1. The Muscular System

2. Muscle Tissues Cardiac Smooth Skeletal Involuntary striated muscle
Found only in heart
Natural contraction cycle determined by pacemaker cells
Smooth
Lines blood vessels, digestive organs, urinary system, and parts of respiratory system, pupils of eyes
Involuntary non-striated muscle
Skeletal
Voluntary striated muscle
Multinucleated cells called muscle fibers
Controlled by motor nerve cells

3. Functions of Skeletal Muscle
Produce Movement
Contractions pull on tendons and move bones
Maintain posture and body position
Continuous contractions maintain posture
Support/protect soft tissues
Abdominal wall
Floor of pelvic cavity
Guard entrances and exits
Voluntary control of swallowing, defecation, and urination
Maintain body temp
Some energy from contractions lost as heat

4. Gross Anatomy of Skeletal Muscle
Each cell is called a “muscle fiber”
Contains several tissues
Connective
Epimysium – collagen fibers surrounding entire muscle
Perimysium – divide skeletal muscles into bundles of fibers (fascicles)
Endomysium – surrounds ea/fiber
Tendons – connect skeletal muscle to periosteum of bones
Blood vessels
Nerves – control contractions
Skeletal muscle

5. Microanatomy of Skeletal Muscle
Sarcolemma – cell membrane
Sarcoplasm – cytoplasm
Myofibrils – bundles of myofilaments
Thin filaments – actin proteins
Thick filaments – myosin proteins
Sarcoplasmic reticulum – smooth ER (stores Ca+)
Sarcomeres – repeating units of myofilaments

6. Muscle Fiber Contraction

7. Muscle Tone Tone – resting tension
Stabilizes the position of your joints
Any skeletal muscle not stimulated on a regular basis will atrophy – fibers become smaller and weaker
Initially atrophy is reversible
Extreme atrophy is permanent

8. Energetics of Muscle Activity
Active Skeletal Muscle fibril requires 600 trillion ATP/sec
Sources of ATP
Stored (ADP + Creatine-P  ATP)
Lasts 15 sec
Aerobic Metabolism (Krebs  Oxidative Phosphorylation)
Provides 30% of ATP needed during peak exertion
Anaerobic Metabolism (glycolysis)
Main E source
Lactic acid builds up
Ineffective
Muscle Fatigue – no contraction despite stimulation
Lack of ATP or lactic acid build up
Recovery Period – returns to pre-exertion levels

9. Muscle Performance Force and endurance depends on:
Types of muscle fibers
Fast Twitch (white)
Powerful contractions
Fatigue rapidly (few mitochondria)
Slow Twitch (red)
Extended contraction (many mitochondria)
Extensive capillary network
Myoglobin binds O2
Physical conditioning ( increase power and endurance)
Anaerobic
Frequent, brief intense workouts (hypertrophy of muscle fibrils)
Aerobic
Sustained low levels of activity
Carb-load the day before; drink glucose rich sports drinks