Chapter 10 Muscular Tissue Copyright 2009 John Wiley

Chapter 10: Muscular Tissue Copyright 2009, John Wiley & Sons, Inc.

Muscular Tissue Chapter 10 n n n 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 Copyright 2009, John Wiley & Sons, Inc.

Overview of Muscular Tissue n Types of Muscular Tissue q The three types of muscular tissue n n Skeletal Cardiac Smooth Skeletal Muscle Tissue q q So named because most skeletal muscles move bones Skeletal muscle tissue is striated: n q Skeletal muscle tissue works mainly in a voluntary manner n q Alternating light and dark bands (striations) as seen when examined with a microscope Its activity can be consciously controlled Most skeletal muscles also are controlled subconsciously to some extent n Ex: the diaphragm alternately contracts and relaxes without conscious control Copyright 2009, John Wiley & Sons, Inc.

Overview of Muscular Tissue n Cardiac Muscle Tissue q q q Found only in the walls of the heart Striated like skeletal muscle Action is involuntary n n n Contraction and relaxation of the heart is not consciously controlled Contraction of the heart is initiated by a node of tissue called the “pacemaker” Smooth Muscle Tissue q Located in the walls of hollow internal structures n q q Blood vessels, airways, and many organs Lacks the striations of skeletal and cardiac muscle tissue Usually involuntary Copyright 2009, John Wiley & Sons, Inc.

Overview of Muscular Tissue Copyright 2009, John Wiley & Sons, Inc.

Overview of Muscular Tissue n Functions of Muscular Tissue q Producing Body Movements n Walking and running q Stabilizing Body Positions n Posture q Moving Substances Within the Body n Heart muscle pumping blood n Moving substances in the digestive tract q Generating heat n Contracting muscle produces heat n Shivering increases heat production Copyright 2009, John Wiley & Sons, Inc.

Overview of Muscular Tissue n Properties of Muscular Tissue q Properties that enable muscle to function and contribute to homeostasis n Excitability q n Contractility q n Ability to contract forcefully when stimulated Extensibility q n Ability to respond to stimuli Ability to stretch without being damaged Elasticity q Ability to return to an original length Copyright 2009, John Wiley & Sons, Inc.

Skeletal Muscle Tissue n Connective Tissue Components q Fascia n q Epimysium n n q Separates individual muscle fibers from one another Tendon n q Surrounds numerous bundles of fascicles Endomysium n q The outermost layer Separates 10 -100 muscle fibers into bundles called fascicles Perimysium n q Dense sheet or broad band of irregular connective tissue that surrounds muscles Cord that attach a muscle to a bone Aponeurosis n Broad, flattened tendon Copyright 2009, John Wiley & Sons, Inc.

Skeletal Muscle Tissue Copyright 2009, John Wiley & Sons, Inc.

Skeletal Muscle Tissue n Nerve and Blood Supply Neurons that stimulate skeletal muscle to contract are somatic motor neurons q The axon of a somatic motor neuron typically branches many times q n q Each branch extending to a different skeletal muscle fiber Each muscle fiber is in close contact with one or more capillaries Copyright 2009, John Wiley & Sons, Inc.

Skeletal Muscle Tissue n Microscopic Anatomy q The number of skeletal muscle fibers is set before you are born n q Most of these cells last a lifetime Muscle growth occurs by hypertrophy n An enlargement of existing muscle fibers Testosterone and human growth hormone stimulate hypertrophy q Satellite cells retain the capacity to regenerate damaged muscle fibers q Copyright 2009, John Wiley & Sons, Inc.

Skeletal Muscle Tissue n Sarcolemma q n Transverse (T tubules) q q n The plasma membrane of a muscle cell Tunnel in from the plasma membrane Muscle action potentials travel through the T tubules Sarcoplasm, the cytoplasm of a muscle fiber q q 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 Copyright 2009, John Wiley & Sons, Inc.

Skeletal Muscle Tissue n Myofibrils q n Sarcoplasmic reticulum (SR) q q q n Membranous sacs which encircles each myofibril Stores calcium ions (Ca++) Release of Ca++ triggers muscle contraction Filaments q q q n Thread like structures which have a contractile function Function in the contractile process Two types of filaments (Thick and Thin) There are two thin filaments for every thick filament Sarcomeres q q Compartments of arranged filaments Basic functional unit of a myofibril Copyright 2009, John Wiley & Sons, Inc.

Skeletal Muscle Tissue n Z discs q q n A band q q n q Lighter, contains thin filaments but no thick filaments Z discs passes through the center of each I band H zone q n Darker middle part of the sarcomere Thick and thin filaments overlap I band q n Separate one sarcomere from the next Thick and thin filaments overlap one another Center of each A band which contains thick but no thin filaments M line q Supporting proteins that hold the thick filaments together in the H zone Copyright 2009, John Wiley & Sons, Inc.

Skeletal Muscle Tissue Copyright 2009, John Wiley & Sons, Inc.

Contraction and Relaxation of Skeletal Muscle Copyright 2009, John Wiley & Sons, Inc.

Skeletal Muscle Tissue n Muscle Proteins q Myofibrils are built from three kinds of proteins n 1) Contractile proteins q n 2) Regulatory proteins q n Generate force during contraction Switch the contraction process on and off 3) Structural proteins q q q Align the thick and thin filaments properly Provide elasticity and extensibility Link the myofibrils to the sarcolemma Copyright 2009, John Wiley & Sons, Inc.

Skeletal Muscle Tissue n Contractile Proteins q Myosin n n q 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 n n n n 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 Copyright 2009, John Wiley & Sons, Inc.

Skeletal Muscle Tissue n Structural Proteins q Titin n n q Stabilize the position of myosin accounts for much of the elasticity and extensibility of myofibrils Dystrophin n Links thin filaments to the sarcolemma Copyright 2009, John Wiley & Sons, Inc.

Contraction and Relaxation of Skeletal Muscle n The Sliding Filament Mechanism Myosin heads attach to and “walk” along the thin filaments at both ends of a sarcomere q Progressively pulling the thin filaments toward the center of the sarcomere q Z discs come closer together and the sarcomere shortens q Leading to shortening of the entire muscle q Copyright 2009, John Wiley & Sons, Inc.

Contraction and Relaxation of Skeletal Muscle Copyright 2009, John Wiley & Sons, Inc.

Contraction and Relaxation of Skeletal Muscle Copyright 2009, John Wiley & Sons, Inc.

Contraction and Relaxation of Skeletal Muscle Copyright 2009, John Wiley & Sons, Inc.

Contraction and Relaxation of Skeletal Muscle n The Contraction Cycle q q 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 Copyright 2009, John Wiley & Sons, Inc.

Contraction and Relaxation of Skeletal Muscle n The contraction cycle consists of 4 steps q 1) ATP hydrolysis n q 2) Formation of cross-bridges n q Myosin head attaches to the myosin-binding site on actin 3) Power stroke n q Hydrolysis of ATP reorients and energizes the myosin head During the power stroke the crossbridge rotates, sliding the filaments 4) Detachment of myosin from actin n 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 Copyright 2009, John Wiley & Sons, Inc.

Contraction and Relaxation of Skeletal Muscle Copyright 2009, John Wiley & Sons, Inc.

Contraction and Relaxation of Skeletal Muscle Copyright 2009, John Wiley & Sons, Inc.

Key: = Ca 2+ 1 Myosin heads hydrolyze ATP and become reoriented and energized ADP P P ATP 4 As myosin heads bind ATP, the crossbridges detach from actin Contraction cycle continues if ATP is available and Ca 2+ level in the sarcoplasm is high 2 Myosin heads bind to actin, forming crossbridges ADP 3 Myosin crossbridges rotate toward center of the sarcomere (power stroke)

Contraction and Relaxation of Skeletal Muscle n Excitation–Contraction Coupling q q q An increase in Ca++ concentration in the muscle starts contraction A decrease in Ca++ stops it Action potentials causes Ca++ to be released from the SR into the muscle cell Ca++ moves tropomyosin away from the myosinbinding sites on actin allowing cross-bridges to form The muscle cell membrane contains Ca++ pumps to return Ca++ back to the SR quickly n q Decreasing calcium ion levels As the Ca++ level in the cell drops, myosin-binding sites are covered and the muscle relaxes Copyright 2009, John Wiley & Sons, Inc.

Contraction and Relaxation of Skeletal Muscle Copyright 2009, John Wiley & Sons, Inc.

Contraction and Relaxation of Skeletal Muscle n Length–Tension Relationship q q q 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 Copyright 2009, John Wiley & Sons, Inc.

Contraction and Relaxation of Skeletal Muscle Copyright 2009, John Wiley & Sons, Inc.

Contraction and Relaxation of Skeletal Muscle n The Neuromuscular Junction q n Neuromuscular junction (NMJ) q n Chemical released by the initial cell communicating with the second cell Synaptic vesicles q n Gap that separates the two cells Neurotransmitter q n Where communication occurs between a somatic motor neuron and a muscle fiber Synaptic cleft q n Action potentials arise at the interface of the motor neuron and muscle fiber Synapse q n Motor neurons have a threadlike axon that extends from the brain or spinal cord to a group of muscle fibers Sacs suspended within the synaptic end bulb containing molecules of the neurotransmitter acetylcholine (Ach) Motor end plate q q The region of the muscle cell membrane opposite the synaptic end bulbs Contain acetylcholine receptors Copyright 2009, John Wiley & Sons, Inc.

Contraction and Relaxation of Skeletal Muscle n Nerve impulses elicit a muscle action potential in the following way q 1) Release of acetylcholine n q 2) Activation of ACh receptors n n q 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 n n q Nerve impulse arriving at the synaptic end bulbs causes many synaptic vesicles to release ACh into the synaptic cleft 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 n Ach effects last only briefly because it is rapidly broken down by acetylcholinesterase (ACh. E) Copyright 2009, John Wiley & Sons, Inc.

Contraction and Relaxation of Skeletal Muscle Copyright 2009, John Wiley & Sons, Inc.

Axon collateral of somatic motor neuron Axon terminal Nerve impulse Synaptic vesicle containing acetylcholine (ACh) Synaptic end bulb Sarcolemma Axon terminal Synaptic end bulb Motor end plate Neuromuscular junction (NMJ) Synaptic cleft (space) Sarcolemma Myofibril (b) Enlarged view of the neuromuscular junction (a) Neuromuscular junction 1 1 ACh is released from synaptic vesicle Synaptic end bulb Synaptic cleft (space) 4 ACh is broken down 2 2 ACh binds to Ach receptor Junctional fold Motor end plate Na+ 3 Muscle action potential is produced (c) Binding of acetylcholine to ACh receptors in the motor end plate

Contraction and Relaxation of Skeletal Muscle Copyright 2009, John Wiley & Sons, Inc.

Nerve impulse 1 Nerve impulse arrives at axon terminal of motor neuron and triggers release of acetylcholine (ACh). 2 ACh diffuses across synaptic cleft, binds to its receptors in the motor end plate, and triggers a muscle action potential (AP). ACh receptor Synaptic vesicle filled with ACh 3 Acetylcholinesterase in synaptic cleft destroys ACh so another muscle action potential does not arise unless more ACh is released from motor neuron. Muscle action potential Transverse tubule 4 Muscle AP travelling along transverse tubule opens Ca 2+ release channels in the sarcoplasmic reticulum (SR) membrane, which allows calcium ions to flood into the sarcoplasm. SR Ca 2+ 9 Muscle relaxes. 8 Troponin–tropomyosin complex slides back into position where it blocks the myosin binding sites on actin. 5 Ca 2+ binds to troponin on the thin filament, exposing the binding sites for myosin. Elevated Ca 2+ active transport pumps 7 Ca 2+ release channels in SR close and Ca 2+ active transport pumps use ATP to restore low level of Ca 2+ in sarcoplasm. 6 Contraction: power strokes use ATP; myosin heads bind to actin, swivel, and release; thin filaments are pulled toward center of sarcomere.

Contraction and Relaxation of Skeletal Muscle n Botulinum toxin q q Blocks release of ACh from synaptic vesicles May be found in improperly canned foods n q A tiny amount can cause death by paralyzing respiratory muscles Used as a medicine (Botox®) n n n 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 Copyright 2009, John Wiley & Sons, Inc.

Contraction and Relaxation of Skeletal Muscle n Curare q q q n 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 used during surgery to relax skeletal muscles Anticholinesterase q q Slow actions of acetylcholinesterase and removal of ACh Can strengthen weak muscle contractions n Ex: Neostigmine q q q Treatment for myasthenia gravis Antidote for curare poisoning Terminate the effects of curare after surgery Copyright 2009, John Wiley & Sons, Inc.

Muscle Metabolism n Production of ATP in Muscle Fibers q A huge amount of ATP is needed to: n n q q q 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 n n n 1) From creatine phosphate 2) By anaerobic cellular respiration 3) By aerobic cellular respiration Copyright 2009, John Wiley & Sons, Inc.

Muscle Metabolism Copyright 2009, John Wiley & Sons, Inc.

Muscle Metabolism n Creatine Phosphate q Excess ATP is used to synthesize creatine phosphate n q q 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 Copyright 2009, John Wiley & Sons, Inc.

Muscle Metabolism n Anaerobic Respiration q q q q 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 Copyright 2009, John Wiley & Sons, Inc.

Muscle Metabolism n Aerobic Respiration q q Activity that lasts longer than half a minute depends on aerobic respiration Pyruvic acid entering the mitochondria is completely oxidized generating n n q q Each molecule of glucose yields about 36 molecules of ATP Muscle tissue has two sources of oxygen n n q q q ATP carbon dioxide Water Heat 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 Copyright 2009, John Wiley & Sons, Inc.

Muscle Metabolism n Muscle Fatigue q q q q 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 Copyright 2009, John Wiley & Sons, Inc.

Muscle Metabolism n Oxygen Consumption After Exercise q q After exercise, heavy breathing continues and oxygen consumption remains above the resting level Oxygen debt n q 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 n n n 1) to convert lactic acid into glycogen 2) to synthesize creatine phosphate and ATP 3) to replace the oxygen removed from myoglobin Copyright 2009, John Wiley & Sons, Inc.

Control of Muscle Tension n The tension or force of muscle cell contraction varies n Maximum Tension (force) is dependent on q q The rate at which nerve impulses arrive The amount of stretch before contraction The nutrient and oxygen availability The size of the motor unit Copyright 2009, John Wiley & Sons, Inc.

Control of Muscle Tension n Motor Units q q 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 n n n q 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 Copyright 2009, John Wiley & Sons, Inc.

Control of Muscle Tension Copyright 2009, John Wiley & Sons, Inc.

Control of Muscle Tension n Twitch Contraction q q q 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) n n q 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) n n n Ca++ binds to troponin Myosin-binding sites on actin are exposed Cross-bridges form Copyright 2009, John Wiley & Sons, Inc.

Control of Muscle Tension q Relaxation period (10– 100 msec) n n n Ca++ is transported into the SR Myosin-binding sites are covered by tropomyosin Myosin heads detach from actin q q q 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 n When a muscle fiber contracts, it temporarily cannot respond to another action potential q q Skeletal muscle has a refractory period of 5 milliseconds Cardiac muscle has a refractory period of 300 milliseconds Copyright 2009, John Wiley & Sons, Inc.

Control of Muscle Tension Copyright 2009, John Wiley & Sons, Inc.

Control of Muscle Tension Copyright 2009, John Wiley & Sons, Inc.

Control of Muscle Tension n Muscle Tone q q 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 Copyright 2009, John Wiley & Sons, Inc.

Control of Muscle Tension n Types of Contractions q Isotonic contraction n q 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 n n 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 Copyright 2009, John Wiley & Sons, Inc.

Control of Muscle Tension Copyright 2009, John Wiley & Sons, Inc.

Types of Skeletal Muscle Fibers n Muscle fibers vary in their content of myoglobin q Red muscle fibers n n q 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 n n Have a low content of myoglobin Appear lighter (white meat in chicken breasts) Copyright 2009, John Wiley & Sons, Inc.

Types of Skeletal Muscle Fibers n n Muscle fibers contract at different speeds, and vary in how quickly they fatigue Muscle fibers are classified into three main types q q q 1) Slow oxidative fibers 2) Fast oxidative-glycolytic fibers 3) Fast glycolytic fibers Copyright 2009, John Wiley & Sons, Inc.

Types of Skeletal Muscle Fibers n Slow Oxidative Fibers (SO fibers) q q q 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 n q q q 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 Copyright 2009, John Wiley & Sons, Inc.

Types of Skeletal Muscle Fibers n Fast Oxidative–Glycolytic Fibers (FOG fibers) q q q q 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 n q Twitch contractions last less than 100 msec Contribute to activities such as walking and sprinting Copyright 2009, John Wiley & Sons, Inc.

Types of Skeletal Muscle Fibers n Fast Glycolytic Fibers (FG fibers) q q q q q 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 n Weight lifting or throwing a ball Copyright 2009, John Wiley & Sons, Inc.

Types of Skeletal Muscle Fibers Copyright 2009, John Wiley & Sons, Inc.

Types of Skeletal Muscle Fibers n Distribution and Recruitment of Different Types of Fibers q q 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 n n n 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 Copyright 2009, John Wiley & Sons, Inc.

Exercise and Skeletal Muscle n Ratios of fast glycolytic and slow oxidative Tissue fibers are genetically determined q Individuals with a higher proportion of FG fibers n q Excel in intense activity (weight lifting, sprinting) Individuals with higher percentages of SO fibers n Excel in endurance activities (long-distance running) Copyright 2009, John Wiley & Sons, Inc.

Exercise and Skeletal Muscle n Various types of exercises can induce Tissue changes in muscle fibers q Aerobic exercise transforms some FG fibers into FOG fibers n q Endurance exercises do not increase muscle mass Exercises that require short bursts of strength produce an increase in the size of FG fibers n Muscle enlargement (hypertrophy) due to increased synthesis of thick and thin filaments Copyright 2009, John Wiley & Sons, Inc.

Cardiac Muscle Tissue n Principal tissue in the heart wall q Intercalated discs connect the ends of cardiac muscle fibers to one another n q Cardiac muscle tissue contracts when stimulated by its own autorhythmic muscle fibers n q q Allow muscle action potentials to spread from one cardiac muscle fiber to another 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 n n Requires a constant supply of oxygen Able to use lactic acid produced by skeletal muscle fibers to make ATP Copyright 2009, John Wiley & Sons, Inc.

Smooth Muscle Tissue n n 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 n n n 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 Copyright 2009, John Wiley & Sons, Inc.

Smooth Muscle Tissue n Microscopic Anatomy of Smooth Muscle q Contains both thick filaments and thin filaments n q q 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 n n Function in the same way as Z discs During contraction the filaments pull on the dense bodies causing a shortening of the muscle fiber Copyright 2009, John Wiley & Sons, Inc.

Smooth Muscle Tissue Copyright 2009, John Wiley & Sons, Inc.

Smooth Muscle Tissue n Physiology of Smooth Muscle q q 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 n n Prolonged presence of Ca++ in the cell provides for a state of continued partial contraction Important in the: q q 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 Copyright 2009, John Wiley & Sons, Inc.

Smooth Muscle Tissue n Physiology of Smooth Muscle q Most smooth muscle fibers contract or relax in response to: n Action potentials from the autonomic nervous system q n In response to stretching q n Food in digestive tract stretches intestinal walls initiating peristalsis Hormones q n Pupil constriction due to increased light energy Epinephrine causes relaxation of smooth muscle in the airways and in some blood vessel walls Changes in p. H, oxygen and carbon dioxide levels Copyright 2009, John Wiley & Sons, Inc.

Smooth Muscle Tissue Copyright 2009, John Wiley & Sons, Inc.

Regeneration of Muscular Tissue n Hyperplasia q n An increase in the number of fibers Skeletal muscle has limited regenerative abilities q q Growth of skeletal muscle after birth is due mainly to hypertrophy Satellite cells divide slowly and fuse with existing fibers n n n Cardiac muscle can undergo hypertrophy in response to increased workload q n Assist in muscle growth Repair of damaged fibers Many athletes have enlarged hearts Smooth muscle in the uterus retain their capacity for division Copyright 2009, John Wiley & Sons, Inc.

Development of Muscle n n 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: q 1) Myotome n q 2) Dermatome n q Forms the connective tissues, including the dermis of the skin 3) Sclerotome n n Forms the skeletal muscles of the head, neck, and limbs Gives rise to the vertebrae Cardiac muscle and smooth muscle develop from migrating mesoderm cells Copyright 2009, John Wiley & Sons, Inc.

Development of Muscle Copyright 2009, John Wiley & Sons, Inc.

Aging and Muscular Tissue n Aging q q n n 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 Copyright 2009, John Wiley & Sons, Inc.

End of Chapter 10 n 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. Copyright 2009, John Wiley & Sons, Inc.