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Lecture

BIOB32H3 Lecture Notes - Phosphocreatine, Myosin Head, Endomysium


Department
Biological Sciences
Course Code
BIOB32H3
Professor
Kenneth Welch

Page:
of 5
Muscle Tissue
Skeletal muscle tissue and the Muscular System
Three types of muscle
Skeletal attached to bone
Cardiac found in the heart
Smooth lines hollow organs
Skeletal muscle functions
Produce skeletal movement
Maintain posture and body position
Support soft tissues
Guard entrances and exits
Maintain body temperature
Anatomy of Skeletal Muscle
Organization of connective tissues
Epimysium surrounds muscle
Perimysium sheathes bundles of muscle fibers
Epimysium and perimysium contain blood vessels and nerves
Endomysium covers individual muscle fibers
Tendons or aponeuroses attach muscle to bone or muscle
Skeletal muscle fibers
Sarcolemma (cell membrane)
Sarcoplasm (muscle cell cytoplasm)
Sarcoplasmic reticulum (modified ER)
T-tubules and myofibrils aid in contraction
Sarcomeres regular arrangement of myofibrils
Myofibrils
Thick and thin filaments
Organized regularly
Muscle Fiber
Thin filaments
F-actin
Nebulin
Tropomyosin
Covers active sites on G-actin
Troponin
Binds to G-actin and holds tropomyosin in place
Thick filaments
Bundles of myosin fibers around titan core
Myosin molecules have elongate tail, globular head
Heads form cross-bridges during contraction
Interactions between G-actin and myosin prevented by tropomyosin during rest
Sliding filament theory
Explains the relationship between thick and thin filaments as contraction proceeds
Cyclic process beginning with calcium release from SR
Calcium binds to troponin
Trponin moves, moving tropomyosin and exposing actin active site
Myosin head forms cross bridge and bends toward H zone
ATP allows release of cross bridge
The Contraction of Skeletal Muscle
Tension
Created when muscles contract
Series of steps that begin with excitation at the neuromuscular junction
Calcium release
Thick/thin filament interaction
Muscle fiber contraction
Tension
Control of skeletal muscle activity occurs at the neuromuscular junction
Action potential arrives at synaptic terminal
ACh released into synaptic cleft
ACh binds to receptors on post-synaptic neuron
Action potential in sarcolemma
Excitation/contraction coupling
Action potential along T-tubule causes release of calcium from cisternae of SR
Initiates contraction cycle
Attachment
Pivot
Detachment
Return
Relaxation
Acetylcholinesterase breaks down ACh
Limits the duration of contraction
Tension Production
Tension production by muscle fibers
All or none principle
Amount of tension depends on number of cross bridges formed
Skeletal muscle contracts most forcefully over a narrow ranges of resting lengths
Twitch
Cycle of contraction, relaxation produced by a single stimulus
Treppe
Repeated stimulation after relaxation phase has been completed
Summation
Repeated stimulation before relaxation phase has been completed
Wave summation = one twitch is added to another
Incomplete tetanus = muscle never relaxes completely
Complete tetanus = relaxation phase is eleminated
Tension production by skeletal muscles
Internal tension generated inside contracting muscle fibers
External tension generated in extracellular fibers
Motor units
All the muscle fibers innervated by one neuron
Precise control of movement determined by number and size of motor unit
Muscle tone
Stabilizes bones and joints
Tension production by skeletal muscles
Internal tension generated inside contracting muscle fibers
External tension generated in extracellular fibers
Motor units
All the muscle fibers innervated by one neuron
Precise control of movement determined by number and size of motor unit
Muscle tone
Stabilizes bones and joints
Contractions
Isometric
Tension rises, length of muscle remains constant
Isotonic
Tension rises, length of muscle changes
Resistance and speed of contraction inversely related
Return to resting lengths due to elastic components, contraction of opposing muscle
groups, gravity
Energy Use and Muscle Contraction
Muscle Contraction requires large amounts of energy
Creatine phosphate releases stored energy to convert ADP to ATP
Aerobic metabolism provides most ATP needed for contraction
At peak activity, anaerobic glycolysis needed to generate ATP
Energy use and level of muscular activity
Energy production and use patterns mirror muscle activity