Strokes
A stroke occurs when one of the arteries carrying blood to the brain ruptures or becomes blocked, depriving a portion of the brain of oxygen. This causes a loss of function in the neurons in this portion of the brain; in the event of a stroke in the precentral gyrus of the frontal lobe, also known as the motor strip, upper motor neurons of the pyramidal tract will lose function and the patient will experience paralysis[40].
Upper motor neuron paralysis is characterized by contralateral hemiplegia, meaning the limbs on the opposite side of the body are affected due to the decussation of the neurons. The patient will experience hypotony for a few days followed by spasticity in the limb caused by false signals received by the intact lower motor neuron. Abnormal reflexes such as the Babinski, seen in the image above (B), and Hoffman reflexes may also be observed since some reflexes are caused by the muscle spindles and their gamma motor neurons. These neurons synapse on the alpha motor neurons which then in turn synapse with the upper motor neuron as part of the reflex pathway. A disruption of the upper motor neuron therefore disturbs and changes the reflex[40].