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Flashcards in Brainstem morphology lecture Deck (34):

How many ascending/descending tracks in the brainstem?

7, all run parallel to the vertical neuroaxis


spinal lemniscus: what it conveys and its location

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


medial lemniscus

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. 


Trigeminal Lemniscus

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


lateral lemniscus

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


medial longitudinal fasciculus (MLF)

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


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

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


lesions of the MLF (clinical observations)

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


Corticospinal tract

conveys descending motor information from cortex.


corticospinal tract in the midbrain

comprises middle 3/5's of crus cerebri


corticospinal tract in the pons

splits into numberous tracks by pontine nucleu and pnotocerebellar fibers


corticopsinal tract in the medulla

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


lesion in the corticospinal track described as

spastic hemiplegia


Corticobulbar tract (CBT)

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.


Unilateral lesions of the corticobulbar fibers

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.


Unilateral lesions of the CBT above the level of the decussation

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.


Unilateral lesions of CBT below the decussation

result in ipsilateral cranial nerve palsies.


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

supranuclear facial palsy

Unilateral lesions of the CBT above the level of the decussation


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

 paresis of the contralateral lower quadrant of the face 


Central lesions of a cranial nerve indicates

indicates involvement of the brainstem at that corresponding level.



Lesions at the level of the Diencephalon or upper midbrain 

[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.


Lesions at the level of the Midbrain

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.


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 

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 


Internuclear Ophthalmoplegia. assume lesion on the right MLF 


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.


Lesions at the level of the Pons

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.


Lesions at the level of the Pontomedullary Sulcus

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.


ipsilateral paralysis of lateral gaze + internal strabismus.


1) Abducens nerve. Central lesion. @ pontomedullary junction 



ipsilateral facial palsy

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


Central lesions of the facial nerve @ pontomedullary sulcus 


 ipsilateral deafness

 equilibrium + posture problems


Central lesions of VIII in the pontomedullary sulcus 


Lesions at the level of the Medulla

may affect:



Lesion in the medulla in the glossopharyngeal nerve

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.


Lesions in the medulla at the level of vagus 

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


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

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.


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

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.