Copyright © 2010 Pearson Education, Inc. Muscles Part I H. Biology II Adapted 2014-2015 Overview of Muscular Tissue Skeletal Muscle Tissue Contraction.

Copyright © 2010 Pearson Education, Inc.

Muscles Part I

H. Biology II Adapted 2014-2015

•Overview of Muscular Tissue

•Skeletal Muscle Tissue

•Contraction and Relaxation of Skeletal Muscle Fibers

•Muscle Metabolism

•Control of Muscle Tension

•Types of Skeletal Muscle Fibers

•Exercise and Skeletal Muscle Tissue

•Cardiac Muscle Tissue

•Smooth Muscle Tissue

•Regeneration of Muscle Tissue

•Development of Muscle

•Aging and Muscular Tissue


Muscular System

9-2

Three Types of Muscle Tissues

Skeletal Muscle• usually attached to bones• voluntary- under conscious control• striated

Smooth Muscle• walls of most viscera, blood vessels, skin• involuntary - not under conscious control• not striated

Cardiac Muscle• wall of heart• involuntary - not under conscious control• striated

Copyright © 2010 Pearson Education, Inc. Table 9.3


Special Characteristics of Muscle Tissue

• Excitability (responsiveness or irritability): ability to receive and respond to stimuli

• Contractility: ability to shorten when stimulated

• Extensibility: ability to be stretched or extended without damage

• Elasticity: ability to recoil to resting length (bounce back)


Functions of a Muscle Tissue

• Movement:

• Skeletal- locomotion, vision, facial expression

• Cardiac- blood pumping

• Smooth- food digestion

• Posture: (skeletal)

• Joint Stability: (skeletal)

• Heat Generation:(skeletal)

• A. shivering to increase heat production

• B. contract muscle to provide heat


Structure of a Skeletal Muscle

Skeletal Muscle• organs of the muscular system• skeletal muscle tissue• nervous tissue• blood•Each muscle is served by one artery, one nerve, and one or more veins

Connective tissues and muscle tissue:

1.fascia – covers the muscle2.tendon – attaches the muscle3.aponeuroses – muscle to

muscle


Macroscopic Anatomy of skeletal muscles

Skeletal muscle fiber (cell)

Muscle Fascicle

Surrounded by perimysium

Surrounded by endomysium

endomysium

perimysium

Skeletal muscle

Surrounded by epimysium

epimysium

tendon

Play IP Anatomy of Skeletal muscles (IP p. 4-6)

Copyright © 2010 Pearson Education, Inc. Figure 9.1

Bone

Perimysium

Endomysium(between individualmuscle fibers)

Muscle fiber

Fascicle(wrapped by perimysium)

Epimysium

Tendon

Epimysium

Muscle fiberin middle ofa fascicle

Blood vessel

Perimysium

Endomysium

Fascicle(a)

(b)


Anatomy of a Skeletal Muscle

Coverings of a muscle1. EpimysiumEpimysium - outer2. PerimysiumPerimysium - middle3. Endomysium. Endomysium - inner

Organization of MuscleOrganization of Muscle• muscle• fascicles• muscle fibers• myofibrils • thick and thin filaments


Anatomy of a Skeletal Muscle

9-4

Coverings of a muscle1. EpimysiumEpimysium – dense regular connective tissue surrounding the entire muscle2. PerimysiumPerimysium – fibrous connective tissue surrounding a fascicle3. Endomysium. Endomysium – thin areolar connective tissue surrounding each muscle cell

Organization of MuscleOrganization of Muscle• musclemuscle• fasciclesfascicles – bundle of muscle cells• muscle fibers muscle fibers – a muscle cell• myofibrilsmyofibrils – a long, filamentous organelle found within muscle cells that has a banded appearance• thick and thin filaments (myofilament)- thick and thin filaments (myofilament)- actin &myosin filaments• sarcomeresarcomere – contractile unit of muscle


Skeletal Muscle Tissue

• The number of skeletal muscle fibers is set before you are born

• Most of these cells last a lifetime

• Muscle growth occurs by hypertrophy

• An enlargement of existing muscle fibers

• Testosterone and human growth hormone stimulate hypertrophy

• Satellite cells retain the capacity to regenerate damaged muscle fibers


Microscopic Anatomy of Skeletal Muscle Fiber

9-5

• sarcolemma• sacroplasm• sarcoplasmic reticulum• transverse tubule• triad

• cisterna of sarcoplasmic reticulum• transverse tubule

• myofibril• actin filaments• myosin filaments• sarcomere


Skeletal Muscle Tissue-Microscopic Anatomy

• Sarcolemma

• The plasma membrane of a muscle cell

• Transverse (T tubules)

• Tunnel in from the plasma membrane

• Muscle action potentials travel through the T tubules

• Sarcoplasm, the cytoplasm of a muscle fiber

• Sarcoplasm includes glycogen used for synthesis of ATP and a red-colored protein called myoglobin which binds oxygen molecules

• Myoglobin releases oxygen when it is needed for ATP production


Skeletal Muscle Tissue- Microscopic Anatomy• Myofibrils

• Thread like structures which have a contractile function

• Sarcoplasmic reticulum (SR)

• Membranous sacs which encircles each myofibril

• Stores calcium ions (Ca++)

• Release of Ca++ triggers muscle contraction

• Filaments

• Function in the contractile process

• Two types of filaments (Thick and Thin)

• There are two thin filaments for every thick filament

• Sarcomeres

• Compartments of arranged filaments

• Basic functional unit of a myofibril


Triad Relationships

• T tubules conduct impulses deep into muscle fiber

• Integral proteins protrude into the intermembrane space from T tubule and SR cisternae membranes

• T tubule proteins: voltage sensors

• SR foot proteins: gated channels that regulate Ca2+ release from the SR cisternae


Sarcomere

• Smallest contractile unit (functional unit) of a muscle fiber

• The region of a myofibril between two successive Z discs

• Composed of thick and thin myofilaments made of contractile proteins

• Each myofibril contains 10,000 sarcomeres end to end.


Check for Understanding 1:


Check for Understanding 2:

16. 19. 20.

22.

17. (outer covering)

18. (middle covering)

21. (inner covering)

23.

24.


Microanatomy of a Muscle Fiber (Cell)

sarcolemma

transverse (T) tubules sarcoplasmic

reticulumterminal cisternae

myofibril

thin myofilamentthick myofilament

triad

mitochondria

Play IP Anatomy of Skeletal muscles (IP p. 7)

nuclei

myoglobin


Muscle fiber

myofibril

Thin filaments Thick filaments

Thin myofilamentMyosin molecule ofthick myofilament

sarcomere

Z-line


Sarcomere

9-6

• I band• A band• H zone• Z line• M line


Skeletal Muscle Tissue

• Z discs

• Separate one sarcomere from the next

• Thick and thin filaments overlap one another

• A band

• Darker middle part of the sarcomere

• Thick and thin filaments overlap

• I band

• Lighter, contains thin filaments but no thick filaments

• Z discs passes through the center of each I band

• H zone

• Center of each A band which contains thick but no thin filaments

• M line

• Supporting proteins that hold the thick filaments together in the H zone


Skeletal Muscle Tissue• Muscle Proteins

• Myofibrils are built from three kinds of proteins

• 1) Contractile proteins

• Generate force during contraction

• 2) Regulatory proteins

• Switch the contraction process on and off

• 3) Structural proteins

• Align the thick and thin filaments properly

• Provide elasticity and extensibility

• Link the myofibrils to the sarcolemma


Contractile Proteins• Myosin

• Thick filaments

• Functions as a motor protein which can achieve motion

• Convert ATP to energy of motion

• Projections of each myosin molecule protrude outward (myosin head)

• Actin

• Thin filaments

• Actin molecules provide a site where a myosin head can attach

• Tropomyosin and troponin are also part of the thin filament

• In relaxed muscle

Myosin is blocked from binding to actin

Strands of tropomyosin cover the myosin-binding sites

• Calcium ion binding to troponin moves tropomyosin away from myosin-binding sites

• Allows muscle contraction to begin as myosin binds to actin


Structural Proteins

• Titin• Stabilize the position of myosin

• accounts for much of the elasticity and extensibility of myofibrils

• Dystrophin• Links thin filaments to the sarcolemma


The Sliding Filament Mechanism• Myosin heads attach to and “walk” along the thin

filaments at both ends of a sarcomere

• Progressively pulling the thin filaments toward the center of the sarcomere

• Z discs come closer together and the sarcomere shortens

• Leading to shortening of the entire muscle

• In the relaxed state, thin and thick filaments overlap only slightly

• During contraction, myosin heads bind to actin, detach, and bind again, to propel the thin filaments toward the M line

• As H zones shorten and disappear, sarcomeres shorten, muscle cells shorten, and the whole muscle shortens


Sliding Filament Mechanism

When sarcomeres shorten, actin and myosin filaments slide past one anotherVIDEO#1VIDEO #2


I

Fully relaxed sarcomere of a muscle fiber

Fully contracted sarcomere of a muscle fiber

IA

Z ZH

I IA

Z Z

1

2


Flexible hinge region

Tail

Tropomyosin Troponin Actin

Myosin 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


Contraction & Relaxation of Skeletal Muscle


Microscopic Contraction Events



• The Contraction Cycle

• The onset of contraction begins with the SR releasing calcium ions into the muscle cell

• Where they bind to actin opening the myosin binding sites



• The contraction cycle consists of 4 steps

• 1) ATP hydrolysis

• Hydrolysis of ATP reorients and energizes the myosin head

• 2) Formation of cross-bridges

• Myosin head attaches to the myosin-binding site on actin

• 3) Power stroke

• During the power stroke the crossbridge rotates, sliding the filaments

• 4) Detachment of myosin from actin

• As the next ATP binds to the myosin head, the myosin head detaches from actin

• The contraction cycle repeats as long as ATP is available and the Ca+

+ level is sufficiently high

• Continuing cycles applies the force that shortens the sarcomere


Cross Bridge Cycle

• Continues as long as the Ca2+ signal and adequate ATP are present

• Cross bridge formation—high-energy myosin head attaches to thin filament

• Working (power) stroke—myosin head pivots and pulls thin filament toward M line

• Cross bridge detachment—ATP attaches to myosin head and the cross bridge detaches

• “Cocking” of the myosin head—energy from hydrolysis of ATP cocks the myosin head into the high-energy state




1 Myosin headshydrolyze ATP andbecome reorientedand energized ADP

P

= Ca2+

Key:

Contraction cycle continues ifATP is available and Ca2+ level inthe sarcoplasm is high

1 Myosin headshydrolyze ATP andbecome reorientedand energized

Myosin headsbind to actin,formingcrossbridges

ADP

ADP

P

P

= Ca2+

Key:

2




Myosin crossbridgesrotate toward center of thesarcomere (power stroke)


ADP

ADP

ADP

P

P

= Ca2+

Key:

2

3



Myosin crossbridgesrotate toward center of thesarcomere (power stroke)

As myosin headsbind ATP, thecrossbridges detachfrom actin


ADP

ADP

ADP

ATP

P

P

= Ca2+

Key:

ATP

2

3

4


1

Actin

Cross bridge formation.

Cocking of myosin head. The power (working) stroke.

Cross bridge detachment.

Ca2+

Myosincross bridge

Thick filament

Thin filament

ADP

Myosin

Pi

ATPhydrolysis

ATP

ATP

24

3

ADP

Pi

ADPPi




Role of Calcium (Ca2+) in Contraction

• At low intracellular Ca2+ concentration:

• Tropomyosin blocks the active sites on actin

• Myosin heads cannot attach to actin

• Muscle fiber relaxes


Role of Calcium (Ca2+) in Contraction

• At higher intracellular Ca2+ concentrations:

• Ca2+ binds to troponin

• Troponin changes shape and moves tropomyosin away from active sites

• Events of the cross bridge cycle occur

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




Muscle Contraction

• The generation of force

• Does not necessarily cause shortening of the fiber

• Shortening occurs when tension generated by cross bridges on the thin filaments exceeds forces opposing shortening


Requirements for Skeletal Muscle Contraction

1. Activation: neural stimulation at aneuromuscular junction

2. Excitation-contraction coupling: (not heavily discussed 2015)

• Generation and propagation of an action potential along the sarcolemma

• Final trigger: a brief rise in intracellular Ca2+ levels


Skeletal Muscle Contraction

?

How does a muscle contract?


Sequence of a Muscle Contraction (Summary)Brain

Spinal Cord

Nerve(Action potential)

Motor Unit

Neuromuscular Junction(Calcium is released)

Acetylcholine(Neurotransmitter)

Contraction


Motor Unit

• single motor neuron (a single nerve)• one motor neuron and many skeletal muscle fibers

9-9



• The Neuromuscular Junction

• Motor neurons have a threadlike axon that extends from the brain or spinal cord to a group of muscle fibers

• Neuromuscular junction (NMJ)

• Action potentials arise at the interface of the motor neuron and muscle fiber

• Synapse

• Where communication occurs between a somatic motor neuron and a muscle fiber

• Synaptic cleft

• Gap that separates the two cells

• Neurotransmitter

• Chemical released by the initial cell communicating with the second cell

• Synaptic vesicles

• Sacs suspended within the synaptic end bulb containing molecules of the neurotransmitter acetylcholine (Ach)

• Motor end plate

• The region of the muscle cell membrane opposite the synaptic end bulbs

• Contain acetylcholine receptors


Neuromuscular Junction

9-8

• site where a motor nerve fiber and a skeletal muscle fiber meet


Muscle Contraction

9-10

• Action potential causes the release of Ca++ at the NMJ.•a neurotransmitter releases a chemical substance from the motor end fiber, causing stimulation of the muscle fiber•That substance is called acetylcholine (ACh)•ACh causes the muscle fibers to become stimulated and contract (shorten).


Contraction & Relaxation of Skeletal Muscle• Nerve impulses elicit a muscle action potential in the

following way

• 1) Release of acetylcholine• Nerve impulse arriving at the synaptic end bulbs causes many synaptic

vesicles to release ACh into the synaptic cleft

• 2) Activation of ACh receptors• Binding of ACh to the receptor on the motor end plate opens an ion channel

• Allows flow of Na+ to the inside of the muscle cell

• 3) Production of muscle action potential• The inflow of Na+ makes the inside of the muscle fiber more positively charged

triggering a muscle action potential

• The muscle action potential then propagates to the SR to release its stored Ca++

• 4) Termination of ACh activity (Relaxation)• Ach effects last only briefly because it is rapidly broken down by

acetylcholinesterase (AChE)


1

Axon terminal

Axon terminal

Axon collateral ofsomatic motor neuron

Sarcolemma

Myofibril

ACh is releasedfrom synaptic vesicle

Junctional fold

Synaptic vesiclecontainingacetylcholine(ACh)

Sarcolemma

Synaptic cleft(space)

Motor end plate


(a) Neuromuscular junction

(b) Enlarged view of the neuromuscular junction

(c) Binding of acetylcholine to ACh receptors in the motor end plate

Synapticend bulb

Synapticend bulb

Neuromuscularjunction (NMJ)

Synaptic end bulb

Motor end plate

Nerve impulse

11

Axon terminal

Axon terminal


Sarcolemma

Myofibril


ACh binds to Achreceptor

Junctional fold


Sarcolemma


Motor end plate





Synapticend bulb

Synapticend bulb


Synaptic end bulb

Motor end plate

Nerve impulse

Na+

1

22

1

Axon terminal

Axon terminal


Sarcolemma

Myofibril



Junctional fold


Sarcolemma


Motor end plate





Synapticend bulb

Synapticend bulb


Synaptic end bulb

Motor end plate

Nerve impulse

Muscle action potential is produced

Na+

1

2

3

2

1

Axon terminal

Axon terminal


Sarcolemma

Myofibril



Junctional fold


Sarcolemma


Motor end plate





Synapticend bulb

Synapticend bulb


Synaptic end bulb

Motor end plate

Nerve impulse

Muscle action potential is produced

ACh is broken down

Na+

1

2

4

3

2


• Pearson NMJ


Relaxation of a Muscle- Review

• acetylcholinesterase – an enzyme that breaks down acetylcholine. NMJ

• muscle impulse stops

• calcium moves back into sarcoplasmic reticulum

• myosin and actin action prevented

• muscle fiber relaxes

• Cd

9-14


Recruitment of Motor Units

9-22

Recruitment - increase in the number of motor units activated

• whole muscle composed of many motor units

• as intensity of stimulation or contraction increases, recruitment of motor units continues until all motor units are activated = all or none principle all or none principle


Applications for M. Contraction/Relaxation• Botulinum toxin

• Blocks release of ACh from synaptic vesicles

• May be found in improperly canned foods

• A tiny amount can cause death by paralyzing respiratory muscles

• Used as a medicine (Botox®)

• Strabismus (crossed eyes)

• Blepharospasm (uncontrollable blinking)

• Spasms of the vocal cords that interfere with speech

• Cosmetic treatment to relax muscles that cause facial wrinkles

• Alleviate chronic back pain due to muscle spasms in the lumbar region


Applications for Muscle Contraction/Relaxation• Curare

• A plant poison used by South American Indians on arrows and blowgun darts

• Causes muscle paralysis by blocking ACh receptors inhibiting Na+ ion channels

• Derivatives of curare are used during surgery to relax skeletal muscles

• Anticholinesterase

• Slow actions of acetylcholinesterase and removal of ACh

• Can strengthen weak muscle contractions

• Ex: Neostigmine

• Treatment for myasthenia gravis

• Antidote for curare poisoning

• Terminate the effects of curare after surgery

Myasthenia GravisCommon symptoms can include:A drooping eyelidBlurred or double visionSlurred speechDifficulty chewing and swallowingWeakness in the arms and legsChronic muscle fatigueDifficulty breathing


Question ????

We now know how a muscle contracts and We now know how a muscle contracts and relaxes, so is energy needed for that to relaxes, so is energy needed for that to happen?happen?

NO NO or or

YESYES

??


How is energy that is stored in food released?

Cellular Respiration

Oxygen

Glucose

Energy ATPEnergy ATP

H2O + CO2


ENERGY

The energy used to power the interaction between actin and myosin filaments comes from ATP (useable chemical energy) produced by cellular respiration.

ATP stored in skeletal muscle last only about six seconds.

ATP must be regenerated continuously if contraction is to continue


Ways to Make Energy Sources for Contraction

• Creatine phosphate – stores energy that quickly converts unusable energy (ADP) to usable energy (ATP) 6 Seconds!!•Cellular respiration is the process by which the chemical energy of "food" molecules is released and partially captured in the form of ATP.

1) Creatine phosphate (ADP) 2) Cellular respiration (Aerobic or Anaerobic)


Muscle Metabolism


Muscle Metabolism

• Creatine Phosphate

• Excess ATP is used to synthesize creatine phosphate

• Energy-rich molecule

• Creatine phosphate transfers its high energy phosphate group to ADP regenerating new ATP

• Creatine phosphate and ATP provide enough energy for contraction for about 15 seconds






Cellular Respiration (CR)

THREE SERIES OF REACTIONS in CRTHREE SERIES OF REACTIONS in CR1. Glycolysis2. Citric acid cycle3. Electron transport chain

Produces• carbon dioxide• water• ATP (chemical energy)• heat

Two Types of ReactionsTwo Types of Reactions• Anaerobic RespirationAnaerobic Respiration (without O2) - produce little ATP• Aerobic RespirationAerobic Respiration (requires O2) - produce most ATP 4-11


Anaerobic Reaction (Glycolysis)

• Recall that glycolysis results in pyruvate acid. If O2 is not present, pyruvate can be fermented into LACTIC ACID.

• Lactic Acid

• It is a waste product of pyruvate acid.

• Occurs in many muscle cells.

• Accumulation causes muscle soreness and fatigue.


Muscle Metabolism

• Anaerobic Respiration

• Series of ATP producing reactions that do not require oxygen

• Glucose is used to generate ATP when the supply of creatine phosphate is depleted

• Glucose is derived from the blood and from glycogen stored in muscle fibers

• Glycolysis breaks down glucose into molecules of pyruvic acid and produces two molecules of ATP

• If sufficient oxygen is present, pyruvic acid formed by glycolysis enters aerobic respiration pathways producing a large amount of ATP

• If oxygen levels are low, anaerobic reactions convert pyruvic acid to lactic acid which is carried away by the blood

• Anaerobic respiration can provide enough energy for about 30 to 40 seconds of muscle activity






Oxygen Supply & Cellular Respiration

• Anaerobic Phase•Steps are called glycolysis.•occur in the cytoplasm• no oxygen• produces pyruvic acid and produces lactic acid• little ATP

• Aerobic Phase•Steps are called citric acid cycle and electron transport chain.• occur in the mitochondrion•oxygen•produces most ATP / CO2/ H2O



Muscle Metabolism

• Aerobic Respiration

• Activity that lasts longer than half a minute depends on aerobic respiration

• Pyruvic acid entering the mitochondria is completely oxidized generating

• ATP

• carbon dioxide

• Water

• Heat

• Each molecule of glucose yields about 36 molecules of ATP

• Muscle tissue has two sources of oxygen

• 1) Oxygen from hemoglobin in the blood

• 2) Oxygen released by myoglobin in the muscle cell

• Myoglobin and hemoglobin are oxygen-binding proteins

• Aerobic respiration supplies ATP for prolonged activity

• Aerobic respiration provides more than 90% of the needed ATP in activities lasting more than 10 minutes






Summary of Cellular Respiration

Total ATP Production

2 ATP – Glycolysis

2 ATP – Citrus Acid Cycle

34 ATP – Electron Transport Chain

38 ATP – Total energy released from one molecule of glucose.


Oxygen Debt

• oxygen not available

• glycolysis continues

• pyruvic acid converted to lactic acid

Oxygen debt – amount of oxygen needed by liver to convert lactic acid to glucose


Muscle Metabolism

• Oxygen Consumption After Exercise

• After exercise, heavy breathing continues and oxygen consumption remains above the resting level

• Oxygen debt

• The added oxygen that is taken into the body after exercise

• This added oxygen is used to restore muscle cells to the resting level in three ways

• 1) to convert lactic acid into glycogen

• 2) to synthesize creatine phosphate and ATP

• 3) to replace the oxygen removed from myoglobin


What happens to the lactic acid once it has accumulated?

•The liver filters the blood and rids the body of toxins. Lactic acid is a toxin.

•liver converts lactic acid to glucose


Muscle Fatigue

• Muscle fatigue-Muscle fatigue- is a state of physiological inability to contract

• commonly caused from – decreased blood flow– ion imbalances– accumulation of lactic acid

• cramp – sustained, involuntary contraction

9-18


Muscle Metabolism• Muscle Fatigue

• Inability of muscle to maintain force of contraction after prolonged activity

Factors that contribute to muscle fatigue:• Inadequate release of calcium ions from the SR

• Depletion of creatine phosphate

• Insufficient oxygen

• Depletion of glycogen and other nutrients

• Buildup of lactic acid and ADP

• Failure of the motor neuron to release enough acetylcholine


Control of Muscle Tension


Contraction and Relaxation of Skeletal Muscle• Length–Tension Relationship

• The forcefulness of muscle contraction depends on the length of the sarcomeres

• When a muscle fiber is stretched there is less overlap between the thick and thin filaments and tension (forcefulness) is diminished

• When a muscle fiber is shortened the filaments are compressed and fewer myosin heads make contact with thin filaments and tension is diminished


Types of Contractions

9-24

2. Isotonic – muscle contracts and changes length

2. Concentric – shortening contraction

1. Eccentric – lengthening contraction

1. Isometric – muscle contracts but does not change length

Two TypesTwo Types

Two Types of Isotonic ContractionsTwo Types of Isotonic Contractions


Muscle ToneMuscle Tone

9-23

Muscle tone Muscle tone – continuous state of partial contraction

-Even when a muscle appears to be at rest, a certain amount of sustained contraction is occurring in its fibers.

AtrophyAtrophy – a wasting away or decrease in size of an organ or tissue.

HypertrophyHypertrophy – Enlargement of an organ or tissue.


Types of Contractions


Smooth and Cardiac Muscle


Smooth Muscle Fibers

9-26

Compared to skeletal muscle fibers• shorter• single nucleus• elongated with tapering ends• myofilaments randomly organized• no striations


Two Types of Smooth Muscle

Visceral Smooth MuscleVisceral Smooth MuscleLocation - walls of most hollow organs (intestine)• contractions are slow and sustained•exhibit rhythmicityrhythmicity – pattern of repeated contractions• exhibit peristalsisperistalsis – wave-like motion that helps substances through passageways.

Multiunit Smooth MuscleMultiunit Smooth Muscle• irises of eye• walls of blood vessels• contractions are rapid and vigorous• similar to skeletal muscle tissue

SEM: Arteriole

SEM: Stomach


Smooth Muscle Tissue

• Microscopic Anatomy of Smooth Muscle

• Contains both thick filaments and thin filaments

• Not arranged in orderly sarcomeres

• No regular pattern of overlap thus not striated

• Contain only a small amount of stored Ca++

• Filaments attach to dense bodies and stretch from one dense body to another

• Dense bodies

• Function in the same way as Z discs

• During contraction the filaments pull on the dense bodies causing a shortening of the muscle fiber


Smooth Muscle Tissue

• Physiology of Smooth Muscle

• Most smooth muscle fibers contract or relax in response to:

• Action potentials from the autonomic nervous system

• Pupil constriction due to increased light energy

• In response to stretching

• Food in digestive tract stretches intestinal walls initiating peristalsis

• Hormones

• Epinephrine causes relaxation of smooth muscle in the air-ways and in some blood vessel walls

• Changes in pH, oxygen and carbon dioxide levels


Smooth Muscle Contraction

• Resembles skeletal muscle contraction• interaction between actin and myosin• both use calcium and ATP• both depend on impulses

• Different from skeletal muscle contraction• hormones affect smooth muscle• stretching can trigger smooth muscle contraction• smooth muscle slower to contract and relax• smooth muscle more resistant to fatigue

9-28


Cardiac Muscle

AnatomyAnatomy• only in the heart• striated uninuclear cells join end-to-end forming a

network• arrangement of actin and myosin are not as organized

as skeletal musclePhysiologyPhysiology• self-exciting tissue (Pacemaker)• rhythmic contractions• involuntary, all or nothing contractionsPumps blood to:Pumps blood to:• 1. lungs for oxygenation• 2. body for distribution of O2 and nutrients

9-29


Cardiac Muscle Tissue• Principal tissue in the heart wall

• Intercalated discs

• Allow muscle action potentials to spread from one cardiac muscle fiber to another

• autorhythmic muscle fibers

• Continuous, rhythmic activity

• Have the same arrangement of actin and myosin as skeletal muscle fibers

• Mitochondria are large and numerous

• Depends on aerobic respiration to generate ATP

• Requires a constant supply of oxygen

• Able to use lactic acid produced by skeletal muscle fibers to make ATP


Aging and Muscular Tissue

• Aging

• Brings a progressive loss of skeletal muscle mass

• A decrease in maximal strength

• A slowing of muscle reflexes

• A loss of flexibility

• With aging, the relative number of slow oxidative fibers appears to increase

• Aerobic activities and strength training can slow the decline in muscular performance


Of Note: Types of Skeletal Muscle Fibers

• Muscle fibers vary in their content of myoglobin

• Red muscle fibers

• Have a high myoglobin content

• Appear darker (dark meat in chicken legs and thighs)

• Contain more mitochondria

• Supplied by more blood capillaries

• White muscle fibers

• Have a low content of myoglobin

• Appear lighter (white meat in chicken breasts)

Copyright © 2010 Pearson Education, Inc. Muscles Part I H. Biology II Adapted 2014-2015 Overview of Muscular Tissue Skeletal Muscle Tissue Contraction.

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