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The Muscular SystemCh. 10-11
Organization of Muscle fibers
Muscle fibers in skeletal muscle form bundles: fascicles
4 main muscle types: based off of fascicle shapes Parallel Convergent Pennate Circular
Parallel Muscles
Fascicles run parallel Tapered ends with broad mid-section
Example: biceps brachii
Convergent Muscles
Fascicles are spread over broad area All fibers taper together at one attachment site
Example: pectoralis
Pennate Muscles Fascicles form a common angle with a tendon
2 types:
1. Unipennate
• Example: extensor digitorum
2. Bipennate
• Example: rectus femoris
Circular Muscles Fascicles form concentrically around an opening Also known as sphincter
Change the diameter of the opening Example: Orbicularis Oris
Anatomy of Skeletal Muscle 3 Layers of tissue in each muscle
1. Epimysium• Surrounds the muscle, separates it from surrounding tissues
2. Perimysium• Divide skeletal muscle into compartments, called fascicles
• Contains blood vessels and nerves
3. Endomysium• Within each fascicle
• Surrounds individual muscle fibers
• At each end where the 3 layers come together form a bundle known as a tendon---attach muscle to bones.
Day 2
Micro-anatomy of Muscle tissue
Skeletal Muscle bundle (covered by Epimysium) Many Muscle Fascicles (covered by perimysium) Many Muscle Fibers (covered by endomysium) Many Myofibrils Many Sarcomeres Many Actin and Myosin Filaments
Myofibril & Sarcomere
I Band (Thin Filaments) Actin
A Band (Thick Filaments) Myosin
Muscle Contraction Terms Tropomyosin (2 stranded, prevents actin-myosin interaction)
Troponin (protein, allows actin-myosin interaction by binding tropomyosin)
Ca++ ions bond to troponin molecule, tropomyosin changes, exposing active site of actin, thus allowing myosin to interact with actin, and initiating contraction.
Sliding Filament Theory(Contraction Cycle )
1. Exposure of Active Sites (Ca++ ions bind with troponin, pulling tropomyosin away from actin)
2. Attachment of cross-bridges (myosin binds with actin)
3. Pivoting of myosin heads (contraction)
4. Detachment of cross-bridges (ATP breaks connection, so another attachment can be made-continuing contraction)
5. Reactivation of myosin (Myosin head splits ATP into ADP and P, energy released “recocks” myosin head so cycle can be repeated.
Rigor Mortis Ca++ keeps pumping in, but no ATP is available to “recock” or pump Ca++
ions out.
Without ATP, cross bridges cannot detach from the active sites.
“Stiff as a board”
Energy Use It takes a lot of ATP to sustain muscle contraction
Muscles store enough to start a contraction
To continue a contraction, ATP must be made by the muscle fiber with the help of creatine phosphate.
Aerobic Metabolism Creates 17 ATP for every unit “fed” into it. (fatty acids)
95% of energy for resting muscles
Happens in mitochondria
Anaerobic Glycolysis Creates 2 ATP/ glucose
Primary source during peak muscle activity Lack of available oxygen
Happens in cytoplasm
Produces lactic acid Lowers pH of blood
Can stop muscle contraction
But, once oxygen is available again, mitochondrial activity resumes, lactic acid is carried through blood to liver and converted back to glucose
Muscle Fatigue and Recovery Muscle Fatique=cannot perform anymore
WHY: Muscle function requires:1. Substantial intracellular energy reserves
2. Normal circulatory supply
3. Normal blood oxygen concentrations
Heat loss-because only about 30% of released energy is captured at ATP-the rest is lost as heat.
Muscle Fibers Fast Twitch Fibers (White muscle)
Contract quickly and powerfully
Few mitochondria
Fatigue quickly
Slow Twitch Fibers (red muscle) Contract slowly
Slow to fatigue
More mitochondria
What you don’t use, You’ll loose. Skeletal muscles become smaller in diameter
Decreased blood supply
Smaller ATP
Skeletal muscles become less elastic Increasing fibrous tissue
Tolerance decreases Cannot eliminate heat generated
Fatigue greater
Ability to recover from injury decreases Less tissues in muscle to help heal
Muscle Decline The rate of decline is the same in all people regardless of exercise patterns
Therefore, to be in good shape later in life; you have to be in good shape earlier in life.