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Muscles & Muscular Tissue• Terminology• “__________________”refers to muscles.• myopathy = disease of muscle (e.g.,

cardiomyopathy)• electromyography = recording of electrical or

activity of muscle.• myoblasts = cells that produce or become

muscle cells.• “__________________”= "flesh“ sarcomere,

sarcoplasmic reticulum and sarcolemma.• Sarcophagus = "flesh eating."

• Muscle is a principal tissue type,Specialized for contraction.

• Like neurons, muscle is an __________tissue, in that it can conduct or transmitelectrical impulses (respond to stimuli).

• 3 muscle types:

• All muscle tissues have 4 characteristicsin common:

1.

2.

3.

4.

Functions1)Skeletal muscle: Movement of skeletonCardiac muscle: Movement (contraction) of heartSmooth muscle: Regulation of blood vessel

diameter, bronchiole diameter, movement ofmaterial in gastrointestinal tract.

2)

3)

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General structure of skeletal muscle

• Tendon ---- Body ofMuscle ----- Tendon

• Tendon Histology:_________________connective tissue

Tendon

Tendon

Body

Aponeurosis• ____________

that is broad orsheet-like.

• Aponeurosis ofGalen

• Lumbaraponeurosis:origin of thelatissimus dorsi.

Levels of Organization• _________: a collection of fascicles• _________: a collection of muscle cells• ___________: collection of myofibrils plus

other cell organelles.• ___________: series of sarcomeres• __________: Basic unit of muscle

structure and function.• ___________: Thick and thin filaments

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Filament Structure Associated Connective TissueOrganizes Muscle Tissue

• Bundles of muscle fibers are grouped orbundled together by connective tissue.

• ____________: surrounds fibers• ____________: surrounds fascicle• ____________: surrounds fascicles• Superficial fascia: layer adjacent to

hypodermis. Deep fascia: binds musclestogether.

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Blood and Nerve Supply• Muscles are highly vascular organs -- high rate of

metabolic activity.• Nerves control or modify muscle contraction.

• A “_______________" nerve is any nerve that innervatesa muscle.

• Skeletal muscles require input from a nerve in order to

contract. They are _____________________• Cardiac and smooth muscle can contract on their own

(they have an intrinsic spontaneous contraction rate and

are _____________________), but the rate is controlledby nerves and hormones.

• Sensory nerves areabundant in musclealso--supply nervoussystem withinformation on musclecontraction and jointposition.

• Muscle Spindles:monitor _________within muscles.

Electrical Nature of Membrane

• Resting Membrane Potential (RMP)– The cell membrane is electrically polarized– Voltage difference across cell membrane is - -

-50 to -90 mV. Unequal conc. of ions.– __________: 10X more concentrated outside– ___________: 15X more concentrated inside– “Fixed” Anions– Chloride

Excitable Cells• Excitable cells (neurons and muscle cells)

do something with the electrical differenceacross the membrane.

• _________________: potential > RMP• __________________: return to RMP• __________________: potential < RMP• _______________: voltage at which

impulse (action potential) is triggered.

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Excitation-Contraction Coupling

• Depolarization

• Propagation

• Repolarization

• Mechanism by which excitation of musclecell membrane stimulates muscle cellcontraction.

Action Potential Neuromuscular Junction3 components

1) ______________________Motor neuron terminal has synapticvesicles that contain the neurotransmitteracetylcholine (ACh). ACh is released bynerve stimulation (nerve action potential).

2) ______________________ Gap thruwhich transmitter diffuses.

3) __________________: Area specializedfor reception of neurotransmitter.

• ACh binds to Ach receptors -- causesendplate potential (EPP). Membranepotential reaches threshold and then amuscle action potential is triggered.

• _____________________: enzyme onendplate that breaks down ACh -- initiationof muscle impulse ends.

Neuromuscular Junction or Endplate

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Sequence of Events atNeuromuscular Junction and

Excitation-Contraction Coupling.1. Nerve impulse (action potential) arrives at

terminal and induces the entry of Calciuminto terminal via voltage-gated calcium___________________.

2. Calcium entry stimulates _____________of ACh filled vesicles.

3. ACh diffuses across synaptic cleft and binds onto ______________________on

muscle endplate.

4. ACh receptors activate Na/K ionchannels. Sodium entry depolarizesendplate --generates an ____________________________(EPP).

5. Endplate membrane is brought tothreshold voltage and adjacent muscle cellmembrane generates an action potential(muscle impulse).

6. Muscle Impulse: travels downsarcolemma and then into myofibrils viathe ___________ _______________

7. Transverse tubulestransmit signal toSarcoplasmicReticulum (S.R.)

• S.R. releasescalcium to myofibrils(initiatescontraction).

8. Actin and myosin filaments interact -- theyslide past each other and muscle cellshortens.

Calcium binds to ______________- pulls___________________away from active

site on actin -- myosin can now bind toactin -- myosin head moves actinfilaments.

This is the ___________ ___________theory of muscle contraction.

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Roles of ATP• ATP provides ___________________.

Myosin head is an ATPase in that itcleaves ATP to form ADP and Pi, yieldingenergy for movement.

• ATP is also need to ________________________ from myosin head.

• Lack of ATP -- rigor mortis sets in.Muscles are stiff because actin andmyosin filaments are cross-linked.

Muscle Relaxation1. ACh is broken down by ____________2. S.R. pumps calcium back inside -- this

uses ATP!3. Without calcium present, troponin and

tropomyosin block active site on actinpreventing cross-bridge formationbetween actin and myosin.

4. Actin and myosin filaments return to theiroriginal positions.

Muscle Contraction• Functional unit of

muscle contraction isthe ______________________: onemotor neuron & all themuscle cells itinnervates

• To increase force ofcontraction, moremotor units need tobe ____________

Tension Developed is Proportionalto Overlap of Filaments

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Isotonic Contraction Isometric Contraction

Effect of Stimulus Frequency Energy Use• Resting muscle uses _________ _______

pathway to supply ATP. Prime energysources are fatty acids and glucose (fromglycogen via glycogenolysis).

• Glucose converted to pyruvic acid, whichis broken down by citric acid cycle(in___________________, aerobic) toproduce ATP.

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Aerobic and Anaerobic Metabolismof Glucose

• Advantage of Aerobic respiration:– ___________________________

• Disadvantage of Aerobic respiration:– ______________________

• Exercising muscle uses ATP, but use soonoutweighs ATP production. Muscle respiresanaerobically (glycolysis -- lactic acid produced).

• ATP is also generated from creatine phosphate

Creatine Phosphate• Creatine Phosphate + ADP ATP +

Creatine• Muscle has large stores of creatine

phosphate but it is rapidly used up duringsustained contraction.

Oxygen Debt*• As a result of heavy exercise, lactic acid accumulates

from anaerobic respiration. Lactic acid then travels to theliver, which converts it to glucose. Conversion to glucoserequires ATP and oxygen. During exercise, availableoxygen is used primarily by muscle, so less is availablefor use by liver.

• The "oxygen debt" created is equal to the amount ofoxygen needed by liver to convert accumulated lacticacid into glucose, plus the amount needed by muscle forATP and CP regeneration. Total process may takehours.

• (*Note: Exercise physiologists prefer to call oxygen debt"EPOC" for "Excess post-exercise oxygenconsumption.")

Muscle Fatigue• Accumulation of _________ _______ and low

________results in fatigue (reduction in ability tocontract).

• Other factors include: change in pH, interruptionof blood supply, depletion of acetylcholine.

• Tolerance to fatigue from athletic training is dueto increased

___________________ & ___________________• Energy use of muscles can be modified as a

result of exercise.

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Effects of Resistance Training• _________________ is from Increase in

Number and Size of Myofibrils.

• “_________________" is from increase inNumber of Fibers -- not from mitosis in thiscase, but from splitting of muscle cells.

Responses to Endurance Training• Numerous factors related to aerobic

metabolism

Loss of Muscle Mass• ________________ wasting away of muscle

tissue. E.g., disuse atrophy, in which musclemass is lost because of inactivity.

• Also from loss of motor neurons.

• ________________literally, "defective nutrition."Tissue fails to develop correctly or thrive.Usually congenital or genetic in cause.

• ______________ means "vanishing flesh." Age-related loss of muscle with replacement by fat.

Skeletal Muscle Fiber Types1) _____________ ____________ (Type I)--e.g., soleus.

100 msec for contraction.• “________________" muscle fibers -- due to myoglobin

& blood supply• High resistance to fatigue, aerobic metabolism.

2) _____________________(Type IIA) e.g.,gastrocnemius. Fast twitch. “Pink fibers” intermediate tohigh resistance to fatigue .

3) ______________________ (Type IIB)--e.g., extraocularmuscles. 7.3 msec for contraction.

____________________ fibers.

• Low resistance to fatigue, anaerobic metabolism.

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• Fiber type dictated by ____________________(experimentally demonstrated) and by genetics.

• Effect of training? Twitch type (fast or slow)stays the same. Aerobic capacity/fatigueresistance can be increased in fast-twitchmuscles. (Fast-twitch fatigable becomeintermediate).

• Fibers also differ in: Myoglobin content (oxygensupply), Vascularization and Myosin ATPaseactivity.

• Ratio of fast to slow fibers varies amongindividuals.

• Gastrocnemius muscles of runners for example:Sprinters have more fast twitch fibers, longdistance runners have more slow twitch fibers.

Cardiac Muscle• Striated, but differs from skeletal muscle in the

following ways:1.2.3. Cells connected by arrays of ______________

called "intercalated discs." Contract as a unit -- a"functional syncytium."

4. Arrangement of sarcoplasmic reticulum andtransverse tubules is different.

5. Strictly _____________________.6. Autorhythmic (has automaticity)

Smooth Muscle• Typically associated with "viscera" and

"involuntary" systems (circulatory, respiratory,digestive, urinary, reproductive andintegumentary).

1. __________________. Actin and myosin havediffuse organization.

2. Spindle-shaped cells with ________,____________ nucleus.

3. Actin is anchored at "dense bodies" scatteredalong the sarcolemma. Dense bodies linkadjacent cells.

4. When the muscle contracts, it may twist orcorkscrew as it shortens.

5. _______________ is calcium binding protein(rather than troponin).

6. Little internal stores of calcium -- most calciumenters from outside of cell.

7. Functions over large range of muscle lengths.8. Motor neuron connections are variable

(____________ and ____________subtypes).9. Sensitive to a number of hormones and

neurotransmitters.

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Muscular Diseases• Muscular Dystrophy:1. Group of diseases - not a single disease2. Progressive skeletal muscle degeneration and increase

in fat and connective tissue.3. Generally begins in childhood.4. Gene Therapy for some forms of MD has begun.

• ____________________ Protein called "dystrophin" iseither lacking or defective. Dystrophin helps organize thestructure of the muscle fiber.

• ________________Muscular Dystrophy is a relateddisease in which dystrophin is present in low amounts.

Dystrophin & MuscularDystrophy

Dystrophin is located atperiphery of muscle cells

Duchenne’s MDNo Dystrophin

• Myasthenia Gravis:• Fatigue is rapid.• Antibody attack on ______________

_________________________• More common in women than men (Note:

autoimmune diseases are generally morecommon in women than men)

• Usually develops in middle age.

• Botulism: Botulinum toxin comes fromClostridium botulinum, a soil bacterium. Thetoxin inhibits the release of ACh from motornerve terminals, causing _________________paralysis.

• Tetanus or Lockjaw: Severe muscle spasmsfrom toxin produced by the bacteriumClostridium tetani. Not a direct muscle effect.The toxin blocks inhibitory neurotransmitters in____________________, so motor neurons areinhibited less.

• Causes ____________________paralysis.