Descending Motor Pathways - Lecture 6 Flashcards
how many descending pathways are there
7
exert their influence on muscle activity
how many pathways derive their fibers from the sensorimotor complex
3
lateral corticospinal
anterior corticospinal
corticobulbar tract
how many derive their fibers from the brainstem
4
tectospinal
rubrospinal
reticulospinal
vestibulospinal
where do ALL the descending motor pathways terminate
spinal cord
EXCEPT THE CORTICOBULBAR TRACT
where does the corticobulbar tract terminate
brainstem
corticobulbar
cranial nerves
fascial muscles
corticospinal
spinal nerves
origin of axons
origin of axons –> corticospinal
1/3 from primary motor cortex (M1)
1/3 from premotor areas
1/3 from somatosensory cortex
where do 85-90% of the axons of the corticospinal tract decussate
in the medulla
referred to as pyramidal decussation
what happens to the axons after decussation –> corticospinal
descend the length of the SC as the lateral corticospinal tract
where do the axons of the corticospinal tract terminate
primarily in the cervical, lumbar and sacral levels
10-15% of the axons of the corticospinal tract
do not decussate
stay ipsilateral
forms anterior corticospinal tract
where do axons of the anterior corticospinal tract terminate
cervical and upper thoracic
lateral corticospinal tract
responsible for the execution of rapid, skilled, voluntary movements of the distal musculature of the upper and lower limbs
specifically the intrinsic and extrinsic muscles of the hand and foot
anterior corticospinal tract
no decussation occurs
descend in the anterior funiculus of the SC to terminate mainly in the anterior horn gray matter of the cervical and upper thoracic spinal cord levels
corticobulbar tract controls
facial muscles
bilateral input to motor neurons controlling muscles of the upper face
contralateral input to motor neurons controlling the lower face
corticobulbar tract
motor pathway connecting the cerebral cortex to the brainstem
what is the corticobulbar tract involved in
carrying out motor fxn of the non-oculomotor cranial nerves
do not directly project to oculomotor, trochlear and abducens nuclei
brain stem pathways –> lateral
rubrospinal tract
–> distal limb control
–> crude
brainstem pathways –> medial
tectospinal tract
reticulospinal tract
vestibulospinal tract
tectospinal tract
eye-head coordination
reticulospinal tract
automatic postural adjustments and movements
vestibulospinal tract
balance (axial muscles)
automatic postural adjustments
brainstem control over spinal reflexes –> vestibulospinal tracts –> medial tract
originates in medial and inferior vestibular nuclei
projects bilaterally to cervical and thoracic SC
mostly controls neck muscles
reflex control of head position through vestibular apparatus (semicircular canals, sacculus, utriculus)
brainstem control over spinal reflexes –> vestibulospinal tracts –> lateral tract
originates in lateral vestibular nucleus
projects ipsilaterally to entire spinal cord
innervates alpha motor neurons (directly or indirectly) that control deep back extensors
maintain balance
antigravity muscles
brainstem control over spinal reflexes –> reticulospinal tracts
innervate (indirectly) antigravity motor neurons
activated by corticoreticular fibers and by somatosensory inputs
especially nociceptive
brainstem control over spinal reflexes –> rubrospinal tract
crosses descending systems controlling mostly upper limbs (proximal flexors)
inputs from cerebral cortex and cerebellum
brainstem reflexes
blink reflexes
feeding mechanisms (rhythmic chewing and licking movements)
micturition reflex (urination)
gaze control
UMN
projection neurons in layer V of the cerebral cortex
UMN execute
voluntary movement via pyramidal and extrapyramidal pathways
where are most UMN located
motor cortex (M1 area or Brodmann’s area 4) and the premotor cortex (M2 area or Brodmann’s area 6)
possible lesion sites
cerebrum
internal capsule
brainstem
SC
upper motor neuron lesions
pyramidal tract
spastic paralysis
hemiplegia or hemiparesis
spasticity
muscular weakness on paretic side
loss of speed and agility on paretic side
complete loss of control over distal muscles (intrinsic muscles of hand)
abnormal reflexes
abnormal reflexes
increased deep tendon reflexes (DTR’s)
clonus
clasp-knife reflex
babinski sign
increased deep tendon reflexes
hyperreflexia
clonus
series of rhythmic alternating contractions of agonist and antagonist muscles
lowered threshold for DTR’s
clasp-knife reflex
increased resistance to stretch followed by loss of resistance
lowered threshold for DTR’s and golgi tendon reflexes
babinski sign
DF of big toe
fanning of little toes after stroking sole of foot
other areas of the brain involved in movement
ventromedial frontal cortex
cerebellum
basal ganglia
branstem
ventromedial frontal cortex
involved in body control, posture and whole body movements
where does all movement funnel through
alpha motor neuron
