Muscular System Notes Unit 6

Random Info 640 muscles in the human body About 40% of body mass The tongue has 16 muscles 17 muscles to smile; 43 to frown

Functions of the muscular system Movement Muscle tone Propel body fluids and food Generate the heartbeat Distribute heat

Types of Muscle Cardiac Smooth Skeletal Heart beat Moves food through GI tract Skeletal Body movement

Structure of Skeletal Muscle Fascicles Muscle Fibers (muscle cell) Myofibrils Thick and thin filaments

Sarcomere One unit of a myofibril Striations in skeletal muscle Made up of actin and myosin filaments Myosin filaments pull actin filaments cause the sarcomere to shorten (contracts)

Neuromuscular Junction Motor neuron meets muscle fiber electrical impulse motor neuron releases neurotransmitters Ach (acetylcholine)

Myosin and Actin Myosin: Actin: Cross-bridge Troponin Tropomyosin Actin Filament

Sliding Filament model Myosin cross-bridge binds to actin filament Pulls actin filaments closer together Contraction occurs

Muscle contraction 1. acetylcholine released (impulse) 2. threshold stimulus is reached -impulse travels through transverse tubules to sarcoplasmic reticulum 3. sarcoplasmic reticulum releases calcium into muscle fiber (muscle is still relaxed) Tropomyosin Troponin Actin molecules ADP + P Myosin Filament

Muscle Contraction Cycle 4. Calcium binds to troponin pulling tropomyosin; exposes actin binding sites Ca+2 Ca+2 Ca+2 ADP + P ADP + P

Muscle contraction cycle 5. Myosin cross-bridges attach to actin binding sites 6. Cross-bridge pulls actin filament (power stroke) ADP + P released from myosin ADP + P ADP + P ADP P ADP P

Muscle contraction cycle 7. ATP binds to myosin causing myosin cross-bridge to release 8. ATP splitting provides energy to “cock” the myosin crossbridge ATP ATP ATP ADP + P ADP + P

Muscle contraction cycle 9. Exposed binding sites on actin allow cycle to occur again

Muscle Relaxation Contraction cycle continues until active transport of Calcium back into sarcoplasmic reticulum Low Calcium = actin binding sites unavailable

Fig08.07 Know This! Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Tropomyosin Troponin Actin lament Actin molecules ADP + P ADP + P Myosin lament 1 Relaxed muscle Ca+2 Ca+2 Muscle contraction Muscle relaxation Release of Ca+2 from sarcoplasmic reticulum exposes binding sites on thin lament: Active transport of Ca+2 into sarcoplasmic reticulum, which requires ATP, makes myosin binding sites unavailable. Ca+2 binds to troponin ATP Tropomyosin pulled aside Binding sites on actin lament exposed Ca+2 Ca+2 Ca+2 ADP + P ADP + P 2 Exposed binding sites on actin allow the muscle contraction cycle to occur ADP + P ADP + P Contraction cycle ADP + P ADP + P 6 ATP splits, which provides power to “Cock” the myosin cross-bridge 3 Cross-bridge binds actin to myosin ADP ADP ATP ATP ATP P P ATP ADP + P 5 New ATP binds to myosin, causing linkage to release 4 Cross-bridge pulls actin lament (power stroke), ADP and released from myosin P

Energy Sources ATP Creatine phosphate Cellular respiration Short time Synthesized by enzyme in mitochondria Cellular respiration Aerobic = oxygen Anaerobic = no oxygen

Oxygen Debt Anaerobic respiration= lactic acid Accumulation of lactic acid = oxygen dept Body needs O2 to make glucose from the lactic acid

Muscle fatigue Prolonged exercise = muscle unable to contract May arise due to lactic acid build-up

Rigor mortis Several hours after death Partially contracted muscles = rigid Results from an increase in Calcium and a decrease in ATP = prevents relaxation Stays contracted until decomposition of muscles begins