The Muscular System 9 BIOLOGY

The Muscular System 3 Types of muscle: 1.Smooth- involuntary, lines internal organs, no striping, one nucleus per cell 2. Cardiac- involuntary, in the heart only, network arrangement for proper contraction, striped appearance, multi-nucleate 3. Skeletal- voluntary, attached to bones by tendons.

Skeletal Muscle Contraction Muscles arranged in antagonistic pairs When one contracts, one is relaxed and vice versa. Muscle fibers: Arranged in myofibrils of actin and myosin Sarcomere: functional unit of muscle Sliding Filament Theory: 1. Once nerve signal reaches muscle, actin filaments slide toward each other causing contraction 2. Nerve signal  release of calcium for relaxation of contraction 3. ATP needed

Muscle Contraction

Energy for Muscle Contraction Oxygen available aerobic respiration Oxygen not available anaerobic Causes lactic acid build- up, fatigue & soreness

Rigor Mortis: State of prolonged muscle contraction * Upon death, ATP is no longer released to relax contraction, so stiffness occurs. After 24 hours, tissue degradation begins Used to determine time of death in forensics

Myoglobin Special kind of hemoglobin that is only in muscle cells Binds only one O2 instead of 4 O2 in hemoglobin Gives extra oxygen reserves to muscle tissue

Myoglobin in Food Dark meat has more myoglobin, thus more iron than white meat. Dark meat is generally more nutritious as a result

Skeletal Muscle Strength Slow twitch: Slow Endurance Resist fatigue Lots of mitochondria Have myoglobin which gives oxygen reserve Exercise causes increase of mitochondria, but not size of muscle Fast twitch: Fatigue easily Great strength For short rapid movements No myoglobin Fewer mitochondria Exercise increases diameter of muscle