Chapter 7 – Muscle System Notes

7.1 FUNCTIONS AND TYPES OF MUSCLES

Smooth Muscle -Cardiac Muscle - Skeletal Muscle

*Connective Tissue Coverings1.Endomysium- connective tissue that covers each muscle fiber;carries nerve and blood vessels to the fibers2.Fascicles-group of muscle fibers

a.Perimysium-sheath of connective tissue around fascicle3.Epimysium- connective tissue layer that covers the muscle; blends with deep fascia4.Deep fascia-layer of fibrous tissue that surrounds a set of muscles and separates muscles from one another5.Superficial fascia (hypodermis)- contains adipose tissue6.Tendon- collagen fibers of epimysium connect as strong and fibrous tissue to bone

a)Epimysium merges with periosteum of bone

*Functions of Skeletal Muscles1.Supports the body2.Makes bone and other parts move3.Help maintains a constant body temperature4.Contractions assist fluid movement in circulatory and lymphatic vessels5.Protect bone and internal organs, stabilize joints

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Skeletal Muscle Cross-Section

Muscle fibers are made of myofibrils

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7.2 MICROSCOPIC ANATOMY AND CONTRACTION OF SKELETAL MUSCLE

Muscle FiberMyo- and sarco- mean muscle1. Sarcolemma- plasma membrane of a muscle cell2. Sarcoplasm- cytoplasm of muscle cell3. Sarcoplastic reticulum- endoplasmic reticulum of a muscle cell; store calcium4. T-tubules (transverse)- pass through cell but do not connect with sarcoplasmic reticulum5. Myofibrils- bundles of myofilaments

a. About 1 micrometer in diameterb. Part of the muscle fiber that contractsc. Located in the sarcoplasm between the myofibrils

1. Mitochondria to cause muscle contraction2. Glycogen for stored energy of muscle contraction3. Myoglobin, red pigment, binds oxygen needed for muscle contractions

Skeletal Muscle Cell (Fiber) Myofibrils

*Myofibrils and Sarcomeres

-Myofibril-cylindrical in shape and run the length of a muscle fiber; made of many sarcomeres-Sarcomere- horizontal segment of the myofibril that extends from two Z lines1. Z-lines-dark vertical lines that mark the end of a sarcomere2. Two types of myofilaments make up a sarcomere longitudinally

a. Thick Filament-made a single protein myosinb. Thin Filament- made up of three globular proteins: actin, tropomyosin, and troponin

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3.Sections of a sarcomere (transverse section)a. A band- dark region in the center of sarcomere where thick and thin filaments overlapb. I band- light colored region where only the thin filaments is attached to the Z linec. H zone- light colored region where only the myosin filament is present

Myofibril Sarcomeres

*Myofilaments Protein Composition-Thick filaments1. Myosin- double protein strand shaped like a golf club. Heads are slanted away from middle of sarcomere towards the thin filament.-Thin filaments1. Actin- two protein strands twisted around each other- like a beaded necklace2. Tropomyosin- double protein strand that coils over actin strands3. Troponin occurs at intervals over the tropomyosin strand

*Sliding Filaments1. Motor nerves send chemical signals down T-tubules to the sarcoplasmic reticulum2. The sarcoplasmic reticulum releases calcium3. Muscle fibers contract as the sarcomere within the myofibrils shorten4. As sarcomeres shorten, the thin filaments (actin) slide past thick filaments (myosin)5. I band shortens and the H zone disappears. 6. Sliding filament theory of muscle contractions- movement of actin filaments in relation to myosin filaments

Skeletal Muscle Contraction1. Muscle fibers are stimulated to contract from a motor neuron2. Axon of one motor neuron has several branches that can stimulate a few to several muscle fibers 3. Neuromuscular junction –consists of the motor nerve axon and the muscle fibers it signals 4. Synaptic cleft- small gap that separates the axon terminal from the sarcolemma

-Neuromuscular Junction1. Axon terminals contain synaptic vesicles that contain acetylcholine (Ach) an neurotransmitter2. Nerve signals cause the synaptic vesicles to be released into the synaptic cleft3. Ach binds quickly to the sarcolemma (plasma membrane) of the muscle fiber4. When the electrical signal is strong enough, the signal threshold (activate the entire cell) is met.5. Then a signal is sent down the T tubules to the sarcoplasmic reticulum where calcium is released.6. Calcium causes the filaments in the sarcomeres to slide past one another- resulting in a contraction

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Neuromuscular Junction

Skeletal Muscle Contraction

The Role of Actin and Myosin

-Thin Filament Preparation: actin, tropomyosin, and troponin1. Actin is composed of two twisted rows2. Tropomyosin wind around each actin filament, with troponin at intervals along the tropomyosin3. Myosin binding sites are found on each actin molecule; when muscles are relaxed these sites are covered by tropomyosin4. Calcium ions (Ca2+) ions released from sarcoplasmic reticulum bind with troponin a. Calcium binds to troponin - then the tropomyosin heads shift and expose myosin binding sites

-Thick Filament Contraction: myosinTwo binding sites: 1. ATP binding site where ATPase enzymes splits ATP → ADP + P2. Myosin binding site is then prepared to bind to actin

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-Steps of muscle contraction1. ATP is split when myosin head is unattached2. ADP + P are bound to myosin as cross-bridge forms between the myosin head and actin.3. Upon ADP+P release, power stroke occurs: myosin head bends and pulls actin

a.Power stroke- pulls thin filament to middle of sarcomere4. Binding of a fresh ATP causes myosin head to detach and to return to the resting position

ATP two roles1. Energize myosin for the power stroke2. To break the link between myosin and actin.

Contraction of Smooth Muscle1. Uninucleate, cylindrical cells with pointed ends2. Contain thick and thin filaments; thin filaments are anchored directly to the sarcolemma or dense bodies3. When smooth muscle contracts, it contracts in all direction changing the cylindrical shape into an oval4. Smooth muscles contraction occur slowly, but can last for long periods without fatigue

Energy for Muscle ContractionATP found in muscles only last a few seconds. Then muscle must manufacture more ATP.

-Creatine Phosphate Breakdown1. Creatine phosphate is high energy molecule found when the muscle is resting2. It supplies the phosphate necessary to transform ADP into ATP3. Useful for 8 seconds of strenuous activity4. Creatine phosphate is recharged when the muscle is resting and phosphates from ATP are used

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-Cellular Respiration1. Both fatty acids and glucose from glycogen can be used to make ATP when oxygen is present2. Myoglobin- greater attraction of oxygen than hemoglobin- allows for oxygen available to muscle    mitochondria3. Carbon dioxide and water are removed as waste by-products4. Used for long-term aerobic activity

-Fermentation1. Supplies ATP without oxygen use2. Anaerobic process that occurs in sarcoplasm3. Glucose is broken down into lactate (lactic acid)--> large amounts make muscle acidic, decrease function4. Useful for short bursts of exercise5. Cramping due to lack of ATP- needed to pump calcium back into sarcoplasmic reticulum and to break linkage between myosin and actin so the muscle can relax.

Oxygen Debt7

Oxygen debt- occurs when muscles use fermentation to provide energy1. Replenishing creatine phosphate and removing lactic acid help repay oxygen debt2. Lactic acid → pyruvate → used then by mitochondria for energy or sent to liver to make glycogen

a.Once liver glycogen stores are exhausted (marathon runner) takes two days to replenish with carbohydrates

3. People who train have more mitochondria in their muscles.

7.3 MUSCLE RESPONSESIn the Laboratory-Muscle fibers1. All-or-none law- a muscle fiber contracts completely or not at all.2. Threshold- the amount of energy required to elicit a muscle contraction3. Muscle fiber contracts all or nothing, while a whole muscle shows degrees of contraction4. Myogram- muscle stimulated electrically and a graph of the force of a muscle contraction is recorded 5. Muscle twitch- a single contraction only lasts for a second.

a. Latent period- time between stimulation and initiationb. Contraction period- when muscle shortens- calcium present from sarcoplasmic reticulumc. Relaxation period- when muscle returns to its former length- calcium returns to reticulum

Myogram showing muscle twitch Myogram showing twitches, summation, tetanic contraction

-Muscle Groups1. Summation-series of rapid stimuli are given and muscle responds without relaxing completely2. Tetanic contraction- maximal sustained contraction (straight line on myogram)3. Fatigue- muscle relaxes even though stimulation continues

a. ATP depletion results in running out of energyb. Lactic acid production lowers pH; inhibits muscle functionc. Motor nerves run out of acetylcholine

In the Body

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Motor unit- a nerve fiber with all of the muscle fibers that it innervates1.Obeys the all-or none contraction2.Number of muscle fibers innervated by a nerve fiber differs by degree of fine motor control 3.Recruitment- as the intensity of the nervous stimulation increases→ more and more motor units are activated

a. Results in stronger and stronger contractions4.Tone- while some muscle fibers are relaxed, others are contracted; important for posture

-Athletics and Muscle Contraction+Exercise and size of muscle1.Atrophy-muscle fibers replaced by fat and fibrous tissue from little or no use of muscle

a. Result from a cast or loss of nerve innervationb. Long term atrophy may lead to contractures- body parts contracted in contorted positions

2.Hypertrophy-increase in muscle sizea.Forceful muscle contractions over long periods of time b. Myofibrils within the muscle fibers increase in size c. Muscle must contract to at least 75% maximum tension to stimulate growth

*Muscle Fiber TypesSome muscle fibers use different metabolic pathways more often than others for energy +Slow-twitch (Type I fibers)1. Aerobic2. Motor units with smaller number of fibers3. Endurance sports like long-distance running and swimming4. Tire only when fuel supply gone5. Have many mitochondria6. Dark color due to abundant presence of myoglobin7. Dense capillary beds for continuous blood supply8. Low maximum tension, develops slowly; are highly resistance to fatigue

+Intermediate-twitch (Type IIa fibers)1.Aerobic2. Supplied well with myoglobin and mitochondria3. Rich blood supply4. Fast aerobic fibers- contract quicker than slow twitch5. Moderate strength for shorter periods like walking, biking or jogging

+Fast-twitch muscle fibers (Type IIb fibers)1.Anaerobic2. Fewer capillaries and less blood supply3. Light in color because have fewer mitochondria and less myoglobin4. Provide explosive energy in sports like sprinting, weightlifting, pitching a baseball5. Develop maximum tension more rapidly and is greater6. Vulnerable to lactic acid build up and fatigue quickly

Rigor Mortis1. Means “stiffness of death” 2. Used by forensic pathologist to determine time of death- 8 hours full condition3. Dying muscle cells use up last of ATP and Calcium remains in muscle- results in contracted state4. Resolves in 24-36 hours after lysosome enzymes rupture and break myosin-actin bonds

Determining time of death

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Body Temperature Body Stiffness Time since deathWarm Not stiff Dead not more than 3 hoursWarm stiff Dead 3 to 8 hoursCold stiff Dead 8 hours to 36 hoursCold Not stiff Dead more than 36 hours

Comparison of Muscle Fiber Types

Body Types

Skeletal Muscles - Muscles and Movements (See colored drawings)10

Head

Facial Expression+Frontalis- raises eyebrows+Orbicularis oculi- close eyes+Orbicularis oris- closes and protrudes lips+Buccinator- compresses cheeks inward+Zygomaticus- raises corner of mouth

Mastication+Masseter-closes jaw+Temporalis- closes jaw

OtherOccipitalis-move the scalp back.

Neck

Move the Head+Sternocleidomastoid- flexes head and rotates head+Trapezius- extends head

Other+Platysma- depresses and wrinkles skin of lower face and mouth. aids forced depression of mandible

Shoulder, Chest, Abdomen (Anterior)

TrunkAbdominal Wall+External obliques-lateral rotation of trunk+Internal obliques- lateral rotation of trunk+Transverse abdominis-tenses abdominal wall+Rectus abdominis- flexes and rotates vertebrae

ShoulderMove Arm & Scapula+Pectoralis major- flexes, adducts, and medially rotates arm+Trapezius- adducts the scapula+Pectoralis minor- pulls the scapula anteriorly and inferiorly toward the ribs (abduction and depression respectively+Serratus anterior- elevates arm above horizontal+Deltoid- abducts arm horizontal

Shoulder and Back (Posterior)

Move Arm & Scapula+Deltoid- abducts arm horizontal+Latissimus dorsi- extends, adducts, and medially rotates armRotator Cuff (shape over the proximal humerus)- angular and rotational movements of the arm

+Supraspinatus-+Infraspinatus+Teres minor

+Teres major- medial rotator and adductor of the humerus+Levator Scapulae- lifts the scapula, pulls the entire scapula medially+Rhomboideus Major- adducts and rotates the shoulder+Trapezius- adducts the scapula

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Leg Muscle (Anterior)

Leg+Sartorius(longest muscle)-flexes leg+Tensor Fasciae Latae-abduct and medially rotate leg-Quadriceps- extends leg

+Rectus femoris+Vastus medalis+Vastus lateralis+Vastus intermedialis

Thigh+Sartorius-flexes, abducts and laterally rotates thigh+Adductor longus- adduct thigh+Gracilis- adduct thigh+Quadriceps(see names above)- helps in thigh flexion and steadies hip joint

Ankle and Foot+Tibialis- anterior- flexes foot upward “shin splints”+Gastrocnemius- pushes body forward during walking; plantar flexion and eversion of foot+Soleus- plantar flexion of the foot

Leg Muscles (Posterior)

LegHamstring Group- flexes and rotates leg medially

+Semitendinosus+Biceps femoris+Semimembranosus

Thigh+Gluteus medius- abducts thigh+Gluteus maximus (largest muscle)- extends thighHamstring group (see above)- extends the thigh

Ankle and Foot+Gastrocnemius- plantar flexion and eversion of foot+Soleus- plantar flexion of foot (points the toes)

Arm Muscles (Anterior)

Moves Forearm+Bicep brachii- flexes arm and forearm; supinates forearm+Brachialis- flexes forearm+Brachioradialis- flex forearm, pronation / supination

Moves Hand & Fingers+Flexor carpi radialis- move hand/wrist+Flexor carpi ulnaris- move hand/wrist+Palmaris longus- wrist flexion

Arm Muscle (Posterior)

Moves Forearm+Triceps brachii- extends forearm

Moves Hand & Fingers+Flexor carpi ulnaris- move hand/wrist+Extensor carpi ulnaris- move hand/wrist+Extensor carpi radialis- move hand/wrist+Extensor digitorum- moves fingers

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7.4 SKELETAL MUSCLES OF THE BODY- See colored drawingsBasic PrinciplesNaming Muscles

MEDICAL FOCUS- Benefits of Exercise

MEDICAL FOCUS- Muscular DIsorders and Neuromuscular Disease

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