Cortico Bulbar, and other pathways Flashcards
an infarction of the posterior limb of the internal capsule damages the
corticospinal and corticobulbar fibers, and somatosensory systems
damage to corticospinal tract in infarction of internal capsule causes
contralateral upper motor neuron syndrome
infarction of internal capsule and damage to somatosensory causes
contralateral sensation losses
damage to corticobulbar fibers that project to hypoglossal nucleus causes
contralateral deviation of the tongue during protrusion
damage to corticobulbar fibers projecting to the contralateral paramedian PPRF in the caudal pons causes
deviation of both eyes towards the lesion
PPRF receives
bilaterally equal tonic innervation
bilateral equal tonic innervation makes it possible to
look straight forward
if PPRF is lost the tonic innervation
of the other side is unopposed causing deviation of eyes towards the side of the damaged upper motor neuron
damage to the corticobulbar fibers innervating the facila nucleus causes
contralateral facial paralysis
the upper facial nucleus receives
bilateral innervation from the ventrolateral primary motor cortex
the lower facial nucleus receives
contralatera projections so in a unilateral central facial lesion the patient will still be able to wrinke the forehead
in a peripheral facial lesion,
the facial nerve itself is damaged and both upper and lower facial muscles are paralyzed
Red Nucleus is located in the
middle portion of the midbrain
Red nucleus receives
exicitatory connections from the ipsilateral motor cortex and from the contralateral cerebellar nuclei.
end of the rubrospinal tract
excitatory synapes of alpha and gamma motor neurons
route of the rubrospinal tract
axons of the red nuclear efferents decussate in the midbrain. Rubrospinal axons descend through the lateral brainstem and anterior horn of spinal cord and end on alpha and gamma motor neurons.
most rubrospinal fibers innervate
neurons of arm muscles
each red nucleus primarily facilitates
voluntary flexion of the muscles of the contralateral arm.
rubral influences on lower limb
minimal
start of medullary(lateral) Reticulospinal tract
reticular neclei in the medula which receive bilateral cortical input from corticoreticulofibers and somatosensory projections through the spinoreticular tract
lateral medullary Reticulo Spinal nuclei receives
Bilateral cortical input from the cortico reticulofibers and somatosensery projections from the spinoreticular tract
the spinoreticular tract is collaterals of
the anterolateral system
medullary RS tract ends on
interneurons that excite alpha and gamma motor neurons
meduallary RS tract route
descends bilaterally through the lateral spinal cord
most Medullary RS fibers facilitate
contraction of the flexor muscles of the limbs
Pontine(medial) RS tract start
reticular nuclei in the pons
Pontine RS nuclei receives
bilateral cortical input through corticoreticular fibers, they also receive somatosensory from spinoreticular tract.
Pontine RS ends on the
interneurons that excited mainly GAMMA motor neurons
pontine RS tract route
descends ipsilaterally through the medulla and VENTRAL anterior horn of spinal cord
Pontine RS tract predominantly affect
gamma motor neurons of axial and limb extensor muscles
Spinoreticular tract starts at
the pain and temperature receptors
the SR tract ends on
the reticular nuclei in the pons and medulla
the SR tract relays
sensory info(pain, temp and pressure) from one side of the body to the contralateral reticular nuclei.
SR tract influence on pontine reticular nuclei may facilitate
contraction of the extensory muscles of the ipsilateral limb and tunk. (postural adjustment may place wieght on the foot not subject to potentially threatening stimuli)
Lateral VS tract starts in
the lateral vestibular nucleus
Lateral VS recieves
input from vestiublar organs and cerebellum
Lateral VS ends on
excitatory interneurons that excite ALPHA motor neurons
Lateral VS Route
axons descend ipislateral through medulla and the anterior horn of the spinal cord
Lateral VS facilitates
regulation of muscular responses necessary for balance. motor nuerons of the axial and limb extensors(anti-grav muscles)
Medial VS tract starts
in the medial vestibular nucleus
Medial VS tract receives
input from the vestibular organs and the cerebellum
Medial VS tract ends
on synapes of ALPHA motor neurons at the cervical and upper thoracic levels.
Medial VS tract route
axons descend ipsilateraly into the spinal cord and run as the caudal exstension of the medial longitudinal fasciulus
Medial VS facilitates
muscular contraction of the neck in close coordination with movements of the eyes. Many neurons release glycine to inhibit the alpha neurons
when extrafusal muscles of the muscle contract
the muscle spindle loses tension and becomes slack
when the muscle spindle is slack it is unable to
measure subsequent muscular stretch
the gamma motor neuron typically innervates
the contractile ends of the intrafusal fibers that shorten the muscle spindle to ensure that spindle is always responsive to muscular stretch
in myotatic reflex the 1a afferent excites
the alpha motor neurons serving the same muscle
descending fibers of the Lateral CS tract, Rubrospinal and RS tract coactivate motor neurons during
voluntary movement
the pontine or medial RS tract has a major excitatory influence on
the gamma motor neurons and can activate the muscle contraction by the gamma loop.
gamma motor neurons stimulate the
muscle spindles and this indrectly stimulates the alpha motor neurons via the 1a fivers forming the afferent limb of the reflex arc
Decorticate posturing
lesion rostral to the red nucleus impairs corticobulbar and coticospinal fibers, this causes flexion of the upper limbs and extension of the lower limbs
Decorticate posturing and what happens to the different tracts
corticospinal tract- interrupted, imparied flexion corticobulbar tract- interrupted, paralysis of cranial nerves rubrospinal tract- intact flexion of arms medullary RS tract- intact, flexion of extremities pontine RS tract- intact extension of extremeties vestibulo spinal tracts- intact extension of extremeties
Arms during decorticate posturing
flexor input from rubrospinal tract is still present so there is strong flexor innervation which is much greater than extensor imput of pontine reticulospinal tract
legs during decorticateposturing
rubrospinal has no impact so the extensor innervation is more relevant so the limbs are extended
Decerebrate posturing
lesion at or caudal to the red nucleus imparis cortico spinal, corticobulbar, rurbrospinal fibers, patent extends both upper and lower limbs
during decerebrate posturing only medullary RS tract
promotes flexion which is overcome by innervation of the pontine RS and VS tracts.
