Corticospinal tract (pyramidal tract)

Question 1

I. Basics
1. What are the 2 tracts of pyramidal system?

Answer 1

corticospinal and corticonuclear (corticobulbar) tracts

Question 2

I. Basics
2. What are the characteristics of The pyramidal system of the motor system?

Answer 2

• The pyramidal system of the motor system consists of two related descending tracts: corticospinal and
  corticonuclear (corticobulbar) tracts
• The most important pathway for voluntary motor function
• Some of its axons, the corticobulbar
  fibers terminate at the cranial nerve
  nuclei
• The corticospinal fibers terminate on
  the motor neurons in anterior horn of
  grey matter

Question 3

II. Corticospinal tracts
1. Explain the pathway of corticospinal tracts

Answer 3

• Originate from the giant
  pyramidal Betz cells (1st neuron) of
  primary motor cortex in the 5th layer
• The fibers pass through the internal
  capsule and then through the cerebral
  peduncles to the pons. In the pons we
  have pontine nuclei which transmit the
  information to the cerebellum to inform
  it about the plan of motor activity
• The fibers will then reach the medulla
  oblongata, where they run through the pyramids. They will descend to the
  pyramidal decussation, where 80% of the fibers cross to the opposite side
  (lateral corticospinal tract). They have somatotropic organization: the fibers for
  the sacral cord are the most lateral, while the fibers for the cervical cord are most
  medially. The remaining 20% of fibers continue to descend without crossing,
  forming the anterior corticospinal tract, which borders the ventral median fissure
• The axons of the pyramidal cells terminate via intercalated cells on alpha and gamma-motoneurons, Renshaw cells and interneurons (2nd neuron)
• Most fibers of anterior corticospinal tract cross at the segmental level (spinal
  cord) to terminate on the same motor neurons (3rd neuron)
• Lateral corticospinal tract is found in the lateral funiculus in the spinal cord and
  will synapse with motoneurons in the ventral horn. Anterior corticospinal tract is found in the anterior funiculus and will, as said, cross over in the spinal cord to
  the opposite side when synapsing with motoneurons (alpha and gamma)
• Lateral: fine + precise movements, anterior: large motor movements

Question 4

II. Corticospinal tracts:
2. Describe 2nd neuron and 3rd neuron

Answer 4

• The axons of the pyramidal cells terminate via intercalated cells on alpha and gamma-motoneurons, Renshaw cells and interneurons (2nd neuron)
• Most fibers of anterior corticospinal tract cross at the segmental level (spinal
  cord) to terminate on the same motor neurons (3rd neuron)

Question 5

II. Corticospinal tracts:
3. Difference between anterior and lateral corticospinal tracts

Answer 5

• Lateral corticospinal tract is found in the lateral funiculus in the spinal cord and
  will synapse with motoneurons in the ventral horn.
• Anterior corticospinal tract is found in the anterior funiculus and will, as said, cross over in the spinal cord to the opposite side when synapsing with motoneurons (alpha and gamma)

Question 6

III. Corticonuclear (corticobulbar) tract
2. Explain the pathway of Corticonuclear (corticobulbar) tract

Answer 6

• It connects the cerebral cortex to the brain stem. Primarily involved in carrying motor function of CN 3-7, 9-12
• Motor neurons in the 5th layer of motor cortex (1st neuron) send their axon to the
  nuclei in the pons and medulla
• Fibers go through the genu of the internal capsule
• Goes to motor nuclei of cranial nerves (2nd neuron). Crosses midline
  Neurons control the conscious movement of the facial mimetic muscles, jaw muscles, swallowing and tongue movements

Question 7

IV. Corticoreticular tract
Explain the pathway of corticoreticular tract

Answer 7

It is reported to originate mainly from the premotor cortex and to terminate at the
pontomedullary reticular formation. It innervates axial muscles and the proximal muscles of the extremities, therefore, it is involved in gait function and postural control