Understanding Motor Pathways: Upper vs Lower Neurons Motor disorders affect skeletal and voluntary muscles, primarily categorized into upper and lower motor neuron lesions. The pyramidal system is crucial for voluntary movement, where upper motor neurons transmit signals from the brain to the spinal cord or brainstem, while lower motor neurons relay these signals to skeletal muscles. Upper motor neuron pathways predominantly travel through lateral corticospinal tracts with a crossover at the medulla before synapsing in the anterior horn of the spinal cord; some axons do not cross until reaching their target level within the spine.
Clinical Indicators of Motor Neuron Lesions Upper motor neuron lesions can result from injuries like strokes or tumors affecting areas such as white matter in either cortex or brainstem. Clinical signs include minimal muscle atrophy but hyperreflexia due to unregulated reflexes; superficial reflexes may be diminished with positive Babinski sign responses observed. In contrast, lower motor neuron lesions lead to significant muscle atrophy and flaccid paralysis alongside absent tendon reflexes yet possible fasciculations due to partial neuronal transmission remaining intact.