Chapter 9: Muscles and Muscle Tissue Diagram | Quizlet

muscle fibers

Skeletal and smooth muscle cells (but not cardiac muscle cells) are elongated

prefixes that refer to muscles

myo, mys, and sacro (flesh)

skeletal muscle tissue

skeletal, striates, and voluntary

fibers are the longest muscle cells and have obvious stripes called striations.

Voluntary muscle because it is the only type subject to conscious control.

cardiac muscle tissue

only in the heart

striated, but involuntary

smooth muscle tissue

visceral, nonstraiated, involuntary

found in the walls of hollow visceral organs, such as the stomach, urinary bladder, and respiratory passages also forms valves to regulate the passage of substances

Characteristics of muscle tissue

1. Excitability - receive and respond to a stimulus

2. Contractility - shorten forcibly

3. Extensibility - extend or stretch

4. Elasticity - recoil and resume its resting length

Functions of muscle tissue

1. Produce movement

2. Maintain posture and boy position

3. Stabilize joints

4. Generate heat

Structure of skeletal muscle

skeletal muscle fibers

blood vessels - rich blood supply

nerve fibers

sustainable amounts of connective tissue

In general, one nerve, one artery, and one or more veins serve each muscle.

connective tissue sheaths

support each cell and reinforce and hold together the muscle, preventing the bulging muscles from bursting during exceptionally strong contractions

epimysium

dense irregular connective tissue that surrounds the whole muscle

fascicle

bundle of nerve or muscle fibers bound together by connective tissue

The ______________ divides the skeletal muscles into compartments, each containing bundles of muscle fibers called a ________ (2 words, comma seperated)

perimysium, fascicles

endomysium

thin connective tissue surrounding each muscle cell

muscles origin

attachment of a muscle that remains relatively fixed during muscular contraction

muscles insertion

movable attachment of a muscle

direct or fleshy attachments

the epimysium of the muscle is fused to the periosteum of a bone or perichondrium of a cartilage

indirect attachment

the muscle's connective tissue wrappings extend beyond the muscle either as a ropelike tendon or as a sheetlike aponeurosis

more common because of their durability and small size

tendon

cord of dense regular connective attaching muscle to bone

aponeurosis

a sheetlike indirect attachment to a skeletal element

fibrous or membranous sheet connecting a muscle and the part it moves

skeletal muscle fibers

long cylindrical cells (up to 30 cm long) with multiple oval nuclei beneath sarcolemma (plasma membrane)

huge cells - diameter of 10-100 micrometers

sacroplasm

cytoplasm of muscle fibers

Contains large amounds of glycosomes ( granules of stored glycogen) and myoglobin (O2 binding red pigment)

myofibrils

rodlike bundle of contractile filaments (myofilaments) found in muscle fibers (cells). made up of a chain of sarcomeres linked end to end.

A single muscle fiber contains hundreds to thousands of rodlike myofibrils that run parallel to its length

striations

repeating series of dark and light bands, are evident along the length of each myofibril. dark A bands and light I bands

sarcomere

region of a myofibril between two successive Z discs

the smallest contractile unit (2 micrometers long) of muscle; extends from one Z disc to the next.

myofilaments

filament that constitutes the myofibrils.

- central thick filaments containing (about 300) myosin (red) extend the entire length of the A band

- lateral thin filaments containing actin (blue) extend across the I band and partway into the A band

myosin

principal contractile protein found in muscle.

Major component of thick filaments.

consists of six polypeptide chains: two heavy (high-molecular-weight) chains and four light chains

actin

cytoskeletal element; a contractile protein of muscles.

Two intertwined actin filaments, resembling a twisted double strand of pearls, form the backbone of each thin filament

Regulatory proteins of thin filaments

tropomyosin (a rod-shaped protein, spiral about the actin core and help stiffen and stabilize it)

troponin (a globular protein with three polypeptide subunits)

The elastic filament we referred to earlier is composed of the giant protein______.

titin

holds the thick filaments in place, maintaining the organization of the A band, and helps the muscle cell spring back into shape after stretching

dystrophin

structural protein

links the thin filaments to the integral proteins of the sarcolemma

proteins that bind filaments or sarcomeres together and maintain their alignment include

nebulin, myomesin, and C proteins

muscular dystrophy

a group of inherited muscle-destroying diseases that generally appear during childhood. The affected muscles initially enlarge due to deposits of fat and connective tissue, but the muscle fibers atrophy and degenerate.

Duchenne muscular dystrophy (DMD)

almost exclusively in males

caused by a defective gene for dystrophin, the cytoplasmic protein

sarcoplasmic reticulum (SR)

an elaborate smooth endoplasmic reticulum, regulates intracellular levels of ionic calcium

T (transverse) tubule

extension of the muscle cell plasma membrane (sarcolemma) that protrudes deeply into the muscle cell.

a rapid communication or messaging system that ensures that every myofibril in the muscle fiber contracts at virtually the same time

contraction

refers only to the activation of myosin's cross bridges, which are the force-generating sites

action potentail (AP)

aka nerve impulses

A large change in membrane potential that spreads rapidly over long distances within a cell

acetylcholine

aka ACh

The neurotransmitter that motor neurons use to "tell" skeletal muscle to contract

Two classes of ion channels

1. chemically gated ion channels - opened by chemical messengers (e.g., neurotransmitters)

2. voltage-gated ion channels - open or close in response to changes in membrane potential.

somatic motor neurons

aka motor neurons of the somatic (voluntary) nervous system

Motor neurons that activate skeletal muscle fibers. reside in the spinal cord (except for those that supply the muscles of the head and neck)

Each neuron has a long threadlike extension called an ________ that extends from the cell body in the spinal cord to the muscle fiber it serves

axon

overview of skeletal muscle contration

1. events at the neuromusular junction - motor neuron releases ACh the stimulates the skeletal muscle fiber

2. muscle fiber excitation - end plat potentail (EPP) triggers an action potential that travels across the entire sarcolemma

3. excitation-contraction coupling - AP in the sarcolemma propagates along the T tubules and causes release of Ca2+ from the terminal cisterns of the SR.

4. cross bridge cycling - muscle contracts as a result of a repeating cycle of steps that cause myofilaments to slide relative to each other

End plat potential (EPP)

local depolarization

result of the events at the neuromuscular junction is a transient change in membrane potential that causes the interior of the sarcolemma to become less negative (a depolarization).

acetylchoinesterase

enzyme that degrades acetylcholine (ACh) and terminates its action at the neuromuscular junction and synapses.

muscle tension

force exerted by a contracting muscle on an object. The opposing force exerted on the muscle by the weight of the object to be moved is called the load

motor unit

consists of one motor neuron and all the muscle fibers it innervates, or supplies

Muscle fibers may be as few as four or as high as several hundred

myogram

a graphic recording of mechanical contractile activity produced by an apparatus that measures muscle contraction. recorded lines called tracings

muscle twitch

the response of a muscle to a single stimulation

Steps:

1. Latent period - first few milliseconds (ms) following stimulation

2. period of contraction - cross bridges are active, from the onset to the peak of tension development, and the myogram tracing rises to a peak.

3. period of relaxation - lasting 10-100 ms, is due to pumping of Ca2+ back into the SR.

a muscle contracts faster than it relaxes

Graded muscle contractions

variation in the degree of muscle contraction by changing either the frequency or strength of a stimulus.

Graded:

1. An increase in the frequency of stimulation causes temporal summation

2. An increase in the strength of stimulation causes recruitment.

temporal or wave summation

occurs because the second contraction begins before the muscle has completely relaxed. The second contraction is greater than the first because the muscle is already partially contracted and because even more calcium is squirted into the cytosol.

isotonic contractions

aka concentric

changes in length and moves the "load"

If the muscle tension developed overcomes the load and muscle shortening occurs.

the thin filaments slide

2 types concentric and eccentric

isometric contractions

muscle does not shorten, but its internal tension increases.

the cross bridges generate force but do not move the thin filaments

concentric versus eccentric

concentric - the muscle shortens and does work

eccentric - the muscle generates force as it lengthens

Basically, eccentric contractions put the body in position to contract concentrically

Pathways for regenerating ATP during muscle activity

(a) direct phosphorylation of ADP by creatine phosphate, (b) anaerobic glycolysis, which converts glucose to lactic acid, and (c) aerobic respiration

direct phosphorylation of ADP by creatine phosphate

As we begin to exercise vigorously, CP a unique high-energy molecule stored in muscles, is tapped to regenerate ATP while other metabolic pathways adjust to the sudden high demand for ATP.

Together, stored ATP and CP provide for maximum muscle power for about 15 seconds—long enough to energize a 100-meter dash

anaerobic glycolysis

As stored ATP and CP are exhausted, more ATP is generated by breaking down (catabolizing) glucose obtained from the blood or glycogen stored in the muscle. 2 ATP per glucose.

inefficient but fast. It harvests only about 5% as much ATP from each glucose molecule as the aerobic pathway, but it produces ATP about 2½ times faster.

aerobic pathway

95% of the ATP used for muscle activity comes from aerobic respiration. As exercise begins, muscle glycogen provides most of the fuel.

Aerobic respiration provides a high yield of ATP (about 32 ATP per glucose), but it is slow because of its many steps and it requires continuous delivery of oxygen and nutrient fuels to keep it going.

muscle fatigue

Ionic imbalances

Increased inorganic phosphate

Decreased ATP and increased Mg

Decreased glycogen

excess post-exercise oxygen consumption (EPOC)

- the difference between the amount of oxygen needed for totally aerobic muscle activity and the amount actually used

NOT increases the level of lactic acid in the muscle

Its oxygen reserves (stored in myoglobin) must be replenished.

The accumulated lactic acid must be reconverted to pyruvic acid.

Glycogen stores must be replaced.

ATP and creatine phosphate reserves must be resynthesized.

Factors that increase the force of skeletal muscle contraction.

1. frequency of stimulation

2. number of muscle fibers recruited

3. size of muscle fibers

4. degree of muscle stretch

Muscle fiber type

1. Muscle fiber type - slow and fast fibers (speed at which myosin ATPases splitting ATP)

2. Major pathways for forming ATP

Using these two criteria, we can classify skeletal muscle cells as: slow oxidative fibers, fast oxidative fibers, or fast glycolytic fibers.

fast glycolytic fiber

best suited for short-term, rapid, intense movements

- uses little O2

- contracts rapidly

plentiful glycogen reserves

- tires quickly

- large diameter

- few mitochondria

slow oxidative fibers

best suited to endurance-type activities

- contract slowly

- depend on O2

- resits fatigue - high endurance

- thin

- little power

- many mitochondria

- rich capillary supplt

- red fibers

- Abundant in muscles used to maintain posture.

fast oxidative fibers

less common

- contract quickly

- O2 dependent

- rich supply of myoglobin and capillaries

muscles of marathon runners have a high percentage of ______.

slow oxidative fibers (about 80%)

muscles of sprinters contain a higher percentage _____.

(about 60%) of fast oxidative and glycolytic fibers

aerobic, endurance, exercise changes

- increase in number of capillaries surrounding the muscle fibers

- increase in number of mitochondria within fibers

- fibers synthesize more myoglobin

Arrangement of smooth muscle in the walls of hollow organs

1. longitudinal layer, the muscle fibers run parallel to the long axis of the organ. when these fibers contract, the organ shortens.

2. circular layer, the fibers run around the circumference of the organ. constricts the lumen (cavity inside) of the organ.

Differences between skeletal and smooth muscle fibers

1. Smooth muscle fibers are small spindle-shaped cells - 5-10 micrometers in diameter - shorter and narrower

2. Smooth muscle lacks the coarse connective tissue sheaths found in skeletal muscle.

3. Smooth muscle has varicosities instead of neuromuscular junctions.

4. Smooth muscle fibers have less elaborate SR and no T tubules

5. Smooth muscle fibers are usually electrically connected by gap junctions

proportion and organization of smooth muscle myofilaments differ from skeletal muscle in the following ways:

1. Thick filaments are fewer but have myosin heads along their entire length. (1:13 compared to 1:2)

2. No troponin complex in thin filaments. a protein called calmodulin acts as the calcium-binding site.

3. Intermediate filament-dense body network

4. Thick and thin filaments arranged diagonally.

smooth muscle contraction

exhibit slow, synchronized contractions, the whole sheet responding to a stimulus in unison. gap junctions that transmit depolarization from fiber to fiber.

Unitary smooth muscle

aka visceral muscle

is in the walls of all hollow organs except the heart, is far more common

cells of unitary smooth muscle:

Are arranged in opposing (longitudinal and circular) sheets

Are innervated by varicosities of autonomic nerve fibers and often exhibit rhythmic spontaneous action potentials

Are electrically coupled by gap junctions and so contract as a unit (for this reason recruitment does not occur in unitary smooth muscle)

Respond to various chemical stimuli

multi unit smooth muscles

the smooth muscles in the large airways to the lungs and in large arteries, the arrector pili muscles attached to hair follicles, and the internal eye muscles that adjust pupil size and allow the eye to focus.

Like skeletal muscle, multi unit smooth muscle:

Consists of muscle fibers that are structurally independent of one another

Is richly supplied with nerve endings, each of which forms a motor unit with a number of muscle fibers

Responds to neural stimulation with graded contractions that involve recruitment

myoblasts

stem cells that fuse to form each muscle fiber that arise from the embryonic mesoderm

Muscle Regeneration

Skeletal muscles: satellite cells (myoblast-like cells) help repair injured fibers and allow limited regeneration of dead skeletal muscle

Cardiac muscle: was thought to have no regenerative capability whatsoever, but recent studies suggest that cardiac cells do divide, but only at about 1% per year - mostly by scar tissue

Smooth muscles: good regenerative capacity, and smooth muscle cells of blood vessels divide regularly throughout life

Women vs men

women's skeletal muscles make up approximately 36% of body mass, whereas men's account for about 42%

sarcopenia

By age 30, even in healthy people, a gradual loss of muscle mass begins. By age 80, muscle strength usually decreases by about 50%

The most efficient means of producing ATP is __________.

aerobic respiration

The final "go" signal for skeletal muscle contraction is __________.

an increase in intracellular calcium ion levels

Which of the following is a special adaptation present in skeletal muscle cells, but absent in most other cells?

Muscle cells have myoglobin; most other cells do not.

Properly controlled skeletal muscle contractions produced by changing the frequency of stimulation or the strength of stimulation are accomplished by __________.

graded muscle response

The __________ are extensions of the sarcolemma, and serve as a rapid communication system that ensures that every myofibril in the muscle fiber contracts at virtually the same time.

T tubules

enhance cellular communication during muscle contraction

When an action potential arrives at the neuromuscular junction, the most immediate result is __________.

the release of acetylcholine from the motor neuron

If a muscle is applied to a load that exceeds the muscle's maximum tension, __________.

the muscle length will not change during contraction

Which of the following statements is false?

a. During contraction, thin filaments slide past thick filaments so that actin and myosin filaments overlap.

b. During contraction, thin filaments slide past thick filaments so that actin and myosin filaments do not overlap.

c. During contraction, the distance between Z disks of a sarcomere decreases.

d. During contraction, actin-myosin cross bridges form.

b. During contraction, thin filaments slide past thick filaments so that actin and myosin filaments do not overlap

Which of the following is false regarding smooth muscle?

a. Smooth muscle is not striated.

b. Smooth muscle tends to be organized in sheets.

c. Contraction of smooth muscle is regulated by the autonomic nervous system.

d. Once damaged, smooth muscle is unable to regenerate.

d. Once damaged, smooth muscle is unable to regenerate.

Choose the true statement.

a. Unlike skeletal muscle, contraction in smooth muscle does not involve a sliding filament mechanism.

b. The final signal for contraction in smooth muscle is a rise in extracellular calcium while the final signal for contraction in skeletal muscle is a rise in intracellular calcium.

c. Unlike skeletal muscle, smooth muscle does not depend on ATP to fuel contractions.

d. Smooth muscle depends on the calcium-calmodulin system to regulate contraction while skeletal muscle relies on the calcium-troponin system to regulate contraction.

d. Smooth muscle depends on the calcium-calmodulin system to regulate contraction while skeletal muscle relies on the calcium-troponin system to regulate contraction.

Acetylcholinesterase __________.

breaks down acetylcholine.

Myofibrils are composed of repeating contractile elements called __________.

sarcomeres

What would occur if a muscle became totally depleted of ATP?

The muscle would remain in a contracted state due to an inability to break actin-myosin cross bridges

T/F Muscle cells initiate nerve impulses.

False

What is the role of tropomyosin in skeletal muscles?

Tropomyosin serves as a contraction inhibitor by blocking the myosin binding sites on the actin molecules.

A - Z disc

B - H zone

C - I Band

D - A band

E - M line

The stimulus above which no stronger contraction can be elicited, because all motor units are firing in the muscle.

Maximal stimulus

Determined by alternating motor units of a muscle organ even when the muscle is at rest.

muscle tone

Continued sustained smooth contraction due to rapid stimulation.

tetanus

The situation in which contractions become stronger due to stimulation before complete relaxation occurs.

wave summation

How a smooth increase in muscle force is produced.

Multiple motor unit summation

A sarcomere is the distance between two ________.

Z discs

The ________ contains only the actin filaments.

I band