Decorticate vs. Decerebrate posturing

[jelly221,RN]

I understand what the two look like, but am unclear on why those positions result from damage to those specific locations of the brain. Also, I'm having some trouble understanding motor pathways in the brain, the difference between upper motor neurons and lower ones that synapse in the brain stem. I've read the chapter in my neuro book several times, and I get the basic gist of it, but I'm not fully grasping the concept. Does anyone have tips that can clarify it for me? Or maybe a good site online?

[giveface]

The body of the upper motor neuron cell lies in the pre-central gyrus of the motor cortex. A lower motor neuron cell body lies in the spinal cord and synapses with the UMN at the level of its respective spinal nerve. UMN are also known as pyramidal tract neurons that directly originate the signal to muscle units to contract to produce movement. Sensory (afferent) neurons are different in that there are 3 distinct cell body and axon segments as they ascend.

The body of the cell of the LMN lies in the ventral horn of the gray matter of the spinal cord.