Corticospinal and Corticobulbar Fibers

Question 1

Prefrontal areas

Answer 1

Mediating motor planning, motivation and social restraint.

Projects to the premotor cortex which then communicates with the primary motor cortex (broadmanns’s 4)

Question 2

Input to the primary motor cortex

Answer 2

• Premotor Cortex
• Primary somatosensory cortex (bm 3,1,2)
• Posterior parietal cortex (bm 5, 7) - integrates sensory information for motor planning in concert with frontal areas.
• Basal ganglia (via thalamus and premotor area)
• Cerebellum (via thalamus)

Question 3

Premotor (supplementary motor) cortex imput

Answer 3

• Posterior parietal area (bm 5, 7)
• Basal ganglia (via thalamus)
• Cerebellum (via thalamus)

Question 4

Main Function of Lateral corticospinal tract

Answer 4

Voluntary contraction and relaxation of muscles (stronger influence over flexion)

Question 5

Roles of the Primary and Premotor Cortices (example)

Answer 5

• Flexion/extension of a finger = primary motor cortex and
  primary somatosensory cortex are active. During

-Repeated flexion/extension of the fingers in
succession = Medial premotor (supplementary motor) area increasingly active.

-Mental rehearsal of the identical sequence, only the
supplementary motor area is active.

Question 6

Lateral Corticospinal Tract

Answer 6

START: layer 5 of the precentral gyrus

END: contralateral spinal ventral horn

ROUTE:

• cortex
• corona radiata
• internal capsule (posterior limb)
• crus cerebri
• basilar pons
• pyramids (medulla)
• pyramidal decussation
• corticospinal tracts in spinal cord
• synapses on alpha and gamma motor neurons in spinal ventral horn

Question 7

Upper Motor Neuron (UMN) Lesions

Answer 7

– Lesion above decussation: symptoms contrlateral to the lesion
– Lesion below the decussation: symptoms ipsilateral to the lesion

– HYPERreflexia
– Extensor plantar response
– First flaccid paralysis, later spastic paralysis
– NO wasting of muscles
– Clonus

Question 8

Lower Motor Neuron (LMN) Lesions

Answer 8

– Symptoms occur ipsilateral to site of the lesion
– HYPOreflexia/areflexia
– Flaccid paralysis
– Wasting of muscles

Examples of diseases that involve LMN syndrome are:

• Amyotrophic lateral sclerosis
• Peripheral nerve trauma

Question 9

Brown–Sequard Syndrome

Answer 9

Hemisection of the spinal cord.

Corticospinal Tract: Caudal to the lesion, UMN lesion syndrome occurs ipsilaterally

Anterolateral System: Caudal to the lesion, contralateral loss of pain and temperature

DC/ML System: ipsilateral loss of touch, vibration and proprioception

Lower Motor Neuron Lesion: at the level of the lesion

• Hypo- or areflexia
• Wasting of muscles
• Flaccid paralysis
• Fasciculations
• Fibrillations

Question 10

Corticobulbar tract

Answer 10

START: Layer 5 of the ventrolateral precentral gyrus.

END: Motor nuclei of cranial nerves.

ROUTE: Distinct bundles of corticobulbar fibers take different routes, depending on cranial nerve nucleus

FUNCTION: Innervation of muscles in the head (including
eyes and mouth) and
part of the neck.