CH. 10.2 Skeletal Muscle Tissue

Titin

-Third most plentiful protein in the skeletal muscle (after actin and myosin) -HUGE molecules (how they got their name) -structural protein that helps sarcomeres return to resting length (elasticity) also provides extensibility (accounts for much of the elasticity and extensity in myofibril) -connects Z disc to M line of sarcomere

Fascia

-a dense sheet of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscles and other organs of the body -holds muscles with similar functions together -allows free movement of muscles; carries nerves, blood vessels, lymphatic vessels; and fills spaces between muscles

Perimysium

-a layer of dense irregular connective tissue -surrounds fascicles (bundles of muscle fibers) -visible to the naked eye

Transverse (T) tubules

-are thousands of tiny invaginations sarcolemma that tunnel in from the surface toward the center of each muscle fiber -filled with interstitial fluid -ensures that an action potential excites all parts of the muscle fiber at the same instant

Tendon

-attaches a muscle to the periosteum of a bone -(ie) calcaneal tendon of the gastrocnemius muscle attaches a muscle to the calcaneus

Aponeurosis

-connective tissue elements extend as a broad and flat sheet -(ie) epicranial aponeurosis on top of the skull between the frontal and occipital bellies of the occipitofrontalis muscle

Muscle Fibers

-each of your skeletal muscles is a separate organ composed of hundreds to thousands of cells called ___ ___ because of their elongated shapes. -number of __ __ is set before you are born, and most of these cells last a lifetime.

sarcoplasmic reticulum (SR)

-fluid-filled system of membranous sacs that encircle each myofibril -stores Calcium ions and release the ions from the terminal cisterns which triggers muscle contraction

I band

-lighter, less sense area of sarcomere that contains remainder of thin filaments but no thick filaments -a Z-disc passes through center of each I band

Actin

-motor protein -contractile protein that is the main component of thin filament -Individual actin molecules join to form an actin filament that is twisted into a helix -each moleules has a myosin-binding site where myosin head of thick filament binds during muscle contraction

Myosin

-motor protein -contractile protein that makes up thick filament -molecule consists of a tail and two myosin head which bind to myosin-binding sites on actin molecules of thin filament during muscle contraction -300 myosin molecules per thick filament with 2 heads per myosin = 600 heads per thick filaments

Nerve and blood supply

-one artery and one or two veins accompany each nerve into a skeletal muscle -the neurons that stimulate skeletal muscle to contract are somatic motor neurons -neuromuscular junction

Endomysium

-penetrates the interior of each fascicle and separates individual muscle fibers from one another -mostly reticular fibers

Myoglobin

-protein only found in muscle that binds oxygen molecules that diffuse into muscle fibers from interstitial -releases oxygen when it is needed by the mitochondria for ATP production -the mitochondria lie in rows throughout the muscle fiber, strategically close to the contractile muscle proteins that use ATP during contraction so that ATP can be produced quickly as needed

Motor proteins

-pull various cellular structures to achieve movement by converting the chemical energy and ATP to mechanical energy and motion that is, the production of force

Myomesim

-structural protein that forms the M line; stabilizes sarcomere -binds to titin molecules and connects adjacent thick filaments to one another.

Connective tissue

-surrounds and protects muscular tissue -subcutaneous (hypodermis) layer separates muscle from skin -is composed of areolar connective tissue & adipose tissue -provides a pathway for nerves, blood vessels, and lymphatic vessels to enter and exit muscles -adipose tissue of the subQ layer stores body's triglycerides, serves as an insulating layer that reduces heat loss, protects muscles from physical trauma

Sarcoplasm

-the cytoplasm of a muscle fiber -includes glycogen used for synthesis of ATP -contains a red-colored protein called myoglobin

Epimysium

-the outer layer, encircling the entire muscle -consists of dense irregular connective tissue

Myofibril

-thread-like and contractile organelles of skeletal muscle -repeated sacomeres made of thin and thick myofilaments

Components of a sarcomere

1. z discs 2. A band 3. I band 4. H zone 5. M line

Relaxed muscle

Myosin is blocked from binding to actin because strands of tropomyosin cover the myosin binding sites on actin

Actinin

The dense material of the Z disc contains molecules of actinin which bind to actin molecules of the thin filaments and titin.

Triad

a transverse tubule and the two terminal cisterns on either side of it

blood capillaries function

bring in oxygen and nutrients and remove heat and the waste products of muscle metabolism

A band

dark, middle part of sarcomere that extends entire length of thick filaments and includes those parts of thin filaments that overlap thick filaments

terminal cisterns

dilated end sacs of the sarcoplasmic reticulum that butt against the T tubule from both sides

muscle fiber (cell)

long cylindrical cell covered by endomysium and sarcolemma; contains sarcoplasm, myofibrils, many peripherally located nuclei, mitochondria, transverse tubules, sarcoplasmic reticulum, and terminal cisterns, the fiber has a striated appearance

H zone

narrow region in center of each A band that contains thick filaments but no thin filaments

Z discs

narrow, plate-shaped regions of dense material that separate one sarcomere from the next

sarcolemma

plasma membrane of a muscle cell

Contractile proteins

protein that generate force during muscle contractions (myosin and actin)

Regulatory proteins

proteins that help switch muscle contraction process on and off (tropomyosin and troponin)

Structural proteins

proteins that keep thick and thin filaments of myofibrils in proper alignment, give myofibrils stability, elasticity and extensibility, and link myofibrils to sarcolemma and extracellular matrix -titin, myomesim, nebulin, dystrophin

M line

region in center of H zone that contains proteins that hold thick filaments together at center of sarcomere

tropomyosin

regulatory protein that blocks/exposes binding sites on actin (component thin filaments) -they are held in place by troponin molecules

troponin

regulatory protein that controls tropomyosin position on thin filament

Nebulin

structural protein that helps anchor thin filaments to Z discs and regulates length of thin filaments during development. -It is a long, nonelastic protein wrapped around entire length of the thin filament

Dystrophin

structural protein that links thin filaments to proteins of the sarcolemma (muscular dystrophy)

Three layers of connective tissue that extend from the fascia to protect and to strengthen skeletal muscle

1. epimysium 2. perimysium 3. endomysium