Adorable animal families that will make you aww. A brain stem stroke is a stroke which originates in the brain stem. Because the brain stem handles many of the body's basic life support functions, such as breathing and heart rate, a brain stem stroke can be fatal.
Muscle fibers are in turn composed of myofibrils. The myofibrils are composed of actin and myosin filaments, repeated in units called sarcomeres, the basic functional units of the muscle fiber.The sarcomere is responsible for the striated appearance of skeletal muscle, and forms the basic machinery necessary for muscle contraction.keletal muscle is made up of individual muscle cells or myocytes, known as muscle fibers. They are formed from the fusion of developmental myoblasts (a type of embryonic progenitor cell that gives rise to a muscle cell) in a process known as myogenesis.
For example, the force of muscle contraction required to lift a 5 kg weight is less than the force required to lift a 25 kg weight, and the effort of muscles used in walking on level ground is less than the effort those same muscles expend in climbing stairs.ach muscle fiber is supplied by a single motor nerve fiber that initiates and controls the contraction of the muscle fiber. One motor nerve fiber controls several muscle fibers simultaneously. The motor nerve fiber and all of the muscle fibers it controls is called a motor unit (Fig. 1.1).