Causes of paralysis The four most common causes of paralysis are stroke, head injury, spinal cord injury and multiple sclerosis.StrokeA stroke is a serious medical condition that occurs when the blood supply to your brain is disturbed.Like all organs, the brain needs a constant supply of blood that contains oxygen and nutrients to function properly.If the blood supply is restricted or stopped, brain cells will begin to die, which can lead to brain damage that often results in paralysis.Head injuryA severe head injury can cause brain damage. The brain's surface can tear or bruise as it bumps against the skull, damaging blood vessels and nerves.Paralysis can occur if a part of the brain that controls specific muscles is damaged during a severe head injury.Damage to the left side of the brain can cause paralysis on the right side of the body, and damage to the right side of the brain can cause paralysis on the left side of the body.Spinal cord injuryThe spinal cord is part of your central nervous system. It is a thick bundle of nerves that runs from your brain, down through the neck and spine, inside a canal of vertebrae.Its main function is to transmit signals to and from the brain and body. For example, the spinal cord passes nerve signals, such as hot or cold sensations, back to the brain.If the neck or spine is injured, the spinal cord can also be damaged. This means the brain may no longer be able to transmit signals to the muscles, causing paralysis.The exact location where the spinal injury occurs can have a significant effect on how severe and wide-ranging the paralysis is. The higher up the spine the injury occurs, the worse the paralysis will be. For example, an injury in the middle of the spine will usually cause paraplegia (paralysis of the lower limbs).A neck injury, such as a broken neck, will usually result in tetraplegia (paralysis in all four limbs, also known as quadriplegia), as well as loss of normal lung function, which means the person will need to use a ventilator to breathe.