Pyramidal system

Clinic

• Pyramidal tracts are a system of efferent nerve fibers that carry signals from the cerebral cortex to either the brain-stem or the spinal cord.
• Pyramidal tracts handle Conscious control of muscles from the cerebral cortex to the muscles of the body and face.
• Pyramidal tracts directly innervates motor neurons of Spinal cord (Corticospinal tract) or Brainstem (Corticobulbar tract) Anterior / Ventral horn cells / Certain cranial nerve nuclei

Corticospinal tract

• It starts at Primary motor cortex / Premotor areas and terminates on LMN / Interneurons in spinal cord.
• It controls movements of the limbs and trunk.
• Also it can originate from Somatosensory cortex / Cingulate gyrus/ Parietal lobe.
• A few of these fibers that are responsible for Fine motor function will synapse directly on LMN.
• At the pyramidal decussation, the 10 to 15% of fibers that did not decussate will continue down uncrossed as the anterior corticospinal tract (ACST). These fibers are involved in controlling proximal muscles such as those in the trunk. Typically lesions of the ACST tend to have a minimal clinical effect.
• Damage to the corticospinal tract will present similarly to upper motor lesion syndrome

Corticobulbar tract

• Corticobulbar tract synapses on lower motor neurons of cranial nerves controlling muscles of the face, head, and neck.
• It originates in Primary motor cortex and follows a similar path to the corticospinal tract.
• Its fibers bilaterally innervate almost every cranial nerve except for cranial nerves VII and XII, which are innervated by the contralateral cortex. What this means is that a corticobulbar tract lesion on the left side of the face will cause weakness of the right side. However, since every other cranial nerve except for VII and XII are innervated bilaterally (both the left and right hemispheres), lesions to both sides of the corticobulbar tract will need to occur for symptoms to appear.
• Damage to the corticobulbar tract can present with pseudobulbar palsy or damage to cranial nerves VII or X.
  • Damage to CN-VII will cause deviation of angle of mouth towards the opposite side of the lesion due to the overaction of the muscles of the opposite side.
  • Damage to CN-X will lead to the deviation of the uvula to the opposite side of the lesion.

Sign / Symptoms

• Pyramidal tracts are part of the UMN system. Pyramidal signs are:
  • Spasticity
  • Weakness
  • Slowing of rapid alternating movements
  • Hyper reflexia
  • Positive Babinski sign

These symptoms are all characteristic of an upper motor neuron lesion. However, certain symptoms are specific to a pyramidal tract lesion.

• More on lower extremities than upper ones.
• In presence of asymmetrical findings, ALS should be considered.

Clinical significance

• Parkinsonian-Pyramidal syndrome (PPS) is a combination of both pyramidal and parkinsonian signs

• Pyramidal tract lesions can occur from any type of damage to the brain or spinal cord such as meningitis, multiple sclerosis, or trauma.

• ALS: It causes symptoms of both upper and lower motor neuron syndrome.

• MS: In early MS stages, corticospinal tract integrity is already affected in the absence of WM lesions or brain atrophy.
• Central Pontine Myelinolysis: It is a condition that involves damage to nerve cells in the pons.

Entity / Miasms

I suggest the same Entities / Miasms of UMN entity which are GSS, JE, CJD, NVCJD, HTLV-1 and WEE/ EEE.