Organization of Descending Pathways and BS motor control

Question 1

dorsolateral descending pathway

Answer 1

located in the lateral columns of the SC, descend unilaterally, and contribute to distal muscles

Question 2

ventromedial descending pathway

Answer 2

located in the ventromedial portion of the SC, descend bilaterally, and contribute to proximal and axial/trunk muscles

Question 3

definition of descending (“upper” motor neuron) pathways

Answer 3

neurons and their axons that directly or indirectly excite or inhibit alpha motor neurons (LMN). For example, cells in the cerebral cortex and brainstem whose axons form the descending motor pathways such as the corticospinal and reticulospinal pathways.

Question 4

are most brainstem motor functions under our conscious control

Answer 4

NO

Question 5

4 motor functions of brainstem motor control

Answer 5

Posture
Muscle tone
Balance
Coordination of movement patterns

Question 6

where are reticular nuclei located

Answer 6

Reticular formations are found throughout the brainstem in the:
pons
medulla
midbrain

Question 7

2 reticulospinal pathways

Answer 7

Medullary reticulospinal

Pontine reticulospinal

Question 8

Medullary reticulospinal

Answer 8

begins in medullary reticular formation and descends to SC

Question 9

Pontine reticulospinal

Answer 9

begins in pontine reticular formation and descends to SC

Question 10

4 motor functions of reticular formation

Answer 10

1. muscle tone
2. posture
3. modification of balance reflexes during head movements
4. coordination of movement patterns

Question 11

muscle tone

Answer 11

contribute to the maintenance of muscle tone - reticular nuclei receive extensive projections from the limbic system that serve to modify muscle tone based on emotions
this provides a mechanism for nervousness and anxiety to affect muscle tone and motor performance (The Big Choke)

Question 12

posture

Answer 12

setting postural tone and making postural adjustments in anticipation of movement

Question 13

modification of balance reflexes during head movements

Answer 13

this is because they receive information from vestibular nuclei and the cerebellum - the reticular system then modifies the balance and righting reactions in response

Question 14

coordination of movement patterns

Answer 14

help regulate the CPG to control speed of locomotion

Question 15

decerebrate rigidity (lesion and presents as)

Answer 15

• caused by bilateral lesion in the pons - presents as extensor rigidity of UE and LE
  easy distinction: “decerebrate” has a lot of E’s, and so does “extended extremities”

Question 16

decorticate rigidity (cause and presents as)

Answer 16

• caused by severe bilateral lesion in cerebral hemispheres/cortices - presents as flexor rigidity in UE and extensor rigidity in LE

Question 17

non-motor functions of reticular nuclei and which brainstem is involved in each function

Answer 17

midbrain - pain modulation - related to PAG
pons - consciousness and respiratory control
medulla - cardiovascular control

Question 18

where is the red nucleus

Answer 18

midbrain

Question 19

corticobulbar tract

Answer 19

a two-neuron path which unites the cerebral cortex with the cranial nerve nuclei in the brainstem involved in motor functions (apart from the oculomotor nerve).

Question 20

Cortical descending pathways regulate

Answer 20

distal, proximal and postural muscles directly to the spinal cord or through brainstem pathways

Question 21

upper motor neuron syndrome (where are lesions)

Answer 21

Lesion in the primary motor cortex, internal capsule or corticobulbar/corticospinal tract in the brainstem or spinal cord.

Primary motor cortex lesions have potential to produce all UMN signs and symptoms.

Question 22

s/s upper motor neuron syndrome

Answer 22

weakness (paresis)
spasticity (usually)
no early atrophy (muscles may atrophy months later due to disuse)
abnormal reflex activity (Babinski reflex, clonus)

Question 23

function of rubrospinal pathway

Answer 23

acts as a redundant pathway to the lateral corticospinal pathway
helps to activate distal muscles

Question 24

where are there are no clinically significant lesion deficits

Answer 24

in the red nucleus or rubrospinal pathway

Question 25

lateral corticospinal pathway - path and function

Answer 25

begins in the cortex -> gives off branch to red nucleus -> crosses at pyramidal decussation -> descends to target level of spinal cord on the opposite side to where it began

functions to innervate the distal muscles of the limbs

Question 26

lesion in lateral corticopsinal pathway

Answer 26

if before crossing at pyramidal decussation = contralateral affectation of entire side of body
s/s (with most significant effect on distal muscles):
UMN s/s

if after crossing = ipsilateral affectation of side of body below level of the lesion
s/s: UMN

Question 27

tectospinal pathway (where it starts and ends)

Answer 27

originates in the sup. colliculus of the midbrain and extends to the cervical spinal segments

Question 28

tectospinal pathway functions

Answer 28

it functions to help coordinate the head/neck with eye movements
important note: this pathways ONLY extends through the cervical spinal segments because of the motor involvement of the head and neck - i.e. just like almost everything else, its location is defined by its function

Question 29

location of vestibular nuclei

Answer 29

lateral caudal pons and open medulla

Question 30

location of vestibulospinal tracts

Answer 30

lateral vestibulospinal
location: ventral column throughout SC and descends ipsilaterally

medial vestibulospinal
location: ventral column throughout cervical and upper thoracic segments of SC and descends bilaterally

Question 31

function of vestibulospinal tracts

Answer 31

lateral fx:
enhances extensor tone and plays a significant role in the regulation of muscle tone especially as it influences balance, posture, and the coordination of movement.
coordinates movement by influencing the trajectory of movement.
control of posture
control of balance with a strong influence on proximal and postural muscles

medial fx: coordinates neck and head righting reactions

Question 32

lesion in vestibular nuclei s/s

Answer 32

ipsilateral hypotonia
balance and postural control dysfunction
ipsilateral motor ataxia; coordination problems
decreased head and neck righting reactions
nausea
vertigo
nystagmus

Question 33

lesion in lateral vestibulospinal tract s/s

Answer 33

ipsilateral hypotonia
balance dysfunction
ipsilateral motor ataxia; coordination problems

Question 34

lesion in medial vestibulospinal tract s/s

Answer 34

decreased head and neck righting

Question 35

hypoglossal lesion

Answer 35

• corticuobulbar lesion to hypoglossal nucleus
• tongue deviates towards side of lesion
  ex) move laptop - when you push R side forward, it turns to the L

Question 36

tract where decerebrate rigidity occurs

Answer 36

pontine reticulospinal

Question 37

tract where decorticate rigidity occurs

Answer 37

medullary reticulospinal