Muscle cells: Rod-shaped cells packed full of thinner fibres called myofibrils
Contraction: Muscle cells get shorter (contract) in response to nerve impulses
Your skeletal muscles are made up of bunches of elongated, rod-shaped cells called muscle fibres. Each of your muscle cells is packed full of thinner fibres called myofibrils. These fibres contain protein filaments, called thick and thin myofilaments, which slide against each other when a muscle contracts.
In a relaxed muscle, thick and thin myofilaments overlap each other a tiny bit. When a muscle cell is stimulated by a nerve impulse, these myofilaments slide past each other until they completely overlap. This makes the muscle cell shorter and fatter. The more shortened muscle cells there are in a muscle, the greater the contraction of the muscle as a whole.