Motor Pathways*

Question 1

What do motor pathways do?

Answer 1

Control movement is initiated in the cerebral cortex. Axons project from the motor cortex to the brainstem or spinal cord.

Question 2

What are upper motor neurons?

Answer 2

Axons from any source in the CNS which travel to the brainstem or spinal cord.

Question 3

Where do upper motor neurons synapse?

Answer 3

In the ventral horn of the spinal cord with the lower motor neurons.

Question 4

What do lower motor neurons form?

Answer 4

The efferent component of the spinal and cranial nerves and innervate voluntary muscles in the head and body.

Question 5

What 3 areas of the frontal lobe are involved in motor movement?

Answer 5

• precentral gyrus
• premotor area
• supplemental motor area

Question 6

What is the role of the premotor area?

Answer 6

It receives inputs from the basal ganglia and the parietal association cortex. It plays a role in storing learned programs for complex movement.

Question 7

What is the supplemental motor cortex?

Answer 7

It is continuous with the premotor cortex and located on the medial aspect of each hemisphere.

It controls postural muscles of the trunk and limbs.

Question 8

Where is the primary motor cortex located? and arranged?

Answer 8

In the precentral gyrus in each hemisphere. It is arranged somatopically (upside down).

Question 9

What 2 major groups are motor pathways divided into?

Answer 9

Pyramidal tracts

Extrapyramidal tracts

Question 10

Explain pyramidal tracts.

Answer 10

Originate in the cerebral cortex, carrying motor fibers to the spinal cord and brainstem. Responsible for voluntary muscular control.

Question 11

Explain extrapyramidal tracts.

Answer 11

Originate in the brainstem, carrying motor fibers to the spinal cord. Responsible for involuntary and automatic control (balance, posture, etc.).

Question 12

What two pathways do the pyramidal tracts consist of?

Answer 12

Corticobulbar tract.

Corticospinal tract.

Question 13

What four tracts do extrapyramidal tracts split into?

Answer 13

The vestibulospinal and eticulospinal

Therubrospinalandtectospinal

Question 14

What happens if there is damage to the corticospinal tract?

Answer 14

They are susceptible to damage because they extend nearly the whole length of the CNS. They pass through the internal capsule which is a common site for CVA.

Signs of an upper motor neuron lesion are:
- spastic paresis.
- hypertonia = increase muscle tone.
- hyperreflexia =increased muscle reflexes.
- clonus = involuntary muscle contractions.

Question 15

What happens if the lower motor neurons are damaged?

Answer 15

By damage to a peripheral nerve, this produces flaccid paralysis. This is because no info from either descending motor pathways or reflex pathways can reach the muscle, it then goes floppy.

Question 16

What could damage the peripheral nerve?

Answer 16

Could be because the nerve has been crushed via a bone fracture for example or cut through a deep wound.

Question 17

How do the peripheral nerves degenerate if they are cut?

Answer 17

The 2 ends will pull apart due to contraction of the connective tissue coverings and the regenerating axons find it very difficult to find the right axon sheath made of Schwann cells to grow their target muscles.

Question 18

How do the peripheral nerves degenerate if they are crushed?

Answer 18

if the axons are squashed but the axon sheaths are undamaged, the nerve axons will regenerate and grow down the same axon sheath to reach its target.

Question 19

What if regeneration is unsuccessful?

Answer 19

Short term - Muscles become flaccid.

Medium-term - Muscle will atrophy (waste away).

Long-term - Muscle is replaced by fibrous tissue (fibrosis). Could produce permanent disfigurement if the affected muscle is superficial.

Question 20

What happens if the corticobulbar tracts are damage?

Answer 20

Due to the bilateral nature of the corticobulbar tracts, a unilateral lesion will affect any muscles supplied by cranial motor nerves arising below the level of the lesion resulting in mild muscle paresis bilaterally.