Muscle Tissues
• Cardiac – 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
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
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
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
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
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
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