Corticobulbospinal Tracts & Basal Ganglia Motor Systems I Flashcards
GSE
somatic motor system
-descending tract
voluntary control of skeletal m.
GVE
visceral motor system
-autonomic nervous system
motor system
motivation - frontal lobes
motor plan - premotor cortex
action - primary motor cortex
motivation
coming up with idea for motor plan
- need input:
- sensory stimuli (parietal motor area)
- emotions/memory (limbic)
motor plan
module or blueprint for movement -what muscles, what order, what timing
premotor cortex
brodmans areas 6 and 8 lateral
supplementary cortex
brodmans areas 6 and 8 medial
action
UMN - from primary motor cortex and brainstem nuclei
UMN
influence LMNs
-spinal cord and cranial nerve
all UMNs converge on LMNs to produce movement
final common pathway
LMNs
alpha-lower motor neurons
ventral horn and cranial nerve motor nuclei synapse on skeletal m. always excitatory release ACh target ipsilateral large cells
gamma-lower motor neurons
muscle spindle
baseline activity
allows for fine adjustment
-in alpha LMNs
sets muscle tone
inputs to LMNs
local reflex arc
local pattern generators
UMN input
motor unit
all muscle fibers innervated by single LMN
- size related to function
- fine control vs. power
small motor unit
less fibers innervated
-fine control
large motor unit
1000 fibers/neuron - power control
each muscle fiber
only innervated by 1 LMN
individual muscle
have motor units of various sizes
-although certain sizes may predominate
action potential
all or none
regulation of muscle contraction strength?
AP frequency
recruitment of motor units
size principle
recruit small > large motor units
small first**
UMN
influence LMNs
- directly
- or indirectly
- excitatory or inhibitory
- never synapse on muscle**
- cell bodies in cerebral cortex and brainstem nuclei
8 different UMN pathways
2 from primary cortex
6 from brainstem
lateral motor system
distal limb movement
-precise movement
medial motor system
proximal limb movement
-postural movement
lateral vs. medial
lateral - lateral funiculus
medial - anterior funiculus
influence on UMNs?
basal nuclei
association cortex
cerebellum
corticobulbar tract
cortex to brainstem
non-cortical UMN systems
reflex - postural movements
-in brainstem
-input from cortex influences these systems (gain voluntary control)
cortical UMN systems
distal limb movements
-fine movement
cortical UMN pathways
lateral corticospinal
-cortex to spinal cord b/l
corticobulbar tract
corticospinal tract lateral
largest tract of humans
contralateral projection
fine, fractionated movement
course of UMN on corticospinal tract
internal capsule cerebral peduncles (midbrain) longitudinal fibers of pons (pons) pyramids (medulla) pyramidal decussation lateral corticospinal tract
brodmans area 4
primary motor cortex
precentral gyrus
voluntary motor movement
posterior limb of internal capsule
facial expression - genu
upper limb - anterior
lower limb - posterior
premotor cortex
lateral brodmans area 6 and 8
- motor planning
- active at START of movement
supplementary cortex
medial brodmans areas 6 and 8
interconnected with contralateral side
-bimanual movements
active right before movement takes place
corticobulbar tract
terminates in brainstem
influence cranial LMNs
also to UMN nuclei
-voluntary control of proximal muscles
cranial nerve motor nuclei
most receive input from both right and left cortex
corticobulbar influence on brainstem UMNs
vestibular nuclei
reticular nuclei
red nucleus
give rise to medial motor systems
-proximal limb
LMN damage signs
hypo to areflexis
hypo to atonia
paralysis/paresis - flaccid
rapid, severe atrophy
partial paralysis
NO
actually a paresis
neurogenic atrophy
due to loss of LMN
spontaneous EMG changes
with LMN damage
fasciculations
can see visually twitching
fibrillations
with EMG
UMN damage signs
normal - hyperreflexia hypertonia pathological reflexia (babinski) spastic paralysis disuse atrophy (slower)
few EMG changes
babinski
is a pathological reflex
- stroking of foot
- UMN damage - toes flare is abnormal
- curling normal
hyperreflexia with UMN damage?
- loss of normal inhibitory background
- sprouting of local afferents - increased input from the initial primary afferent imput
- receptors to membrane
denervation hypersensitivity
increased expression of receptors on surface of LMNs and interneurons
partial paralysis
NO
paresis
plegia
stroke
hemi
half
para
pair of limbs
quadra
four limbs
stroke lesions
affects many different systems
damage to corticospinal systems
levels below lesion
LMN signs at lesion level
UMN signs inferior to lesion
lesion above decussation
contralateral signs
lesion below decussation
ipsilateral signs
extrapyramidal system
non-contrical UMN system
non-cortical UMN systems
proximal limb
- reflex posture
- also voluntary control - corticobulbar tract
medial vestibulospinal tract
descending medial longitudinal fasciculus
anterior corticospinal tract
technically a cortical UMN tract
-but, its bilaterally, neck muscles, posture function
rubrospinal tract
lateral motor system
-begins in brainstem
rubrospinal tract
cell bodies in red nucleus
- axons decussate in midbrain
- descend contralaterally in lateral funiculus
-to cervical cord only
- *distal muscles of arm
- arm/forearm flexors
very small in humans
vestibulospinal tracts
medial and lateral tracts
medial vestibulospinal tract
aka descend MLF
cell bodies in medial/inferior vestibular nucleus
-axons descend bilaterally through cervical and upper thoracic
**neck muscles, head posture
lateral vestibulospinal tract
cell bodies in lateral vestibular nucleus
-axons descend ipsilateral
** antigravity muscles
entire cord to trunk posture
*** damage - ipsilateral deficits
medial longitudinal fasciculus
ascending
cell bodies in medial.inferior vestibular nucleus
- *ascends to innervate III, IV, VI
- extraocular muscles of eye
**bilateral
reticulospinal tract
medial and lateral
cell bodies - reticular formation
back up when corticospinal fibers are damaged (theory)
pontine reticulospinal tract
medial
**ipsilateral
medullar reticulospinal tract
lateral
**bilateral
tectospinal tract
superior colliculus - cell bodies
- axons decussate in midbrain
- descend contralateral
end in cervical levels
**neck, postural muscles
**visual grasp reflex
