The Muscle System

Muscles

• Found in every organ of body

• Three types• Skeletal

• Cardiac

• Smooth

Function of Muscles

• Movement

• Tension

• Heat generation

Muscle Anatomy

Anatomy of A Muscle

Anatomy of A Muscle

Single Muscle Fiber Fascicle

Muscle

Muscle Fiber

Muscle Fiber• Elongated

• Multinuleated

• Myofibrils running entire length

• SR surrounds each myofibril

•Mitochondria embedded throughout

Sarcomere

• The contractile unit

Anatomy of a Muscle

Fascicle

Single Muscle Fiber

Muscle

Fascicle

Muscle Cell

Muscle Movement

Muscle Contraction

• All muscles work the same way – Contract and relax

– All muscles are excitable: • Nerves stimulate• Muscle contracts

Mechanism of Nerve Stimulation

1. Nerve impulse reaches terminal

2. ACh released

3. ACh diffuses across cleft

4. ACh attaches to receptors

5. Sarcolemma becomes permeable to Na+

6. Action Potential (charge) travels down cell

1. Calcium released from SR, triggering exposure of binding sites on actin

2. Myosin binds with actin

3. The power stroke: Actin filaments pulled - slide past myosin

4. ATP binds to cross bridge, disconnects from actin

5. ATP re-energizes cross bridge

6. Calcium ions go back to SR

Mechanism of Muscle Contraction

Muscle Metabolism

Muscle Metabolism

ATP used to:

– Energize myosin cross bridge

– Disconnect myosin cross bridge from actin

– Energize calcium pump

ATP: The Energy Source

Adenine P P P

Adenine P P + Energy

Muscle cells use stored ATP

Within seconds, stored ATP is used up

The First Seconds of Contraction

20-ish Seconds of Contraction

creatine phosphate creatine

ATP

40-ish Seconds of Intense Contraction

pyruvic acid

glycogen

glucose

2 ATP

lactic acid

Anaerobic metabolism

Long Term Muscle Activity

Aerobic metabolism

glycogen

glucose

36 ATP

CO2 + H20

Muscle MetabolismStored ATP

Creatine Phosphate 1 ATP

Anaerobic MetabolismStored Glycogen 2 ATP

Aerobic MetabolismGlucose/glycogen 36 ATP

Contraction Strength and Control

Motor Units

• A neuron and all the cells it stimulates

• All cells of motor unit contract together

• Size of motor unit determines precision

Recruitment

Muscle recruitment:

more motor units are activiated

Summation

Summation:

Rate of muscle stimulation is increased

White or Dark Muscle:

Slow or Fast Twitch

Fast Twitch: White Muscle

• Rapid, powerful response• Depend on anaerobic pathways• Packed with actin and myosin

• Muscles fatigue rapidly

Slow Twitch: Red Muscle

• Contract slowly, but with great endurance

• Depend on aerobic pathways

• Packed with mitochondria, myoglobin

• Strength training

– Builds more fast-twitch myofibrils

• Aerobic training

– Builds endurance

– Increases blood supply to muscle cell

Exercise and Training

• Anabolic – induces muscle growth• Mimic testosterone• Stimulates protein formation in muscle cells• May cause:

– Increase in muscle strength without increase in tendon strength

– Liver/heart disease– Sterility

Anabolic Steroids

Androgenic Steroids

• Androgenic steroids – male/female hormones

• Andro – testosterone precursor

Side Effects of Steroids

•

Side Effects of Steroids

•

•

Facial Hair in Women

•

Gynecomastia

•

Diseases and Disorders

• Muscular dystrophy

• Tetanus

• Muscle cramps

• Sprains/Strains

Diseases and Disorders of the Muscular System

Muscular Dystrophy

Tetanus

•

Muscle Cramps

•

Sprains/Strains

Strength versus Size

Moving Bones

Skeletal Muscle Moves Bones

• More than 600 skeletal muscles

• Origin: attachment to stationary bone

• Insertion: attachment to moving bone

origin

insertioninsertion

origin

Antagonistic Pairs

Antagonistic muscles oppose each other