KEY CONCEPT Muscles are tissues that can contract, enabling movement.

Humans have three types of muscle. The muscular system moves substances throughout the body. bones of the skeletal system food through digestive system blood through circulatory system fluids through excretory system

There are three types of muscle tissue. skeletal muscle smooth muscle cardiac muscle SKELETAL MUSCLE SMOOTH MUSCLE CARDIAC MUSCLE

Skeletal muscle attaches to the skeleton by tendons. Tendons connect muscle to bone. Skeletal muscles are mostly voluntary. SKELETAL MUSCLE

Smooth muscle lines organs and is involuntary. move food through digestive organs empty liquid from the bladder control width of blood vessels Smooth muscle around this artery allows the artery to regulate blood flow by shrinking and expanding. SMOOTH MUSCLE

Cardiac muscle is found only in the heart. pumps blood throughout body controlled by pacemaker contains more mitochondria than skeletal muscle cells CARDIAC MUSCLE

Muscle fibers are cells of the muscular system. Muscles contract when the nervous systems causes muscle filaments to move. Muscle fibers are cells of the muscular system. muscle muscle fiber

Myofibrils are long strands of protein in the muscle fiber.

Each myofibril is divided into sarcomeres. Sarcomeres contain filaments that cause contraction. myofibril muscle fiber muscle sarcomere

Neuron stimulates muscle at the neuromuscular junction.

Each myofibril is divided into sarcomeres. Sarcomeres contain filaments that cause contraction. Actin filaments are pulled during contraction. Myosin filaments pull actin during contraction. CONTRACTION RELAXATION M line myosin Z line

Neuron stimulates muscle at the neuromuscular junction. Neurotransmitters cause calcium channels in the sarcomere to open. regulatory protein Calcium exposes binding sites. Myosin binds to actin and pulls it. As the sarcomere shortens, the muscle contracts. myosin actin Z line