Exam 2 - Chapter 11: Muscles - Human Physiology

As axons of autonomic motor neurons enter smooth muscle, they divide into branches that have swollen regions called ______________.

varicosities

In all three cases, contraction occurs because the Ca2+ concentration in the sarcoplasm increases. The increase in sarcoplasmic Ca2+ concentration that triggers contraction of a smooth muscle fiber can be caused by the opening of one or more of the following types of channels. What are the channels?

voltage-gated, Ca2+ release, receptor-activated, IP3-gated, store-operated, and mechanically-gated.

Explain the load-velocity relationship for concentric isotonic contraction.

(1) When the load is zero, the velocity of shortening is maximal (2) as the load increases, the velocity of shortening decreases (3) when the load is equal to or exceeds the maximum tetanic tension that the muscle can produce, the velocity of shortening is zero and the contraction becomes isometric. For a concentric isotonic contraction, the load and the velocity of muscle shortening are inversely related. You can lift a light object (a magazine) very quickly, a moderately weighted object (a textbook) less quickly, and a heavy object (a box of textbooks) only very slowly.

Skeletal muscle fibers have three ways to produce ATP, what are they?

(1) from creatine phosphate, (2) by anaerobic glycolysis, and (3) by aerobic respiration

skeletal muscle fibers are classified into three main types, what are they?

(1) slow oxidative fibers (2) fast oxidativ-glycolytic fibers (3) fast glycolytic fibers.

Oxygen consumption will increase for a while after exercise, what are three reasons why?

(1) to convert lactic acid back into glycogen stores in the liver, (2) to resynthesize creatine phosphate and ATP in muscle fibers, and (3) to replace the oxygen removed from myoglobin.

Define skeletal muscle

- attached to bones and moves parts of the skeleton - It is striated; that is, striations, or alternating light and dark bands, are visible under a light microscope - Voluntary (mainly), some are involuntary (diaphragm) - controlled by motor neurons that are part of the somatic nervous system

Myofibrils are built from three kinds of proteins, what are they?

1. contractile proteins 2. regulatory proteins, 3. structural proteins

when an action potential is generated in a mass of cardiac muscle fibers, it quickly spreads to all of the muscle fibers in that mass and then the muscle fibers contract _______________? a. Together B. One by one

A. Together

Define this muscle property: Electrical excitability

Ability to respond to certain stimuli by producing action potentials. a property of both neurons and muscle cells, is the ability to respond to certain stimuli by producing action potentials. Chapter 7 provided details about how action potentials arise (see Section 7.3). For muscle cells, two main types of stimuli trigger action potentials. One is chemical stimuli, such as neurotransmitters released by neurons and hormones distributed by the blood. The other is autorhythmic electrical signals arising in the muscle tissue itself, as in the heart's pacemaker

What is an end plate potential?

Action potential generated at the muscle membrane

Define this muscle function: Generating heat

As muscle contracts, it produces heat, a process known as thermogenesis. Much of the heat generated by muscle is used to maintain normal body temperature. Involuntary contractions of skeletal muscles, known as shivering, can increase the rate of heat production.

Cardiac muscle does not need external stimulation to contract, it does it on it's on periodically. What is this called?

Autorhythmicity - The ability to repeatedly generate spontaneous action potentials.

What is a ligament?

Connective tissue that connects bone to bone

What are the four properties of muscles?

Electrical excitability Contractility Extensibility Elasticity

What are the two main phases of skeletal muscle action potential?

Rising (depolarization) (closure of the voltage-gated Na+ channels) Falling (Repolarizaing) (the opening of voltage-gated K+ channels)

Only the heart contains ____________ muscle

cardiac

___________________________ for a skeletal muscle fiber indicates how the forcefulness of muscle contraction (tension) depends on the length of the sarcomeres within a muscle fiber before contraction begins

length-tension relationship A muscle fiber develops its greatest tension when there is an optimal zone of overlap between thick and thin filaments.

What are the muscles four key functions?

producing body movements stabilizing body positions storing and moving substances within the body generating heat

Myosin functions as a motor protein in all three types of muscle tissue. What do motor proteins do?

push or pull various cellular structures to achieve movement by converting the chemical energy in ATP to the mechanical energy of motion or the production of force

What parts make up the conduction system of the heart?

sinoatrial (SA) node, atrioventricular (AV) node, atrioventricular (AV) bundle or bundle of His, the right and left bundle branches, and the Purkinje fibers

What are the two regulatory proteins?

tropomyosin and troponin

Define cardiac muscle

- cardiac muscle is striated - cardiac muscle is involuntary - heart - regulated by motor neurons that are part of the autonomic nervous system and by hormones released by endocrine glands.

Describe components of cardiac muscle.

- found only in the heart - They are branched and usually have only one centrally located nucleus - striated - The thick filaments contain myosin, and the thin filaments contain actin, troponin, and tropomyosin. - transverse (T) tubules and a moderately developed sarcoplasmic reticulum (SR) - rely almost exclusively on aerobic respiration to generate the ATP they need for muscle contraction. As a result, these fibers contain large numbers of mitochondria

What are Fast oxidative-glycolytic (FOG) fibers?

- generate considerable ATP by aerobic respiration, which gives them a moderate resistance to fatigue - hydrolyzes ATP three to five times faster than the myosin ATPase in SO fibers - twitches of FOG fibers reach peak tension more quickly than those of SO fibers but are briefer in duration—less than 100 msec. FOG fibers contribute to activities such as walking and sprinting.

explain fast glycolytic fibres (FG).

- generate the most powerful contractions - low myoglobin content, relatively few blood capillaries, few mitochondria, and appear white in color. - contract strongly and quickly. These fast-twitch fibers are adapted for intense anaerobic movements of short duration, such as weight lifting or throwing a ball, but they fatigue quickly.

Define smooth muscle

- located in the walls of hollow internal structures, such as blood vessels, the airways, stomach, intestines, and uterus - smooth muscle lacks the striations that are present in skeletal and cardiac muscle (why it is called smooth muscle) - Involuntary - regulated by motor neurons that are part of the autonomic nervous system and by hormones released by endocrine glands.

The total force or tension that a single muscle fiber can produce depends on what three things? The total tension a whole muscle can produce depends on what?

1. the frequency of stimulation (the rate at which the muscle fiber is stimulated by a motor neuron) 2. the length of the muscle fiber before contraction begins 3. the diameter of the muscle fiber. the number of muscle fibers that are contracting in unison

In smooth muscles, what is the difference between a pacemaker potential and a slow-wave potential?

A pacemaker potential is a spontaneous depolarization that always reaches threshold and therefore triggers the production of an action potential. After repolarization, the pacemaker potential starts to develop again and the cycle repeats. The pacemaker potential in an autorhythmic smooth muscle fiber is caused by either an increase in Ca2+ movement into the cell or a decrease in K+ movement out of the cell Slow-wave potentials are cycles of alternating depolarization and repolarization that do not necessarily reach threshold . Sometimes, threshold is reached and an action potential is generated; on other occasions, threshold is not reached and an action potential does not occur. The mechanism underlying slow-wave potentials is thought to involve fluctuations in Na+ movement out of the cell caused by periodic changes in the activity of Na+/ K+ pumps.

The slow start and longer duration of contraction in smooth muscle occur because of what factors?

1. There are no transverse tubules in smooth muscle fibers, so it takes longer for Ca2+ to reach the filaments in the center of the fiber and trigger the contraction process. 2. Myosin light chain kinase works rather slowly. 3. The ATPase activity of myosin heads in smooth muscle is much slower than in striated muscle. 4. The myosin heads in smooth muscle can enter a latch state, in which they stay attached to actin for a longer portion of the crossbridge cycle compared to myosin heads in striated muscle. Although the latch state is poorly understood, it is important because it allows smooth muscle to maintain tension for long periods of time with minimal ATP consumption.

Relaxation of smooth muscle involves two main steps, what are they?

1. decreasing the Ca2+ concentration in the sarcoplasm to resting levels 2. dephosphorylating (removing the phosphate group from) light chains in the myosin heads

At the onset of contraction, the sarcoplasmic reticulum releases calcium ions (Ca2+) into the sarcoplasm. There, they bind to troponin. Troponin then moves tropomyosin away from the myosin-binding sites on actin. Once the binding sites are "free," the contraction cycle—the repeating sequence of events that causes the filaments to slide—begins .What are the four steps of the contraction cycle?

ATP hydrolysis Attachment of myosin to actin Power stroke Detachment of myosin from actin

What are the functions of the three types of proteins? (Contractile, regulatory, and structural)

Contractile: which generate force during contraction Regulatory: help switch the contraction process on and off Structural: keep the thick and thin filaments in the proper alignment, give the myofibril extensibility and elasticity, and link the myofibrils to the sarcolemma and extracellular matrix

What factors contribute to muscle fatigue?

Fatigue results mainly from changes within muscle fibers. Even before actual muscle fatigue occurs, a person may have feelings of tiredness and the desire to cease activity; this response, called central fatigue, is caused by changes in the central nervous system (brain and spinal cord) One is inadequate release of calcium ions from the SR, resulting in a decline of Ca2+ concentration in the sarcoplasm. Depletion of creatine phosphate is also associated with fatigue, but surprisingly the ATP levels in fatigued muscle often are not much lower than those in resting muscle. Other factors that contribute to muscle fatigue include insufficient oxygen, depletion of glycogen and other nutrients, buildup of lactic acid and ADP, and failure of action potentials in the motor neuron to release enough acetylcholine.

What are the two main muscle actions? How do they differ?

Flexion and Extension Flexion is the act of bending a limb at a joint, whereas extension is the act of straightening a limb at a joint.

Know the different frequency's of stimulation

If a second stimulus occurs in a skeletal muscle fiber after the refractory period of the first stimulus is over but before the muscle fiber has relaxed, the second contraction will actually be stronger than the first. This phenomenon, in which stimuli arriving at different times cause contractions with greater tension, is called wave summation. If a skeletal muscle fiber is stimulated at a higher rate, it can relax only slightly between stimuli. The result is a sustained but wavering contraction called unfused (incomplete) tetanus. If a skeletal muscle fiber is stimulated at an even higher rate, it does not relax at all. The result is fused (complete) tetanus, a smooth, sustained contraction in which individual twitches cannot be detected and maximum tension is reached.

What is the difference between a mechanical advantage and a mechanical disadvantage?

If the load is closer to the fulcrum than the effort, then only a relatively small effort is required to move a large load over a small distance. This is called a mechanical advantage If the load is farther from the fulcrum than the effort, then a relatively large effort is required to move a small load (but at greater speed). This is called a mechanical disadvantage.

What is muscular atrophy?

Individual muscle fibers decrease in size because of progressive loss of myofibrils. Atrophy that occurs because muscles are not used is termed disuse atrophy If instead the nerve supply to a muscle is disrupted or cut, the muscle undergoes denervation atrophy.

Do smooth muscle cells exhibit autorhythmicity or do external stimulation cause them to contract?

They exhibit autorhythmicity

_________________, a structural protein, is the third most plentiful protein in skeletal muscle (after actin and myosin). This molecule's name reflects its huge size. With a molecular weight of about 3 million daltons, titin is 50 times larger than an average-sized protein

Titin (titan = gigantic)

When a contractile single-unit smooth muscle fiber produces an action potential, the action potential can be either a __________ potential or an action potential with a ____________.

Spike; plateau As its name implies, a spike potential is an action potential that is shaped like a spike; you are already familiar with examples of spike potentials—namely, the action potentials that occur in neurons and skeletal muscle fibers. An action potential with a plateau is similar to the action potential that occurs in contractile cardiac muscle fibers In an action potential with a plateau, the plateau phase is caused by prolonged opening of L-type voltage-gated Ca2+ channels, along with the partial opening of voltage-gated K+ channels.

____________ are the series elastic elements of a muscle because they are elastic and in series with the contractile elements of the muscle.

Tendons

Define this muscle property: Contractility

The ability of cells or parts of cells to generate force actively to undergo shortening for movements. Muscle fibers (cells) exhibit a high degree of contractility. the ability of muscle to contract forcefully when adequately stimulated. When a muscle contracts, it generates tension (force of contraction) while pulling on its attachment points. If the tension generated is great enough to overcome the resistance of the object to be moved, the muscle shortens and movement occurs

Define this muscle property: Elasticity

The ability of muscle to return to its original length and shape after contraction or extension.

The ___________ (upper chambers) and _____________ (lower chambers) of the heart behave as two distinct functional syncytiums. Thus, the atria and ventricles contract independently of each other, with the atria contracting before the ventricles. This allows the ventricles to fill with blood from the atria before the ventricles eject blood out of the heart to the rest of the body.

atria; ventricles

The heart beats because it has a pacemaker that initiates each contraction. This built-in rhythm is termed ______________________

autorhythmicity

What are fascicles?

bundles of 10 to 100 to more muscle fibers

The main component of the thin filament is the protein ____________.

actin

If sufficient oxygen is present, the pyruvic acid formed by glycolysis enters the mitochondria, where it undergoes ______________, a series of oxygen-requiring reactions that produce ATP, carbon dioxide, water, and heat

aerobic respiration

If two stimuli are applied to a skeletal muscle fiber, one immediately after the other, the muscle fiber will respond to the first stimulus but not to the second. When a muscle fiber receives enough stimulation to contract, it temporarily loses its excitability and cannot respond for a time. The period of lost excitability is called the ____________________

refractory period,

The multiple nuclei of a skeletal muscle fiber are located just beneath the ________________, the plasma membrane of a muscle fiber. Thousands of tiny invaginations of the sarcolemma, called _________________, 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 extracellular fluid. Muscle action potentials travel along the sarcolemma and through the T tubules, quickly spreading throughout the muscle fiber. This arrangement ensures that an action potential excites all parts of the muscle fiber at essentially the same instant.

sarcolemma; transverse (T) tubules

The thin and thick filaments inside a myofibril do not extend the entire length of a muscle fiber. Instead, they are arranged in compartments called _______________, which are the repeating units of a myofibril

sarcomeres

The sarcolemma surrounds the _____________, the cytoplasm of a muscle fiber. Within the sarcoplasm are mitochondria, which produce large amounts of ATP for muscle contraction. The sarcoplasm also contains _____________, a large polysaccharide consisting of thousands of glucose molecules covalently linked together. Glycogen serves as a storage form of glucose. It can be broken down into individual glucose molecules that can be used to synthesize ATP. Also present in the sarcoplasm are molecules of ________________, a red-colored, oxygen-binding protein that is found only in muscle. Myoglobin stores oxygen until it is needed by mitochondria to generate ATP.

sarcoplasm; glycogen; myoglobin

Narrow, plate-shaped regions of dense protein material called Z discs perform what function?

separate one sarcomere from the next. Thus, a sarcomere extends from one Z disc to the next Z disc.

What are the three types of muscle?

skeletal, cardiac, smooth

Most of the excess ATP is used to synthesize ________________, an energy-rich molecule that is found in muscle fibers.

creatine phosphate

The sequence of events that links the muscle action potential to muscle contraction is known as __________________ coupling

excitation-contraction (EC)

a mass of interconnected muscle fibers acts as a single, coordinated unit or ___________________

functional syncytium

Then a series of reactions known as ____________ quickly breaks down each glucose molecule into two molecules of pyruvic acid. During heavy exercise, however, not enough oxygen is available to skeletal muscle fibers. Under these anaerobic conditions, the pyruvic acid generated from glycolysis is converted to lactic acid. The entire process by which the breakdown of glucose gives rise to lactic acid when oxygen is absent or at a low concentration is referred to as _____________

glycolysis; anaerobic glycolysis

Because mature skeletal muscle fibers have lost the ability to undergo cell division, growth of skeletal muscle after birth is due mainly to _________________, the enlargement of existing cells, rather than to ________________, an increase in the number of fibers

hypertrophy; hyperplasia Hypertrophy - enlargement of existing cells, occurs in all muscle types, can help repair damaged tissue Hyperplasia - Increase in number of cells (Myofibers). Occurs via cell division, can occur in limited types of smooth muscle, some literature records of hyperplasia after muscle damage in skeletal muscle.

Define this muscle property: Extensibility

the ability of muscle to stretch without being damaged. Extensibility allows a muscle to contract forcefully even if it is already stretched. Normally, smooth muscle is subject to the greatest amount of stretching. For example, each time your stomach fills with food, the muscle in its wall is stretched. Cardiac muscle is also stretched each time the heart fills with blood

___________________ are irregular transverse thickenings of the sarcolemma that connect the ends of cardiac muscle fibers to one another

intercalated discs (contain desmosomes, which hold the fibers together, and gap junctions, which allow muscle action potentials to spread from one cardiac muscle fiber to another)

A myosin molecule consists of six polypeptide chains: two _______________ chains and four _________________ chains

large heavy; small light

A ______________ consists of a somatic motor neuron plus all the muscle fibers it innervates

motor unit

When a muscle needs to generate more force during a contraction, more of its motor units are activated. The process of increasing the number of active motor units is called __________________

motor unit recruitment

Each of your skeletal muscles is composed of hundreds to thousands of muscle cells, called _______________ , arranged parallel to one another

muscle fibers

The term _________________________ refers to a group of inherited muscle-destroying diseases that cause progressive degeneration of skeletal muscle fibers. The most common form of muscular dystrophy is Duchenne muscular dystrophy (doo-SHĀN) or DMD

muscular dystrophy (DIS-trō-fē) In DMD, the gene that codes for the protein dystrophin is mutated, so little or no dystrophin is present in the muscle fiber. Without the reinforcing effect of dystrophin, the sarcolemma tears easily during muscle contraction, causing muscle fibers to rupture and die

Together, all of the skeletal muscles of the body comprise the ___________________.

muscular system

Because each skeletal muscle fiber arises during embryonic development from the fusion of many small, undifferentiated cells called ________________

myoblasts

Extending throughout the sarcoplasm are ______________, the contractile elements of the skeletal muscle fiber. Within myofibrils are smaller structures called ____________, which can have either a thin or thick diameter. Thin filaments are 8 nm in diameter and 1-2 μm long, while thick filaments are 16 nm in diameter and 1-2 μm long. Both thin and thick filaments are directly involved in the contraction process.

myofibrils; filaments

Dephosphorylation of myosin heads occurs via the enzyme ______________________

myosin phosphatase,

The synapse between a somatic motor neuron and a skeletal muscle fiber is known as the __________________________

neuromuscular junction (NMJ).

Most skeletal muscles cross at least one joint and are usually attached to the articulating bones that form the joint. When the muscle contracts, it pulls one bone toward the other. The two bones do not move equally in response to contraction. One bone remains near its original position, whereas the other bone undergoes more movement. The attachment of a muscle's tendon to the more stationary bone is called the _________; the attachment of the muscle's other tendon to the more movable bone is called the __________

origin; insertion

What are the three phases of a twitch?

the latent period, the contraction period, and the relaxation period

When smooth muscle fibers are stretched, they initially contract, developing increased tension. Within a minute or so, the tension decreases. This phenomenon, called __________________________, allows smooth muscle to undergo great changes in length while retaining the ability to contract effectively

the stress-relaxation response

A ______________ is the brief contraction of a group of muscle fibers within a muscle in response to a single action potential The record of a muscle contraction, called a ___________

twitch; myogram

Main point of contraction during excitation-contraction?

When an action potential travels along the T tubule, the DHP receptors detect the change in voltage and undergo a conformational change that ultimately causes the Ca2+ release channels to open

Main point of relaxation during excitation-contraction?

When the T tubule is at resting membrane potential, the part of the Ca2+ release channel that extends into the sarcoplasm is blocked by a given cluster of DHP receptors, which prevents Ca2+ from leaving the SR

Explain the four steps of the contraction cycle.

1. ATP Hydrolysis - A myosin head includes an ATP-binding site that functions as an ATPase—an enzyme that hydrolyzes ATP into ADP (adenosine diphosphate) and a phosphate group. Energy generated from this hydrolysis reaction is stored in the myosin head for later use during the contraction cycle. The myosin head is said to be energized when it contains stored energy. The energized myosin head assumes a "cocked" position, like a stretched spring 2. Attachment of myosin to actin - The energized myosin head attaches to the myosin-binding site on actin and releases the previously hydrolyzed phosphate group. When a myosin head attaches to actin during the contraction cycle, the myosin head is referred to as a crossbridge. Although a single myosin molecule has a double head, only one head binds to actin at a time 3. After a crossbridge forms, the myosin head pivots, changing its position from a 90° angle to a 45° angle relative to the thick and thin filaments. As the myosin head changes to its new position, it pulls the thin filament past the thick filament toward the center of the sarcomere, generating tension (force) in the process. This event is known as the power stroke. The energy required for the power stroke is derived from the energy stored in the myosin head from the hydrolysis of ATP. Once the power stroke occurs, ADP is released from the myosin head. 4. Detachment of myosin from actin - At the end of the power stroke, the crossbridge remains firmly attached to actin until it binds another molecule of ATP. As ATP binds to the ATP-binding site on the myosin head, the myosin head detaches from actin.

Explain the contraction of smooth muscle.

1. Ca2+ binds to calmodulin, a regulatory protein in the sarcoplasm that is similar in structure to troponin. 2. The Ca2+-calmodulin complex activates an enzyme called myosin light chain kinase (MLCK), which is also present in the sarcoplasm. 3. Activated MLCK in turn phosphorylates (adds a phosphate group to) light chains in the myosin heads. 4. The phosphorylated myosin heads bind to actin, and muscle contraction begins.

Define this muscle function: Producing body movements

Movements of the whole body such as walking and running, and localized movements such as grasping a pencil or nodding the head, rely on the integrated functioning of skeletal muscles, bones, and joints

What are the fluid-filled system of membranous sacs that encircles each myofibril? What are their function?

Sarcoplasmic reticulum A network of sacs and tubes surrounding myofibrils of a muscle fiber (cell), comparable to endoplasmic reticulum; functions to reabsorb calcium ions during relaxation and to release them to cause contraction.

There are two major types of smooth muscle. What are they and what are the differences?

Single-unit smooth muscle, the most common type, is so-named because its fibers contract together as a single unit. It is also referred to as visceral smooth muscle because it is found in the walls of viscera (internal organs) such as the stomach, intestines, uterus, urinary bladder, and many blood vessels multi-unit smooth muscle, consists of fibers that act independently of each other as multiple units. Gap junctions are rare in multi-unit smooth muscle. As a result, the fibers must be stimulated individually by nerves to contract. Whereas stimulation of one single-unit smooth muscle fiber causes contraction of adjacent fibers, stimulation of one multi-unit smooth muscle fiber causes contraction of that fiber only. Multi-unit smooth muscle is found in the airways to the lungs, the iris and ciliary body of the eye, the arrector pili muscles of the skin, and some blood vessels.

Define this muscle function: Stabilizing body positions

Skeletal muscle contractions stabilize joints and help maintain body positions, such as standing or sitting. Postural muscles contract continuously when you are awake; for example, sustained contractions of your neck muscles hold your head upright.

_________________________ are smallest in diameter and thus are the least powerful type of muscle fibers

Slow oxidative (SO) fibers - appear dark red - generate ATP mainly by aerobic respiration - maintaining posture and for aerobic, endurance-type activities such as running a marathon

Define this muscle function: Storing and moving substances throughout the body

Storage is accomplished by sustained contractions of ringlike bands of smooth muscle called sphincters, which prevent outflow of the contents of a hollow organ. Temporary storage of food in the stomach or urine in the urinary bladder is possible because smooth muscle sphincters close off the outlets of these organs. Cardiac muscle contractions of the heart pump blood through the blood vessels of the body. Contraction and relaxation of smooth muscle in the walls of blood vessels help adjust blood vessel diameter and thus regulate the rate of blood flow. Smooth muscle contractions also move food and substances such as bile and enzymes through the gastrointestinal tract, push gametes (sperm and oocytes) through the passageways of the reproductive systems, and propel urine through the urinary system. Skeletal muscle contractions promote the flow of lymph and aid the return of blood to the heart.

_____________ is a rod-shaped protein that joins with other tropomyosin molecules to form two long strands that wrap around the F actin double helix.

Tropomyosin

____________ is a protein that consists of three globular subunits—one that binds to tropomyosin, one that binds to actin, and one that has binding sites for calcium ions (Ca2+). When Ca2+ binds to troponin, troponin undergoes a change in shape; this conformational change moves tropomyosin away from the myosin-binding sites on actin, and muscle contraction subsequently begins as myosin attaches to actin.

Troponin

What is muscular dystrophy?

An increase in the diameter of muscle fibers due to increased production of myofibrils, mitochondria, sarcoplasmic reticulum, and other organelles. It results from very forceful, repetitive muscular activity, such as strength training. Because hypertrophied muscles contain more myofibrils, they are capable of more forceful contractions.

Individual actin molecules are known as ___ actin because they are globular proteins. On each G actin molecule is a myosin-binding site, where a myosin head can attach. G actin molecules are linked together to form a long polymer called __ actin, which is so-named because it has a fibrous structure

G; F

_____________ refers to decreased or lost muscle tone. Such muscles are said to be flaccid _______________ refers to increased muscle tone and is expressed in two ways: spasticity or rigidity

Hypotonia; Hypertonia

Understand Excitation contraction coupling in cardiac muscles

In a contractile cardiac muscle fiber, an action potential opens L-type voltage-gated Ca2+ channels; extracellular Ca2+ moves into the cell through these channels and then causes Ca2+-induced Ca2+ release (CICR) from the sarcoplasmic reticulum. An action potential opens L-type voltage-gated Ca2+ channels; extracellular Ca2+moves into the cell through these channels and then causes Ca2+ releasef rom the sarcoplasmic reticulum.

What are the two major categories of muscle contractions?

Isotonic (concentric and eccentric) Isometric (holding steady)

The two contractile proteins in muscle are __________ and ___________, which are the main components of thick and thin filaments, respectively

Myosin; actin

What are the two cells that make up cardiac muscle, as a functional system?

a small number of autorhythmic fibers (also known as pacemaker cells) and a large number of contractile fibers

The biceps and triceps muscles are examples of antagonistic muscles because they promote opposite actions at the same joint. With a given pair of antagonistic muscles, when one muscle ____________, the other muscle _______________

contracts; relaxes

A ________ is a cord of connective tissue that attaches the muscle to a bone

tendon