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
What symptoms indicate UMN syndrome?
Muscle weakness, babinski sign, spasticity, rigidity, hyperreflexia, clasp-knife phenomenon, pronator drift
How do you determine the location of a LMN lesion?
Exactly where the deficits are, same side
How do you determine the location of a lMN lesion?
Above pyramidal decussation symptoms will mean contralateral lesion, in SC symptoms mean ipsilateral cord lesion
What causes decorticate or decerebrate rigidity?
UMN lesions
What is decorticate posture?
Lesion above the red nucleus (midbrain still intact), arms flexed, pronated forearm, foot inversion
What is decerebrate posture?
Lesion below red nucleus (past midbrain) but above reticulospinal and vestibulospinal nuclei. UE pronated and extended, LE extended
What is Brown-Sequard?
Contralateral loss of pain/temp two segments below hemisection of SC due to ALS damage. Ipsilateral loss of discrim. touch and proprioception at and below level of SC hemisection due to PCMLS damage
What is syringomyelia?
Cyst within central canal of SC that affects AWC first (pain/temp) in cape-like distribution. Sometimes motor loss too (UMN if lateral CST affected or LMN if anterior horns affected). Arms first to be compromised in lateral CST impingement.
Highly correlated with Chiari I malformation
What can cervical hyperextension cause?
Central cord syndrome - compression/damage to central portion of spinal cord
What is central seven palsy?
Lesion to corticobulbar tract involving CN VII (above facial nucleus). Causes drooping to contralateral side not involving forehead since forehead is additionally innervated by ipsilateral side
What is Weber Syndrome?
Damage to P1 of PCA. Causes CST deficits (contralateral hemiplegia), CBT deficits (contralateral facial droop), and CN III palsy (ptosis, dilated pupil)
What is spastic cerebral palsy?
Damage to CST in telencephalon or diencephalon. Failure of normal neuronal selection, aberrant muscle development, paresis, reflex irradiation, abnormal co-contraction of muscles
What is ALS?
Amylotrophic latearl sclerosis - destroys only somatic motor neurons (UMNs or LMNs). Leads to paresis, hyperreflexia, babinski, atrophy, fasciculations. CN involvement leads to difficulty breathing, swallowing, and speaking
What is polyneuropathy?
Progressive neuron damage from distal to proximal. Feet first, then hands (glove/stocking distribution)
