Lower Motor Neurons Flashcards
What are lower motor neurons?
Alpha motor neurons that innervate muscles, heavily myelinated, fast conducting
Where are the cell bodies of lower motor neurons?
Brainstem motor nuclei + spinal cord ventral horn (lamina IX)
What are upper motor neurons?
Neurons that project from brainstem/cortex to brainstem/spinal cord. NOT MUSCLES
Where are lower motor neurons’ nuclei located?
Spinal cord ventral horn (lamina IX) or in brainstem nuclei
Where are cell bodies in the spinal cord located relatively for proximal vs. distal muscles? Flexors vs. extensors?
Proximal: medial, distal: lateral
Flexors: dorsal, Extensors: ventral
What are the symptoms of a LMN syndrome?
1 Weakness/paralysis 2 Atrophy 3 Hyporeflexia or areflexia 4 Decreased tone 5 Fibrillations, positive sharp waves or fasciculations measured by EMG
What is electromyography and what does it measure?
Helps to find source of muscle weakness by determining denervation of muscle
What happens to neurons in ALS and where?
Loss of motor neurons in the ventral horn
What is a fibrillation potential? What does it indicate?
a short duration, spontaneous potential produced by a single muscle fiber
indicates a denervated muscle
What is a fasciculation? What does it indicate?
A larger potential caused by spontaneous activity in a motor unit
indicates a lower motor neuron lesion
Why does post-polio period occur?
New sprouts generated during the stable/recovery period cannot be sustained
How does polio virus invade the nervous system and what does it cause?
It attacks ventral horn motor neurons, causing LMN syndrome
What is Werdnig-Hoffmann disease? How is it inherited and what are the symptoms?
abnormality in chromosome 5 causes degeneration of anterior horns
Autosomal recessive
symptoms are weakness/muscle wasting in limbs, respiratory muscles and bulbar muscles (sucking, swallowing, breathing)
What are spinal muscle atrophy conditions? What are the affected neurons?
abnormality in chromosome 5 causes degeneration of anterior horns
motor neurons in spinal cord, cranial nerve motor nuclei
What pathological changes occur with sustained lower motor neuron disease? (3)
1 Lose innervation because alpha motor neuron died
2 Axons sprout and innervate muscle fiber to the R/L of it and produce giant motor units and type grouping
3 Motor neurons die and produce muscle atrophy
