Lecture 18 (Corticospinal) Flashcards
M1
Primary motor cortex
CST
Corticospinal tract
PMC
Premotor cortex
SMA
Supplementary motor area
BA
Brodman’s area
MC
Motor cortex
RF
Reticular formation
SC
Spinal cord
SS ctx
Somatosensory cortex
m.
Muscle
LCST
Lateral CST
VCST
Ventral CST
FF
Feedforward
FB
Feedback
p/w
Pathway
Mvt
Movement
M1 location
Precentral gyrus of the frontal lobe - BA4
M1 cells
Pyramidal cells (layer V)
M1 projections
Afferent projections from PMC & SMA
- predominantly ipsilateral
Afferents also from 1* sensory cortex
Basal nuclei & cerebellum function as “consultants”
M1 functions
- Mvts coordinated by M1 & BA 6
- Simple muscle contraction combinations
- BA 6 helps combine those combinations into complex mvts
Premotor Cortex
Somatotopic representation of complete body musculature
PMC - input
Sensory areas of parietal cortex
PMC - output
M1 & spinal cord
PMC - function
Involved in control of proximal limb - used to position arm for movement tasks
Supplementary Motor Area
Contains complete map of body musculature
SMA - function
Planning & learning complex, internally generated movements
- Blood flow increases even if movement is mentally rehearsed
- Bilateral movements are produced
SMA - input
Parietal lobe
SMA - output
M1 & spinal cord
Posterior Parietal Cortex
BA 5 & 7
Posterior Parietal Cortex - function
Carries out background computation
BA 5 - receives input from somatosensory & vestibular systems
BA 7 - processes visual info related to location of objects in space
Posterior Parietal Cortex - output
SMA & PMA
- few BS & spinal cord projections
Pyramidal system
Descending pathway from motor cortex
- UMN and LMN
- Corticospinal and corticonuclear tracts
Functional divisions motor system
- direct activation p/w
- indirect activation p/w
- control circuits
- final common p/w
Corticospinal p/w
- Corticonuclear tracts
- Lateral CS tracts
- Anterior CS tracts
Medial p/w
- Vestibulospinal tracts
- Tectospinal tracts
- Reticulospinal tracts
Lateral p/w
- Rubrospinal tracts
CST
Corticospinal Tract
- Corona radiata
- Internal capsule
- Cerebral peduncle of the midbrain
- Pontine nuclei
- Decussation at the medulla
- Uncrossed: anterior corticospinal tract (ACST)
- Crossed: lateral corticospinal tract (LCST)
LCST
- Terminates in ventral horn or intermediate gray matter
- Topographically organized
- Fractionation of movement
- Influence exerted depend on # of synapses
ACST
- Terminates on MN or interneurons in medial region of ventral horn or intermediate gray matter
- Affects activity of MN for axial muscles
How is voluntary movement accurate?
Tactile, visual, proprioceptive information
Corticonuclear Tracts
- Bilateral projection: UMN descend bilaterally, majority fibers project to contralateral LMN
- Except for to the facial motor nucleus
Facial nucleus
Upper face: both crossed and uncrossed corticobulbar input
Lower face: only crossed corticobulbar input
Motor Cortex - nuclei
- Tectum: mainly contralateral, tectospinal
- Red nucleus: mainly contralateral, rubrospinal
- Reticular formation: bilateral projection, reticulospinal
- Vestibular nuclei: mainly ipsilateral, vestibulospinal
Positive vs. negative signs
negative: loss of capacity
positive: abnormal, stereotyped responses
UMN lesions
- spasticity
- denervation atrophy, reduced muscle volume
- distributed diffusely, large group of muscles
LMN lesions
- no spasticity
- affects muscles in achy way
- may be limited to single muscles
Pyramidal tract - damage (corticospinal)
- above decussation: contralateral paralysis
- below decussation: ipsilateral paralysis
Pyramidal tract - damage (corticonuclear)
- effects are less severe than effects of corticospinal lesions
- symptoms vary depending on cranial nerve
Rhythmic motor patterns
- chewing, swallowing, scratching, walking
- circuits lie in spinal cord & brain stem
- usually triggered by stimulus
