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plz explain this

drmon

Junior Member
10+ Year Member
5+ Year Member
Feb 22, 2006
32
1
  1. Pre-Dental
    hi,

    here is what i understand by UMN & LMN lesion:

    UMN lesion:

    With an UMN lesion, voluntary control of only the lower muscles of facial expression on the side contralateral to the lesion will be lost.

    Voluntary control of muscles of the forehead will be spared due to the bilateral innervation of the portion of the motor nucleus of CN VII that innervates the upper muscles of facial expression.
    Characteristics of an UMN lesion of the facial nerve include:
    Facial asymmetry


    Atrophy of muscles of lower portion of the face on affected side*


    No eyebrow droop*


    Intact folds on forehead*


    Intact conjunctival reflex (orbicularis oculi innervation is intact)


    Smoothing of nasolabial folds on affected side


    Lips cannot be held tightly together or pursed


    Difficulty keeping food in mouth while chewing on affected side


    whereas in LMN lesion:
    A LMN lesion results in the paralysis of all muscles of facial expression (including those of the forehead) ipsilateral to the lesion.

    i think the best way to distinguish is by observing the affect on muscles of forehead.

    hope this helps
     

    starvr

    New Member
    10+ Year Member
    Feb 6, 2007
    9
    0
    1. Dental Student
      Amrita, Drmon is right.

      The portion of the nucleus that innervates the muscles of the forehead receives corticobulbar fibers from both the contralateral and ipsilateral motor cortex.
      pixel.gif

      The portion of the nucleus that innervates the lower muscles of facial expression receives corticobulbar fibers from only the contralateral motor cortex.
      pixel.gif

      This is very important clinically as central (upper motor neuron) and peripheral (lower motor neuron) lesions will present differently.

      With an UMN lesion, voluntary control of only the lower muscles of facial expression on the side contralateral to the lesion will be lost.
      pixel.gif

      Voluntary control of muscles of the forehead will be spared due to the bilateral innervation of the portion of the motor nucleus of CN VII that innervates the upper muscles of facial expression.

      A LMN lesion results in the paralysis of all muscles of facial expression (including those of the forehead) ipsilateral to the lesion.
      A LMN lesion of CN VII which occurs at or beyond the stylomastoid foramen is commonly referred to as a Bell's Palsy.Characteristic indications of a LMN lesion or Bell's Palsy on the affected side.

      In UMN, spastic paralysis - hyperreflexia & disuse atrophy of skeletal muscle.
      In LMN, flaccid paralysis - Areflexia,fasciculations & atrophy.

      Good luck.
       
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