brain stem centers for motor activity

Question 1

rubrospinal tract

Answer 1

few magnocellular neurons exit, small (parvocellular) neurons in rend nucleus project to inferior olive

inferior olivary nucleus sends input to cerebellum (olivo-cerebellar tract) to modulate cerebellum activity (participates memory functions of cerebellum)

Axons from cerebellum to thalamus send collaterals to red nucleus.

Red nucleus (via inferior olivary nucleus) provides feedback loop to cerebellum to allow adaptation of cerebellar circuits

Question 2

upper midbrain damage

Answer 2

–> decorticate posturing/rigidity

pt exhibits upper limbs flexed at the elbow, lower limbs extended

Question 3

lower midbrain damage

Answer 3

–> decerebrate posturing

Pt exhibits extension of both upper and lower limbs

Question 4

benedikts Syndrome

Answer 4

unilateral lesion of red nucleus

CN3 injury –> ipsilateral oculomotor palsy eye deviates laterally ptosis, pupil is fixed and dilated

Contralteral tremor

rubrospinal tract lesion usually in conjunction with corticospinal tract lesions

Question 5

tectospinal tract

Answer 5

pathway for reflexive turning movements of the eyes and head; and upward gaze

fibers arise in retina, visual cortex, and inferior parietal lobes and project to the superior colliculus

The fibers leave the superior colliculus and decussate in the dorsal tegmentum

Tectospina fibers terminate in the contralateral cervical sp cd (Cn 11 nucleus to control head movements!)

Other axons from the superior colliculus project to the pontine paramedian reticular formation then via MLF to nuclei controlling extraocular m that facilitate upward gaze

Question 6

parinauds syndrome, dorsal midbrain syndrome, collicular syndrome

Answer 6

a lesion in the of the superior colliculi or posterior commissure leads to eye abnormalities including impaired vertical gaze, large irregular pupils

eyelid abnormalities

convergense

Pineal gland tumor or hydrocephalus is the main cause

Question 7

lateral vestibulospinal tract

Answer 7

input to vestibular nuclei: vestibular nerve (CNVIII) semicircular canals and maculae in utricle and saccule, cerebellum (flocculonodular lobe)

LVST Description- cell bodies in vestibular nuclei within brainstem (lateral vestibular nucleus), projects ipsilaterally within anterior funiculus to all levels of spinal cord

LVST function- innervates extensor (antigravity), muscles mainly in the trunk and lower limbs to maintain balance and posture

lesion of the vestibular nerve or vestibular nucleus–> stumbling and/or falling toward the side of the lesion

Question 8

lateral medullary syndrome of Wallenberg

Answer 8

cause: vertebral artery or PICA occlusion
On the side of the lesion: Dysphagia, Dysarthria, diminished gag reflex (nucleus ambiguus- CN 9 and 10)
Loss of pain and temp from face (spinal tract of V descends ipsilaterally to spinal nucleus of V)
Vertigo, nausea, vomiting, nystagmus (vestibular nuclei)

Contralateral to lesion: loss of pain and temp sensation from body (anterolateral system- spinothalamic tract) decussated in sp cd at or just above level of entry oof sensory fibers

chercker board pattern of loss of pain and temp- face ipsilateral; body contralateral

Question 9

medial vestibulospinal tract

Answer 9

Input to Vestibular Nuclei (from vestibular nerve, cerebellum)

MVST Description: Cell bodies in vestibular nuclei within brainstem (medial vestibular nucleus), projects bilaterally within anterior funiculus to cervical sp cd and to LMNs associated with the spinal accessory nerve

MVST function: adjusts head position in response to postural changes, coordinate eye movements with each other, vestibuloocular reflex- coordinates to compeensate for head movements

axons project to CN 3, 4, 6

Question 10

reticulospinal tracts

Answer 10

the reticular formation is composed of scattered groups of neuron cell bodies and fibers that extend throughout the brainstem

input to reticular nuceli: from cortex

medullary/lateral RST: bilateral, inhibits LMNs–> inhibits extensor muscle contraction

Pontine/medial RST: ipsilateral, excites LMNs–> stimulates muscle contraction

RSTs convey autonomic information from higher levels to influence respiration, circulation sweating shivering pupil dilation and sphincters

Question 11

decerebrate posturing/Decerebrate rigidity

Answer 11

if the superior and inferior colliculi are cut apart

Clinical scenario: brainstem lesions caudal to the red nucleus

increased muscle tone, extension of upper and lower limbs with arms adducted and medially rotated arched back, feet extended , toes curled

explanation: midbrain transsection removes excitatory cortical input to the inhibitory LRST. ascending input to the MRST is still intact. The facilitory influence of the MRST is now unopposed byt the inhibitory influence of the LRST–> facilitation of extensor motor neurons