Motor Pathways and Damage

• Voluntary movement involves a two-neuron pathway:
  • Upper motor neuron (UMN):
    • Originates in the motor cortex.
    • Sends signals down the brainstem and spinal cord.
  • Lower motor neuron (LMN):
    • Innervates muscles directly.
• Damage to the pathway:
  • UMN damage: causes spastic paralysis, hyperreflexia.
  • LMN damage: causes flaccid paralysis.

Abnormal Posturing

• Decorticate Posture:
  • Seen with cerebral cortex damage.
  • Flexed arms, adducted limbs, flexed legs.
  • Indicates severe brain injury at or above the brainstem.
• Decerebrate Posture:
  • Damage below the level of the red nucleus in the midbrain.
  • Extended arms and legs, arched back.
  • Often associated with brainstem injury.
• Opisthotonos (damage to extrapyramidal tract): spastic paralysis in spinal muscles (rigid, arched back)
• Mixed (hemiplegic):
  • One side flexed (decorticate), one side extended (decerebrate).

Somatic Motor Nerve Pathways & Symptoms

• UMN damage:
  • Causes either flaccid or spastic paralysis (depending on brain lesion) on the contralateral (opposite) side of the body.
  • Hyperactive reflexes (hyperreflexia).
  • Positive (Abnormal) Babinski sign (flared toes in individuals older than infants)
  • Clonus: repetitive muscle contractions.

• LMN damage:
  • Causes flaccid paralysis on ipsilateral (same) side of body.
  • Muscle weakness, atrophy.

Reflexes and Signs of Brain Damage

1. Babinski Sign

• Normal in infants:
  • Stroking lateral side of foot causes toes to flare.
• Pathologic in adults:
  • Same stimulus causes toes to curl downward (negative Babinski).
• Implication:
  • Flaring toes indicates damage to UMN pathways.

2. Hyperreflexia

• Exaggerated reflexes (e.g., patellar reflex).
• Might be accompanied by clonus (repetitive contraction).
• Indicates UMN lesion.

Summary

• Damage to cortical or brainstem pathways produces characteristic postures and reflex changes.
• Signs like Babinski and hyperreflexia help localize lesions.
• Presence of reflexes indicates brainstem integrity, critical in coma assessment.