Ch. 10

Muscle Types:

  • Skeletal

  • Cardiac

  • Smooth


Skeletal Muscle:

  • Maintain posture and body position

  • support soft tissues

  • guard entrances and exits

  • maintain body temp

  • store nutrients


SKM Layers:

  • Epimysium - Covers the entire muscle

  • Perimysium - Covers bundles of muscle fibers / Contains BV and nerves for muscle

  • Endomysium - Covers each individual muscle fiber / Contains BV and nerves for muscle


SKM Features:

  • Sarcolemma - Plasma membrane

  • Sarcoplasm - Cytoplasm

  • Sarcoplasmic Reticulum - Similar to smooth endoplasmic reticulum

  • Transverse tubules - aid in contraction

  • Myofibrils - aid in contraction, filaments are organized into functional units called sarcomeres


Myofibrils:

  • Contain myofilaments called Think & Thick Filaments


Thin filaments:

  • F-actin

  • Nebulin

  • Tropomyosin - covers active sites on G-actin, prevents myosin heads from attaching

  • Troponin - binds to G-actin and tropomyosin and hold tropomyosin in position


Thick Filaments:

  • Contain bundles of myosin molecules around a Titin core

  • Each myosin molecule has a long Tail and a globular Head that form Cross-bridges with a thin-filament during contraction


Action Potential:

  • A the Neuromuscular junction the neurons axon terminal releases ACH into the synaptic cleft


Excitation-contraction coupling:

  • occurs when an AP along the T tubule triggers the release of Ca 2+ from the cristae of the Sarcoplasmic Reticulum at triads.


Contraction Cycle:

  • Starts when the release of Ca 2+ triggers the cycle of

    • Myosin head

    • Cross-bridge formation

    • pivoting of myosin head

    • Cross-bridge detachment

    • Myosin head reactivation


Explained:

  • Ca 2+ binds to troponin

  • Moves tropomyosin away from active sites on actin

  • Cross-bridges of myosin heads bind to actin

  • Myosin head pivots

  • Pulls actin filament towards center of sarcomere

  • Detaches


Acetylcholinesterase:

  • breaks down ACH and limits the duration of muscle contraction


Twitch:

  • is a cycle of contraction and relaxation produced by a single stimulus


Treppe:

  • repeated stimulation at a slow rate, progressive increase in twitch tension


Isotonic Contraction:

  • Tension in a muscle rises and the length of muscle changes

  • can be concentric or eccentric


Isometric Contraction:

  • Tension rises, but length of the muscle stays the same


Creatine phosphate:

  • can be release stored energy to convert ADP to ATP


Aerobic metabolism

  • Provides the most ATP for muscle contractions

  • Used at rest or moderate activity


Anaerobic metabolism:

  • Glycolysis

  • Used at peak levels of to generate ATP


Fiber Types:

  • Fast - Rapid powerful contractions / White Muscle

  • Slow - 3x as long to contract as fast / Red muscle

  • Intermediate - Similar to fast but have greater resistance to fatigue


Aerobic Endurance:

  • over time the muscle contraction can continoue due to support from mitochondrial activites


Anaerobic Endurance:

  • Over time the muscle contraction can continue due to support from glycolysis and ATP and CP reserves


Cardiac Muscle:

  • Involuntary

  • Only in the heart

  • Muscle cells are small and only have a singular nucleus

  • broad T-tubules

  • Dependent on aerobic metabolism


Automaticity:

  • Cardiac cells contract without neural stimulation and last longer


Smooth Muscle:

  • Involuntary muscle

  • SM cells lack sarcomeres, thin filaments are anchored by dense bodies

  • Exhibits plasticity, able to contract over a wide range of lengths


SM Contraction:

  • contracts when Ca 2+ ions interact with Calmodulin, which activates myosin light chain kinase


Multiunit SM cells:

  • Each SM cells acts relatively independently of other SM cells in the organ


Visceral SM cells:

  • Not always innervated by motor neurons