

Question 14

Corticobulbar tract (CBT)

Answer 14

corticobulbar fibers decussate in the lower pons between the levels of the trigeminal and abducens nerves. CBT is a two neuron white matter motor pathway. it connects the motor cortex in the cerebrum to the Medullary pyramids, which are part of the brainstem’s medulla oblongata (also called “bulbar”) region primarily involved in carrying the motor function of the non-oculomotor cranial nerves. The corticobulbar tract is one of the pyramidal tracts, the other being the corticospinal tract.

Question 15

Unilateral lesions of the corticobulbar fibers

Answer 15

result in denervation of the brainstem motor nuclei below the level of the lesion. Some motor nuclei such as part of the facial motor nucleus receive fibers from both hemispheres and, therefore, are not affected by unilateral lesions of the head region of the motor cortex or CBT.

Question 16

Unilateral lesions of the CBT above the level of the decussation

Answer 16

results in a contralateral paralysis or paresis of the mimetic muscles of the lower half of the face (supranuclear facial palsy) + other cranial palsies due to denervation of the abducens nucleus, hypoglossal nucleus and the nucleus ambiguus. Lesions below the decussation result in ipsilateral cranial nerve palsies.

Question 17

Unilateral lesions of CBT below the decussation

Answer 17

result in ipsilateral cranial nerve palsies.

Question 18

paresis of the mimetic muscles of the lower half of the face

Answer 18

supranuclear facial palsy

Unilateral lesions of the CBT above the level of the decussation

Question 19

unilateral lesions to the corticobulbar fibers going to the facial nucleus result in

Answer 19

paresis of the contralateral lower quadrant of the face

Question 20

Central lesions of a cranial nerve indicates

Answer 20

indicates involvement of the brainstem at that corresponding level.

Question 21

Lesions at the level of the Diencephalon or upper midbrain

Answer 21

[diencephalon means all the “-mus” anatomy, thalamus/hypothalamus/epithalamus]

affects: Optic Nerve, Chiasma or Tract. any of those.

will result in a specific pattern of visual field blindess.

Question 22

Lesions at the level of the Midbrain

Answer 22

1) CN III: may destroy the fibers of the oculomotor nerve, and result in

a. external strabismus

b. pupillary dilation

c. complete ptosis.

2) CN IV: Trochlear nerve. [CN IV courses posteriorly around cerebral aqueduct, decussates, exits just below inferior colliculus.]
a. Lesions IV distal to decussation result in ipsilateral deficits.

b Lesions of the trochlear nerve proximal to the decussation result in contralateral deficits.

patient is not able to look in (adduct) and down (depress) the affected eye.

Question 23

The patient is complaining of diplopia when looking straight ahead and you notice they’re tilting their head up and away in order to see better

Answer 23

This indicates a lesion in the trochlear never proximal to the point of decussation

patient is unable to adduct eye + depress eye downward so they tilt their head to maintain binocular vision

Question 24

Internuclear Ophthalmoplegia. assume lesion on the right MLF

Answer 24

UP to DATE:

Internuclear ophthalmoparesis (INO), also commonly referred to as internuclear ophthalmoplegia, is a specific gaze abnormality characterized by impaired horizontal eye movements with weak adduction of the affected eye, and abduction nystagmus of the contralateral eye. It is one of the most localizing brainstem syndromes, resulting from a lesion in the medial longitudinal fasciculus (MLF) in the dorsomedial brainstem tegmentum of either the pons or the midbrain [1].

OTHER DETAILS: In INO, there is damage to the MLF, giving a deficit in adduction of the corresponding eye during conjugate lateral gaze, but convergence (eye crossing) is classically preserved because that is controlled by a different pathway.

Question 25

Lesions at the level of the Pons

Answer 25

Trigeminal nerve

trigeminal nerve courses through the bulk of the middle cerebellar peduncle.

Lesions of the nerve in this area results in:

ipsilateral loss of sensations from 1⁄2 of the face

paralysis/atrophy of the ipsilateral muscles of mastication

When the patient opens his mouth wide, the chin deviates toward the side of the lesion.

Question 26

Lesions at the level of the Pontomedullary Sulcus

Answer 26

1) Abducens nerve. Central lesions result in ipsilateral paralysis of lateral gaze + internal strabismus.
2) Facial nerve. In lower pons, fibers of facial nerve loop over ventricular surface of abducens nucleus (facial colliculus), course ventrolaterally to exit next to the vestibulocochlear nerve in the pontobulbar sulcus.

Central lesions of the nerve result in ipsilateral facial (Bell’s) palsy; loss of taste sensations from the anterior 2/3 of the tongue; and hyperacusis.

3) Vestibulocochlear nerve. Central lesions of VIII result in ipsilateral deafness; equilibrium + posture problems; and nystagmus.

Question 27

ipsilateral paralysis of lateral gaze + internal strabismus.

Answer 27

1) Abducens nerve. Central lesion. @ pontomedullary junction

Question 28

ipsilateral facial palsy

loss of taste sensations from the anterior 2/3 of the tongue

hyperacusis.

Answer 28

Central lesions of the facial nerve @ pontomedullary sulcus

Question 29

ipsilateral deafness

equilibrium + posture problems

nystagmus

Answer 29

Central lesions of VIII in the pontomedullary sulcus

Question 30

Lesions at the level of the Medulla

Answer 30

may affect:

CN IX, CN X, CN XI, CN XII

Question 31

Lesion in the medulla in the glossopharyngeal nerve

Answer 31

Central lesions of the glossopharyngeal nerve result in:

decreased sensations from the palate & pharynx (diminished gag reflex).

a loss of taste from the posterior third of tongue.

Question 32

Lesions in the medulla at the level of vagus

Answer 32

lesions of vagus result in:

dysphagia, dysarthria, hoarseness

paralysis + paresis of the muscles of palate

uvula may deviate to the side opposite the lesion;

transient parasympathetic effects

Question 33

Lesions in the medulla at the level of the hypoglossal n.

Answer 33

Central lesions of the hypoglossal nerve result in:

paralysis + atrophy of ipsilateral intrinsic muscles of tongue.

patient may complain of dysphagia and dysarthria.

protruded tongue deviates toward side of the lesion.

Question 34

Lesions in the medulla at the level of the spinal accessory nerve

Answer 34

arises from accessory nucleus in the upper cervical spinal cord (C1-6).

Central lesions involving the rootlets of this nerve result in:

ipsilateral paresis of the sternocleidomastoid.

patient has difficulty in turning his head away from affected side

bending head forward at the same time

shrugging his shoulders.