Descending Motor Pathways - Lecture 6

Question 1

how many descending pathways are there

Answer 1

7

exert their influence on muscle activity

Question 2

how many pathways derive their fibers from the sensorimotor complex

Answer 2

3

lateral corticospinal

anterior corticospinal

corticobulbar tract

Question 3

how many derive their fibers from the brainstem

Answer 3

4

tectospinal

rubrospinal

reticulospinal

vestibulospinal

Question 4

where do ALL the descending motor pathways terminate

Answer 4

spinal cord

EXCEPT THE CORTICOBULBAR TRACT

Question 5

where does the corticobulbar tract terminate

Answer 5

brainstem

Question 6

corticobulbar

Answer 6

cranial nerves

fascial muscles

Question 7

corticospinal

Answer 7

spinal nerves

origin of axons

Question 8

origin of axons –> corticospinal

Answer 8

1/3 from primary motor cortex (M1)

1/3 from premotor areas

1/3 from somatosensory cortex

Question 9

where do 85-90% of the axons of the corticospinal tract decussate

Answer 9

in the medulla

referred to as pyramidal decussation

Question 10

what happens to the axons after decussation –> corticospinal

Answer 10

descend the length of the SC as the lateral corticospinal tract

Question 11

where do the axons of the corticospinal tract terminate

Answer 11

primarily in the cervical, lumbar and sacral levels

Question 12

10-15% of the axons of the corticospinal tract

Answer 12

do not decussate

stay ipsilateral

forms anterior corticospinal tract

Question 13

where do axons of the anterior corticospinal tract terminate

Answer 13

cervical and upper thoracic

Question 14

lateral corticospinal tract

Answer 14

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

Question 15

anterior corticospinal tract

Answer 15

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

Question 16

corticobulbar tract controls

Answer 16

facial muscles

bilateral input to motor neurons controlling muscles of the upper face

contralateral input to motor neurons controlling the lower face

Question 17

corticobulbar tract

Answer 17

motor pathway connecting the cerebral cortex to the brainstem

Question 18

what is the corticobulbar tract involved in

Answer 18

carrying out motor fxn of the non-oculomotor cranial nerves

do not directly project to oculomotor, trochlear and abducens nuclei

Question 19

brain stem pathways –> lateral

Answer 19

rubrospinal tract
–> distal limb control
–> crude

Question 20

brainstem pathways –> medial

Answer 20

tectospinal tract

reticulospinal tract

vestibulospinal tract

Question 21

tectospinal tract

Answer 21

eye-head coordination

Question 22

reticulospinal tract

Answer 22

automatic postural adjustments and movements

Question 23

vestibulospinal tract

Answer 23

balance (axial muscles)

automatic postural adjustments

Question 24

brainstem control over spinal reflexes –> vestibulospinal tracts –> medial tract

Answer 24

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)

Question 25

brainstem control over spinal reflexes –> vestibulospinal tracts –> lateral tract

Answer 25

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

Question 26

brainstem control over spinal reflexes –> reticulospinal tracts

Answer 26

innervate (indirectly) antigravity motor neurons

activated by corticoreticular fibers and by somatosensory inputs

especially nociceptive

Question 27

brainstem control over spinal reflexes –> rubrospinal tract

Answer 27

crosses descending systems controlling mostly upper limbs (proximal flexors)

inputs from cerebral cortex and cerebellum

Question 28

brainstem reflexes

Answer 28

blink reflexes

feeding mechanisms (rhythmic chewing and licking movements)

micturition reflex (urination)

gaze control

Question 29

UMN

Answer 29

projection neurons in layer V of the cerebral cortex

Question 30

UMN execute

Answer 30

voluntary movement via pyramidal and extrapyramidal pathways

Question 31

where are most UMN located

Answer 31

motor cortex (M1 area or Brodmann’s area 4) and the premotor cortex (M2 area or Brodmann’s area 6)

Question 32

possible lesion sites

Answer 32

cerebrum

internal capsule

brainstem

SC

Question 33

upper motor neuron lesions

Answer 33

pyramidal tract

Question 34

spastic paralysis

Answer 34

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

Question 35

abnormal reflexes

Answer 35

increased deep tendon reflexes (DTR’s)

clonus

clasp-knife reflex

babinski sign

Question 36

increased deep tendon reflexes

Answer 36

hyperreflexia

Question 37

clonus

Answer 37

series of rhythmic alternating contractions of agonist and antagonist muscles

lowered threshold for DTR’s

Question 38

clasp-knife reflex

Answer 38

increased resistance to stretch followed by loss of resistance

lowered threshold for DTR’s and golgi tendon reflexes

Question 39

babinski sign

Answer 39

DF of big toe

fanning of little toes after stroking sole of foot

Question 40

other areas of the brain involved in movement

Answer 40

ventromedial frontal cortex

cerebellum

basal ganglia

branstem

Question 41

ventromedial frontal cortex

Answer 41

involved in body control, posture and whole body movements

Question 42

where does all movement funnel through

Answer 42

alpha motor neuron