Physiology-Descending Motor Pathways

Question 1

What are the higher motor areas in the cerebral cortex?

Answer 1

Prefrontal motor cortex, lateral premotor area and supplementary motor area

Question 2

What is the definition of a lower motor neuron? What are the 2 places lower motor neurons original from?

Answer 2

Nerves that directly innervate muscle. They can come from the spinal cord (alpha motor neurons) and the brainstem (cranial nerves)

Question 3

What are the different types of inputs that go into the lower motor neurons?

Answer 3

Pattern generators (repetitive movements like walking), reflex interneurons and upper motor neurons from the CNS

Question 4

Describe the somatotopic arrangement of the lower motor neurons in the spinal cord.

Answer 4

Medially: lower motor neurons innervating trunkal muscles. Laterally: more distal parts of the limbs. Dorsal: flexors. Ventral: extensors.

Question 5

What are 3 descending motor pathways that originate in the cerebral cortex?

Answer 5

Corticobulbar tract (cranial nerves), corticospinal tract (all crossed) and other tracts that originate in the cerebellum.

Question 6

What regions of the brain contribute fibers to the lateral corticospinal tract?

Answer 6

Premotor cortex, primary motor cortex, somatosensory cortex

Question 7

What path does the corticospinal tract take on its way to the spinal cord?

Answer 7

Cortex -> Corona Radiata -> Posterior limb of internal capsule -> Crus cerebri -> Basilar Pons -> Medullary Pyramid -> Pyramidal decussation -> Lateral funiculus down the whole spinal cord

Question 8

A patient comes to see you in clinic complaining of difficulty drawing pictures. He also has trouble with other fine movements of his hands. What region of the corticospinal tract may be affected in this patients spinal cord?

Answer 8

Lateral region

Question 9

What path does the rubrospinal tract take on its way to the spinal cord?

Answer 9

Red nucleus -> Midbrain decussation -> Lateral funiculus -> Lateral region of ventral horn in cervical area

Question 10

What muscles may be affected if a lesion impinged the rubrospinal tract?

Answer 10

The flexor muscles of the upper limb

Question 11

What path does the anterior corticospinal tract take on its way to the spinal cord?

Answer 11

Cortex -> Corona radiata -> Midbrain -> Spino-medullary junction -> Anterior funiculus of the spinal cord to the cervical region

Question 12

A patient comes to see you in clinic with a lesion in his spinal cord and difficulty with postural movements of the head and upper extremity on the right side. Where in the spinal cord is the likely location of this lesion? What side of the CNS do signals originate that go through this pathway?

Answer 12

Anterior corticospinal tract. Note that these fibers do not cross over at the spinomedullary junction and travel on the ipsilateral (right in this patient) side of their location in the CNS.

Question 13

What path does the vestibulospinal tract follow on its way down the spinal cord?

Answer 13

Lateral vestibular nucleus -> Ipsilateral side of the spinal cord. Medial vestibular nucleus -> bilateral descent down cervical spinal cord

Question 14

A patient comes to see you because they slipped and fell on the ice. He cracked his head open because he did not have any reflex to maintain his balance. In what region of the descending motor system does this patient have a problem?

Answer 14

Medial descending system: specifically the lateral vestibulospinal tract. This system is responsible for extensors of the upper liimbs, lower limbs and the righting reflex.

Question 15

A patient comes to see you in clinic with problems coordinating his head movements with his eye movements. He also has problems with head posture. Where is the likely problem in his descending motor system?

Answer 15

Medial vestibulospinal tract.

Question 16

You are working in Africa on a child with malaria. He is showing signs of increased intracranial pressure. What causes him to posture himself as seen below?

Answer 16

Increased intracrainial pressure puts pressure on the brainstem near the midbrain/pons junction. Because the lateral vestibular tract is below this region he has unopposed extensor and posturing of the upper and lower limbs, decerebrate rigidity.

Question 17

What path does the reticulospinal tract follow on its way down from the brainstem?

Answer 17

Pontine reticulospinal tract goes ipsilaterally, the medullary reticulospinal tract goes down bilaterally.

Question 18

A patient comes to see you with problems with truncal/proximal postural muscles. What part of the descending motor system has likely been affected?

Answer 18

Pontine reticulospinal tract

Question 19

A patient comes to see you with sleep atonia. What descending motor tract has likely been affected?

Answer 19

Medullary reticulospinal tract. It plays a role in inhibiting the truncal and proximal musculature.

Question 20

Clinical signs of lower motor neuron lesions?

Answer 20

Flaccid paralysis, reduced muscle tone, reduced myotatic (stretch) reflex, rapid atrophy

Question 21

Clinic signs of upper motor neuron lesions?

Answer 21

Increased muscle tone, spastic paralysis, Babinski sign, exaggerated myotatic (stretch) reflex and slow atrophy

Question 22

How do you know if a patient presenting with upper motor neuron symptoms has a lesion above or below the spino-medullary junction?

Answer 22

Above: contralateral symptoms. Below: ipsilateral symptoms

Question 23

A patient comes to see you with increased muscle tone, exaggerated stretch reflexes and spastic paralysis in the right arm leg and trunk. Physical exam reveals a + Babinski sign. Where is the most likely location of the lesion?

Answer 23

C. The pyramid. This is before the pyramidal decussation, so symptoms present on the contralateral side of the body. This is will also affect all of regions of the body.

Question 24

A patient comes to see you with increased muscle tone, exaggerated stretch reflexes and spastic paralysis in the right leg. Physical exam reveals a + Babinski sign. Where is the most likely lesion causing these symptoms?

Answer 24

A: The left medial precentral gyrus. He is presenting with upper motor neuron symptoms and the lesion is in the contralateral region that controls the lower limbs.

Question 25

A patient comes to see you with increased muscle tone, exaggerated stretch reflexes and spastic paralysis in the left arm, leg and trunk. Where is the most likely lesion causing these symptoms?

Answer 25

This patient is presenting with upper motor neuron symptoms. and the only choice that would cause symptoms on the left side is D: left lateral funiculus of the cervical spinal cord.

Question 26

A patient comes to see you with increased muscle tone, exaggerated stretch reflexes and spastic paralysis in the right arm, trunk and lower face. What region is most likely affected by this lesion?

Answer 26

This patient is presenting with upper motor neuron symptoms. B: Primary motor cortex in the precentral gyrus. The face is affected because the upper motor neuron fibers (corticobulbar fibers) start in the primary motor cortex and go to the lower motor neurons located in the brainstem.

Question 27

Why do you have difficulty smiling and whistling, but still can chew when you damage the corticobulbar fibers?

Answer 27

Many of the lower motor neurons to the face that come from the medulla split and work bilaterally so one upper motor neuron lesion will be compensated for by the other side. The lower motor neurons in the lower face only have crossed input and will manifest with these symptoms.

Question 28

The patient seen below comes to see you with complaints of weakness in his legs. Physical exam reveals lower limb weakness, atrophy and fasciculations. Reflexes were brisk and hyperactive. Babinski sign was also noted. What is your diagnosis?

Answer 28

Amyotrophic Lateral Sclerosis. This is characterized by both upper and motor neuron symptoms because both areas are degenerating.