As with all organs in the body, the brain needs oxygen and nutrients in order to function properly. These life-sustaining products are delivered to the brain via the blood that travels through the circulatory system. A stroke occurs when there is a lack of blood to a portion of the brain, resulting in tissue death and loss of brain function. A stroke can be caused by a ruptured blood vessel, such as an aneurysm, or by an embolism, which is a small free-floating clot or particle that becomes lodged in one of the arteries of the brain and interrupts blood flow. Depending on which area of the brain is affected, a stroke can cause speech impairments, paralysis, unconsciousness, or even death.