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MUSCULAR SYSTEM
CHAPTER 10 THE MUSCULAR SYSTEM AND HOMEOSTASIS
IN THIS CHAPTER, YOU WILL LEARN:
• THERE ARE THREE TYPES OF MUSCLE TISSUE.
• SKELETAL MUSCLE PRODUCES BODY MOVEMENT, MAINTAINS
BODY TEMPERATURE, AND PROVIDES SUPPORT FOR THE BODY.
• MUSCLE FIBRES ARE FILLED WITH MYOFIBRILS THAT HOUSE THIN
(ACTIN) AND THICK (MYOSIN) CONTRACTILE PROTEIN
MYOFILAMENTS.
• ACTIN AND MYOSIN SLIDE PAST EACH OTHER DURING A MUSCLE
CONTRACTION.
THE MUSCULAR SYSTEM & HOMEOSTASIS
IN THIS CHAPTER, YOU WILL LEARN:
• CREATINE PHOSPHATE, FERMENTATION, AND AEROBIC CELLULAR RESPIRATION PROVIDE
ENERGY FOR MUSCLE CONTRACTIONS.
• THREE TYPES OF SKELETAL MUSCLE ARE FOUND IN DIFFERENT PARTS OF THE BODY.
• MUSCLES ATROPHY WITH INADEQUATE STIMULATION AND CAN HYPERTROPHY WITH
APPROPRIATE REPEATED STIMULATION.
• THE MUSCULAR SYSTEM WORKS WITH OTHER BODY SYSTEMS TO MAINTAIN
HOMEOSTASIS.
MOVEMENT AND MUSCLE TISSUE
IN THIS SECTION, YOU WILL:
• OBSERVE & COMPARE THE 3 TYPES OF MUSCLE TISSUE
• DESCRIBE THE ACTION OF ACTIN & MYOSIN IN MUSCLE CONTRACTION & HEAT PRODUCTION
• IDENTIFY SOURCES OF ENERGY FOR MUSCLE CONTRACTION
THREE TYPES OF MUSCLES
MUSCLE CELLS
THREE TYPES OF MUSCLES
SMOOTH MUSCLE
• INVOLUNTARY
• LONG CELLS WITH TAPERED ENDS
• MONONUCLEATE
• SLOW CONTACTING – DOES NOT FATIGUE EASILY
• FOUND IN CERTAIN BLOOD VESSELS, IRIS OF
THE EYE, DIGESTIVE SYSTEM (INTESTINE)
THREE TYPES OF MUSCLES
CARDIAC MUSCLE
• UNIQUE TO THE HEART
• STRIATED & BRANCHED
• MONONUCLEATE
• INVOLUNTARY WITH INNATE
ABILITY TO BEAT
THREE TYPES OF MUSCLES
• SKELETAL MUSCLE
• LONG POLYNUCLEATE CELLS (FIBRES)
• CONTRACTION IS VOLUNTARY
(35% ♀ MASS
42% ♂ MASS)
• TUBULAR AND STRIATED
IDENTIFY THE MUSCLE TYPE
Skeletal Muscle
Smooth
Muscle
Cardiac Muscle
FUNCTIONS OF SKELETAL MUSCLES
• SUPPORT – ALLOW US TO STAND
AND REMAIN UPRIGHT
• MOVE BONES – ALLOW US TO
MOVE AND HAVE FACIAL
EXPRESSION
• HELP MAINTAIN BODY TEMP –
RELEASE LARGE AMOUNTS OF HEAT
• HELP PROTECT ORGANS AND
STABILIZE JOINTS
COOPERATION OF SKELETAL MUSCLE
• WHEN MUSCLES CONTRACT THEY SHORTEN
• THEY CAN ONLY PULL
• BECAUSE OF THIS MUSCLES MUST WORK TOGETHER TO
BEND JOINTS (WORK IN PAIRS - ANTAGONISTIC MUSCLES )
• EXAMPLE: BICEP AND TRICEP
MUSCLE FUNCTION
• MUSCLES ARE ONLY CAPABLE
OF CONTRACTING THUS MUST
OCCUR IN PAIRS
MUSCLE STRUCTURE
• MUSCLES -> BUNDLES OF MUSCLE FIBRES ->
BUNDLES OF MYOFIBRILS ->MYOFIBRILS ARE MADE OF MYOFILAMENTS (ACTIN &
MYOSIN)
Muscle Fibre
Myosin
Actin
Muscle
Muscle Fibre Bundle
Myofibril
Myofilaments
MUSCLE
↓
MUSCLE-FIBRE BUNDLE
↓
MUSCLE FIBRE
↓
MYOFIBRILS
↓
MYOFILAMENTS
MUSCLE STRUCTURE
• BLOOD VESSELS & NERVES RUN BETWEEN THE FIBRES BUNDLES
• MUSCLE CELLS CONTAIN ORGANELLES COMMON TO OTHER
CELLS AND MANY MITOCHONDRIA
• NOTE:
CELL MEMBRANE = SARCOLEMMA
CYTOPLASM = SARCOPLASM
HEMOGLOBIN ≈ MYOGLOBIN
COMPONENTS OF SKELETAL MUSCLE FIBRES
Component
Description
Function
Muscle fibre
single muscle cell
responsible for muscle contractions
myoglobin
O2-binding pigment in a skeletal muscle
fibre
stores oxygen for use during muscle contractions
sarcolemma
membrane of a muscle fibre
surrounds the muscle fibre and regulates the
entry and exit of materials
sarcoplasm
cytoplasm of a muscle fibre
site of metabolic processes for normal cell
activities; contains myoglobin and glycogen
(which stores energy for muscle contractions)
COMPONENTS OF SKELETAL MUSCLE FIBRES
Component
Description
Function
sarcoplasmic
reticulum
smooth endoplasmic reticulum in a muscle fibre
stores calcium ions needed for muscle
contractions
Myofibrils
organized bundles of myofilaments; cylindrical
structures, as long as the muscle fibre itself
contain myofilaments that are
responsible for muscle contractions
thick filament
fine myofilament composed of bundles of protein called binds to actin and causes muscle
myosin (about 11 nm in diameter)
contractions
thin filament
fine myofilament composed of strands of protein called binds to myosin and causes muscle
actin (about 5 nm in diameter)
contractions
MUSCLE CONTRACTIONS
• INVOLVE THE ACTIONS OF TWO TYPES OF MYOFILAMENTS
• ACTIN MYOFILAMENT
• THIN
• HAVE TWO STRANDS OF ACTIN MOLECULES THAT WRAP AROUND EACH OTHER
• MYOSIN FILAMENT
• THICK
• TWO STRANDS OF PROTEIN MOLECULES WOUND AROUND EACH OTHER
• 10X LONGER THAN ACTIN AND A DIFFERENT SHAPE
HOW MYOFILAMENTS CONTRACT
• WHEN A MYOFILAMENT CONTRACTS THE HEADS OF MYOSIN
MOVE FIRST
• THESE HEADS ARE ATTACHED TO ACTIN MYOFILAMENTS
• HEAD BENDS BACK AND INWARD PULLING THE ACTIN
MYOFILAMENT
• REQUIRES ATP TO WORK
• PART OF THE SLIDING FILAMENT MODEL
•
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ROLE OF CALCIUM
• WHEN AT REST MYOSIN HEADS ARE NOT BOUND TO
ACTIN BECAUSE THEY ARE BLOCKED BY TROPOMYOSIN
• CALCIUM IS NEEDED TO MOVE THE TROPOMYOSIN
• CALCIUM AND TROPONIN BIND TO MAKE A COMPLEX
WHICH BINDS TO TROPOMYOSIN, MOVING IT OUT OF
THE WAY
•
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ON.SWF
ENERGY FOR MUSCLE CONTRACTION
• CREATINE PHOSPHATE (AKA PHOSPHOCREATINE)(CF. ATP)
• ANAEROBICALLY DONATES A PHOSPHATE GROUP TO ADP TO FORM ATP
DURING INITIAL INTENSE MUSCULAR EFFORT (SIMILAR NEURONAL
FUNCTION IN THE BRAIN)
Creatine phosphate builds up and is
stored in resting muscle. For the muscle to
contract, it needs to acquire ATP. (A)
When the muscle starts contracting, it
breaks down stored creatine phosphate.
This generates some ATP that is used
immediately. (B) To continue contracting,
the muscle carries out aerobic cellular
respiration as long as oxygen is
available. When the oxygen has been
used up, the muscle can carry out
fermentation for a limited period of
time. Fermentation results in only a small
amount of ATP compared with the
amount produced by aerobic cellular
respiration, and lactate builds up. Once
the muscle resumes resting (purple box),
creatine phosphate builds up again.
ENERGY FOR MUSCLE CONTRACTION
• AEROBIC RESPIRATION
• PROVIDES ATP ENERGY AS O2 IS AVAILABLE
• OCCURS IN MITOCHONDRIA
• MYOGLOBIN (CF. HEMOGLOBIN) IN THE MUSCLES STORES O2 TO BE
USED BY THE MUSCLE WHEN ACTIVITY BEGINS
ENERGY FOR MUSCLE CONTRACTION
• ANAEROBIC RESPIRATION
• SMALL AMOUNTS OF ATP PRODUCING LACTIC ACID
• CRAMPING & FATIGUE AFTER 2-3 MINS
• LACTIC ACID IS METABOLIZED BACK TO PYRUVATE
OXYGEN DEBT
• MUSCLES CAN FUNCTION WITH AN O2 DEBT MORE THAN
OTHER TISSUES
• BENEFITS OF AEROBIC TRAINING:
• INCREASED ABILITY OF CARDIOVASCULAR SYSTEM TO DELIVER O2
• INCREASED MITOCHONDRIA TO PROCESS O2
ISOMETRIC & ISOTONIC CONTRACTION
• ISOMETRIC
• MUSCLE VS. MUSCLE
• CAN RAPIDLY INCREASE MUSCLE
SIZE & STRENGTH
• ISOTONIC
• INVOLVES MOVEMENT
BODY POSTURE
• MANY OF THE MUSCLES OF THE BODY
EMPLOY ISOMETRIC CONTRACTIONS TO
SUPPORT THE BODY OR SOME PART OF
IT (EXAMPLE: HEAD SUPPORT)
MUSCLE TONE
• IS THE RESULT OF SUSTAINED CONTRACTIONS OF DIFFERENT PARTS OF A
MUSCLE
(GOOD MUSCLE TONE – MUSCLE ALWAYS UNDER A SMALL AMOUNT OF
TENSION AND READY FOR ACTION)
TENDONS & LIGAMENTS
• TENDONS ATTACH MUSCLE TO BONE
• LIGAMENTS ATTACH BONE TO BONE
MUSCLE TWITCH
• INDIVIDUAL MUSCLE CELLS CONTRACT FULLY OR NOT AT ALL (ALL-ORNONE RESPONSE)
• HEAVY LOADS USE MORE CELLS
• LIGHT LOADS USE LESS CELLS
SLOW TWITCH FIBERS
• SLOW TWITCH FIBERS ARE USED FOR JOGGING AND BIKING
• CONTRACT SLOWLY AND RESIST FATIGUE
• PRODUCE MOST OF THEIR ENERGY AEROBICALLY (WITH
OXYGEN)
• THEY ARE DARK IN COLOR BECAUSE THEY HAVE MANY
MITOCHONDRIA AND MYOGLOBLIN (RESPIRATORY PIGMENT)
THEY ALSO HAVE MORE CAPILLARY BEDS TO BE CONTINUALLY
SUPPLIED WITH OXYGEN.
FAST TWITCH FIBERS
• FAST TWITCH FIBERS RE USED IN SPRINTING AND WEIGHT
LIFTING
• THEY GENERATE POWER QUICKLY BUT CAN FATIGUE
QUICKLY
• THEY ARE RICH IN GLYCOGEN (GLUCOSE) BECAUSE THEY
DEPEND ON ANAEROBICALLY (NO OXYGEN) PRODUCED
ENERGY
• THEY ARE LACKING MITOCHONDRIA AND MYOGLOBIN
(OXYGEN)
DIFFERENT TYPES OF MUSCLE FIBRES
• INTERMEDIATE-TWITCH (TYPE III)
• FAST TWITCH WITH HIGH AEROBIC CAPACITY
• ENDURANCE TRAINING CAN INCREASE PROPORTION OF
THESE FIBERS IN A MUSCLE
• GENETIC COMPONENT
DIFFERENT TYPES OF MUSCLE FIBRES
• SKELETAL MUSCLES HAVE DIFFERENT PROPORTIONS OF FAST-TWITCH
AND SLOW-TWITCH FIBRES. THUS, THE FORCE AND RESPONSE TIMES OF
THEIR CONTRACTIONS DIFFER.
MYOGRAMS
These graphs show the force of muscle
contraction with time. (A) A simple
muscle twitch has three periods: latent,
contraction, and relaxation. (B) When
a muscle is not allowed to relax
completely between stimuli, the
contraction gradually increases in
intensity until it reaches a maximum,
which is sustained until the muscle
fatigues.
MUSCLES, HEALTH, AND HOMEOSTASIS
IN THIS SECTION, YOU WILL:
• EXPLAIN HOW THE SKELETAL MUSCLES OF THE MOTOR SYSTEM
SUPPORT OTHER BODY SYSTEMS TO MAINTAIN HOMEOSTASIS
• IDENTIFY CONDITIONS THAT IMPAIR THE HEALTHY FUNCTIONING OF
MUSCLES AND TECHNOLOGIES THAT ARE USED TO TREAT OR PREVENT
THESE CONDITIONS
• DESCRIBE THE BENEFITS OF EXERCISE FOR MAINTAINING THE HEALTHY
STRUCTURE AND FUNCTIONING OF MUSCLES
MUSCLE ATROPHY
• UNUSED MUSCLES WILL LOSE SIZE, TONE
AND POWER
• INITIALLY REVERSIBLE BUT MAY BECOME
PERMANENT
Fig. 10.10
MUSCLE HYPERTROPHY
• EXERCISE INDUCED INCREASE IN MUSCLE MASS
• MUSCLE FIBRES GET LARGER (NOT MORE)
• MYOFIBRILS GET THICKER & SPLIT
BENEFITS OF TRAINING
• MUSCLES
• STAY AEROBIC LONGER
• HAVE INCREASED BLOOD SUPPLY
• BETTER GLYCOGEN STORAGE
MUSCLES & HOMEOSTASIS
• MUSCLE CONTRACTION PRODUCES HEAT -> THERMAL
HOMEOSTASIS
• CARDIAC & LYMPHATIC SYSTEMS RELY ON WELL FUNCTIONING
MUSCLES
• SUPPORT OF INTERNAL ORGANS & MANY OTHER ACTIVITIES
ARE SUPPORTED BY THE MUSCULAR SYSTEM
DISORDERS OF THE MUSCULAR SYSTEM
• MUSCULAR DYSTROPHY
• HEREDITARY CONDITION
• SKELETAL MUSCLES DEGENERATE
AND ARE REPLACED BY FATTY AND
FIBROUS TISSUE
• POOR BLOOD CIRCULATION ->
ACCELERATED MUSCLE
DEGENERATION
DISORDERS OF THE MUSCULAR SYSTEM
• BOTULISM (C. BOTULINUM)
• POTENTIALLY FATAL MUSCULAR PARALYSIS
• TOXIN PRODUCED BY BACTERIA PREVENTS THE RELEASE OF A ACETYLCHOLINE BY
CELLS OF THE NERVOUS SYSTEM -> PARALYSIS
ASIDE: BOTOX
• BOTOX® = TRADE NAME FOR BOTULINUM TOXIN A
• WHY ANYONE WOULD WANT TO HAVE A BOTULINUM TOXIN
INJECTION?
• ANSWER: IF AN AREA OF THE BODY CAN'T MOVE, IT CAN'T WRINKLE!
Hillary Clinton: before and after Botox
DISORDERS OF THE MUSCULAR SYSTEM
• CRAMPS
• PAINFUL MUSCLE SPASMS TRIGGERED BY
STRENUOUS EXERCISE, EXTREME COLD,
DEHYDRATION, SALT (ELECTROLYTE)
IMBALANCE, LOW BLOOD GLUCOSE, OR
REDUCED BLOOD FLOW
DISORDERS OF THE MUSCULAR SYSTEM
• CONTRACTURE
• ABNORMAL MUSCLE SHORTENING (NOT CAUSED BY NERVE
STIMULATION)
• CAN RESULT FROM INABILITY TO REMOVE CALCIUM IONS FROM THE
SARCOPLASM OR FROM THE CONTRACTION OF SCAR TISSUE
(EXAMPLE: SEVERE BURNS)
DISORDERS OF THE MUSCULAR SYSTEM
• FIBROMYALGIA
• CHRONIC MUSCULAR PAIN AND TENDERNESS OFTEN
ASSOCIATED WITH FATIGUE AND SLEEP DISTURBANCES
• CAN BE CAUSED BY INFECTIOUS DISEASES, PHYSICAL
OR EMOTIONAL TRAUMA, OR MEDICATIONS
• CONSIDERED A CONTROVERSIAL DIAGNOSIS, DUE TO LACKING
SCIENTIFIC CONSENSUS TO ITS CAUSE
• 9:1 (♀:♂)
DISORDERS OF THE MUSCULAR SYSTEM
• CRUSH SYNDROME
• SHOCK-LIKE STATE FOLLOWING MASSIVE CRUSHING OF THE MUSCLES (EG.
COLLAPSE OF A BUILDING OR A TRAFFIC ACCIDENT)
• ASSOCIATED WITH HIGH FEVER, HEART IRREGULARITIES (CAUSED BY K+ RELEASED
FROM THE MUSCLES) , AND KIDNEY FAILURE
(CAUSED BY BLOCKAGE OF THE RENAL TUBULES
WITH MYOGLOBIN RELEASED BY THE TRAUMATIZED
MUSCLES)
DISORDERS OF THE MUSCULAR SYSTEM
• DELAYED ONSET MUSCLE SORENESS
• PAIN & STIFFNESS FELT AFTER NOVEL STRENUOUS EXERCISE (BEGINS 8-24 HOURS
AFTER EXERCISE, PEAKS 24-72 HOURS AFTER EXERCISE AND SUBSIDES OVER THE NEXT 5-7 DAYS)
• ASSOCIATED WITH TRAUMA TO THE MUSCLES, DISRUPTIONS IN THE MYOFIBRILS
& SARCOLEMMA, AND INCREASED LEVELS OF BLOOD MYOGLOBIN AND MUSCLEFIBRE ENZYMES
DISORDERS OF THE MUSCULAR SYSTEM
• MYOSITIS
• MUSCLE INFLAMMATION AND WEAKNESS RESULTING
FROM INFECTION OR AN AUTOIMMUNE DISEASE
CHAPTER REVIEW
• WHAT BODY SYSTEMS DO MUSCLES SUPPORT?
• HOW DO MUSCLES SUPPORT THESE SYSTEMS?
• EXPLAIN THE DIFFERENCE IN MUSCLE COMPOSITION BETWEEN
A PERSON WHO IS NOT ACTIVE VERSUS SOMEONE WHO IS
VERY ACTIVE?
• DESCRIBE TWO DIFFERENT TYPES OF MUSCLE INJURIES.
RECOMMEND APPROPRIATE TREATMENTS FOR EACH.
• EXPLAIN HOW MUSCLES CHANGE WITH STRENGTH TRAINING?
WITH ENDURANCE TRAINING? WITH INACTIVITY?
CONCEPT ORGANIZER
CHAPTER SUMMARY
• ALL MUSCLES DO THEIR WORK BY CONTRACTING. RELAXATION IS
THE PASSIVE STATE OF A MUSCLE. THERE ARE THREE TYPES OF
MUSCLE CELLS: SKELETAL, SMOOTH, AND CARDIAC.
• SKELETAL MUSCLE CELLS ARE ATTACHED TO THE BONES OF THE
SKELETON, HAVE MANY NUCLEI, ARE STRIATED AND TUBULAR, AND
CONTRACT VOLUNTARILY.
• SMOOTH MUSCLE CELLS ARE FOUND IN THE WALLS OF INTERNAL
ORGANS, HAVE ONE NUCLEUS, ARE NOT STRIATED, AND
CONTRACT INVOLUNTARILY.
• CARDIAC MUSCLE CELLS FORM THE WALLS OF THE HEART; HAVE
ONE NUCLEUS, ARE STRIATED, TUBULAR, AND BRANCHED; AND
CONTRACT INVOLUNTARILY.
CHAPTER SUMMARY
• THE FACT THAT SKELETAL MUSCLES CAN ONLY EITHER CONTRACT OR RELAX MEANS THEY
CAN PULL BUT NOT PUSH. THEREFORE, THEY MUST WORK IN PAIRS TO MOVE ANY PART OF
THE BODY—A RELAXED MUSCLE IS ONLY LENGTHENED WHEN THE OPPOSING MUSCLE
CONTRACTS TO STRETCH IT. SKELETAL MUSCLE CONTRACTIONS ARE EXPLAINED BY THE
SLIDING FILAMENT MODEL.
• SKELETAL MUSCLE PRODUCES HEAT AS WELL AS MOVEMENT AND ALSO SUPPORTS AND
PADS THE BODY.
• EACH MUSCLE IS MADE UP OF CLUSTERS OF BUNDLES OF MUSCLE FIBRES, WHICH ENCLOSE
BUNDLES OF MYOFIBRILS CONTAINING THIN MYOFILAMENTS OF ACTIN AND THICK
MYOFILAMENTS OF MYOSIN.
• BLOOD VESSELS SUPPLY NUTRIENTS AND OXYGEN TO THE FIBRE BUNDLES AND REMOVE
WASTES. THE OXYGEN FUELS THE CELLULAR RESPIRATION THAT SUPPLIES MOST OF THE
ENERGY MUSCLES USE.
CHAPTER SUMMARY
• NERVES TRIGGER AND CONTROL MUSCLE CONTRACTIONS,
WHICH LAST FOR ONLY A FRACTION OF SECOND IN EACH
MUSCLE FIBRE.
• IT IS THE WAVE OF SUCCESSIVE CONTRACTIONS, OR
TWITCHES, THAT RESULT IN A MUSCLE CONTRACTION.
• SKELETAL MUSCLES HAVE BOTH SLOW AND FAST-TWITCH
FIBRES THAT ARE GOOD FOR EITHER ENDURANCE (SLOWTWITCH) OR INTENSE (FAST-TWITCH) ACTIVITIES.
• USING THE SKELETAL MUSCLES IS THE ONLY WAY TO
MAINTAIN AND BUILD THEIR FUNCTION.