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Upper and Lower motor neuron lesions
1. UPPER & LOWER
MOTOR NEURON
LESIONS
Prepared by: Anish Dhakal
MBBS 3rd Year
anishdhakal718@gmail.com
2. OBJECTIVES
• To define Upper motor neurons and Lower motor neurons
• To describe and differentiate between Upper and Lower
motor neuron lesions
3. • Lower Motor Neurons:
Ventral horn of spinal cord and in cranial nerve nuclei in
brain stem
Integral motor component of the spinal reflexes
• Upper Motor Neurons:
Cerebral cortex and brain stem
Direct the activity of lower motor neurons
A least two neuron pathway needed for skeletal muscle
contraction
4.
5. LESIONS OF THE CORTICOSPINAL
(PYRAMIDAL) TRACTS
• Babinski sign: Present in Newborns: (Incomplete
myelination)
• Inability to suppress usual withdrawal reflex
6. UMN LESIONS(PYRAMIDAL)
• Muscle weakness
• Loss of superficial
abdominal reflex
• Loss of cremasteric reflex
• Absence of voluntary fine
skilled movements
7. CLINICAL SIGNIFICANCE OF
LEVEL OF DECUSSATION
• Variable ipsilateral
or contralateral
motor weakness
based on the level
of corticospinal
tract lesion
9. • Upper motoneurons provide descending control over the
reflexes
• Results in hyperactive muscle stretch reflexes (tendon jerks &
Clonus)
(Upper motor neurons have Net inhibitory effect on
muscle stretch reflexes)
10. CLASP KNIFE REFLEX
• Oversensitive Golgi tendon
organs (loss of inhibitory
commands from UMN)
11. LOWER MOTOR NEURON
LESIONS
• Flaccid paralysis
• Loss of reflexes
• Muscular contracture
• Reaction of degeneration
12. LOWER MOTOR NEURON
LESIONS
• Muscular fasciculation & fibrillations (denervation super
sensitivity)
• Atrophy secondary to denervation of LMN
(Neither stretch reflex nor voluntary contraction)
In UMN lesions, can still be contracted by stretch reflexes
Disuse atrophy may be evident