What are the clinical features of UMN Weakness?

Features of UMN weakness are the following

1. UMN weakness is characterized by movement paralysis.
2. The midline structures such as pharynx,larynx, neck, chest, abdomen are spared because they have bilateral innervation.
3. There is a definite pattern for weakness in UMN lesion.The extensors and abductors of upper limb and the flexors and abductors of lower limb are affected.
4. According to the Jacksons law of resolution the fine distal movements are the first to to be affected and the last to be recovered.
5. The  proximal movements of limbs are the last to be affected and they are the  first to recover.
6. The rapid repetitive movements are affected and they  become slow.
7. There is automatisms of movements.
8. Mirror movements are also observed in UMN lesions.
9. On recovery choreoathetotic movements are common in UMN lesions.
10. Clasp knife spasticity and an irradiation of reflexes also observed.

Features of Pyramidal Weakness

1. No wasting
2. No fasciculations
3. Hypertonia - spasticity, clasp knife type
4. Exaggerated deep reflexes
5. Absent superficial reflexes
6. Extensor plantar responses

Why there is hypertonia in UMN Lesion?

Hypertonia in UMN lesion is seen due to the loss of inhibitory effect of dorsal reticulospinal tract.

Why there is spasticity in UMN Lesion? .

Spasticity is because of  reticulospinal and corticospinal tracts inhibit the antigravity muscles preferentially.

Why there is Hypereflexia in UMN Lesion?

It is due to the loss of  inhibitory effect of dorsal reticulospinal tract.

Basis of Paraplegia in Extension

This is due to the loss of inhibitory effect of dorsal reticulospinal tract.

Basis of Paraplegia in Flexion

Is produced due to the loss of inhibitory effect of ventral reticulospinal tract.