36 - Posture and Locomotion

Question 1

Postural signs of damage to the brainstem - decerebrate

Answer 1

Upper and lower limbs extended (overactivity, upper motor neuron sign).

Question 2

Postural signs of damage to the brainstem - decorticate

Answer 2

Upper limbs flex, lower limbs extend.

Question 3

Which spinal tract controls postural muscles?

Answer 3

Medial brain stem pathways.
Ipsilateral.
Vestibulospinal tract, reticulospinal tract and tectospinal tract.

Question 4

Example of an input into medial brainstem pathways for posture

Answer 4

Tectum (or superior colliculus) detects visual cues.

EG: If visual world suddenly looms, reflex to alter posture (EG when falling over)

Question 5

Tract that controls upper cervical distal motor neurons

Answer 5

Rubrospinal tract (beginning in the Red nucleus)

Question 6

Types of projections to lower motor neurons from reticulospinal tract

Answer 6

Positive and negative connections from medullary reticular formation onto muscle.
Mostly negative (inhibitory) synapses between cortical neurons and reticular formation lower motor neurons.

Question 7

What does the red nucleus mostly control?

Answer 7

Flexors of the arms.

Question 8

Why do the arms flex and the legs extend in decorticate rigidity?

Answer 8

Motor cortex not influencing brainstem.
Lose inhibitory control of red nucleus (to upper limb flexors) and reticular formation (extensors, on balance, dominate in legs)

Question 9

Why do the arms and legs extend in decerebrate rigidity?

Answer 9

Brainstem function impaired.
Loss of inhibition to both flexors and extensors in limbs, but antigravity extensors have a greater resting tone, so get extension.

Question 10

When do adults demonstrate Babinski sign?

Answer 10

If there is damage to cortical control of spinal cord

Question 11

Distribution of innervation of lower motor neurons

Answer 11

Bilateral, except for those innervating lower face and tongue

Question 12

Effect of an upper motor neuron lesion of facial muscles

Answer 12

Weakness of contralateral inferior facial muscles

Question 13

Effect of a lower motor neuron lesion of facial muscles

Answer 13

Weakness of entire ipsilateral half of face

Question 14

Why does an upper motor neuron lesion of facial muscle innervation only affect inferior face?

Answer 14

Muscles of upper face are innervated by both cingulate cortices.
Need to lesion lower motor neuron, where these two tracts fuse, to immobilise half the face.

Question 15

How can movement be measured?

Answer 15

Electromyography (EMG)

Question 16

Two broad types of movement (muscle contraction)

Answer 16

EG: when a ball is dropped into someone’s hand:
Anticipatory (increase in muscle tone, anticipating catching ball).
Reflex (when ball hits hand, pushing arm out of position, muscle spindles respond)

Question 17

How can decerebrate cats alter speed on a treadmill?

Answer 17

Sensory afferents from muscle spindles make extension of limb stop past a point, initiate swing phase of movement.

Golgi tendon organs inhibit flexion while they are bearing load (bearing weight of animal).

Question 18

Role of cortex in gait

Answer 18

Altering motor pattern (EG: step over an obstacle)

Question 19

Examples of abnormal gait patterns with CNS disorders
1
2
3
4

Answer 19

1) Ataxic gait
2) Choreaform gait
3) Hemiparetic gait (lost cerebral cortical control of spinal pathways)
4) Parkinsonian gate

All very stereotypic of a particular type of pathology