Chapter 10 Muscles

Incomplete tetanus

A muscle producing almost peak tension during rapid cycles of contraction and relaxation

Creatine

A nitrogenous compound, synthesized in the body, that can form a high-energy bond by connecting to a phosphate group and that serves as an energy reserve. Is also a small molcule that muscle cells assemble from fragments of amino acids.

Fasciculus

A small bundle; usually refers to a collective of nerve axons or muscle fibers.

white muscle

-mostly fast fibers -pale (chicken breast)

length-tension relationship of smooth muscle

Because the thick and thin filaments are scattered and are not organized into sarcomeres in smooth muscle, tension development and resting length are not directly related. A stretched smooth muscle soon adapts to its new length and retains the ability to contract on demand. This ability to function over a wide range of lengths is called plasticity. Smooth muscle can contract over a range of lengths four times greater than that of skeletal muscle. Plasticity is especially important in digestive organs, such as the stomach, that change greatly in volume. Despite the lack of sarcomeres, smooth muscle contractions can be just as powerful as those of skeletal muscles. Like skeletal muscle fibers, smooth muscle cells can undergo sustained contractions (as anyone who has experienced the uterine contractions that happen during labor can confirm).

M line

Center of the A band. Proteins of the band connect the central portion of each thick filament to neighboring thick filaments. These dark-staining proteins help stabilize the potions of the thick filaments

Voltage-gated ion channels

Channels that open or close in response to a change in the membrane potential.

triad

Combination of terminal cisternae and T tubule is known as _____

neuromuscular junction (NMJ)

Communication between a neuron and another cell occurs at a synapse. When the other cell is a skeletal muscle fiber, the synapse is known as a _______. The NMJ is made up of an axon terminal (synaptic terminal) of a neuron, a specialized region of the sarcolemma called the motor end plate, and , in between, a narrow space called the synaptic cleft.

Sacromere

The smallest contractile unit of striated muscle cell.

resting length.

There is no active mechanism for returning shortened muscle fibers to their _______ _________ .After a contraction, a muscle returns to its original length through a combination of elastic forces, opposing muscle contractions, and gravity.

Terminal cisternae

When a T tubule encircles a myofibril, the tubule is tightly bound to the membranes of the SR. on either side of a T tubule, the tubule of the SR enlarge, fuse, and form expanded chambers called _______ _______

Normal muscle function

______ _______ requires 1. Substantial intracellular energy reserves 2. Normal circulatory supply 3. Normal blood oxygen level 4. A blood pH within normal limits. anything that interferes with nay of these factors will reduce the efficiency of muscle activity an cause premature muscle fatigue

smooth muscle

_________ _________ differs from other muscles in 1. excitation-contraction coupling 2. Length-tension relationships 3. control of contractions 4. smooth muscle tone

Extensibility

ability to be stretched

Excitability

ability to receive and respond to stimuli. Also known as responsiveness or irritability. Muscle tissues responds to a chemical stimulus from a nerve cell with a change in membrane potential

Improvements in aerobic endurance result from

altering the characteristics of muscle fibers and improving cardiovascular performance

hypertrophy

an enlargement of the stimulated muscle. Repeated exhaustive simulations causes muscle fibers to develop more mitochondria, a higher concentration of glycolytic enzymes, and larger glycogen reserves. Such muscle fibers have more myofibrils than do less-stimulated fibers, and each myofibril contains more thick and thin filaments.

intermediate fibers

are intermediate between those of fast fibers and slow fibers. In appearance, intermediate fibers most closely resemble fast fibers because they contain little myoglobin and are relatively pale. They have an intermediate capillary network and mitochondrial supply around them and are more resistant to fatigue than are fast fibers

aponeurosis

broad, flattened tendon

sacoplasm

cytoplasm of a muscle fiber

Myofilaments

fine protein filaments composed primarily of the proteins actin and myosin

internal organization

like skeletal and cardiac muscle tissues, smooth muscle contains actin, and myosin but unlike the internal organization of cardiac and skeletal muscles which have sarcomeres, with thin and thick filaments, the ________ ________ of smooth muscle is different.

generate

most cells in the body _______ ATP through 1. glycolysis in cytoplasm 2. Aerobic metabolism in mitochondria.

red muscle

mostly slow fibers, dark because of the extensive blood vessels and myoglobin in slow fibers.

asynchronous motor unit summation

motor units activated on a rotating basis to maintain a sustained contraction. Gives some muscle fibers time to rest and recover while others are contracting. This will eventually result in muscles producing slightly less maximum tension.

Wave summation

occurs when successive stimuli arrive before the relaxation phase has been completed. The duration of a single twitch determines the maximum time available for wave summation. For example, if a twitch lasts 20 msec (1/50 sec), subsequent stimuli must be separated by less than 20 msec—a stimulation rate of more than 50 stimuli per second. This rate is usually expressed in terms of stimulus frequency, which is the number of stimuli per unit time. In this instance, a stimulus frequency of greater than 50 per second produces wave summation, whereas a stimulus frequency of less than 50 per second produces individual twitches and treppe.

Intercalated disc

regions where adjacent cardiac muscle cells interlock and where gap junctions permit electrical coupling between cells

Cori cycle

shuffling of lactate to the liver and glucose back to muscle cells

sacroplasmic reticulum

specialized smooth endoplasmic reticulum, releases calcium on demand when the muscle fiber is stimulated to contract

isotonic contraction

tension rises and the skeletal muscle's length changes. Lifting an object off a desk, walking, and running involve isotonic contractions. These are two types of isotonic contractions; concentric and eccentric.

Sliding-filament theory

the concept that a sarcomere shortens as the thick and thin filaments slide past one another

latent period

the time between the stimulation of a muscle and the start of the contraction phase

atrophy

the wasting away of tissues from lack of use

Differences of skeletal muscle

Difference of in skeletal muscle fibers from typical cells. 1. Size. Skeletal muscle fibers are enormous 2. Multinucleated. Each contains hundreds of nuclei just internal to the plasma membrane. The genes in these nuclei control the production of enzymes and structural proteins required for normal muscle contraction. The more copies of these genes, the faster these proteins can be produced. 3. Muscle cells are banded or striated.

A bands and I bands

Differences in the size, density, and distribution of thick filaments and thin filaments account for the banded apperance of each myofibirl. Each sacromere has dark bands called ____ ____ and light bands called ____ ____

single muscle fiber

Each cell in skeletal muscle tissue is a ________ _______ ______

Creatine Kinase

Enzyme that catalyzes ATP/CP/Creatine reaction is _______ _______. When muscle cells are damaged, CK leaks across the membranes and into the bloodstream. A high blood concentration of CK usually indicates serious muscle damage

bodybuilder

Hypertrophy occurs in muscles that have been repeatedly stimulated to produce near-maximal tension. The intracellular changes that occur increase the amount of tension produced when these muscles contract. The muscles of a _____________ are excellent examples of muscular hypertrophy.

complete tetanus

If stimulation frequency is high enough, muscle never begins to relax and elimates the relaxation phase, and is in continuous contraction. In this situation, action potentials arrive so rapidly that the SR does not have time to reclaim the calcium ions. The high Ca2+ concentration in the cytosol prolongs the contraction, making it continuous. During a tetanic contraction, there is enough time for essentially all of the potential cross-bridges to form, and tension peaks.

Action potential

In neurons and skeletal muscle fibers, the depolarization and repolarization events produce an electrical impulse or _____ _________

Titin

Myofibrils contain _____, elastic myofilaments associated with the thick filaments

Endurance

The amount of time during which a person can perform a particular activity.

creatine phosphate

The energy transfer of creatine and ATP creates another high energy compound __________ also known as phosphocreatine

Perimysium

A connective tissue partition that separates adjacent fasciculi in a skeletal muscle. Divides skeletal muscle into a series of compartments. Each compartment contains a bundle of fibers called a fascicle. Contains collagen and elastic fibers as well as the blood vessels and nerves that supply the muscle fibers within the fascicles.

Thick filaments

A cytoskeletal filament in a skeletal or cardiac muscle cell; composed of myosin, with a core of titin

Thin filaments

A cytoskeletal filament in a skeletal or cardiac muscle cell; consists of actin, troponin, nebulin, and tropmyosin.

Z line

A dark thin protein band made up of actininsto which actin filaments are attached in a striated muscle fiber, marking the boundaries between adjacent sarcomeres.

Endomysium

A delicate network of connective tissue fibers that surrounds individual muscle cells. Surrounds the individual skeletal muscle cells, called muscle fibers, and loosely interconnects adjacent muscle fibers. Contains the capillary networks, myosatellite cells, and nerve fibers that control the muscle

Creatine phosphate

A high-energy compound in muscle cells; during muscle activity, the phosphate group is donated to ADP, regenerating ATP; also called phosphroylcreatine

Action potential

A propagated change in the membrane potential of excitable cells, initiated by a change in the membrane permeability to sodium ions

aerboic metabolism

Aerobic metabolism normally provides 95 percent of the ATP demands of a resting cell. In this process, mitochondria absorb oxygen, ADP, phosphate ions, and organic substrates (such as pyruvate) from the surrounding cytoplasm. The molecules then enter the citric acid cycle (also known as the tricarboxylic acid cycle or the Krebs cycle), an enzymatic pathway that breaks down organic molecules. The carbon atoms of the organic substrate are released as carbon dioxide. The hydrogen atoms are shuttled to respiratory complexes in the inner mitochondrial membrane, where their electrons are removed. After a series of intermediate steps involving the electron transport chain, the protons and electrons are combined with oxygen to form water. Along the way, large amounts of energy are released and used to make ATP. The entire process is very efficient: For each molecule of pyruvate "fed" into the citric acid cycle, the cell gains 15 ATP molecules.

polarized

All cells of the body maintain a membrane potential due to an unequal distribution of positive and negatives charges across their plasma membrane. The unequal charge distribution means cells are _____

Motor unit

All the muscle cells controlled by a single motor neuron.

draw backs of glycolysis

Although, as mentioned, the muscle fiber can generate additional ATP by the anaerobic process of glycolysis during times of peak energy demands, this process has two important drawbacks. First, any underutilized pyruvate molecules produced through glycolysis are converted to lactate. At the same time, the hydrolytic breakdown of ATP during muscle contraction releases hydrogen ions. During aerobic metabolism, these hydrogen ions are transported into the mitochondria. However, when ATP production is relying on glycolysis, the hydrogen ions remain in the cytosol. At peak activity, both hydrogen ions and lactate build up (Figure 10-20). This results in an increased lactate blood level and metabolic acidosis, often referred to as lactic acidosis. The hydrogen ions can then lower the intracellular pH. Buffers in the sarcoplasm resist pH shifts, but these mechanisms are limited. Eventually, changes in pH affect the workings of key enzymes so that the muscle fiber can no longer contract. Second, glycolysis is a relatively inefficient way to generate ATP. Under anaerobic conditions, each glucose molecule generates 2 pyruvate molecules, which are converted to 2 lactate. In this process, the fiber gains 2 ATP molecules. However, had those 2 pyruvate molecules been catabolized aerobically in a mitochondrion, the cell would have produced 30 additional ATP.

extensively intertwined

At an intercalated disc, the sarcolemma of two adjacent cardiac muscle cells are _________ ________ and bound together by gap junctions and desmosomes. These connections help stabilize the positions of adjacent cells and maintain the three-dimensional structure of the tissue. They also allow ions to move from one cell to another so that cardiac muscle beats in rhythm. Two cardiac muscle cells can "pull together" with maximum efficiency because their myofibrils are essentially locked together at intercalated discs.

smooth muscle tone

Both multiunit and visceral smooth muscle tissues have a normal background level of activity, or smooth muscle tone. Neural, hormonal, or chemical factors can also stimulate smooth muscle relaxation, producing a decrease in muscle tone. For example, smooth muscle cells at the entrances to capillaries regulate the amount of blood flow into each vessel. If the tissue becomes starved for oxygen, the smooth muscle cells relax, allowing blood flow to increase and, hence, delivering additional oxygen. As conditions return to normal, the smooth muscle regains its normal muscle tone.

Important structural differences pf cardiac muscle

Cardiac muscle cells are relatively small, averageing 10-20 um in diameter and 50-100 um in length. Cardiac muslce cells have a single, centrally placed nucleus, although a few may have two or more nuclei. Unlike skeletal muscle, cardiac muscle cells are typically branched. The T tubules in a cardiac muscle cell are short and broad, and there are no triads. The tubules encircle the sarcomeres at the Z lines rather than at the zones of overlap. The SR of a cardiac muscle cell lacks terminal cisternae and store fewer calcium ions. Its tubules contact the plasma membrane as well as the T tubules. Cardiac muscle cells are almost totally dependent on aerobic metabolism for the energy they need to continue contracting. They have energy reserves in the form of glycogen and lipid inclusions. The sarcoplasm of a cardiac muscle cell contains large numbers of mitochondria as well as abundant reserves of myoglobin, which store the oxygen needed to break down energy reserves during times of peak activity. Each cardiac muscle cell contracts several others at specialized sites known as intercalated disc

four major functional specialties of cardiac muscle.

Cardiac muscle tissue contracts without neural stimulation. This property is called automaticity. Specialized cardiac muscle cells called pacemaker cells normally determine the timing of contractions. The nervous system can alter the pace or rate set by the pacemaker cells and adjust the amount of tension produced during a contraction. Cardiac muscle cell contractions last about 10 times as long as do those of skeletal muscle fibers. They also have longer refractory periods and do not readily fatigue. The properties of cardiac muscle sarcolemmas differ from those of skeletal muscle fibers. As in skeletal muscle fibers, an action potential triggers the release of calcium ions from the SR and the contraction of sarcomeres. However, an action potential in a cardiac muscle cell also makes the sarcolemma more permeable to extracellular calcium ions. Because their contractions require both intracellular and extracellular calcium ions, cardiac muscle cells are more sensitive to changes in the extracellular calcium ion concentration than are skeletal muscle fibers. As a result, individual twitches cannot undergo wave summation, and cardiac muscle tissue cannot produce tetanic contractions. This difference is important, because a heart in a sustained tetanic contraction could not pump blood.

A band

Contains regions of overlapping thick (myosin) and think (actin filaments. The thick filaments are at the center of each sacromere, in the A band. The A band is about as long as a typical thick filament. THe A band also includes portions of thin filaments and contains these three subdivisons. 1. The M line 2. The H band 3. THe zone of overlap

Zone of overlap

Dark region where thin filaments are located between the thick filaments. Here three thick filaments surrounds each thin filament, and six thin filaments surround each thick filament

Heat Production During Muscle Activity

During a catabolic process, such as the breakdown of glycogen or the reactions of glycolysis, a muscle fiber captures only a portion of the released energy—the rest escapes as heat. A resting muscle fiber relying on aerobic metabolism captures about 42 percent of the energy released in catabolism. The other 58 percent warms the sarcoplasm, interstitial fluid, and circulating blood. Active skeletal muscles release roughly 85 percent of the heat needed to maintain normal body temperature. When anaerobic metabolism is the primary method of ATP generation, muscle fibers become less efficient at capturing energy. At peak levels of exertion, only about 30 percent of the released energy is captured as ATP, and the remaining 70 percent warms the muscle and surrounding tissues

Action potentials

Electrical impulse that are generated from the sacrolemma travel along the T-tubules into the cell interior. These impulse, called __________ _______, trigger muscle fiber contraction

Tropomyosin

Fibrous muscle protein that covers active sites on G actin and prevents actin-myosin interaction

Hormones and Muscle Metabolism

Hormones of the endocrine system adjust metabolic activities in skeletal muscle fibers. Growth hormone from the pituitary gland and testosterone (the primary sex hormone in males) stimulate the synthesis of contractile proteins, such as actin and myosin, and the enlargement of skeletal muscles. Thyroid hormones elevate the rate of energy consumption in resting and active skeletal muscles. During a sudden crisis, hormones of the adrenal gland, notably epinephrine (adrenaline), stimulate muscle metabolism and increase both the duration of stimulation and the force of contraction.

excitation-contraction coupling in smooth muscle

In skeletal and cardiac muscles, the trigger for contraction is the binding of calcium ions to troponin. In contrast, the trigger for smooth muscle contraction is the appearance of free calcium ions in the cytoplasm. On stimulation, a surge of calcium ions enters the cell from the extracellular fluid, and the sarcoplasmic reticulum releases additional calcium ions. The net result is a rise in the Ca2+ concentration throughout the cell. Once in the sarcoplasm, the calcium ions interact with calmodulin, a calcium-binding protein. Calmodulin then activates the enzyme myosin light chain kinase, which in turn enables myosin heads to attach to actin.

inversely related

Load and the speed of contraction are _________ ______. If the load is less than the tension produced, an isotonic concentric contraction will occur, and the muscle will shorten. The heavier the load, the longer it takes for the movement to begin, because muscle tension (which increases gradually) must exceed the load before shortening can occur (Figure 10-19). The contraction itself proceeds more slowly. In the muscle fiber, the speed of cross-bridge power strokes is reduced as the load increases.

Control of contractions

Many smooth muscle cells are not innervated by motor neurons, and the neurons that do innervate smooth muscles are not under voluntary control. We categorize smooth muscle cells as either multiunit or visceral. Multiunit smooth muscle cells are innervated in motor units comparable to those of skeletal muscles, but each smooth muscle cell may be connected to more than one motor neuron. In contrast, many visceral smooth muscle cells lack a direct contact with any motor neuron.

Excitable membrane

Membranes that propagate action potentials, a characteristic of muscle cells and nerve cells. Permits rapid communication between different parts of a cell.

Fast fibers

Most of the skeletal muscle fibers in the body are called fast fibers, because they can reach peak twitch tension in 0.01 sec or less after stimulation. Fast fibers are large in diameter and contain densely packed myofibrils, large glycogen reserves, and relatively few mitochondria. Muscles dominated by fast fibers produce powerful contractions because the tension produced by a muscle fiber is directly proportional to the number of myofibrils. However, fast fibers fatigue rapidly because their contractions use ATP in massive amounts, and they have relatively few mitochondria to generate ATP. As a result, prolonged activity is supported primarily by anaerobic metabolism.

Isotonic contraction

Muscle length changes with a constant force

Common properties

Muscle tissue shares these _________ ______: excitability, contractility, extensibility, and elasticity

Peak tension

Occurs when all motor units in the muscle contract in a state of complete tetanus. These powerful contractions do not last long, however, because the individual muscle fiber soon use up their available energy reserves.

Transverse tubules

Or T-Tubules transmit muscle impulses into the cell interior. They are narrow tubes that are continuous with the sarcolemma and extend deep into the sarcoplasm. They are filled with extracellular fluid and form passageways through the muscle fiber, like a network of tunnels through a mountain. They can orioagate an electrical impulse

excess postexercise oxygen consumption

Oxygen demand of the body's cells remains elevated above normal resting level. The more ATP required for recovery, the more oxygen will be needed. The amount of oxygen required to restore normal, pre-exertion condition's is called this. Most of the additional oxygen consumption occurs in skeletal muscle fibers, which must restore ATP, CP, and glycogen concentrations to their former levels, and in liver cells, which generate the ATP needed to convert excess lactate to glucose. However, several other tissues also increase their rate of oxygen consumption and ATP generation during the recovery period. For example, sweat glands increase their secretory activity until normal body temperature is restored. While the oxygen debt is being repaid, breathing rate and depth are increased. As a result, you continue to breathe heavily after you stop exercising.

Muscle changes with age

Skeletal muscle fibers become smaller in diameter, skeletal muscles become less elastic, tolerance for exercise decreases, and the ability to recover from muscular injuries decreases

Muscle metabolism

Sum of the chemical and physical changes that occur within muscle tissue. Involves generating the energy for contraction, using that energym and then recovering from energy expenditure.

Different

The internal organization of smooth muscle is very ___________. Smooth muscle is relatively long and slender, each cell is spindle shaped, smooth muscle fiber has no T tubules, and the sarcoplasmic reticulum forms a loose network through the sarcoplasm, smooth muscle lacks myofibrils and sarcomeres, thick filaments are scattered throughout the sarcoplasm of a smooth muscle cell, thick filaments are scattered throughout the sacroplasm of a smooth muscle cell. The myosin proteins are organized differently than in skeletal or cardiac muscle cells. Smooth muscle cells are attached to dense bodies, adjacent smooth muscle cells are bound together at dense bodies, transmitting the contractile forces from cell to cell through the tissue, collagen fibers never form tendons as they do in skeletal muscles.

H band

The lighter region on either side of the M line. Contains thick filaments and no thin filaments

intermingled

The muscle fibers of each motor unit are ___________ with those of other motor units. Because of this intermingling, the direction of pull exerted on the tendon does not change when the number of activated motor unit changes

ATP

The only energy source used directly for muscle contraction is ____, and available stores are depleted within 4-6 seconds in active muscles. ATP is generated by direct phosphorylation of ADP by creatine phosphate (CP), anaerobic metabolism (glycolysis_, and aerobic metabolism (citric acid cycle and electron transport chain)

Relaxation phase

The period after a contraction when the tension in the muscle fiber returns to resting levels

Creatine

The primary function of ATP is to transfer energy from one location to another rather than to store it long term. At rest, a skeletal muscle fiber produces more ATP than it needs. Under these conditions, ATP transfers energy to __________.

Striated muscle

The striations are due to the precise arrangements of thin (actin) and thick (myosin) filaments in these myofibrils. The arrangement of these filaments forms the repeating functional unit called a sarcomere

recovery period

The time required after exertion for muscles to return to normal. After a period of moderate activity, muscle fibers may need several hours to recover. After sustained activity at a higher level, complete recovery can take a way

fatigued

We say an active skeletal muscle is ___________ when it can no longer perform at the required level of activity. Many factors are involved in muscle fatigue. For example, muscle fatigue has been correlated with (1) depletion of metabolic reserves within the muscle fibers; (2) damage to the sarcolemma and sarcoplasmic reticulum; (3) a decline in pH within the muscle fibers and the muscle as a whole, which decreases calcium ion binding to troponin and alters enzyme activities; and (4) a sense of weariness and a reduction in the desire to continue the activity, due to the effects of low blood pH and sensations of pain. Muscle fatigue is cumulative—the effects become more pronounced as more neurons and muscle fibers are affected. The result is a gradual reduction in the capabilities and performance of the entire skeletal muscle.

Human muscle

________ ________ contains a mixture of fiber types and appear pink. However, there are no slow fibers in muscles of the eye or hand, where swift, but brief, contractions are required. Many of our back and calf muscles are dominated by slow fibers, and these muscles contract almost continuously to maintain an upright posture. Our genes determine the percentage of fast versus slow fibers in each muscle.

Neuromuscular junction

a synapse between a motor neuron and skeletal muscle

functional syncytium

cardiac muscle cells are physically, chemically, and electrically connected to one another, the entire tissue resembles a single, enormous muscle cell. For this reason cardiac muslce has been called a ________ _____________

slow fibers

have only about half the diameter of fast fibers and take three times as long to reach peak tension after stimulation. These fibers are specialized in ways that enables them to continue contracting long after a fast fiber would have become fatigued. The most important specializations support aerobic metabolism in the numerous mitochondria. Some specializations are they are surround by a more extensive network of capillaries than fast tissue which increases oxygen supply to mitochondrial activity. They are more dependent on ATP and less dependent on anaerobic metabolism than fast fibers. Glycogen reserves of slow fibers are also smaller than those of fast fibers, because some of the mitochondrial energy production involves the breakdown of stored lipids rather than glycogen.

fasciculation

involuntary twitch of muscle fibers.

aerobic endurance

is the length of time a muscle can continue to contract while supported by mitochondrial activities. Aerobic activities do not promote muscle hypertrophy. Conditioning for aerobic endurance improves an individual's ability to continue an activity for longer periods of time. Aerobic endurance is determined primarily by the availability of substrates for aerobic respiration, which muscle fibers can obtain by breaking down carbohydrates, lipids, or proteins. Initially, many of the nutrients broken down by muscle fibers come from reserves in the sarcoplasm. Prolonged aerobic activity, however, must be supported by nutrients provided by the circulating blood. Training to improve aerobic endurance generally involves sustained low levels of muscular activity. Examples include jogging, distance swimming, and other exercises that do not require peak tension production.

Anaerobic endurance

is the length of time muscular contraction can continue to be supported by the existing energy reserves of ATP and CP and by glycolysis. Conditioning for anaerobic endurance improves an individual's power. Anaerobic endurance is limited by (1) the amount of ATP and CP available, (2) the amount of glycogen available for breakdown, and (3) the ability of the muscle to tolerate lactate and the buildup of hydrogen ions generated during the period of anaerobic metabolism. Typically, the onset of muscle fatigue occurs within 2 minutes of the start of maximal activity. Short exercises such as the 50meter race

common

isotonic eccentric contractions are very _________ and are important in a variety of movement. In these movements, you exert precise control over the amount of tension produced. By varying the tension in an eccentric contractions, you can control the rate of elongation, just as you can vary the tension in a concentric contraction

smooth tissue

muscle tissue in the walls of many visceral organs: Characterized as nonstriated, involuntary muscle

myofibril

organized collections of myofilaments in skeletal and cardiac muscle cells

Sacrolemma

plasma membrane of a muscle fiber. Surrounds the sarcoplasm, or cytoplasm of the muscle fiber. Has a characteristic membrane potential

glycolysis

the anaerobic breakdown of glucose to pyruvate, which makes a small amount of energy available to cells in the form of ATP

Force

the maximum amount of tension produced by a particular muscle or muscle group.

Isometric contractions

the muscle as a whole does not change length, and the tension produced never exceeds the load

isotonic eccentric contraction

the peak tension developed is less than the load, and the muscle elongates due to the contraction of another muscle or the pull of gravity

treppe

(staircase) Phenomenon in which each successive twitch contracts more forcefully than the previous one. The rise is thought to result from a gradual increase in the concentration of Ca2+ in the cytosol, in part because the calcium ion pumps in the SR have too little time to recapture the ions between stimulations. Most skeletal muscles don't undergo treppe. However, treppe is a phenomenon in cardiac muscle. It occurs if stimuli of the same intensity are sent to the muscle fiber after a latent period.

Tendon

A collagenous band that connects a skeletal muscle to an element of the skeleton

Epimysium

A dense layer of collagen fivers that surrounds a skeletal muscle and is continuous with the tendons/ aponeuroses of the muscle and with the perimysium. Separates the muscle from nearby tissues and organs. The epimysium is connected to the deep fascia, a dense connective tissue layer

myogram

A recording of the tension produced by muscle fibers on stimulation.

frequency of stimulation

A single stimulation produces a single contraction, or twitch, that may last 7-100 milliseconds, depending the muscle stimulated. A single twitch is so brief that there isn't enough time to activate a significant percentage of the available cross-bridges. But if a second twitch occurs before tension returns to zero, tension will peak at a higher level, because additional cross-bridges will form. Each successive contraction that begins before the tension has fallen to the resting level, will cause the tension to increase until it peaks.

metabolism

Activated muscle fibers use energy, so the greater the muscle tone, the higher the "resting" rate of __________ (all the chemical reactions occuring in the body). Increasing this rate is one of the significant effects of exercise in weight-loss programs

Contraction

Branches of the T tubules and the sarcoplasmic reticulum encircle each myofibril. The active shortening of myofibrils is responsible for skeletal muscle fiber ________

Troponin

Globular muscle protein that binds to tropomyosin

isometric contraction

Muscle lenght does not change with a constant force

myofilaments

Myofibrils consist of bundles of protein filaments called __________. Myofibrils contain two types of myfilaments. Thin filaments composed primarily of action, and thick filaments composed primarily of myosin.

Skeletal muscle functions

Producing movement, maintaining posture and body position, Supporting soft issues, guarding body entrances and exists, maintaining body temperature, storing nutrients.

Sarcomere efficiency

Skeletal muscle fibers contract most forcefully when stimulated within the range of their optimal resting lengths. The arrangement of skeletal muscles, connective tissues, and bones normally prevents extreme compression or excessive stretching of muscle fibers. For example, straightening your elbow stretches your biceps brachii, but the bones and ligaments of the elbow stop this movement before the muscle fibers stretch too far. During an activity such as walking, in which muscles contract and relax cyclically, muscle fibers are stretched to a length very close to "ideal" before they are stimulated to contract. When muscles must contract over a larger range of resting lengths, they often "team up" to improve efficiency. (We discuss the mechanical principles involved in

Muscle tone

Some motor units are always active, even when the entire muscle is not contracting. Their contractions do not produce enough tension to cause movement, but they do tense and firm the muscle. This resting tension in skeletal muscle is called ______ _______

Factors of tension

Tension produced by an individual muscle fiber does vary. Tension production is greatest when a muscle is stimulated at its optimal length. A couple of factors are important. 1. Tension production depends on the fibers resting length at the time of stimulation, which determines the amount of overlap between thick and thin filaments. 2. It also depends on the frequency of stimulation, which affects the internal concentration of calcium ions and thus the amount bound to troponin

size

The _____ of a motor unit indicates how fine, or precise, a movement can be. Small motor units, with 4-6 muscle fibers are found in the muscle of the eyes and ginre, where precise control is extremely important. Large motor units, with 1000-2000 muscle fibers, are found in weight-bearing muscles of the thights and hips, where precise control is less urgent

Elasticity

The ability of a muscle to recoil

Tendon

The collagen fibers of the perimysium and endomysium are interwoven and blend into one another. At each end of the muscle, the collagen fibers of the epimysium, perimysium, and endomysium come together to form either a bundle known as a ________ or a broad sheet called an aponeurosis

Skeletal muscle

a muscle that is connected to the skeleton to form part of the mechanical system that moves the limbs and other parts of the body. It is very long, cylindrical, multinucleate cells with obvious striations. It also contains connective tissues, blood vessels, and nerves. Attaches directly or indirectly to bones

Contractility

ability to shorten forcibly when stimulated

lenght-tension relationship

as length increases, tension decreases.

Isotonic concentric contraction

muscle tension exceeds the load and the muscle shortens

I band

region of the sarcomere that contains thin filaments but no thick filaments. Extends from the A band of sarcomere to the A band of the next sarcomere. Z lines bisect the bands and mark the boundary between the adjacent sarcomeres

twitch

single stimulus-contraction-relaxation cycle in a muscle fiber. May vary in duration depending on the type of muscle, its location, internal and external environmental conditions, and other factors

myoblasts

stem cells that fuse to form each muscle fiber

myosatellite cells

stem cells that help repair damaged muscle tissue

Contraction phase

tension increases to a peak. As the tension increases, calcium ions are binding to troponin, active sites on thin filaments are being exposed, and cross-bridge interactions are occurring. For this muscle fiber, the contraction phase ends roughly 15 msec after stimulation.

recruitment

the smooth but steady increase in muscular tension produced by increasing the number of active motor units