Lecture by DR SHAIK ABDUL RAHIM Upper Motor Neuron Lesion (UMNL , Pyramidal Lesion) & Lower Motor Neuron Lesion (LMNL) Lecture by DR SHAIK ABDUL RAHIM
Upper Motor Neuron Lesion (UMNL) In upper motor neuron (pyramidal) lesion , the spinal cord is disconnected from the modulating influences of the supraspinal controlling centers. Therefore , in UMNL , after a period of “spinal shock” the stretch reflex recovers , but resumes function in a primitive and uninhibited manner: there are exaggerated tendon reflexes and “ spastic ” increase in muscle tone , greater in the extensors of the lower limbs (LLs ) and the flexors of the upper limbs ( ULs) .
Lower Motor Neuron Lesion ( LMNL) The lower motor neuron ( LMN) constitutes part of the reflex arc - the integrity of the reflex arc is essential for (1) maintenace of muscle tone (2) adequate nutrition of the muscle itself. LMN lesion leads to atonia or hypotonia , lost or depressed tendon reflexes , and muscle atrophy (wasting ).
Examples of Conditions in Which there is UMNL or LMNL Upper Motor Neuron Lesion (UMNL) Can result from Haemorrhage , thrombosis or embolism in the internal capsule (e.g. Hemiplegia) (2) Spinal cord transection or hemisection (e.g. Brown- Sequard syndrome) Lower Motor Neuron Lesion (LMNL) Can result from (1) Spinal root lesions or peripheral nerve lesion (e.g. nerve injury by trauma or compressive lesion (2) Anterior horn cell lesions (e.g. , poliomyelitis, motor neuron disease )
Principal Features of UMNL & LMNL UMNL: (1) No muscle wasting, except from disuse ( disuse atrophy) (2) Spasticity ( hypertonia ), called “ clasp-knife spasticity ” (3) Clonus present (4) Brisk ( exaggerated ) tendon jerks (5) Extensor plantar reflex , Babinski sign ( dorsiflexion of the big toe and fanning out of the other toes ) (6) Absent abdominal reflexes (7) No fasciculations (8) No fibrillation potential in EMG LMNL: (1) Marked muscle wasting (atrophy ) (2) Flacidity (Hypotonia ) , hence given the name “ flaccid paralysis ” (3) No clonus (4) Diminished or absent tendon reflexes (5) Absent plantar reflex (normally it is flexor ) (6) Absent abdominal reflexes (7) Fasciculations may occur (8) Fibrillation potentials present
Hemiplegia Causes : cerebral heamorrhage , thrombosis or embolism results in paralysis of the oppsite half of the body. The commonest cause of cerebral haemorrhage is hypertension, usually associated with rupture of the lenticulo-striate branch of the middle cerebral artery in the internal capsule. Features : (1)UMNL involving the half of the body contralateral to the site of the lesion . (2) Hypertonia causes the limbs to acquire a specific posture A/ upper limb is (a) adducted to the side of the trunk , (b) flexed at the elbow ,(c) the forearm is semipronated,(d) with flexion of the wrist and fingers.
Hemiplegia B/ lower limb is (a) adducted and (b) extended at the knee and ankle. In extensive lesions the patient may have , in addition : (3) Loss of sensation on the opposite side of the body (Hemianesthesia), due to damage of the thalamocortical fibers. (4) Homonymous hemianopia ( loss of vision in two corresponding halves of the visual fields in both eyes), may occur if the optic radiation is lesioned
Brown-Sequard syndrome (Hemi section of the spinal cord) Occurs as a result of unilateral lesion or hemisection of the spinal cord (e.g. due to stab injury, bullet , car-accident, or tumor). The manifestations of the Brown-Sequard syndrome depend on the level of the lesion. A/ At the level of the lesion, all manifestations occur on the same side: Paralysis of the lower motor neuron type, involving only the muscle supplied by the damaged segments.
Brown-Sequard syndrome (Hemi section of the spinal cord) 2. Vasodilatation of the blood vessels that receive vasoconstrictor fibres from the damaged segments. 3. Loss of all sensations in the areas supplied by the afferent fibres that enter the spinal cord in the damaged segments +/- band of hyperesthesia B/ Ipsilaterally ( on the same side of lesion ) below the level of the lesion : 1.spastic lower limb (with upper motor neuron type of lesion ).
Brown-Sequard syndrome (Hemi section of the spinal cord) 2. Fine touch, position and vibration sense are lost as a result of damage of the dorsal column tracts . 3. Vasodilatation due to interruption of the descending pathways from the medullary vasomotor centres. C/ On the opposite side to the lesion : Pain and temperature sensations are lost.
COMPARISON OF MOTOR SYSTEMS http://library. med. utah