Upper Motor Neuron

Upper motor neurons (often abbreviated as UMNs) are neurons (nerve cells) in the motor cortex (an area in the front part of the brain that helps control motor functioning) that compose two types of nerve tracts (paths). The first are the corticospinal tracts, which are nerve paths connecting the cortex (outermost part of the brain) and the spinal cord. The second are the corticobulbar tracts, which are nerve paths from the top part of brain to the lower part of the brain called the brain stem. The brain stem area is referred to as bulbar because is has a bulb-shaped appearance. The brainstem connects the brain with the spinal cord and controls many functions crucial for life to continue such as breathing. Lower motor neurons send messages via the upper motor neurons to the skeletal muscles (e.g., muscles in the arms and legs).

The term "upper motor neuron" is actually misleading because upper motor neurons are not really motor neurons. They are called motor neurons because when they are stimulated they produce movement and when they are destroyed, severe movement disorders result. As an example, in upper motor neuron paralysis, paralysis (loss of movement and/or sensation) is caused by damage to the cell bodies and/or axons (parts of nerve cells that send messages) of the upper motor neurons.