chapter 10: muscular tissue copyright 2009, john wiley & sons, inc

Chapter 10: Muscular Tissue

Copyright 2009, John Wiley & Sons, Inc.

Overview of Muscular Tissue Skeletal Muscle Tissue- (because most skeletal muscles move bones)

Striated: Alternating light and dark bands when examined microscopically Voluntary : its activity can be consciously controlled Some skeletal muscles also are controlled subconsciously to some

extent Ex: diaphragm - alternately contracts & relaxes w/o conscious control

Cardiac Muscle Tissue - found only in the walls of the heart Striated – like skeletal muscle Involuntary - Contraction of the heart is initiated by the “pacemaker”

Smooth Muscle Tissue - located in the walls of hollow internal structures Blood vessels, airways, and many organs Lacks the striations of skeletal and cardiac muscle tissue Spindle shaped – tapered ends Usually involuntary


Functions of Muscular Tissue Producing Body Movements

Walking and running Stabilizing Body Positions

Posture Moving Substances Within the Body

Heart muscle pumping blood Moving substances in the digestive tract

Generating heat Contracting muscle produces heat Shivering increases heat production

Properties of Muscular Tissue

Excitability - ability to respond to stimuli Contractility - ability to contract forcefully when stimulated Extensibility - ability to stretch without being damaged Elasticity - ability to return to an original length


Skeletal Muscle Tissue Connective Tissue Components

Fascia Dense sheet or broad band of irregular connective tissue that

surrounds muscles Epimysium - the outermost layer

Separates 10-100 muscle fibers into bundles called fascicles Perimysium- surrounds numerous bundles of fascicles Endomysium - separates individual muscle fibers from one another

Also contains b.v., nerves, and satellite cells (embryonic stem cells function in repair of muscle tissue

Collagen fibers of all 3 layers come together at each end of muscle to form a tendon or aponeurosis Tendon

Cord that attach a muscle to a bone Aponeurosis

Broad, flattened tendon


Skeletal Muscle Structure Composed of muscle cells (fibers),

connective tissue, blood vessels, nerves

Fibers are long, cylindrical, and multinucleated

Tend to be smaller diameter in small muscles and larger in large muscles. 1 mm- 4 cm in length

Develop from myoblasts; numbers remain constant

Striated appearance Nuclei are peripherally located

Skeletal Muscle Tissue Nerve and Blood Supply Somatic Motor neurons - stimulate muscle fibers to contract Neuron axons branch so that each muscle cell (fiber) is innervated Form a neuromuscular junction (= myoneural junction)

Capillary beds surround muscle fibers Muscles require large amts of energy Extensive vascular network delivers necessary oxygen and nutrients

and carries away metabolic waste produced by muscle fibers

Microscopic Anatomy Number of skeletal muscle fibers is set before you are born Most of these cells last a lifetime Muscle growth occurs by hypertrophy - enlargement of existing muscle

fibers Testosterone and human growth hormone stimulate hypertrophy

Satellite cells retain the capacity to regenerate damaged muscle fibersCopyright 2009, John Wiley &

Sons, Inc.

Skeletal Muscle Tissue 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 myoglobin, a red-colored protein that binds oxygen molecules

Myoglobin releases oxygen when it is needed for ATP production Myofibrils- thread like structures which have a contractile function Sarcoplasmic reticulum (SR)- membranous sacs encircling each

myofibril ; it is modified ER 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


Skeletal Muscle Tissue Z discs

Separate one sarcomere from the next 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 Zone of Overlap

Thick and thin filaments overlap each other


Levels of Functional Organization in Skeletal Muscle Fiber

Contraction and Relaxation of Skeletal Muscle

Skeletal Muscle Tissue

Muscle Proteins

1) Contractile proteins- Generate force during contraction 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 - composed of G-actin + nebulin 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→ myosin binds to actin →muscle contraction begins


Skeletal Muscle Tissue 2) Regulatory proteins- Switch the contraction process on and off

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

3) Structural proteins- Align the thick and thin filaments properly Provide elasticity and extensibility Link the myofibrils to the sarcolemma Titin- stabilize the position of myosin - functions in elasticity and extensibility of myofibrils Dystrophin - links thin filaments to the sarcolemma Myomesin – forms M line ; holds thick filaments together α- actinin and connectins – makes Z discs


Contraction and Relaxation of Skeletal Muscle The Sliding Filament Mechanism- Explains the relationship between

thick and thin filaments as contraction proceeds Cyclic process beginning with calcium release from SR Calcium binds to troponin Troponin moves, moving tropomyosin and exposing actin active site Myosin head forms cross bridge and bends toward H zone ATP allows release of cross bridge

Structure of Actin and Myosin

Contraction and Relaxation of Skeletal Muscle 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


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

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


Contraction and Relaxation of Skeletal Muscle Excitation–Contraction Coupling

An increase in Ca++ concentration in the muscle starts contraction

A decrease in Ca++ stops it An Action potential causes Ca++ to be released from the

SR into the muscle cell Ca++ moves tropomyosin away from the myosin-binding

sites on actin allowing cross-bridges to form The muscle cell membrane contains Ca++ pumps to

return Ca++ back to the SR quickly Decreasing calcium ion levels in sarcoplasm

As the Ca++ level in the cell drops, myosin-binding sites are covered and the muscle relaxes


Figure 10–11

Exposing the Active site

Contraction and Relaxation of Skeletal Muscle 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


SEM of Neuromuscular Junction

Contraction and 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 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

Skeletal Muscle Innervation

Nerve impulse arrives ataxon terminal of motorneuron and triggers releaseof acetylcholine (ACh).

Synaptic vesiclefilled with ACh

ACh receptor

Muscle action potential

Nerveimpulse

1

ACh diffuses acrosssynaptic cleft, bindsto its receptors in themotor end plate, andtriggers a muscle action potential (AP).



ACh receptor


Nerveimpulse

1

2 ACh diffuses acrosssynaptic cleft, bindsto its receptors in themotor end plate, andtriggers a muscle action potential (AP).



ACh receptorAcetylcholinesterase insynaptic cleft destroysACh so another muscleaction potential does notarise unless more ACh isreleased from motor neuron.


Nerveimpulse

1

2

3

ACh diffuses acrosssynaptic cleft, bindsto its receptors in themotor end plate, andtriggers a muscle action potential (AP).



ACh receptorAcetylcholinesterase insynaptic cleft destroysACh so another muscleaction potential does notarise unless more ACh isreleased from motor neuron. Ca2+


Nerveimpulse

SR

Muscle AP travelling alongtransverse tubule opens Ca2+

release channels in thesarcoplasmic reticulum (SR)membrane, which allowscalcium ions to flood into the sarcoplasm.

1

2

3

4

Transverse tubuleACh diffuses acrosssynaptic cleft, bindsto its receptors in themotor end plate, andtriggers a muscle action potential (AP).





Nerveimpulse

SR

Ca2+ binds to troponin onthe thin filament, exposingthe binding sites for myosin.



1

2

3

4

5






Nerveimpulse

SR

Contraction: power strokesuse ATP; myosin heads bindto actin, swivel, and release;thin filaments are pulled towardcenter of sarcomere.




Elevated Ca2+

1

2

3

4

5

6






Nerveimpulse

SR


Ca2+ activetransport pumps

Ca2+ release channels inSR close and Ca2+ activetransport pumps use ATPto restore low level of Ca2+ in sarcoplasm.




Elevated Ca2+

1

2

3

4

5

67






Nerveimpulse

SR


Troponin–tropomyosincomplex slides back into position where it blocks the myosinbinding sites on actin.






Elevated Ca2+

1

2

3

4

5

67

8






Nerveimpulse

SR


Troponin–tropomyosincomplex slides back into position where it blocks the myosinbinding sites on actin.

Muscle relaxes.






Elevated Ca2+

1

2

3

4

9

5

67

8

Transverse tubule

Muscle Relaxation

After contraction, a muscle fiber returns to resting length by: elastic forces (tendons & ligaments) opposing muscle contractions gravity

A Review of Muscle Contraction

Table 10–1 (1 of 2)

A Review of Muscle Contraction

Table 10–1 (2 of 2)

Contraction and Relaxation of Skeletal Muscle Botulinum toxin- Blocks release of ACh from synaptic vesicles

May be found in improperly canned foods 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 (lumbar region)

Curare- Plant poison used American Indians on arrows & blowgun darts Blocks ACh receptors & inhibits Na+ channels→ muscle paralysis

Curare derivatives used during surgery to relax skeletal musclesAnticholinesterase - Slows 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


Muscle Metabolism Production of ATP in Muscle Fibers

A huge amount of ATP is needed to: Power the contraction cycle Pump Ca++ into the SR

The ATP inside muscle fibers will power contraction for only a few seconds

ATP must be produced by the muscle fiber after reserves are used up

Muscle fibers have three ways to produce ATP 1) From creatine phosphate 2) By anaerobic cellular respiration 3) By aerobic cellular respiration


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


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


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


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


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


Control of Muscle Tension The tension or force of muscle cell

contraction varies

Maximum Tension (force) is dependent on The rate at which nerve impulses arrive The amount of stretch before contraction The nutrient and oxygen availability The size of the motor unit


Control of Muscle Tension Motor Units

Consists of a motor neuron and the muscle fibers it stimulates The axon of a motor neuron branches out forming neuromuscular

junctions with different muscle fibers A motor neuron makes contact with about 150 muscle fibers Control of precise movements consist of many small motor units

Muscles that control voice production have 2 - 3 muscle fibers per motor unit

Muscles controlling eye movements have 10 - 20 muscle fibers per motor unit

Muscles in the arm and the leg have 2000 - 3000 muscle fibers per motor unit

The total strength of a contraction depends on the size of the motor units and the number that are activated


Control of Muscle Tension


Control of Muscle Tension Twitch Contraction

The brief contraction of the muscle fibers in a motor unit in response to an action potential

Twitches last from 20 to 200 msec L Latent period (2 msec)

A brief delay between the stimulus and muscular contraction

The action potential sweeps over the sarcolemma and Ca++ is released from the SR

Contraction period (10–100 msec) Ca++ binds to troponin Myosin-binding sites on actin are exposed Cross-bridges form


Control of Muscle Tension Relaxation period (10–100 msec)

Ca++ is transported into the SR Myosin-binding sites are covered by tropomyosin Myosin heads detach from actin

Muscle fibers that move the eyes have contraction periods lasting 10 msec

Muscle fibers that move the legs have contraction periods lasting 100 msec

Refractory period When a muscle fiber contracts, it temporarily cannot

respond to another action potential Skeletal muscle has a refractory period of 5 milliseconds Cardiac muscle has a refractory period of 300 milliseconds


Control of Muscle Tension


Control of Muscle Tension Muscle Tone

A small amount of tension in the muscle due to weak contractions of motor units

Small groups of motor units are alternatively active and inactive in a constantly shifting pattern to sustain muscle tone

Muscle tone keeps skeletal muscles firm Keep the head from slumping forward on the

chest


Control of Muscle Tension Types of Contractions

Isotonic contraction The tension developed remains constant while the

muscle changes its length Used for body movements and for moving objects Picking a book up off a table

Isometric contraction The tension generated is not enough for the object

to be moved and the muscle does not change its length

Holding a book steady using an outstretched arm


Isotonic and Isometric Contractions

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)


Types of Skeletal Muscle Fibers Muscle fibers contract at different speeds, and

vary in how quickly they fatigue Muscle fibers are classified into three main types

1) Slow oxidative fibers 2) Fast oxidative-glycolytic fibers 3) Fast glycolytic fibers


Types of Skeletal Muscle Fibers Slow Oxidative Fibers (SO fibers)

Smallest in diameter Least powerful type of muscle fibers Appear dark red (more myoglobin) Generate ATP mainly by aerobic cellular respiration Have a slow speed of contraction

Twitch contractions last from 100 to 200 msec Very resistant to fatigue Capable of prolonged, sustained contractions for

many hours Adapted for maintaining posture and for aerobic,

endurance-type activities such as running a marathon


Types of Skeletal Muscle Fibers Fast Oxidative–Glycolytic Fibers (FOG fibers)

Intermediate in diameter between the other two types of fibers

Contain large amounts of myoglobin and many blood capillaries

Have a dark red appearance Generate considerable ATP by aerobic cellular

respiration Moderately high resistance to fatigue Generate some ATP by anaerobic glycolysis Speed of contraction faster

Twitch contractions last less than 100 msec Contribute to activities such as walking and sprinting


Types of Skeletal Muscle Fibers Fast Glycolytic Fibers (FG fibers)

Largest in diameter Generate the most powerful contractions Have low myoglobin content Relatively few blood capillaries Few mitochondria Appear white in color Generate ATP mainly by glycolysis Fibers contract strongly and quickly Fatigue quickly Adapted for intense anaerobic movements of short

duration Weight lifting or throwing a ball


Fast versus Slow Fibers

Types of Skeletal Muscle Fibers Distribution and Recruitment of

Different Types of Fibers Most muscles are a mixture of all three types

of muscle fibers Proportions vary, depending on the action of

the muscle, the person ’s training regimen, and genetic factors Postural muscles of the neck, back, and legs have

a high proportion of SO fibers Muscles of the shoulders and arms have a high

proportion of FG fibers Leg muscles have large numbers of both SO and

FOG fibers


Exercise and Skeletal Muscle Tissue Ratios of fast glycolytic and slow oxidative

fibers are genetically determined Individuals with a higher proportion of FG

fibers Excel in intense activity (weight lifting, sprinting)

Individuals with higher percentages of SO fibers Excel in endurance activities (long-distance

running)


Exercise and Skeletal Muscle Tissue Various types of exercises can induce

changes in muscle fibers Aerobic exercise transforms some FG fibers

into FOG fibers Endurance exercises do not increase muscle mass

Exercises that require short bursts of strength produce an increase in the size of FG fibers Muscle enlargement (hypertrophy) due to increased

synthesis of thick and thin filaments


Cardiac Muscle Tissue Principal tissue in the heart wall

Intercalated discs connect the ends of cardiac muscle fibers to one another Allow muscle action potentials to spread from one cardiac muscle

fiber to another Cardiac muscle tissue contracts when stimulated by its own

autorhythmic muscle fibers Continuous, rhythmic activity is a major physiological difference

between cardiac and skeletal muscle tissue Contractions lasts longer than a skeletal muscle twitch 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


Figure 10–22

Smooth Muscle Tissue Usually activated involuntarily Action potentials are spread through the fibers

by gap junctions Fibers are stimulated by certain

neurotransmitter, hormone, or autorhythmic signals

Found in the Walls of arteries and veins Walls of hollow organs Walls of airways to the lungs Muscles that attach to hair follicles Muscles that adjust pupil diameter Muscles that adjust focus of the lens in the eye


Smooth Muscle • Cells are not striated• Fibers smaller than those in

skeletal muscle• Spindle-shaped; single,

central nucleus• More actin than myosin• No sarcomeres

– Not arranged as symmetrically as in skeletal muscle, thus NO striations.

• Caveolae: indentations in sarcolemma;– May act like T tubules

• Dense bodies instead of Z disks – Have noncontractile

intermediate filaments• Free Ca2+ in cytoplasm

triggers contraction→Ca2+ binds w/ calmodulin: – in the sarcoplasm→ activates

myosin light chain kinase, an enzyme that breaks down ATP→ initiates contraction

Smooth Muscle Tissue


Smooth Muscle Tissue Physiology of Smooth Muscle

Contraction lasts longer than skeletal muscle contraction

Contractions are initiated by Ca++ flow primarily from the interstitial fluid

Ca++ move slowly out of the muscle fiber delaying relaxation

Able to sustain long-term muscle tone Prolonged presence of Ca++ in the cell provides for a state of

continued partial contraction Important in the:

Gastrointestinal tract where a steady pressure is maintained on the contents of the tract

In the walls of blood vessels which maintain a steady pressure on blood


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


Regeneration of Muscular Tissue Hyperplasia

An increase in the number of fibers Skeletal muscle has limited regenerative abilities

Growth of skeletal muscle after birth is due mainly to hypertrophy

Satellite cells divide slowly and fuse with existing fibers Assist in muscle growth Repair of damaged fibers

Cardiac muscle can undergo hypertrophy in response to increased workload Many athletes have enlarged hearts

Smooth muscle in the uterus retain their capacity for division


Development of Muscle Muscles of the body are derived from mesoderm As the mesoderm develops it becomes arranged on

either side of the developing spinal cord Columns of mesoderm undergo segmentation into

structures called somites The cells of a somite differentiate into three regions:

1) Myotome Forms the skeletal muscles of the head, neck, and limbs

2) Dermatome Forms the connective tissues, including the dermis of the skin

3) Sclerotome Gives rise to the vertebrae

Cardiac muscle and smooth muscle develop from migrating mesoderm cells


Development of Muscle


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


End of Chapter 10

Copyright 2009 John Wiley & Sons, Inc.All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.


chapter 10: muscular tissue copyright 2009, john wiley & sons, inc

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