The types of cerebral palsy are classified based on the type of physical and mental impairments described. The three basic types of muscle impairments are called spastic, athetoid and ataxic. Mental impairments to varying degrees may occur in addition to the motor skills problems. Spastic hemiplegia usually involves a hand and arm and maybe a leg on one side of the body. Spastic diplegia is characterized by muscle stiffness mostly in the legs with milder stiffness in the arms and face. Spastic quadriplegia is a severe form of cerebral palsy that causes stiffness in all the limbs and the person will not be able to hold their head up. In addition, mental retardation is usually present. Dyskinetic cerebral palsy presents as uncontrolled twisting motions in the legs, feet and arms. Speaking is usually affected. Ataxic cerebral palsy is less common and impacts mostly balance and depth perception. Finally there is mixed types cerebral palsy which is actually a catch-all for those children with symptoms that don't fall into a single category.