It results from damage of descending motor tracts (pyramidal tract alone or together with extra-pyramidal tract). The most common site is the internal capsule where the fibers condense together. The most common causes are hemorrhage or thrombosis of cerebral blood vessels.
Effects of UMNL:
Extent: It is usually wide spread because pyramidal tract fibers condense together. So, there is mono-plegia (paralysis of one limb), hemi-plegia (paralysis of UL & LL in one side or paraplegia (paralysis of both LL.).
Side: Usually in the opposite side because pyramidal tract fibers cross to the opposite side in its pathway from CC to AHC.
Type of paralysis: Spastic paralysis because it is accompanied with ↑ MT.
Recovery: No recovery in UMNL due to absence of neurilemma in its fibers (no cellular sheath in the CNS).
NB: In hemi-plegia some muscles recover (e.g. trunk muscles) because they receive innervation also from the same side.
(2) MT ↑ (hypertonia): It is due to
- ↓ supra spinal inhibition caused by damage of the extra-pyramidal inhibitory fibers coming from the basal ganglia and suppressor areas of CC.
- ↑ Supra spinal facilitation because the facilitatory centers lie below the lesion (e.g. vestibular nucleus & bulbo-reticular facilitatory area) become released from inhibition coming from the basal ganglia.
NB: Immediately after lesion MT↓ ( in stage of shock) then MT ↑.
(3) Deep reflexes (tendon jerks):
Tendon jerks ↑ in paralyzed muscles due to ↑ MT. Colonus (ankle or patellar) can be produced.
(4) Superficial reflexes:
Abdominal and cremastric reflexes are lost in the affected side. Planter reflex is changed to “Babinski’s sign” which means abnormal response to planter reflex. Scratch of the lateral border of the sole produces dorsi-flexion of big toe (due to pyramidal tract lesion or lesion of area 4) and fanning of the outer 4 toes (due to lesion of extra-pyramidal tract or area 6).
NB: Babinski’s sign may be physiological e.g.:
- In infants below one year due to lack of myelination of pyramidal tract.
- In adults during deep sleep, anesthesia, coma and fainting.
(5) Wasting: Slight wasting due to lack of use of paralyzed muscles (disuse atrophy).Wasting is not marked because the muscle can contract reflexly (due to intact reflex arc), and good blood supply due to ↑ MT which helps VR & blood flow.
(6) Response to electrical stimulation:
In UMNL the muscles respond normally to electrical stimulation.
Normal response of the healthy muscles to electrical stimulation:
The healthy muscle responds to 2 types of currents:
a) Faradic current: Produces tetanus (i.e. continuous contraction)
b) Galvanic current:
- If we stimulate the muscle by cathode, 2 contractions occur, the stronger with closure of the circuit (Cathode Closing Contraction, CCC), the weaker with opening of the circuit (Cathode Opening Contraction, COC), but not during continuous passage of current.
- If we stimulate the muscle by anode, 2 contraction occur, the stronger with closure of the circuit (Anode Closing Contraction, ACC), the weaker with opening of the circuit (Anode Opening Contraction, AOC).
Conclusion, we observe that CCC > ACC > AOC > COC.
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