Motor Systems: UMNs

Question 1

are upper motor neurons part of CNS or PNS

Answer 1

CNS only
brain –> spinal cord

Question 2

function of UMNs

Answer 2

inhibit lower motor neurons:

initiate the process of voluntary movement
maintain muscle tone
regulate posture

Question 3

UMN systems

Answer 3

1. pyramidal
2. extrapyramidal

Question 4

where are neurons of pyramidal system located

Answer 4

cell bodies: primary motor cortex
axons: brainstem and spinal cord

Question 5

pyramidal pathways

Answer 5

1. corticospinal tract
2. corticonuclear tract
3. corticopontocerebellar tract

Question 6

corticospinal tract pathway

Answer 6

cortex –> internal capsule –> axons through corticospinal tract –> splits into lateral and ventral

lateral: decussates at junction of brainstem and spinal cord –> synapses on LMNs in spinal cord

ventral: continues ipsilateral to synapse on LMNs in spinal cord

Question 7

what do corticospinal tract neurons innervate

Answer 7

synapses with LMNs that innervate skeletal muscle of trunk, limbs, and tail

Question 8

function of corticospinal tract

Answer 8

facilitate contralateral flexors
inhibit contralateral extensors

Question 9

corticonuclear tract pathway

Answer 9

cortex –> internal capsule –> axons through corticonuclear tract –> decussates at different level of brainstem –> terminates at cranial nerve nuclei

Question 10

what do corticonuclear tract neurons innervate

Answer 10

synapses with LMNs that innervate cranial nerves

Question 11

function of corticonuclear tract

Answer 11

eye movement (CN III, IV)
mastication (CN V)
facial expression (CN VII)
neck movement (CN XI)
tongue movement (CN XII)

Question 12

corticopontocerebellar tract pathway

Answer 12

cortex –> pons –> cerebellum

corticopontine tract: cortex –> pontine nuclei

pontocerebellar tract: pontine nuclei –> decussates –> cerebellum

Question 13

function of corticopontocerebellar tract

Answer 13

feedback pathway from cortex to cerebellum to allow cerebellum to plan movements

Question 14

signs of pyramidal tract lesions

Answer 14

loss of skilled voluntary movement
- contralateral postural reaction deficits

NORMAL gait - NO paresis/paralysis

Question 15

extrapyramidal systems

Answer 15

1. basal nuclei
2. substantia nigra
3. rubrospinal tract
4. reticular formation
5. vestibulospinal tracts
6. tectospinal tracts

Question 16

basal nuclei

Answer 16

subcortical nuclei in each cerebral hemisphere

caudate nuclei
putamen
globus pallidus
claustrum

Question 17

function of basal nuclei

Answer 17

modulation of motor activity from the motor cortex

goes through the thalamus

Question 18

direct pathway of basal nuclei function

Answer 18

facilitates execution of motor command

1. caudate/putamen inhibit medial globus pallidus
2. medial globus pallidus can’t inhibit thalamus
3. thalamus excites cerebral cortex
4. executes motor function

Question 19

indirect pathway of basal nuclei

Answer 19

inhibits execution of motor command

1. caudate/putamen inhibit lateral globus pallidus
2. later globus pallidus can’t inhibit subthalamic nuclei
3. subthalamic nuclei excites medial globus pallidus
4. medial globus pallidus inhibits thalamus
5. thalamus can’t excite cerebral cortex
6. no execution of motor function

Question 20

signs of basal nuclei dysfunction

Answer 20

young animals normal until 4 months old
- lack of movement initiation
- festination

Question 21

yellow star thistle toxicity

Answer 21

necrosis of global pallidus and substantia nigra

Question 22

substanstia nigra

Answer 22

midbrain nucleus involving dopaminergic neurons

Question 23

function of substantia nigra

Answer 23

synapses onto dopamine receptors in caudate and putamen to INCREASE thalamic excitation of motor cortex
- facilitates D1 receptors
- inhibits D2 receptors

Question 24

D1 receptors

Answer 24

located in medial caudate and putamen; ACTIVATED by substantia nigra

activates direct pathway –> facilitates motor execution

Question 25

D2 receptors

Answer 25

located in lateral caudate and putamen; INHIBITED by substantia nigra activates indirect pathway --> inhibits motor execution

Question 26

rubrospinal tract

Answer 26

tracts the extend to and from the midbrain red nucleus

Question 27

function of the rubrospinal tract

Answer 27

facilitates flexors inhibits extensors

Question 28

red nucleus

Answer 28

located in midbrain near midline reticular formation - receives inputs from cortex, basal nuclei, cerebellum - send outputs from midbrain --> pons --> medulla --> spinal cord

Question 29

olivocerebellar tract pathway

Answer 29

rubrospinal tract --> olivary nucleus in medulla --> decussates to contralateral cerebellum

Question 30

olivocerebellary tract function

Answer 30

monitors extrapyramidal systems lesions cause loss of coordination

Question 31

reticular formation

Answer 31

meshwork of nuclei throughout the brainstem 1. pontine reticulospinal tract 2. medullary reticulospinal tract

Question 32

function of reticular formation

Answer 32

posture and locomotion tracts are used to balance facilitation and inhibition of LMNs

Question 33

pontine reticulospinal tract function

Answer 33

facilitates extensors inhibits flexors

Question 34

pontine reticulospinal tract pathway

Answer 34

pontine reticular formation (pons) --> ipsilateral ventral funiculus --> spinal cord

Question 35

medullary reticulospinal tract function

Answer 35

facilitates flexors inhibits extensors

Question 36

medullary reticulospinal tract pathway

Answer 36

medullary reticular formation (medulla) --> ipsilateral ventral funiculus --> spinal cord

Question 37

vestibulospinal tracts

Answer 37

tracts that extend from vestibular nuclei to spinal cord 1. medial vestibulospinal tract 2. lateral vestibulospinal tract

Question 38

function of vestibulospinal tracts

Answer 38

maintain balance of body against gravity facilitates extensors inhibits flexors

Question 39

medial vestibulospinal tract

Answer 39

maintains head position by synapsing on neck/shoulder muscle LMNs medial vestibulospinal nuclei --> ipsilateral ventral funiculus --> spinal cord

Question 40

lateral vestibulospinal tract

Answer 40

stabilizes body posture by synapsing on trunk/limb muscle LMNs lateral vestibulospinal nuclei --> ipsilateral ventral funiculus --> spinal cord

Question 41

tectospinal tract

Answer 41

tracts extending from colliculi to spinal cord

Question 42

function of tectospinal tract

Answer 42

turns head toward visual or auditory stimuli facilitates extensors of cervical LMNs

Question 43

tectospinal tract pathway

Answer 43

rostral/caudal colliculi --> decussates to contralateral ventral funiculus --> spinal cord

Question 44

most significant UMN lesion

Answer 44

medullary reticulospinal tract signs: excessive extensor tone

Question 45

signs of extrapyramidal lesions

Answer 45

loss of voluntary movement gait: paresis, delayed/absent protraction, spasticity (stiff gait) posture: decerebrate rigidity, opisthotonus mentation: comatose reflexes: hyperreflexia, cross extensor reflex in lateral recumbency