Paralysis is the loss or impairment of voluntary muscular power. Paralysis can result from either diseases involving changes in the makeup of nervous or muscular tissue or those that are the result of metabolic disturbances that interfere with the function of nerves or muscles. Depending upon the cause, paralysis may affect a specific muscle group or region of the body, or a larger area may be involved. When only one side of the body is affected, the condition is known as hemiplegia. In other instances, both sides of the body may suffer the effects, leading to diplegia or bilateral hemiplegia. When only the lower limbs are affected by paralysis, it is called paraplegia. When all four limbs are affected, it is referred to as quadriplegia. The term palsy is sometimes used to refer to the loss of muscle power in a body part.