When there is no measurable activity in the brain and the brainstem, this is called brain death. In a person who has been declared brain dead, removal of breathing devices will result in cessation of breathing and eventual heart failure. Brain death is considered irreversible.
The functional unit of a skeletal muscle is called a sarcomere. Hole's Anatomy 12th edition, pg 287 states: Muscle fibers, and in a way muscles themselves, are basically collections of sarcomeres, discussed later in this chapter as the functional units of muscle contraction.. sarcomere. Tina Wright.
The functional unit of the nervous tissue is the neuron, or nerve cell, which has a unique structure that is specialized to transmit signals called nerve impulses. A nerve cell consists a body and two or more extensions called dendrites and axons, which may be as long as a meter in humans.