Motor Tracts Flashcards
What is the difference between direct and indirect motor pathways?
Direct - cortex to spinal cord
Indirect - synapses in brainstem, basal ganglia, thalmus, reticular formation, and cerebellum
What type of pathway is the corticospinal tract?
Direct motor
What are the two divisions of the corticospinal tract and what do they do?
Medial (not clinically significant) - postural muscles. Stays ipsilateral.
Lateral - contralateral limb muscles and fractionation
What is the CST pathway?
UMNs arise in cortex (primary motor cortex). Descend through posterior limb of internal capsule, go through cerebral peduncles (middle 1/3), anterior pons, pyramids, and cross in the pyramidal decussation (lower medulla). Descends in lateral column of SC as lateral CST. Synapses with LMNs in anterior horn of SC.
What is the blood supply for the CST?
Midbrain - P1 of PCA
Pons - Paramedian branches of basilar a
Medulla - Sulcal branches of ASA
What is the somatotopic arrangement of fibers in the CST?
Legs lateral, trunk, and arms medial
What is the blood supply to the posterior limb of the internal capsule?
Lenticulostriate a
What type of pathway is the corticobulbar tract?
Direct motor
What does the corticobulbar tract do?
Influences muscles innervated by cranial nerves except for eyes
Which cranial nerves are involved in the CBT?
V, VII, IX, X, XI, XII
5, 7, 9, 10, 11, 12
What is the pathway of the CBT?
UMNs arise from ventral part of primary motor cortex and travel down through the GENU of the internal capsule.They pass through the cerebral peduncles, anterior pons, and pyramids. They then stop at the specific motor nucleus for the CN
Where are the CN nuclei located for the CBT?
V and VII - pons
IX, X, XII - rostral medulla
XI - SC
Where do CBT fibers go for CN V nucleus?
Bilaterally to CN V motor nucleus
Where do CBT fibers go for CN VII nucleus?
Bilateral input for forehead, contralateral input for lower face
Where do CBT fibers go for CN XII nucleus?
Contralateral nucleus
Where do CBT fibers go for CN IX and X?
Contralateral nucleus ambiguus
Where do CBT fibers go for CN XI nucleus?
Ipsilateral nucleus
What is the topographical organization of LMNs in the anterior horn of the SC?
Axial muscles - medial
Limb muscles - lateral
Extensor muscles - anterior
Flexor muscles - posterior
What are the indirect pathways? (6)
Medial UMN tracts: tectospinal, medial (pontine) reticulospinal, medial vestibulospinal, lateral vestibulospinal
Lateral UMN tracts: rubrospinal, lateral (medullary) reticulospinal
What are the vestibulospinal tracts?
Lateral - vestibular nuclei to SC, ipsilateral LMNs innervate postural muscles and limb extensors
Medial - vestibular nuclei to SC, to neck and shoulder muscles for head movement (C/T levels of SC)
What is the rubrospinal tract?
Red nucleus to SC, contralateral upper limb flexor innervation
What are the reticulospinal tracts?
Medial (pontine) - Pontine reticular formation to SC, ipsilateral LMNs to postural muscles and limb extensors
Lateral (medullary) - Medullary reticular formation to SC, facilitates flexor motor neurons and inhibits extensor motor neurons
What is the tectospinal tract?
Superior colliculus (midbrain) to upper SC, goes to contralateral neck muscles for coordination of head with eye movements
What symptoms indicate a LMN lesion?
Flaccid paralysis, wasting/atrophy, hyporeflexia, hypotonia, fasciculations
