Motor Cortex

Question 1

What does decorticate rigidity look like and what causes it?

Answer 1

Decorticate rigidity is flexion of the upper limbs and extension of the lower limbs. It is caused by a lack of cortical inhibition to the brainstem. This means that the rubrospinal tract flexes the upper limbs and the reticulospinal tract causes extension of the lower limbs due to lack of inhibition.

Question 2

What does decerebrate rigidity look like and what causes it?

Answer 2

Decerebrate rigidity is extension of the upper and lower limbs. It is caused by a lack of cortical inhibition to the brainstem that has extended further down than in decorticate rigidity so that the red nucleus of the midbrain can no longer cause flexion of the upper limbs and only the reticulospinal tract is maintained causing extension of the whole body. This is a very bad sign, death is imminent.

Question 3

What is the babinski sign and what does it indicate?

Answer 3

the babinski sign is abnormal dorsal fanning of the toes in respond to a noxious stimulus to the sole of the foot - it indicates an upper motor neuron lesion

Question 4

Which cranial motor nerves only get contralateral innervation from upper motor neurons?

Answer 4

the lower nucleus of the facial nerve and the hypoglossal nucleus

Question 5

Clinically, how can you tell if a facial nerve lesion is an upper or lower motor neuron lesion?

Answer 5

if the patient can raise both eyebrows then its an upper motor nerve lesion, if there is bilateral muscle weakness in the forehead then its a lower motor nerve lesion

Question 6

Do all neurons in the corticospinal tract travel in the lateral part of the spinal cord?

Answer 6

No - 10-15% are ventromedial and travel ipsilaterally - this is the ventral corticospinal tract

Question 7

What is the role of the ventral corticospinal tract?

Answer 7

anticipatory postural movements

Question 8

How can decerebrate cats adjust their speed of locomotion to treadmill speeds?

Answer 8

initiation of swing phase is controlled by sensory feedback from extensor muscles - stimulation of spindles in the extensor muscle will result in an early swing and stimulation of tendon organs in the extensor muscle will result in a delayed swing

Question 9

What is the functional organisation of locomotion?

Answer 9

there is a pattern generator in the spinal cord that encodes the pattern of locomotion without any cortical input