Overview Of Motor System

Question 1

What is motor system modulation?

Answer 1

• The motor signals generated by the cerebral cortex are coarse and require modulation.
• The basal ganglia and cerebellum are two major modulatory centers.
• Sensory feedback is vital to cerebellar regulation of motor centers.

Question 2

Summarize motor system organization

Answer 2

Motor systems interact to mediate strength, posture and enable smooth and precise purposeful movements.

• The cortically influenced tracts gain voluntary control of skeletal muscles
• The vestibulospinal tracts are influenced only weakly and indirectly by the cerebral cortex. They are thus largely involuntary motor pathways.

Question 3

What motor tracts are needed for skeketal muscle control?

Answer 3

Most clinically significant

Corticospinal- lateral corticospinal= lumbs
- anterior corticospinal= trunks

Corticobulbar= head and neck

These tracts are responsible for the voluntary control of skeletal muscles of the body.
Injury will yield marked clinical findings.

Question 4

What are the non-voluntary descending motor tracts?

Answer 4

• Apart from the Corticobulbar and the Corticospinal tracts there are other descending pathways that influence motor activity
• These pathways arise from the brainstem
• Play a major role in coordinating subconscious motor activity

Rubrospunal
Lateral reticulospinal
Medial reticulospinal
Lateral vestibulospinal
Medial vestibulospinal

Question 5

What are lower motor neurons?

Answer 5

Lower motor neurons
– Motor neurons that communicate directly between the CNS and somatic muscle
– Can arise from spinal cord (spinal nerves) or brainstem(cranial nerves)

Question 6

What are the upper motor neurons?

Answer 6

Upper motor neurons
– Neurons originating in the brain that communicate closely with lower motor neurons
-Many undergo decussation allowing them to exert bilateral or contralateral contro

Question 7

Describe the upper motor neurons of the spinal cord

Answer 7

Upper Motor Neurons
• located in the white matter (anterior, medial and lateral funiculus)

• Communicate with lower motor neurons

Question 8

Describe the lower motor neurons in the spinal cord

Answer 8

Lower Motor Neurons
• Cell bodies located within the anterior gray matter (ventral horn)

• Communicate with somatic muscles

Question 9

Where does the upper motor neuron end?

Answer 9

Upper motor neurons terminate on lower motor neurons.

Upper motor neurons thus gain control of muscles controlled by spinal nerves

Question 10

What is the function of lateral and medial pathways?

Answer 10

Upper motor neurons in the lateral column primarily gain control of muscles responsible for flexion.

Upper motor neurons in the medial column primarily gain control of muscles responsible for extension.

Question 11

Whst is the location of lower motor neurons in relation to function?

Answer 11

• In the ventral horn of the spinal cord, flexor and adductor neurons lie dorsal to the extensor and abductor neurons.

• Cells for distal muscles lie
laterally to those for truncal structures (i.e., proximal muscles).

Question 12

How to study spinal motor pathways?

Answer 12

Know the location of the lateral corticospinal tract.
• For the other motor tracts you must be able to identify them as laterally versus ventrally located
• What do you know about the lateral corticospinal pathway thus far?

Start: Cortex End: Spinal Cord
Function: Voluntary motor activity of the limbs

Question 13

What is Amyotrophic Lateral Sclerosis?

Answer 13

• Also known as Lou Gehrig’s disease/ Motor neuron disease

* A progressive degenerative disease of the motor system

Question 14

How does Amyotrophic Lateral Sclerosis (ALS)?

Answer 14

– Amyotrophy = atrophy of muscle
– Lateral Sclerosis = hardening of the lateral columns of the spinal cord

• Degeneration of motoneurons in the primary motor cortex, brainstem and spinal cord
• Degeneration of anterior horn cells and motor CN (V,VII, X, XII), parts of pyramidal tract and primary motor area.
• Limb-onset ALS (70%) - a combination of upper and lower motor neuron (UMN and LMN) signs in the limbs
• Bulbar-onset ALS - speech and swallowing difficulties, limb features develop later

Question 15

Summarize the etiology of amyotrophic lateral sclerosis

Answer 15

Etiology:
• Sporadic (90-95%)
• Hereditary form Familial ALS (5-10%)

Question 16

Describe the epidemiology of amyotrophic lateral sclerosis

Answer 16

Epidemiology
• Prevalence -3 : 100,000
• Incidence- 2 : 100,000
• xy : xx – 1.5-2 :1
• Onset : 50 – 65 years

Question 17

What are the limb manifestations of Amyotrophic Lateral Sclerosis?

Answer 17

– Atrophy, weakness, fasciculations, loss of muscle bulk (Lower motor neuron symptoms)

– Hyperreflexia (Upper motor neuron symptom, abnormally brisk deep tendon reflexes)reflexes

– Spasms, and cramping of affected muscles,

Question 18

What are the bulbar manifestations of Amyotrophic Lateral Sclerosis?

Answer 18

– Reduction of cough reflex → risk of aspiration pneumonia

– Involvement of bulbar motor nuclei → difficulty in swallowing, coughing, and speaking ( can lead to aspiration pneumonia and respiratory insufficiency)

– Weakness,atrophy,and fasciculations in tongue

– Involvement of pharyngeal and laryngeal muscles

Question 19

How do motor neurons affect diseases?

Answer 19

In the spinal cord there are:

• Upper motor neurons
• Lower motor neurons

• The location and extent of a lesion in the spinal cord will determine what fibers are affected.

Question 20

What is Anterior Spinal Artery Syndrome?

Answer 20

• The anterior spinal artery travels the length of the anterior median fissure, supplying up to two thirds of the spinal cord (ventrally).

Etiology
• Infarction
• Tumors and epidural spinal abscesses
• Trauma
• Diseases of the aorta
• Connective tissue disease
• Disk herniation

Question 21

Describe the epidemiology and clinical features of anterior spinal artery syndrome

Answer 21

Epidemiology
• Rare, about 12 in 100,000

Clinical Features :
• Paresis or Paralysis
• Bilateral extensor plantar response
• Bilateral loss of pain and temperature below lesion
• Touch, vibration, proprioception intact

Question 22

Describe the pathology of central cord syndrome- syringomhelia

Answer 22

• A pathological fluid filled cavity within the central region of the spinal cord that may extend into the medulla.
• It is most common in the cervical cord.
• Commonly compresses the anterior white commissure and extends to the anterior horns.
• It may expand in a more dorsal direction to damage the dorsal horn and columns.

Question 23

What are the clinical features of syringomyelia?

Answer 23

• Unilateral or bilateral paralysis of upper extremities
• Loss of pain and temperature in the affected spinal levels - Cape like distribution of sensory loss seen with cervical cord involvement