6 - Cortical Control of Motor Activity: The Corticospinal Tract

Question 1

What are the three main types of movement?

Answer 1

Reflexes: stereotypes responses to stimuli

Automatic postural adjustments

Voluntary: goal-directed, internally generated, and improve with practice.

Question 2

What are the characteristics of the corticospinal tract? What is the function?

Answer 2

One upper motor neuron that projects to the lower motor neurons in the ventral horn of ALL levels of spinal cord.

Controls voluntary movement of distal extremities.

Question 3

What are the steps in the path of the upper motor neuron (UMN)?

Answer 3

Cerebral cortex
Corona radiata
Internal capsule (posterior limb)
Crus cerebri 
Ventral pons 
Medullary pyramid (decussation)
Lateral funiculus

Question 4

Where are the cell bodies of upper motor neuron in the corticospinal tract?

Answer 4

Cerebral cortex in the primary motor cortex and premotor cortex (brodmanns area 4)

This is the top of the hierarchy

Question 5

What is the somatotopy of the cerebral cortex? What is the benefit of this part of the pathway?

Answer 5

Feet and legs in center, hands top and more lateral, face and mouth very lateral.

There’s lots of redundancy such that axons project from more than one area. This allows for plasticity and less loss of function with injury.

Question 6

When can you have an alteration of the brain homunculus?

Answer 6

If someone undergoes an amputation, you will see more representation of the contralateral limb that’s still present in order to compensate for the loss.

Question 7

Where do the axons of the corticospinal tract go after the cerebral cortex?

Answer 7

They contribute to the corona radiata.

Question 8

Where do the axons of the corticospinal tract go after the internal corona radiata?

Answer 8

They pass through the posterior limb of the internal capsule

Question 9

Where do the axons of the corticospinal tract go after they pass through the posterior limb of the internal capsule?

Answer 9

They travel through the middle portion of the crus cerebri in the midbrain (anterior surface of the midbrain tegmentum)l.

Question 10

Where do the axons of the corticospinal tract go after the crus cerebri?

Answer 10

Fibers coalesce to form the medullary pyramids.

In the caudal medulla, the fibers decussate (90% of fibers)

Question 11

Where do the axons of the corticospinal tract go after the medullary pyramid?

Answer 11

They descend in the cord in the lateral funiculus.

Question 12

What does the corticospinal tract innervate?

Answer 12

Lower motor neurons located laterally within the ventral horn.

Question 13

What symptoms occur with a corticospinal tract (UMN) lesion?

Answer 13

Contralateral paresis or paralysis, spasticity, hyperreflexia, positive babinksi sign, positive hoffman sign.

Question 14

What do corticospinal tract lesions above the medullary decussation (in the internal capsule or brainstem) result in?

Answer 14

Contralateral symptoms.

Question 15

What do corticospinal tract lesions below the medullary decussation (in the spinal cord) result in?

Answer 15

Ipsilateral symptoms.

Question 16

What is a positive babinski sign? Who has this?

Answer 16

When stroking the bottom of the foot, an upper motor neuron lesion will result in flaring of the toes.

Normal response is toe flexion.

Positive babinski occurs in infants before 12-15 months because their tract isn’t fully myelinated yet.

Question 17

What is a positive Hoffman sign?

Answer 17

When you flick the middle finger, a patient with an upper motor neuron lesion will have their thumb and pointer finger come together.

Question 18

What cranial nerve is effected when there’s a corticospinal tract lesion in the midbrain? What is this called?

Answer 18

CN III - oculomotor

Weber Syndrome

Question 19

What cranial nerve is effected when there’s a corticospinal tract lesion in the pons?

Answer 19

CN VI - Abducens

Question 20

What cranial nerve is effected when there’s a corticospinal tract lesion in the medulla? What is this called?

Answer 20

CN XII - hypoglossal

Medial Medullary Syndrome.

Question 21

What deficits are associated with Wber’s Syndrome?

Answer 21

Contralateral paralysis or paresis and ipsilateral oculomotor nerve palsy.

This is associated with a lesion of the cortisospinal tract in the midbrain.

Question 22

What deficits are associated with medial medullary syndrome?

Answer 22

Wipes out medullary pyramids (axons that make up corticospinal tract) resulting in loss of fractionated movements of distal extremities.

IPSI hypoglossal nerve injury and CONTRA paralysis

Question 23

What results from damage to the corticospinal tract/pyramidal system?

Answer 23

Problems with voluntary movement of distal extremities.