3 Motor II

• Descending pathways


  • Pyramidal system
  • Extrapyramidal system
• Pyramidal system


  Passes through the pyramids in ventral medulla oblongata
• Pyramidal system


  • Corticospinal tract
  • Corticobulbar tract
• Lateral corticospinal tract


  • Constitutes 80% of the fibers
  • Fibers cross at the midline of the medullary pyramid
  • Occupies the lateral portion of the spinal cord
  • Concerned with the control of distal musculature (hands and fingers)
  • Mediates fine and skilled movements
  • Descends along with rubrospinal tract

  
• Medial/Anterior/Ventral corticospinal tract


  • Constitutes 20% of the fibers
  • Fibers do not cross at the midline of the medullary pyramid
  • Occupies the ventral (anterior) and medial portion of the spinal cord
  • Concerned with the control of axial and proximal musculature (trunk and proximal limbs)
  • Projection fibers mostly coming from the premotor cortex
  • Mediates postural adjustments and gross movements
  • Descends along with reticulospinal, vestibulospinal and tectospinal

  
• Corticospinal tract


  1. Descends from the cerebrum to the thalamus passing through VA and VL nucleus, base of midbrain, lower pons, and then going down to the lower medulla oblongata

  2. 80-90% will decussate (pyramidal decussation) to move to the lateral side of the white matter

  3. Remaining 10-20% will not decussate but descend ipsilaterally passing through the medial side
• Lateral corticospinal tract


  • Supplies the interneuron that releases glycine, which inhibits anterior horn and prevents contraction of muscles
  • 10% will supply directly the anterior horn cell, leading to contraction
• Medial/Anterior corticospinal tract


  Directly supplies anterior horn cells, leading to release of ACh and contraction of muscles
• Damage to both lateral and medial corticospinal tracts and glycine-releasing interneurons


  Leads to spastic paralysis
• Damage to deep tendon reflex pathway

  Leads to hyperreflexia
• Babinski sign


  Fanning of the toes and dorsiflexion of the big toe, indicating an upper motor neuron lesion
• Fasciculation and fibrillation are not present in upper motor neuron lesion
• Atrophy secondary to disuse occurs later in upper motor neuron lesion
• Spinal nerve cut


  Leads to flaccid paralysis
• Damage to deep tendon reflex pathway


  Leads to areflexia
• Babinski sign is negative in lower motor neuron lesion
• Fasciculation and fibrillation are present in lower motor neuron lesion
• Denervation atrophy occurs immediately in lower motor neuron lesion
• Poliomyelitis damages anterior horn, leading to flaccid paralysis
• Differences between upper and lower motor neuron lesions


  • Spastic paralysis vs Flaccid paralysis
  • Hyperreflexia vs Areflexia
  • Positive Babinski sign vs Negative Babinski sign
  • Absence of fasciculation and fibrillation vs Presence of fasciculation and fibrillation
  • Disuse atrophy vs Denervation atrophy
• Posturing in upper motor neuron lesion with damage to both lateral and medial corticospinal tracts


  1. Lateral and medial corticospinal tracts damaged, leading to predominance of medial reticulospinal and lateral & medial vestibulospinal tracts

  2. Results in decorticate posturing with flexion of upper extremities and extension of lower extremities

  
• Posturing in midbrain lesion


  1. Lateral corticospinal (pyramidal) and rubrospinal tracts (extrapyramidal) both damaged, leading to predominance of extensors

  2. Results in decerebrate posturing
• Babinski sign


  Normal plantar reflex consists of flexion of the great toe or no response, while positive Babinski sign consists of dorsiflexion of the great toe with fanning of the other toes
• The only primitive reflex that adults have is salivation
• Reflexes present in infants but not in adults


  • Parachute reflex
  • Rooting reflex
  • Moro reflex
  • Sucking reflex
  • Grasp reflex
• Babinski-like responses


  • Bing sign
  • Cornell sign
  • Chaddock sign
  • Doug's sign
  • Gonda sign
  • Gordon sign
  • Moniz sign
  • Oppenheim sign
  • Schaeffer sign
  • Silva sign
  • Stransky sign
  • Strümpell sign
  • Throckmorton reflex
• Corticobulbar tract


  Innervates motor neurons of motor cranial nerves except CN III, CN IV and CN VI, which form the medial longitudinal fasciculus

  
• Gonda sign


  • Flexing and suddenly releasing the 4th toe
• Gordon sign


  • Squeezing the calf muscle
• Moniz sign


  • Forceful passive plantar flexion of the ankle
• Oppenheim sign


  • Applying pressure to the medial side of the tibia
• Schaeffer sign


  • Squeezing the Achilles tendon
• Silva sign


  • Pinching the rectus femoris muscle
• Stransky sign


  • Vigorously abducting and suddenly releasing the little toe
• Strümpell sign


  • Patient attempts to flex the knee against resistance
• Throckmorton reflex


  • Percussion over the metatarsophalangeal joint of the big toe
• Corticobulbar tract


  Will innervate motor neurons of motor cranial nerves except CN III, CN IV and CN VI, because these cranial nerves will form the medial longitudinal fasciculus and are responsible for the extraocular movements

  
• Corticobulbar tract originates from where corticospinal came from because remember that they are both pyramidal systems
• Corticobulbar tract


  1. Goes down the cerebrum to the thalamus through VA/VL

  2. Passes through the midpons where the motor nucleus of CN V is located

  3. Innervates ipsilaterally and contralaterally: CN V, CN VII, CN IX, CN X, CN XI

  4. Innervates contralaterally: CN XII
• Supratentorial lesion (cerebrum or diencephalon)


  • Manifestation on the face: contralateral to the lesion
  • Manifestation on the body: contralateral to the lesion