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
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.
conveys pain, temperature, crude tactile sensations from opposite 1/2 of face. located between medial lemniscus + spinal 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
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
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 .
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 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
equilibrium + posture problems
Central lesions of VIII in the pontomedullary sulcus
Lesions at the level of the Medulla
CN IX, CN X, CN XI, CN XII
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.