UNIT 7: MUSCULAR SYSTEM Chapter 9

GENERAL OVERVIEW: STRUCTURE –Hierarchy of skeletal muscles: muscle, fascicles, fibers, myofibrils, myofilaments –Coverings and connective tissues: fascia, epimysium, perimysium, endomysium –Parts of a sarcomere: I band, A band, H zone, Z line, M line FUNCTION –Muscle contractions – sliding filament theory –Energy sources for muscle contractions –Body heat production ANTATOMY –Know major muscles of the human body –Origins, Insertions and Actions

STRUCTURE OF MUSCLE TISSUE Muscles are collections of smaller functional units –Fascia – connective tissue separating different muscles TendonAponeurosisEpimysium Fasicles – bundles of muscle fibers –Perimysium –Smaller units  vascularization and innervation

STRUCTURE OF MUSCLE TISSUE Muscle Fiber – individual cellsMuscle Fiber – individual cells Long, multinucleated, lots of mitochondriaLong, multinucleated, lots of mitochondria StriatedStriated EndomysiumEndomysium Sarcolemma – cell membraneSarcolemma – cell membrane SarcoplasmSarcoplasm Sarcoplasmic reticulum – E.R.Sarcoplasmic reticulum – E.R. CristernaeCristernae Transverse TubulesTransverse Tubules Myofibrils – bundles of muscle proteinsMyofibrils – bundles of muscle proteins Myofilaments – individual muscle proteinsMyofilaments – individual muscle proteins Actin – thin filamentsActin – thin filaments Myosin – thick filamentsMyosin – thick filaments AnimationsAnimationsAnimations

SARCOMERE Basic unit of striation –Functional unit  collective force of millions of sarcomeres working together Parts: –I band – light regions Actin only –Z-line – dark line in I bands Sarcomere boundary Where actin binds to other actin –Titin –A band – dark regions Actin and myosin present –H zone – lighter part of dark region Myosin only, no actin –M-line – dark line in middle of H zone Enlarged portion of myosin

MUSCLE CONTRACTIONS Stimulation –Neuromuscular Junction Motor neuron Synapse and Acetylcholine –Neurotransmitter action Neurotransmitter actionNeurotransmitter action –Motor end plate Ach causes muscle impulse –Acetylcholine esterase – decompose Ach –Causes Ca++ to be released from sarcoplasmic reticulum –Single neuron stimulates many muscle fibers Motor Unit - One contract, all contract –Few (10) – fine movements; eye –Many (100) – coarse movement; back

MUSCLE CONTRACTIONS Sliding Filament Theory –Mechanism of Filament Sliding Mechanism of Filament SlidingMechanism of Filament Sliding –Ach causes Ca++ to be released from sarcoplasmic reticulum  muscle impulse T-tubules allow impulse to travel deep in muscle tissue quickly –Troponin-tropomyosin complex 2 other muscle proteins Lie in grooves of actin w/o Ca++, troponin covers cross bridge binding sites w/ Ca++, complex uncovers cross bridge sites & myosin temporarily attaches to actin –ATP causes myosin cross bridge heads to bend and pull ATP decompose – release and reattach, repeat Z lines get closer Rigor Mortis

1. Acetylcholine is released at neuromuscular junction 2. AP is propagated along membrane and at T-tubules 3. Ca released from SR via a voltage gated Ca channel 4. Ca binds to Troponin-C - conformation changes favor tropomyosin opening actin sites 5. myosin cross-bridges attach- detach from actins... pulls filament toward M- line 6. Ca is removed (uptake by SR) 7. tropomyosin blocks actin sites and muscle relaxes.

Energy Sources for Contraction Need ATP – Cell Respiration –Myoglobin – red color Similar to hemoglobin Store oxygen –Fast vs. Slow Twitch Muscle Fibers –ATP decomposes quickly  use creatine phosphate cycle Creatine Phosphate –More stable and abundant than ATP in muscles –Can not directly supply energy for contraction –Used to form ATP Glucose stored as Glycogen

Energy Sources for Contraction Oxygen Debt –Amt of oxygen needed to replenish depletion + decompose lactic acid –Anaerobic respiration  lactic acid formation Muscle Fatigue –Prolonged contractions –Lactic acid most likely cause – low pH causes the muscles to not respond to stimulation –Cramp – spasmodic contraction

Muscle Responses