Review
> Upper Motor Neurons
Upper
Motor Neurons
The upper motor neurons are responsible for commanding and controlling
the LMN. Theses neurons are organized into various tracts.
| • |
Corticospinal
Tract |
| |
This
is the major pathway for purposeful and skilled voluntary movement.
It is well developed in primates and carnivores and less developed
in ungulates and lower mammals. |
| • |
Reticulospinal
Tract |
| |
This
pathway arises from motor centers in the medulla and descends in
the lateral and venteral funiculi of the spinal cord. It has an
inhibitory or dampening effect on the LMN unit. This is the pathway
responsible for antigravity (extensor) function. |
| • |
Tectospinal
Tract |
| |
This
is the pathway responsible for controlling reflex reactions to sudden
visual or auditory stimuli. Thus the startle reflex tests this pathway
as an animal will turn, alert and be able to respond to the stimuli. |
| • |
Vestibulospinal
Tract |
| |
This
is the pathway responsible for reactions of skeletal muscles to
changes in head position. It is fascilatory to ipsilateral extensor
muscles and inhibitory to contralateral flexor muscles. |
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