The Muscular System

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.

Videos Muscle Structure

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.