anatomy muscles

(Chapter 9; pp. 276-311)

2.3.1 Describe the microscopic structure of skeletal muscle fibers and explain the cellular mechanisms of excitation-contraction

2.3.2 Describe the neuromuscular junction

2.3.3 Describe the contractile properties of skeletal muscle (motor unit, isotonic & isometric contractions, spatial & temporal

summation, etc)

2.3.4 Associate various muscle types with their metabolism and their speed of contraction and rate of fatigue

2.3.5 Compare the properties of smooth muscle with those of skeletal muscle

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Muscle Similarities Skeletal and smooth muscle cells are elongated

(not cardiac muscles…) and are called muscle fibers

Muscle contraction depends on two kinds of myofilaments – actin and myosin

Muscle terminology is similar Sarcolemma – muscle plasma membrane Sarcoplasm – cytoplasm of a muscle cell Prefixes – myo, mys, and sarco all refer to muscle

Pacemaker

Can contract rapidly;Tires easily & must rest;Strong but Adaptable

Neural input canIncrease rate

Slow, sustainedcontraction

Muscle Functions1. Generate movement: locomotion, manipulation, blood flow & pressure,

respiration, propelling of food, urine, etc..2. Maintain posture: constantly working against gravity3. Joint stabilization: eg: shoulders, knees when moving parts of skeleton4. Generation of heat: maintenance of body temperature

esp: skeletal muscle (at least 40% of body mass)

Functional Characteristics of Muscle1. Excitability (Irritability): “ability to receive and respond to a stimulus”

stimulus usually a chemical (NT, hormone, pH)response = AP along sarcolemma + muscle contraction

2. Contractility: “ability to shorten forcibly when adequately stimulated”3. Extensibility: “ability to be stretched or extended” 4. Elasticity: “ability to resume resting length after being stretched”

2.3.1.2 list & briefly describe 4 muscle functions as well as 4 2.3.1.2 list & briefly describe 4 muscle functions as well as 4 functional characteristics of musclefunctional characteristics of muscle


Skeletal Muscle Each muscle is a discrete organ composed of

muscle tissue, blood vessels, nerve fibers, and connective tissue


Skeletal Muscle: Nerve and Blood Supply Each muscle is served by one nerve, an artery, and

one or more veins Each skeletal muscle fiber is supplied with a nerve

ending that controls contraction Contracting fibers require continuous delivery of

oxygen and nutrients via arteries Wastes must be removed via veins


Structure and Organization of Skeletal Muscle

Table 9.1a


Skeletal Muscle: 3 connective tissue sheaths

Endomysium – fine sheath of connective tissue composed of reticular fibers surrounding each muscle fiber

Perimysium – fibrous connective tissue that surrounds groups of muscle fibers called fascicles

Epimysium – an overcoat of dense irregular connective tissue that surrounds the entire muscle


Structure and Organization of Skeletal Muscle

Table 9.1b

2 µm long


Microscopic Anatomy of a Skeletal Muscle Fiber

Each fiber is a long, cylindrical cell with multiple nuclei just beneath the sarcolemma

Fibers are 10 to 100 µm in diameter, and up to 30 cm long Each cell is a syncytium produced by fusion of embryonic

cells


Microscopic Anatomy of a Skeletal Muscle Fiber Sarcoplasm has numerous glycosomes and a unique

oxygen-binding protein called myoglobin Fibers contain the usual organelles, and myofibrils,

sarcoplasmic reticulum, and T tubules

Myofibrils

Myofibrils are densely packed, rodlike contractile elements

They make up most of the muscle cell volume (80%) The arrangement of myofibrils within a fiber is such that a

perfectly aligned repeating series of dark A bands and light I bands is evident (striated appearance)


Sarcomeres

Thick filaments – extend the entire length of an A band

Thin filaments – extend across the I band and partway into the A band

Z-disc – coin-shaped sheet of proteins (alpha-actinin; desmin IF) that (i) anchors the thin filaments and (ii) connects myofibrils to one another

Thin filaments do not overlap with thick filaments in the lighter H zone (and no myosin head)

M lines appear darker due to the presence of the protein myomesin (holding thick filaments together)


Sarcomeres

Copyright © 2010 Pearson Education, Inc. Figure 9.3

Flexible hinge region

Tail

Tropomyosin Troponin ActinMyosin head

ATP-bindingsite

Heads Active sitesfor myosinattachment

Actinsubunits

Actin-binding sites

Thick filamentEach thick filament consists of manymyosin molecules whose heads protrude at opposite ends of the filament.

Thin filamentA thin filament consists of two strandsof actin subunits twisted into a helix plus two types of regulatory proteins(troponin and tropomyosin).

Thin filamentThick filament

In the center of the sarcomere, the thickfilaments lack myosin heads. Myosin heads are present only in areas of myosin-actin overlap.

Longitudinal section of filamentswithin one sarcomere of a myofibril

Portion of a thick filamentPortion of a thin filament

Myosin molecule Actin subunits


Ultrastructure of Myofilaments: Thick Filaments

Figure 9.4a,b

Thick filaments are composed of the protein myosin

Each myosin molecule has a rod-like tail and two globular heads Tails – two interwoven, heavy

polypeptide chains Heads – two smaller, light

polypeptide chains called cross bridges

Heads bear actin-binding site and ATPase activity


Ultrastructure of Myofilaments: Thin Filaments

Figure 9.4c

Thin filaments are chiefly composed of the protein actin (microfilaments)

Each actin molecule is a helical polymer of globular subunits called G actin (F actin is the fibrous or filamentous form)

The subunits contain the active sites to which myosin heads attach during contraction

Tropomyosin and troponin (TnI, TnT and TnC) are regulatory subunits bound to actin

Sliding Filament Model of Contraction

• muscle fiber shortens because sarcomeres shorten; filaments remain same length

• thin filaments slide over thick filaments1° - Relaxed: only slight overlap of thick & thin filaments2° - Contracted: thin filaments penetrate more deeply into A band - Z discs pulled toward thick filaments

Overall:distance between Z discs reduced

I bands shortenH zones disappear

A bands move closer together, but stay same length

A. Endomysium; B. Epimysium; C. Fascicle; D. Fiber;

E. Myofilament; F. Myofibril; G. Perimysium; H. Sarcolemma;

I. Sarcomere; J. Sarcoplasm; K. Tendon

1. Connective tissue surrounding a fascicle.

2. Contractile unit of muscle.

3. A muscle cell.

4. Thin connective tissue investing each muscle cell.

5. Plasma membrane of the muscle cell.

6. Cordlike extension of CT beyond muscle - attaches it to bone.

7. A discrete bundle of muscle cells.

J. Carnegie, UofO


Sarcoplasmic Reticulum (SR)Figure 9.5

SR is an elaborate, smooth endoplasmic reticulum that mostly runs longitudinally and surrounds each myofibril

Paired terminal cisternae form perpendicular cross channels

Functions in the regulation of intracellular calcium levels


T TubulesFigure 9.5

T tubules are continuous with the sarcolemma They conduct impulses to the deepest regions of the

muscle (at each A band–I band junction) These impulses signal for the release of Ca2+ from

adjacent terminal cisternae


Triad Relationships

T tubules and SR provide tightly linked signals for muscle contraction A double zipper of integral membrane proteins protrudes into the

intermembrane space T tubule proteins act as voltage sensors SR foot proteins are receptors that regulate Ca2+ release from the SR

cisternae

• Skeletal muscles are stimulated by somatic motor neurons

• Axons of motor neurons travel from the central nervous system via nerves to skeletal muscles

• Each axon forms several branches as it enters a muscle

• Each axon ending forms a neuromuscular junction with a single muscle fiber


Nucleus

Actionpotential (AP)

Myelinated axonof motor neuron

Axon terminal ofneuromuscular junction

Sarcolemma ofthe muscle fiber

Ca2+ Ca2+

Axon terminalof motor neuron

Synaptic vesiclecontaining AChMitochondrionSynapticcleft

Junctionalfolds ofsarcolemma

Fusing synaptic vesicles

ACh

Sarcoplasm ofmuscle fiber

Postsynaptic membraneion channel opens;ions pass.

Na+ K+

Ach–

Na+

K+

Degraded ACh

Acetyl-cholinesterase

Postsynaptic membraneion channel closed;ions cannot pass.

1 Action potential arrives ataxon terminal of motor neuron.

2 Voltage-gated Ca2+ channels open and Ca2+ enters the axon terminal.

3 Ca2+ entry causes some synaptic vesicles to release their contents (acetylcholine)by exocytosis.

4 Acetylcholine, aneurotransmitter, diffuses across the synaptic cleft and binds to receptors in the sarcolemma.

5 ACh binding opens ionchannels that allow simultaneous passage of Na+ into the musclefiber and K+ out of the muscle fiber.

6 ACh effects are terminated by its enzymatic breakdown in the synaptic cleft by acetylcholinesterase.

PLAY A&P Flix™: Events at the Neuromuscular Junction


Na+

Na+

Open Na+

Channel

Closed Na+

Channel

Closed K+

Channel

Open K+

Channel

Action potential++++++

++++++

Axon terminal

Synapticcleft

ACh

ACh

Sarcoplasm of muscle fiber

K+

2 Generation and propagation ofthe action potential (AP)

3 Repolarization

1 Local depolarization: generation of the end plate potential on the sarcolemma

K+

K+Na+

K+Na+

Wave of dep

olar

izat

io n

Copyright © 2010 Pearson Education, Inc. Figure 9.11, step 1

Axon terminalof motor neuron

Muscle fiber Triad

One sarcomere

Synaptic cleft

Sarcolemma

Action potentialis generated

Terminal cisterna of SR ACh

Ca2+

Events of Excitation-Contraction (E-C) Coupling


1 - Action potential is propagated alongthe sarcolemma and down the T tubules.

Steps in E-C Coupling:

Troponin Tropomyosinblocking active sites

Myosin

Actin

Active sites exposed and ready for myosin binding

Ca2+

Terminal cisterna of SR

Voltage-sensitivetubule protein

T tubule

Ca2+

releasechannel

Myosincross bridge

Ca2+

Sarcolemma

2 - Calcium ions are released.

3 - Calcium binds to troponin andremoves the blocking action oftropomyosin.

4 - Contraction begins

The aftermath



Steps inE-C Coupling:

Terminal cisterna of SR

Voltage-sensitivetubule protein

T tubule

Ca2+

releasechannel

Ca2+

Sarcolemma

Action potential ispropagated along thesarcolemma and downthe T tubules.

1



Troponin Tropomyosinblocking active sitesMyosin

Actin

Ca2+

The aftermath




Actin


Ca2+

Calcium binds totroponin and removesthe blocking action oftropomyosin.

The aftermath

3


Figure 9.11



Actin


Ca2+

Myosincross bridge

Calcium binds totroponin and removesthe blocking action oftropomyosin.

Contraction begins

The aftermath

3

4


Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.12

Each power stroke =1% shortening

Routine contraction = 30-35% shortening

Many suchCross Bridge Cycles

are required!

(High Energy)

(Bent Low Energy)

Pulls on actinfilament…


Contraction of Skeletal Muscle Fibers

Contraction – refers to the activation of myosin’s cross bridges (force-generating sites)

Shortening occurs when the tension generated by the cross bridge exceeds forces opposing shortening (load)

When nervous stimulation ceases, Ca2+ is pumped back into the SR and contraction ends

Contraction ends when cross bridges become inactive, the tension generated declines, and relaxation is induced (Ca2+ removal => blockage restored)

http://www.youtube.com/watch?v=DeTen4GVb-Q


PUT IN THE CORRECT ORDER:

1. Myosin heads bind to active sites on actin molecules

2. ATP is hydrolyzed

3. Myosin heads return to high-energy shape, ready for the next power stroke

4. Calcium binds to troponin

5. Cycling continues until calcium ions are sequestered by the SR

6. Myosin cross brides detach from actin

7. Troponin changes shape

8. ADP and Pi (inorganic phosphate) are released from the thick filament

9. Myosin heads pull on the thin filaments (power stroke) and slide them toward the centre of the sarcomere

10. ATP binds to the thick filament

11. Tropomyosin is moved exposing active sites on F-actin J. Carnegie, UofO



IV. CONTRACTION OF A WHOLE SKELETAL MUSCLE2.3.3.1 define motor unit; describe the influences of wave summation and motor

unit summation on the contractile response of skeletal muscle; define tetanus in terms of muscular contraction

The Motor Unit

motor nerve (at least 1/muscle)

hundreds of motor neuron axons

each axon to many axonal terminals

each axonal terminal to NMJ of a single muscle fiber (cell)

• avg. no muscle fibers/neuron = 150 (range = 4 to hundreds)

• when neuron fires, all fibers contract

MOTOR UNIT = 1 motor neuron + all muscle fibers it supplies

Fig. 9.12

Innervated fibers notclustered

1 motor unit = weak contractionof the entire muscle!Depends on specific muscle function…


Phases of a Muscle Twitch

A muscle twitch is the response of a muscle to a single, brief threshold stimulus

Latent period – first few msec after stimulus; EC coupling taking place

Period of contraction – cross bridges form; muscle shortens

Period of relaxation – Ca2+ reabsorbed; muscle tension goes to zero

Figure 9.14a

Myogram

The force exerted by a contracting muscle on an object is called muscle tension

The opposing force exerted on the muscle is called the load


Muscle Twitch Comparisons

Figure 9.14b


Graded Muscle Responses Graded muscle responses are:

Variations in the degree of muscle contraction Required for proper control of skeletal

movement

Responses are graded by: Changing the frequency of stimulation Changing the strength of the stimulus

Speed of stimulation: wave summation & tetanus:• rapid rate of stimuli: each contraction builds on the previous one ([Ca2+]; Heat)• but AP refractory period is always honored (repolarization)• tetanus: fused contractions - inter-stimulus interval too short to allow

inter-twitch muscle relaxation - eventually followed by muscle fatigue• Affects force, but primary goal is to generate smooth, continuous contractions

Fig. 9.15

(Rare…)

Treppe – Staircase Effect


Muscle Response: Stimulation Strength Threshold stimulus – the

stimulus strength at which the first observable muscle contraction occurs

Beyond threshold, muscle contracts more vigorously as stimulus strength is increased

Force of contraction is precisely controlled by multiple motor unit summation

This phenomenon, called recruitment, brings more and more muscle fibers into play

In the lab

In the body…

Not random…


Size Principle

Figure 9.17

Motor units with the smallest fibers are controlled by highly excitable motor neurons – activated first

As contractile strength increases – larger and larger muscle fibers are recruited

controlled by motor neurons that are least excitable (highest threshold)

Usually asynchronous in the body… delays fatigue!

Also explains wide rangeof possible force…


Muscle tone: It is the constant, slightly contracted state of all muscles, which

does not produce active movements Keeps the muscles firm, healthy, and ready to respond to

stimulus Spinal reflexes account for muscle tone by:

Activating one motor unit and then another Responding to activation of stretch receptors in muscles and

tendons (Chapter 13)

1. After ACh attaches to its receptors at the neuromuscular junction, the next step is:a) K+-gated channels openb) Ca++ binds to troponinc) the T tubules depolarized) cross bridges attache) ATP is hydrolyzed

2. Which of these bands or lines does NOT narrow when skeletal muscle contracts?

a) H zoneb) A bandc) I bandd) M linee) b and d

3. is a continuous contraction that shows no evidence of relaxation.a) tetanusb) all or nonec) isometricd) treppe J. Carnegie,

UofO

2.3.3.2 differentiate between isotonic and isometric contractions, giving an example of each

(1) isotonic: muscle changes in length & moves load - what are concentric vs eccentric isotonic contractions?

NB: eccentric contractions are 50% more forceful, use less ATP/O2 & fewer muscle fibers but more prone to delayed-onset soreness than concentric

contractions

2.3.3.2 differentiate between isotonic and isometric contractions, giving an example of each

(2) isometric: tension increases but muscle remains same length• most body movements are a mix of isotonic and isometric contractions• realize that in isotonic contractions, the thin filaments are sliding, but in

isometric contractions the cross bridges are generating force, but do not move thin filaments

2.3.3.3 Define the optimal length-tension relationship for muscle in terms of muscle anatomy

Fig. 9.21

Fig. 9.22

Factors influencing the Force ofMuscle Contraction

Degree of muscle stretch – length/tension relationship

J. Carnegie, UofO

2.3.3.4 Indicate the influence of load on the velocity and duration of skeletal muscle contraction

Fig. 9.23

Velocity & Duration of Contraction depends on:Load: greater load = longer latent period = slower contraction = shorter

contraction duration

Also depends on Fiber type and Recruitment

The more the merrier!

Copyright © 2010 Pearson Education, Inc. Figure 9.19a

Coupled reaction of creatinephosphate (CP) and ADP

Energy source: CP

(a) Direct phosphorylation

Oxygen use: NoneProducts: 1 ATP per CP, creatineDuration of energy provision:15 seconds

Creatinekinase

ADPCP

Creatine ATP

Creatine Kinase

ATP is the only source used directly for contractile activity

As soon as available stores of ATP are hydrolyzed (4-6 seconds), they are regenerated by:

Anaerobic glycolysis (Fast Glycolytic Fibers):

• only 2 ATP/glucose but O2 not used and is 2.5x faster than aerobic pathway

• Together, ATP, CP and Anaerobic glycolysis can support strenuous muscle activity for ~ 1 min.

• usually pyruvic acid enters aerobic pathway

When muscle contractile activity reaches 70% of maximum:

Bulging muscles compress blood vessels Oxygen delivery is impaired Pyruvic acid is converted into lactic acid

The lactic acid: Diffuses into the bloodstream Is picked up and used as fuel by the liver,

kidneys, and heart Is converted back into pyruvic acid by the

liver


Muscle Metabolism: Energy for Contraction

Figure 9.19

(Slow Oxydative Fibers)

Energy systems used during sports activities:• weight lifting, diving, sprinting: ATP & CP - very short surge of power• tennis, soccer, 100 m swim: almost entirely anaerobic - on-and-off; burstlike• marathon runs, jogging: mainly aerobic; but anaerobic may function until

aerobic reaches full efficiency – Mainly endurance rather than power

aerobic endurance: length of time a muscle can use aerobic anaerobic threshold: point at which muscle converts to anaerobic


Muscle Fatigue – there’s an end to every good thing…

Muscle fatigue – the muscle is in a state of physiological inability to contract

Muscle fatigue occurs when: ATP production fails to keep pace with ATP use There is a relative deficit of ATP, causing contractures

(cramps! = myosin head can not be released) Lactic acid accumulates in the muscle Ionic imbalances are present (e.g. dehydration; sweat)

Na+-K+ pumps cannot restore ionic balances quickly enough (intense exercise)


Oxygen Debt Vigorous exercise causes dramatic changes in muscle

chemistry For a muscle to return to a resting state:

Oxygen reserves must be replenished Lactic acid must be converted to pyruvic acid (liver) Glycogen stores must be replaced ATP and CP reserves must be resynthesized

Oxygen debt – the extra amount of O2 needed for the above restorative processes


Heat Production During Muscle Activity Only 40% of the energy released in muscle activity is

useful as work The remaining 60% is given off as heat Dangerous heat levels are prevented by radiation of heat

from the skin and sweating What is shivering then?


FO

FG

SO


Effects of Exercise Aerobic exercise (endurance) results in an increase of:

Muscle capillaries Number of mitochondria Myoglobin synthesis

Resistance exercise (typically anaerobic) results in: Muscle hypertrophy Increased mitochondria, myofilaments, and glycogen

stores

Check the appropriate boxes to characterize each type of skeletal muscle fiber:

Characteristics Slow Oxidative Fast Glycolytic Fast Oxidative

Rapid twitch rate

Fast myosin ATPases Use mostly aerobic metabolism

Large myoglobin stores

Large glycogen stores

Fatigue slowly

Fibers are white

Fibers are smallFibers contain many capillaries & mitochondria

J. Carnegie, UofO


Smooth Muscle Composed of spindle-shaped fibers with a diameter of 5-10 µm and lengths of

several hundred µm – Sk. M. are ~10x wider; 1000x longer Lack the coarse connective tissue sheaths of skeletal muscle, but have fine

endomysium Organized into two layers (longitudinal and circular) of closely apposed fibers

Found in walls of hollow organs (except the heart) Have essentially the same contractile mechanisms as skeletal muscle

OrganDilates

& Contracts

OrganElongates

Peristalsis

Parallel to organ…


Innervation of Smooth Muscle Smooth muscle lack neuromuscular junctions Innervating nerves have bulbous swellings called varicosities Varicosities release neurotransmitters into wide synaptic clefts called

diffuse junctions


Microscopic Anatomy of Smooth Muscle SR is less developed than in skeletal muscle and

lacks a specific pattern T tubules are absent Plasma membranes have pouchlike infoldings

called caveolae

Ca2+ is sequestered in the extracellular space near the caveolae, allowing rapid influx when channels are opened

SR still releases some Ca2+ and contributes to its removal

1 nucleus per cell!


Proportion and Organization of Myofilaments in Smooth Muscle Ratio of thick to thin filaments is much lower (1:13)

than in skeletal muscle (1:2) Thick filaments have heads along their entire

length (more strength) There is no troponin complex

Thick and thin filaments are arranged diagonally (no sarcomere; no striations), causing smooth muscle to contract in a corkscrew manner

Noncontractile intermediate filament bundles attach to dense bodies (analogous to Z discs) at regular intervals (linked to thin filaments)


Contraction of Smooth Muscle Whole sheets of smooth muscle exhibit slow,

synchronized contraction They contract in unison, reflecting their

electrical coupling with gap junctions Action potentials are transmitted from cell to

cell

Some smooth muscle cells (stomach and small intestine): Act as pacemakers and set the contractile pace for whole sheets

of muscle Are self-excitatory and depolarize without external stimuli

Figure 9.29

Stimuli can vary Different autonomic nerves

release diff. NT NT may excite or inhibit a

particular group of smooth muscle cells

e.g. ACh (+) vs NE (-) in the bronchioles

vs NE (+) in most blood vessels…

Non-neuronal signals: hormones (gastrin), histamine, hypoxia, excess CO2, low pH

Relaxation requires:

• Ca2+ detachment from calmodulin

•Active transport of Ca2+ into SR and ECF

•Dephosphorylation of myosin to reduce myosin ATPase activity


Special Features of Smooth Muscle Contraction Unique characteristics of smooth muscle include:

Smooth muscle tone (24h maintenance in blood vessel; visceral organs) Slow, prolonged contractile activity – 30x longer than Sk. M. Low energy requirements – 1% the energy cost Few mitos; most ATP generated aerobically Sluggish ATPases (Myosin heads)


Special Features of Smooth Muscle Contraction Response to Stretch: Sk. M. can still contract when stretch up to

60%; Smooth muscle can still generate tension if stretch up to 150%! Smooth muscle exhibits a phenomenon called stress-relaxation

response in which: Smooth muscle responds to stretch only briefly, and then adapts

to its new length The new length, however, retains its ability to contract This enables organs such as the stomach to temporarily store

contents


Hyperplasia Certain smooth muscles can divide and increase their

numbers by undergoing hyperplasia (vs Hypertrophy) This is shown by estrogen’s effect on the uterus

At puberty, estrogen stimulates the synthesis of more smooth muscle, causing the uterus to grow to adult size

During pregnancy, estrogen stimulates uterine growth to accommodate the increasing size of the growing fetus

Secretory functions: collagen, elastin - make their own CT


Types of Smooth Muscle: Single Unit The cells of single-unit smooth muscle, commonly called

visceral muscle: Contract rhythmically as a unit Are electrically coupled to one another via gap

junctions – no recruitment Often exhibit spontaneous action potentials (presence

of some Pacemaker cells) Few nerve terminals – usually where pacermaker cells

are… Are arranged in opposing sheets and exhibit stress-

relaxation response… and pretty much what we saw so far!


Types of Smooth Muscle: Multiunit Multiunit smooth muscles are found:

In large airways to the lungs, large arteries In arrector pili muscles, attached to hair follicles In the internal eye muscles (focus)

Their characteristics include: Rare gap junctions Infrequent spontaneous depolarizations Structurally independent muscle fibers A rich nerve supply (still Autonomic/Involuntary), which, with a

number of muscle fibers, forms motor units Graded contractions in response to neural stimuli – recruitment Can also reponsd to Hormonal control

1. The first energy source used to regenerate ATP when muscles are extremely active is:

a) fatty acidsb) glucosec) creatine phosphated) pyruvic acid

2. When paying back the oxygen debt:a) lactic acid is formedb) lactic acid is converted to pyruvic acidc) ATP formation requires creatine phosphated) muscle cells utilize glycogen reserves

3. Holding up the corner of a heavy couch to vacuum under it involves which type(s) of contraction?a) tetanicb) isotonicc) isometricd) tonee) a and c

J. Carnegie, UofO

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