1. Muscular System Notes
Unit 6

2. 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

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

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

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

6. 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)

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

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

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

10. 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

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

12. 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

13. 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

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

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

16. Fig08.07
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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

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

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

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

20. 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