MUSCLES!!

3 Types of Muscles

• Smooth

• Cardiac

• Skeletal

Smooth Muscle

• No striations• Single nucleus• No/underdeveloped transverse tubules• Involuntary• Contracts in waves called peristalsis

Peristalsis

• Educational:• http://www.youtube.com/watch?

v=o18UycWRsaA

Cardiac Muscle

• Like skeletal muscle but found only in the heart

• Mononucleated• Involuntary• Well developed transverse tubule system• Contracts as a unit

Skeletal Muscles• Move bones at joints• Voluntary• Striated• Multiple nuclei• Transverse tubules systems– WELL DEVELOPED

Structure of a muscle

Know this!

Myofilaments• Within each myofibril are myofilament.• Filaments:– Actin: Thin– Myosin: Thick

• When a muscle contracts, actin slides past the myosin, shortening the sarcomere.

Tropomyosin-troponin complex• Calcium is like a key.• Tropomyosin is like a chain around your bike

tires• Troponin is the lock attached to the chain.• The tires are the crossbridge of actin and

myosin• The pedals are like ATP

The Sarcomere:The functional unit of the muscle

Sliding Filament Theory

Neuromuscular Junction• Where the terminal button of the motor

neuron meets the motor endplate of the muscle. Includes the synaptic cleft.

• Acetylcholine (ACh)is the neurotransmitter for muscles.

• The synaptic vesicles release ACh into the synapse where it stimulates ACh receptors on the muscle fiber to begin contraction.

1. Sarcoplasmic reticulum releases calcium ions2. Calcium binds to the actin filaments sites, opening

them.3. Myosin heads form cross bridges with actin at the

binding site.4. Cocked position -> Power stroke5. ATP binds to cross bridge, releasing myosin from

the actin6. ATP breakdown provides energy to “cock”

unattached myosin cross bridge.7. Process repeats as long as there is ATP and

calcium available.

Energy Supply• Myofibrils need oxygen for cellular respiration,

which creates a lot of ATP.– Muscles can also use creatine phosphate to make ATP.

• Glycolysis does not need oxygen but only makes a small amount of ATP. A by-product of this reaction is lactic acid.

Muscle Conditions

• Muscle fatigue: Lactic acid build up

• Muscle cramps: A lack of ATP.

• Soreness : Rips in the muscle.

Slow oxidative twitch

• Slow-oxidative twitch muscles have a protein called myoglobin which temporarily holds oxygen. This makes the muscle look dark or red.

• That way, slow-oxidative twitch is used for aerobic long distance exercise.

Fast Twitch Glycolytic• Uses glycolysis.• White meat because few myoglobin proteins• Short distance, anaerobic • Less mitochondria

Fast twitch oxidative

• In the middle of slow twitch oxidative and fast twitch glycolytic

• Well vascularized

• Pink meat

Types of Contractions

• Isotonic: Change in length– Concentric: Shortening of the distance (flexing)– Excentric: Elongating muscle (extending)

• Isometric: Change in force• Tetanus– Fused: Smooth contraction– Unfused: Shaky contraction

Disease• Myasthenia Gravis (MG): Autoimmune

disorder that attacks receptors for ACh at neuromuscular junctions.– Symptoms: Abnormal muscle weakness (esp.

facial muscles), chronic fatigue, trouble breathing

Things to ponder

• Do all muscles have fascia?– Discuss with class