Chapter 10 muscles

A band

- M line - H band - zone of overlap

Structure of thin filaments

- attached to z line with actin - 5-6nm in diameter - composed primarily of actin - individual G-actin molecules (with active site for binding myosin) - G-actin strand held together with nebulin (going through center)

Axon of somatic motor nerve.....

- branches many times - each branch extends to a different skeletal muscle fiber

Sarcolemma

- cell membrane of a muscle fiber ( cell ) - surrounds sarcoplasma (cytoplasm of muscle fiber) - a change in transmembrane potential begins contractions

Myosin molecules

- composed of 2 twisted myosin - arranged with tail facing M-line and heads in spiral fashion, each facing a surrounding thin filament - free head has 2 globular units - this forms a cross-bridge with actin during contraction -connection between head and tail allows a hinge like pivot motion - A-band

Cisternae

- concentrate Ca2+ (via pumps) bound to CALESQUESTRAN - calcium ion concentration in terminal cisternae is 40,000 times that of cytosol - release Ca2+ into sarcomeres to begin muscle contraction

Sarcomeres

- contractile units of muscle -structural units of myofibrils - go visible patterns within myofibrils - striped or striated pattern with in myofibrils - dark (A bands)thick - light thin (I band)

Tropomyosin

- covers G-actin active sites and prevents actin myosin interaction when muscles relaxed - attached to troponin

Epimysium

- exterior collagen layer - connected to deep fascia - separates muscles from surrounding tissues

Triad

- in SR - formed by T tubule and 2 terminal cisternae

Types of actin in thin filaments

- individual G-actin molecules (with active sites for binding myosin) link together to form F-actin - G-actin strand held together with nebulin (going through center)

Thin filaments

- made of protein actin, troponin, tropomyosin

Sarcoplasmic Reticulum

- membranous structure surrounding each myofibril - helps transmit action potential to myofibril - similar structure to smooth ER - forms chambers (terminal cristae) attached to T tubules - stores calcium

Somatic motor neurons

- neurons that stimulates skeletal muscle contraction

Contractile proteins

- proteins that generate force during muscle contraction -myosin -actin

Tropomyosin

- regulatory protein that is a component of thin filaments. When skeletal muscle fiber is relaxed, tropomyosin covers myosin binding sites on actin molecules. There by preventing myosin from binding to actin.

Endomysium

- surrounds individual muscle cells ( muscle fibers aka myofibrils) - contains capillaries and nerve fibers contacting muscle cells - contain myosatellite cells (stem cells) that repair damage - too much damage cannot be fixed

Perimysium

- surrounds muscle fiber bundles ( fascicles) - contain blood vessel and nerve supply to fascicles - separates 10-100 muscle fibers into bundles called fascicles -fascicles: surrounding muscle fibers. Contains blood vessels and nerves going into fascicles

Types of myofilaments

- thin filaments -thick filaments

Transverse T tubules

- transmit action potential through cell - allow entire muscle fiber to contact SIMULTANEOUSLY - same properties as sarcolemma

Skeletal muscle cells

- very long - develop through fusion of mesodermal cells (myoblasts) - become very large - contain hundreds of nuclei

Microscopic anatomy on muscles

-# of skeletal muscle fibers is set before you are born - muscle growth occurs by hypertrophy - testosterone and human growth hormone stimulate hypertrophy - more filaments are made to stimulate hypertrophy

Structure of thick filaments

-10-12 nm in diameter - have core of titin that connects to 2 lines. - elastic and recoil after stretching - contain 300 myosin molecules

Function of sarcoplasmic Reticulum

-SR contains calcium ions - pumps (SERCA uses ATP) on membrane move calcium from cytosol to inside SR - SR calcium occurs both as free ions and bound to proteins

Portion of muscle between Z disc and end of thick filament

-can stretch to 4 times its resting length and spring back unharmed -role in recovery of muscle from being stretched

M line

-center of A-band (myomeeism) -At midline of sarcromere

Beginning of a muscle contraction

-change in membrane potential of a T tubule - triggers release of calcium ions and is charged - action potential comes down

All 3 layers...

-come together at ends of muscles - form connective tissue attachment to bone matrix - ex. Tendon (bundle) oraphoneurosis (sheet)

Zone of overlap

-densest darkest area - where thick and thin filaments overlap

Myofibrils

-length wise subdivisions within muscle fiber - made up of bundles of protein filaments (myofilaments)

Troponin

-regulatory protein that is a component of thin filaments. When calcium ions bind to troponin, it changed shape. This conformational change moved troponin ion away from myosin binding sites on molecules. Muscle contraction subsequently begins as myosin binds to actin.

H band

Area around M line of A band - thick but NO thin filaments

Muscles are...

Contractible (can shorten in length) Extensible( can extend or stretch) Elastic (can return to original shape)

Actin

Contractile protein that is the main component of thin filaments. Each actin molecule has a myosin binding site where myosin head of thick filaments bind during muscle contraction.

Myosin

Contractile protein that makes up thick filament. Molecule consists of a tail and two myosin heads which bind to myosin binding sites on actin molecules of thin filaments during muscle contraction.

Thick filaments

Made of myosin

Myofilaments

Responsible for muscle contraction - in overlap region, six thin filaments surround each thick filament (2:1)

Myomesin

Structural protein that forms M line of sarcomeres. Binds titin molecules and connects adjacent thick filaments to one another

Dystrophin

Structural protein that links tbin filaments of sarcomeres to integral membrane proteins in sarcolemma which are attached in turn to proteins in connective tissue of matrix that surrounds muscle fibers. Is thought to help reinforce sarcolemma and help transmit tension generated by sarceres tendons.

Nebulin

Structural protein that wraps around entire length of each thin filament. Helps anchor thin filaments to Z discs and regulates length of thin filaments during development.

3 layers of muscles

1. Epimysium (above) 2. Perimysium ( around fassicles) 3. Endomysiym (around individual muscle fibers)

Functions of skeletal muscle tissue

1. Produce skeletal movement 2. Maintain posture and body position 3. Support soft tissues 4. Guards entrances and exits 5. Maintains body temp 6. Store nutrient reserves

Thin filaments contain 2 regulatory proteins

1. Tropomyosin 2. Troponin

Trponin

3 subunits -1. Binds to tropomyosin (tropomyosin complex) -2. Binds to G-actin (holding complex position) -3. Binds 2 calcium ions (activation during contraction)

I bands

In sarcomeres - have Z lines that are the center of I band - at 2 ends of sarcomere

Structural protein

Kept in thick and thin filaments of myofibril in proper alignment. Give myofibrils elasticity and extensibility and link myofibrils to sarcolemma

Regulatory proteins

Proteins that help switch contraction processes on and off. - tropomyosin - troponin

Titin

Structural protein that connects Z disc to M line of sarcomere. Thereby helping to stabilize thick filaments position. Can stretch and then spring back unharmed. Thus accounts for much of the elasticity and extensibility of myofibrils.

a-Actin

Structural protein of Z discs that attaches to actin