Chapter 10 Muscular Tissue

Outer layer, encircling the entire muscle. It consists of dense irregular connective tissue.

also a layer of dense irregular connective tissue, but surrounds groups of 10 to 100 or more muscle fibers, separating them into bundles called fascicles. If you tear a piece of meat, it rips apart along the fascicles.

penetrates the interior of each fascicle and separates individual muscle fibers from one another. The endomysium is mostly reticular fibers.

This built in rhythm of the heart is termed autorhythmicity

storage is accomplished by sustained contractions of ringlike bands of smooth muscle called sphincters, which prevent outflow of the contents of a hollow organ.

as a muscular tissue contracts it produces heat,

Electrical excitability is a property of both muscle and nerve cells, is the ability to respond to certain stimuli by producing electrical signals called action potential (impulses)

dense sheet or broad band of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscles and other organs of the body.

attaches muscle to the periosteum of a bone

when the connective tissue elements extend as a broad, flat sheet. =flat tendon

a chronic, painful, nonarticular rheumatic disorder that affects the fibrous connective tissue components of muscles, tendons, and ligaments

Perimysium bundles groups of muscle fibers into fascicles

the neurons that stimulate skeletal muscle to contract are somatic motor neurons. Each SMN has a threadlike axon that extends from the brain or spinal cord to a group of skeletal muscle fibers

adenosine triphosphate These reactions require oxygen, glucose, fatty acids, and other substances that are delivered to the muscle fiber in the blood.

Because each skeletal muscle fiber arises during embryonic development from the fusion of a hundred or more small mesodermal cells called myoblasts, each mature skeletal muscle fiber has a hundred or more nuclei. Once fusion has occurred, the muscle fiber loses its ability to undergo cell division.

the multiple nuclei of a skeletal muscle fiber are located just beneath the sarcolemma, the plasma membrane of a muscle cell.

Thousands of tiny invaginations of the sarcolemma, called (T) tunnel in from the surface toward the center of each muscle fiber. Because T tubules are open to the outside of the fiber, they are filled with interstitial fluid.

within the sarcolemma is the sarcoplasm, the cytoplasm of a muscle fiber. Sarcoplasm includes a substantial amount of glycogen, which is a large molecule composed of many glucose molecules. Glycogen can be used for synthesis of ATP. In addition. the sarcoplasm contains a red colored protein called Myoglobin.

The sarcoplasm contains a red colored protein called myoglobin. This protein, found only in muscle, binds oxygen molecules that diffuse into muscle fibers from interstitial fluid. Myoglobin released oxygen when it is needed by the mitochondria for ATP production.

at high magnification, the sarcoplasm appears stuffed with little threads. These small structures are the myofibrils, the contractile organelles of skeletal muscle. About 2 nanometers and extend the entire length of a muscle fiber. They make the entire skeletal muscle fiber appear striated.

A fluid filled system of membranous sacs. They encircle each myofibril.

dilated end sacs of the sarcoplasmic reticulum called TC, butt against the T tubule from both sides.

A transverse tubule and the two terminal cisterns on either side of it form a triad. In a relaxed muscle fiber, the sarcoplasmic reticulum stores calcium ions. Release of CA from the terminal cisterns of the sarcoplasmic R. triggers muscle contraction.

the muscle growth that occurs after birth occurs by enlargement of existing muscle fibers. (muscle size increases) not in length. due to increased production of myofibrils, mitochondria, SR, and other organelles.

the replacement of muscle fibers by fibrous scar tissue.

a decrease in size of individual muscle fibers as a result of progressive loss of myofibrils. Muscle atrophy is when muscles waste away. The main reason for muscle wasting is a lack of physical activity. This can happen when a disease or injury makes it difficult or impossible for you to move an arm or leg. You may have muscle loss if one of your limbs appears smaller (not shorter) than the other.

within myofibrils are smaller protein structures called filaments. thin filaments are 8 nm in diameter and 1-2 um longs. composed mostly of the protein actin, Thick filaments are directly involved in the contractile process. Overall, two thin filaments for every thick.

the filaments inside a myofibril do not extend the entire length of a muscle fiber. instead they are arranged in compartments called sarcomeres, which is the basic functional unites of a myofibril.

narrow plate shaped regions of dense protein material called z-discs separate one sarcomere from the next. Thus a sarcomere extends from one Z-disc to the next Z-disc.

the darker middle part of the sarcomere is the a-band. which extends the entire length of the thick filaments. toward each end of the A band is a zone of overlap, where the thick filaments lie side by side.

is a lighter, less dense area that contains the rest of the thin filaments but NO THICK FILAMENTS, and a Z-Disc passes through the center of each I band.

a narrow H-zone in the center of each A band contains THICK BUT NOT THIN FILAMENTS.

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

is the main component of thick filaments and functions as a motor protein in all three types of muscle tissue. The myosin tail points toward the M line in the center of the sarcomere.

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

Arranged from smallest to largest, 1. thick filament, 2. Myofibril 3. Muscle Fiber

thin filaments are anchored to Z-Discs. Their main component is the protein actin. Individual actin molecules join to form an actin filament that is twisted into a helix. On each actin molecule is a myosin-binding-site, where a myosin head can attach.

(a) a thick filament contains abut 300 myosin molecules. The myosin fails form the shaft of the thick filament, and the myosin heads project outward towards the surrounding thin filaments. (b) thin filaments contain actin, troponin, and tropomyosin.

Regulatory protein that is a component of thin filament; when skeletal muscle fiber is relaxed, tropomyosin covers myosin binding sites on actin molecules, thereby preventing myosin from binding to actin.

Regulatory protein that is a component of thin filament; when calcium ions (Ca2+) bind to troponin, it changes shape; this conformational change moves tropomyosin away from myosin-binding sites on actin molecules, and muscle contraction subsequently begins as myosin binds to actin.

Structural protein that connects Z discs to M line of sarcomere, thereby helping to stabilize thick filament position; can stretch and then spring back unharmed, and thus accounts for much of the elasticity and extensibility of myofibrils.

structural protein of Z discs that attaches to actin molecules of thin filaments and to titin molecules.

Structural protein of Z discs that attaches to actin molecules of thin filaments and to titin molecules.

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.

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

organ made up of fascicles that contain muscle fibers, blood vessels, and nerves; wrapped in epimysium.

bundle of muscle fibers wrapped in perimysium

long cylindrical cell covered by endomysium and sarcolemma; contains sarcoplasm, myofibrils, many peripherally located nuclei,mitochondria, Transverse T, SR, and terminal cisterns. The fiber has a striated appearance.

threadlike contractile elements within sarcoplasm of muscle fiber that extend entire length of fiber; composed of filaments.

The I band and H zone disappears during muscle contraction; The lengths of the thick and thin filaments do not change.

skeletal muscle shortens during contraction because the thick and thin filaments slide past one another.

*During muscle contractions, thin filaments move toward the M line of each sarcomere

If ATP were not available, the cross-bridges would not be able to detach from actin. The muscles would remain in a state of rigidity, as occurs in rigor mortis.

1. ATP hydrolysis 2. attachment of myosin to actin to form cross-bridges 3. Power stroke 4. Detachment of myosin from actin

*During the power stroke of contraction, cross-bridges rotate and move the thin filaments past the thick filaments toward the center of the sarcomere.

Three functions of ATP in muscle contraction are the following: (1) its hydrolysis by an ATPase activates the myosin head so it can bind to actin and rotate (2) its binding to myosin causes detachment from actin after the power stroke and; (3) it powers the pumps that transport Ca2+ from the cytosol back into the SR.

*an increase of the Ca2+ level in the sarcoplasm starts the sliding of thin filaments. When the level of Ca2+ in the sarcoplasm declines, sliding stops.

As a muscle action potential propagates along the sarcolemma and into the T tubules, it causes Ca2+ release channels in the SR membrane to open. When these channels open, Ca2+ flows out of the SR into the sarcoplasm around the thick and thin filaments.

Inside the SR, molecules of a calcium-binding protein, appropriately called calsequestrin bind to the Ca2+ enabling even more Ca2+ to be sequestered or stored within the SR.

the synapse between a somatic motor neuron and a skeletal muscle fiber.

a region where communication occurs between two neurons, or between a neuron and a target cell- in this case between a somatic motor neuron and a muscle fiber.

separates the two cells

first cell communicates with the second by releasing a chemical messenger

A sarcomere length of 2.2 um gives a generous zone of overlap between the parts of the thick filaments that have myosin heads and the thin filaments without the overlap being so extensive that sarcomere shortening is limited.

The part of the sarcolemma that contains acetylcholine receptors is the motor end plate.

*synaptic end bulbs at the tips of axon terminals contain synaptic vesicles filled with acetylcholine ACh

uncontrollable blinking

*Acetylcholine released at the neuromuscular junction triggers a muscle action potential, which leads to muscle contraction.

glycolysis, exchange of phosphate between creatine phosphate and ADP, and glycogen breakdown occur in the cytosol. Oxidation of pyruvic acid, amino acids, and fatty acids (aerobic respiration) occurs in mitochondria.

small amino acid-like molecule that is synthesized in the liver, kidneys, and pancreas and then transported to muscle fibers.

Motor units having many muscle fibers are capable of more forceful contractions than those having only a few fibers.

term used to refer to the added oxygen, over and above the resting oxygen consumption, that is taken into the body after exercise. The extra oxygen is used to "pay back" or restore metabolic conditions to the resting level in three ways; (1) to convert lactic acid back into glycogen stores in the liver (2) to resynthesize creatine phosphate and ATP in muscle fibers (3) to replace the oxygen removed from myoglobin

consists of a somatic motor neuron plus all of the skeletal muscle fibers it stimulates. a single somatic motor neuron makes contact with an average of 150 skeletal muscle fibers, and all of the muscle fibers in one motor unit contract in unison.

During the latent period, the muscle action potential sweeps over the sarcolemma and calcium ions are released from the SR.

record of a muscle contraction

the muscle action potential sweeps over the sarcolemma and calcium ions are released from the sarcoplasmic reticulum.

2nd phase. Ca binds to troponin, myosin-binding sites on actin are exposed, and cross bridges form.

Ca is actively transported back into the SR. myosin binding sites are covered by the tropomyosin, myosin heads detach from actin, and tension in the muscle fiber decreases.

when a muscle fiber receives enough stimulation to contract, it temporarily loses its excitability and cannot respond for a time

when a second stimulus occurs after the refractory period of the first stimulus is over but before the skeletal muscle fiber has relaxed, the second contraction will actually be stronger than the first.

holding your head upright without movement involves mainly isometric contractions.

refers to decreased or lost muscle tone. such muscles are said to be flaccid.

characterized by loss of muscle tone, loss or reduction of tendon reflexes, and atrophy (wasting away) and degeneration of muscles

increased muscle tone and is expressed in two ways ; spasticity or rigidity.

characterized by increased muscle tone associated with an increase in tendon reflexes and pathological reflexes

partial paralysis in which the muscles exhibit spasticity

increased muscle tone in which reflexes are not affected, as occurs in tetanus.

disease caused by bacterium, clostridium tetani, that enters the body through exposed wounds. it leads to muscle stiffness and spasms that can make breathing difficult and can become life threatening as a result.

the tension, force of contraction developed in the muscle remains almost constant while the muscle changes in length. used for body movements and for moving objects.

tension generated is not enough to exceed the resistance of the object to be moved, and the muscle does not change its length.

visceral smooth muscle is more like cardiac muscle; both contain gap junctions, which allow action potentials to spread from each cell to its neighbor.

an increase in the number of fibers.

the myotome of a somite differentiates into skeletal muscle

forms the skeletal muscles of head, neck, limbs

forms the connective tissues including the dermis of the skin.

gives rise to the vertebrae

cardiac muscle develops from mesodermal cells that migrate to and envelop the developing heart while it is still in the form of endocardial heart tubes

smooth muscle develops from mesodermal cells that migrate to and envelop the developing GI tract and viscera