MUSCLE ANATOMY AND PHYSIOLOGY

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MUSCLE ANATOMY AND PHYSIOLOGY

• MOVEMENT
• ALTERATION OF DIAMETERS
• PROPULSION OF MATERIALS
• EXCRETION OF MATERIALS
• MAINTENANCE OF BODY TEMPERATURE
• MAINTENANCE OF HOMEOSTASIS

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MUSCLE TYPES

• SKELETAL MUSCLE
• SMOOTH MUSCLE
• CARDIAC MUSCLE

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SKELETAL MUSCLE

• ATTACHES TO BONES OF SKELETON
• EXERT FORCES TO CAUSE MOVEMENT
• VOLUNTARY--NORMALLY UNDER CONSCIOUS CONTROL
• REGULATED BY SOMATIC NERVOUS SYSTEM
• STRIATED
• MULTIPLE, PERIPHERAL NUCLEI

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SMOOTH MUSCLE

• LACKS STRIATIONS
• IN WALLS OF HOLLOW ORGANS, TUBES
• CONTRACTION CONTROL MOVEMENT OF MATERIALS IN BODY
• INVOLUNTARY--NOT NORMALLY UNDER OUR CONTROL
• CONTROLLED BY AUTONOMIC NERVOUS SYSTEM, INTRINSIC
  FACTORS AND HORMONES

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CARDIAC MUSCLE

• SPECIALIZED MUSCLE
• FOUND ONLY IN HEART
• INVOLUNTARY
• CONTROLLED BY AUTONOMIC NERVOUS SYSTEM, INTRINSIC
  FACTORS, AND HORMONES
• STRIATED

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EMBRYONIC DEVELOPMENT OF MUSCLE
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SKELETAL MUSCLE

• HEAD OF EMBRYO DEVELOPS FROM GENERAL MESODERM
• LIMBS DEVELOP FROM MESODERMAL CONDENSATIONS
• SOME PROBABLY MIGRATE TO LIMBS FROM MYOTOMES

• EXCEPT FOR HEAD AND LIMBS --DEVELOP FROM SOMITES
• SOMITES MASSES OF MESODERMAL CELLS ALONG
  VERTEBRAE
• MYOTOMES DIFFERENTIATE TO MUSCLE CELLS

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SKELETAL MUSCLE

• MUSCLE FIBERS ARISE FROM MYOBLASTS
• INDIVIDUAL MYOBLASTS FUSE TO FORM MULTINUCLEATED
• AS MATURE FORMS EXTENSIVE MEMBRANE SYSTEM AND
  CONTRACTILE PROTEINS

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SKELETAL MUSCLE

• GENERALLY CANNOT UNDERGO MITOSIS
• HAVE SATELLITE CELLS --INACTIVE MYOBLASTS--THAT
  CAN DIVIDE
• MORE IN CHILDREN
• LOSE AS MUSCLE MATURES
• LESS THAN 1 IN MATURE MUSCLE

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SMOOTH MUSCLE

• DIGESTIVE TUBE AND BODY ORGANS
• MESODERM MIGRATES AND FORMS THIN LAYER
• DEVELOP INTO SMOOTH MUSCLE

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CARDIAC MUSCLE

• FORMATION SIMILAR TO SMOOTH
• MIGRATION OF MESODERM TO HEART TUBE
• HAS INTRINSIC CONTRACTION

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GROSS ANATOMY OF MUSCLE

• CONNECTIVE TISSUE COVERINGS
• ATTACHMENTS
• MUSCLE SHAPE

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CONNECTIVE TISSUE COVERINGS

• MUSCLE HAS MANY INDIVIDUAL MUSCLE FIBERS HELD
  TOGETHER BY FASCIA
• ENDOMYSIUM COVERS INDIVIDUAL MUSCLE FIBERS
• INDIVIDUAL FIBERS ARE BUNDLED INTO FASCICULI BY
  PERIMYSIUM
• WHOLE MUSCLE IS COVERED BY EPIMYSIUM

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SKELETAL MUSCLE ATTACHMENTS

• EXTENSIONS OF ENDOMYSIUM, PERIMYSIUM AND
  EPIMYSIUM ANCHOR MUSCLE
• CAN BLEND INTO TENDON WHICH IS CONTINUOUS WITH
  PERIOSTEUM OR PERICHONDRIUM
• SOME TENDONS SHORT -- SOME TENDONS LONGER THAN A
  FOOT
• BROAD FLAT THIN SHEETS ARE APONEUROSES

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SKELETAL MUSCLE ATTACHMENTS

• ORIGIN IS LESS MOVABLE END
• INSERTION IS MORE MOVABLE END
• BELLY IS IN BETWEEN
• MUSCLE ARISES FROM ORIGIN
• INSERTS INTO INSERTION
• ORIGIN GENERALLY BROADER THAN INSERTION

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SKELETAL MUSCLE SHAPES

• ARRANGEMENT OF MUSCLE FIBERS VARIES GREATLY
• MAY BE ARRANGED PARALLEL TO LONG AXIS
• GIVES MAXIMUM MOVEMENT BUT LITTLE POWER
• MAY INSERT DIAGONALLY INTO A TENDON
• PRODUCES LESS MOVEMENT BUT MORE POWER

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MICROSCOPIC ANATOMY OF SKELETAL MUSCLE
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COMPOSITION OF THE MYOFILAMENTS

• MULTINUCLEATE, 10 TO 100 MICRONS IN DIAMETER,
  MANY CENTIMETERS LONG FIBER HAS SEVERAL HUNDRED
  TO SEVERAL THOUSAND MYOFIBRILS
• ALTERNATE LIGHT AND DARK BANDS

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ISOTROPIC BANDS

• ALSO CALLED I BANDS OR LIGHT BANDS
• DENSE Z LINE OR Z DISC CROSSES CENTER
• Z LINES DIVIDE INTO SARCOMERES
• Z LINE CONTAINS ALPHA-ACTININ PROTEIN

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ANISOTROPIC BANDS

• LESS DENSE H ZONE IN CENTER
• H ZONE HAS M LINE

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TYPES OF MYOFILAMENTS

• THICK FILAMENTS
• THIN FILAMENTS

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MYOSIN--THICK FILAMENTS

• MADE OF SIX POLYPEPTIDE CHAINS
• TWO HEAVY CHAINS--FOUR LIGHT CHAINS
• LOOKS LIKE GOLF CLUBS WITH LONG HANDLES
• HAS ABOUT 200 MYOSIN MOLECULES
• CLUB PORTION CALLED CROSS BRIDGES

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THIN FILAMENTS

• OCCUPY I BAND AND PART OF A BAND
• ATTACH TO Z LINES
• MAKE HEXAGONAL ARRANGEMENT AROUND THICK FILAMENTS

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ACTIN, TROPONIN, AND TROPOMYOSIN--THIN FILAMENTS

• ACTIN HAS SUBUNITS OF GLOBULAR (G) ACTIN
• G ACTIN ARE HELD TOGETHER BY FILAMENTOUS F ACTIN
• TROPOMYOSIN LIKE END TO END ALONG SURFACE OF
  ACTIN
• EACH EXTENDS ALON ABOUT SEVEN G ACTIN UNITS
• TROPONIN ATTACHES TO BOTH ACTIN AND TROPOMYOSIN

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TRANSVERSE TUBULES

• TUBULAR INVAGINATIONS OF SARCOLEMMA
• EXTEND DEEPLY INTO SKELETAL MUSCLE FIBER
• IMPORTANT FOR TRANSMISSION OF ACTION POTENTIAL

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SARCOPLASMIC RETICULUM

• SIMILAR TO SMOOTH ENDOPLASMIC RETICULUM
• TERMINAL CISTERNAE LIE CLOSE TO TUBULES
• NEAR A AND I BANDS OF SARCOMERE
• THIS REGION IS CALLED A TRIAD
• CONTAINS HIGH LEVELS OF CA IONS
• IONS ARE BOUND TO CALSEQUESTRIN
• WHEN STIMULATED CALCIUM IONS ARE RELEASED AND
  CAUSE CONTRACTIONS

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SKELETAL MUSCLE CONTRACTION

• EXPERIMENTALLY ARE TWO TYPES OF CONTRACTIONS WE
  CAN SEE
• ISOTONIC
• ISOMETRIC
• IN REALITY BOTH OCCUR AND ARE HARD TO SEPARATE

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ISOMETRIC

• LENGTH OF MUSCLE STAYS CONSTANT
• DEVELOPS FORCE AND TENSION
• OCCUR WHEN LIFT OBJECTS TO HEAVY OR FIXED IN PLACE

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ISOTONIC

• MUSCLE SHORTENS UNDER A CONSTANT LOAD
• EVEN THOUGH NOT PURE --WALKING, RUNNING, LIFTING
  ARE CALLED ISOTONIC

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SKELETAL MUSCLE CONTRACTION

• OCCURS AT CELLULAR LEVEL
• MUST HAVE STIMULATION FROM NERVOUS SYSTEM
• INTERACTION BETWEEN ACTIN AND MYOSIN
• DEVELOP TENSION AND SHORTENS FIBERS

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NEUROMUSCULAR JUNCTION

• MOTOR NEURONS SUPPY INNERVATION
• SPECIALIZED JUNCTIONS --DO NOT TOUCH
• MOST SKELETAL MUSCLE FIBERS HAVE ONLY ONE
  NEUROMUSCULAR JUNCTION

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SKELETAL MUSCLE EXCITATION

• BRIEF INTERMITTENT ELECTRICAL IMPULSES CALLED
  ACTION POTENTIALS OR NERVE IMPULSES
• NERVE IMPULSE DOES NOT DIRECTLY STIMULATE
  SKELETAL MUSCLE FIBER
• MUST CROSS SYNAPTIC CLEFT
• ACETYLCHOLINE (ACh) CROSSES FROM NEURON TO
  SARCOLEMMA
• BINDS TO RECEPTORS AND CAUSES MEMBRANE
  PERMEABILITY TO INCREASE

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EXCITATION-CONTRACTION COUPLING

• PROPOGATED ACTION POTENTIAL CAUSES INTERACTIONS
  BETWEEN THICK AND THIN FILAMENTS
• ACTION POTENTIAL TRAVELS DOWN SARCOLEMMA INTO T
  TUBULES AND INTO CENTER OF MUSCLE FIBER
• TRIGGERS RELEASE OF CALCIUM IONS FROM TERMINAL
  CISTERNAE
• CALCIUM BINDS TO TROPONIN CAUSING INTERACTIONS
  BETWEEN THICK AND THIN FILAMENTS

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CONTRACTION MECHANISMS

• REQUIRED ENERGY FROM ATP
• ATP OCCUPIES BINDING SITE ON MYOSIN GLOBULAR HEAD
• MYOSIN HAS ENZYME ACTION
• SPLITS ATP TO ADP AND PHOSPHATE
• ADP AND PHOSPHATE STAY ATTACHED TO MYOSIN HEAD
• REACTION RELEASES ENERGY
• LEADS TO A HIGH ENERGY MYOSIN MOLECULE

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CONTRACTION MECHANISMS

• MYOSIN HEAD ALSO HAS BINDING SITE THAT COMBINES
  WITH COMPLEMENTARY SITE ON ACTIN
• HIGH ENERGY MYOSIN LIKES TO BIND TO ACTIN
• TROPOMYOSIN PREVENTS THIS IN RESTING MUSCLE
• STIMULATED MUSCLE RELEASES CA WHICH OPENS
  TROPONIN AND CAUSE TROPOMYOSIN TO MOVE OUT OF WAY

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CONTRACTILE MECHANISMS

• BINDING OF CALCIUM IONS TO TROPONIN WEAKENS LINK
  BETWEEN TROPONIN AND ACTIN
• THIS ALLOWS TROPOMYOSIN TO MOVE AWAY FROM ITS
  POSITION
• ALLOWS HIGH ENERGY MYOSINS TO BIND TO ACTIN

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CONTRACTION MECHANISMS
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CONTRACTION MECHANISMS

• INITIAL BINDING WEAK BETWEEN MYOSIN AND ACTIN
• BINDING CAUSES RELEASE OF PHOSPHATE BOUND TO
  MYOSIN
• RELEASE CAUSES MYOSIN TO BIND TIGHTLY TO ACTIN
• ENERGY IN MYOSIN RELEASED CAUSING MYOSIN HEAD TO
  MOVE
• MYOSIN HEAD SWIVELS TOWARD CENTER PULLING ON THIN
  FILAMENT

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CONTRACTION MECHANISMS

• ADP IS RELEASED FROM MYOSIN BUT MYOSIN IS STILL
  ATTACHED TO ACTIN
• ANOTHER ATP MOLECULE ATTACHES TO MYOSIN CAUSING
  RELEASE OF ACTIN
• MYOSIN SPLITS ATP INTO ADP AND PHOSPHATE
• PRODUCING HIGH ENERGY MYOSIN THAT ATTACHES TO
  ACTIN
• AND SO ON

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CONTRACTION MECHANISMS

• DURING CONTRACTION ABOUT 50 PERCENT OF MYOSIN
  HEADS ARE ATTACHED TO ACTIN SUBUNITS
• REST ARE AT INTERMEDIATE STAGES
• TWO HEADS OF MYOSIN MOLECULES ARE THOUGHT TO
  CYCLE SEPARATELY

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CONTRACTION MECHANISMS

• FORCE OF MYOSIN HEADS PULLING ON ACTIN FILAMENTS
  IS TRANSFERED TO PLASMA MEMBRANE AND EVENTUALLY
  TO LOAD
• MUST OVERCOME RESISTANCE OF LOAD
• IF DO WILL PULL Z LINES CLOSER TOGETHER AND
  SHORTEN MUSCLE FIBER

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CONTRACTILE REGULATION
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WHY DONT INTERACTIONS BETWEEN THICK AND THIN
FILAMENTS OCCUR INDEFINITELY?

• CALCIUM IONS RELEASED FOR ONLY SHORT PERIOD
• ACTIVE TRANSPORT REMOVE IONS
• BACK TO SARCOPLASMIC RETICULUM
• TROPONIN STRENGTHENS HOLD ON ACTIN
• DOES NOT ALLOW INTERACTIONS BETWEEN MYOSIN AND
  ACTIN
• CONTRACTILE PROCESS STOPS
• RAPID SUCCESSION OF ACTION POTENTIALS CAN KEEP
  CALCIUM FROM BEING TOTALLY REMOVED
• CALCIUM IONS ARE AVAILABLE AND FIBER DOES NOT
  RELAX UNTIL IMPULSES STOP

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ENERGY SOURCES FOR MUSCLE CONTRACTION

• ATP IS IMMEDIATE ENERGY SOURCE
• ONLY HAVE ENOUGH ATP TO CONTRACT MUSCLE FOR FEW
  SECONDS
• MUST HAVE AN ADDITIONAL ENERGY SUPPLY

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CREATINE PHOSPHATE

• FOUND IN SKELETAL MUSCLE
• ALLOWS RAPID ATP FORMATION
• PHOSPHATE AND ENERGY CAN BE TRANSFERRED TO ATP
• CREATINE KINASE
• SKELETAL MUSCLE CONTAINS MORE CREATINE PHOSPHATE
  THAN ATP
• CREATINE PHOSPHATE ADDS JUST A FEW MORE SECONDS
  OF CONTRACTION
• IMPORTANT JUST AFTER INITIATION OF MUSCLE
  CONTRACTION

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NUTRIENTS

• METABOLIC BREAKDOWN OF GLUCOSE, GLYCOGEN, AND
  FATTY ACIDS PROVIDE ATP FOR CONTINUED MUSCULAR
  ACTIVITY
• RESTING AND SLIGHTLY ACTIVE MUSCLES USE FATTY
  ACIDS
• WITH INCREASE IN ACTIVITY MUSCLES USE MORE AND
  GLYCOGEN AND GLUCOSE FOR ENERGY
• GLYCOGEN STORED IN MUSCLES
• GLUCOSE AND FATTY ACIDS BROUGHT BY BLOOD STREAM

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AEROBIC METABOLISM

• MUST HAVE SUFFICIENT OXYGEN
• BREAKS DOWN GLUCOSE, GLYCOGEN AND FATTY ACIDS TO
  CARBON DIOXIDE AND WATER
• EXERCISE CAUSES RESPIRATION AND BLOOD FLOW TO
  SKELETAL MUSCLE TO INCREASE
• YIELDS UP TO 38 ATPS FROM ONE MOLECULE OF GLUCOSE
• HAS MANY STEPS AND IS VERY SLOW
• MUST HAVE AN ADEQUATE AND CONTINUAL SUPPLY OF
  OXYGEN
• OCCURS DURING LIGHT TO MODERATE EXERCISE--WALKING
  OR JOGGING
• AEROBIC OR ENDURANCE EXERCISES

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ANAEROBIC METABOLISM

• INTENSE MUSCULAR ACTIVITY
• OXYGEN CANNOT BE DELIVERED FAST ENOUGH
• LACTATE FERMENTATION
• PRODUCES ONLY 2 ATP
• PROCEED MUCH FASTER
• USES LARGE AMOUNTS OF GLUCOSE OR GLYCOGEN
• PRODUCES LACTATE AND HYDROGEN IONS
• LACTATE CONVERTED BACK TO GLUCOSE IN LIVER BY
  CORI CYCLE

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MUSCLE FATIGUE

• INTENSE MUSCLE ACTIVITY CANNOT CONTINUE FOREVER
• INABILITY OF A MUSCLE TO MAINTAIN A PARTICULAR
  STRENGTH OF CONTRACTION OR TENSION OVER TIME

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MUSCLE FATIGUE

• NOT WELL UNDERSTOOD
• APPEARS TO DIFFER WITH TYPES OF EXERCISE
• MAJOR FACTOR IS THE INABILITY OF MUSCLE TO
  GENERATE ENERGY AT HIGH ENOUGH RATE
• MAY BE DUE TO DEPLETION OF METABOLIC RESERVES
• A BUILD UP OF HYDROGEN IONS
• PSYCHOLOGICAL FATIGUE CAN CAUSE A PERSON TO QUIT

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OXYGEN DEBT

• WHEN MUSCLE CONTRACTION ENDS CREATINE PHOSPHATE
  LEVEL MUST BE REINSTATED
• LACTIC ACID MUST BE RETURNED TO GLUCOSE
• GLYCOGEN LEVELS MUST BE REPLENISHED
• THESE REQUIRE ATP
• AEROBIC PROCESSES PROVIDE ENERGY
• TO SUPPYL OXYGEN REATHING CONTINUES AT INCREASED
  RATE FOR SOME TIME AFTER EXERCISE

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MOTOR UNITS

• MUSCLE HAS MORE FIBERS THAT NEURONS
• EACH NEURON BRANCHES TO SUPPLY SEVERAL MUSCLE
• SINGLE NEURON AND ALL THE MUSCLE FIBERS IT
  SUPPLIES
• FUNCTIONAL UNIT OF MUSCLE
• MUSCLES OF FINE MOVEMENT HAVE LOW RATIO
• MUSCLES OF GROSS MOVEMENTS HAVE HIGH RATIO

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SKELETAL MUSCLE RESPONSES

• MOTOR UNITS COMBINE TO CAUSE CONTRACTION OF THE
  MUSCLE AS A WHOLE
• CONTRACTIONS WILL VARY IN BOTH STRENGTH AND
  DURATION

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MUSCLE TWITCH
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GRADED MUSCULAR CONTRACTIONS
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MULTIPLE MOTOR UNIT SUMMATION
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WAVE SUMMATION
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TETANUS
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ASYNCHRONOUS MOTOR UNIT SUMMATION
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DEVELOPMENT OF MUSCLE TENSION
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LENGTH OF MUSCLE AND MUSCLE TENSION
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LOAD AND VELOCITY OF SHORTENING
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ACTION OF MUSCLE
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LEVERS AND MUSCLES
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CLASSES OF LEVERS
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CLASS I LEVERS
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CLASS II LEVERS
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CLASS III LEVERS
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LEVERS AND MOVEMENT
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SKELETAL MUSCLE FIBER TYPES
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SLOW TWITCH, RED, FATIGUE RESISTANT FIBERS

• TYPE I FIBERS-SLOW OXIDATIVE FIBERS
• SPLIT ATP AT SLOW RATE
• SLOW CROSS-BRIDGE CYCLING
• MANY MITOCHONDRIA
• HIGH CAPCITY FOR AEROBIC RESPIRATION
• SURROUNDED BY MANY CAPILLARIES
• LARGE AMOUNTS OF MYOGLOBIN
• EXTREMELY RESISTANT TO FATIGUE

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FAST TWITCH, RED, FATIGUE RESISTANT FIBER

• TYPE II a FIBERS-FAST OXIDATIVE FIBERS
• MANY MITOCHONDRIA--HIGH CAPACITY FOR AEROBIC
  RESPIRATION
• WELL SUPPLIED WITH BLOOD VESSELS
• LARGE AMOUNTS OF MYOGLOBIN
• SPLIT ATP AT RAPID RATE
• FAST CROSS BRIDGING
• CAN SUPPLY MOST OF THEIR NEEDS BY OXIDATIVE
  RESPIRATION
• QUITE RESISTANT TO FATIGUE

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FAST TWITCH, WHITE, FATIGABLE FIBER

• TYPE II b FIBERS-FAST GLYCOLYTIC FIBERS
• FEWER MITOCHONDRIA
• NOT WELL SUPPLIED BY BLOOD VESSELS
• LITTLE MYOGLOBIN
• SPIT ATP RAPIDLY
• GEARED FOR ANAEROBIC RESPIRATION
• FATIGUE EASILY

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UTILIZATION OF FIBERS IN SKELETAL MUSCLE
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EXERCISE AND ITS EFFECT ON THE SKELETAL MUSCLES
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MUSCLES AND NERVOUS SYSTEM

• SOMATIC MOTOR SYSTEM

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PYRAMIDAL VS EXTRAPYRAMIDAL TRACTS
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PYRAMIDAL TRACTS

• ORIGINATE IN PRECENTRAL GYRUS
• PRIMARY MOTOR CORTEX
• ARISE FROM PYRAMIDAL CELLS
• PROVIDES VOLUNTARY CONTROL OVER SKELETAL MUSCLES

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EXTRAPYRAMIDAL TRACTS

• ARISE IN ANY AREA OTHER THAN THE PRECENTRAL GYRUS
• MODIFY OR DIRECT MUSCLE CONTRACTIONS

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PROPRIOCEPTION

• KINESTHETIC SENSE
• PROPRIOCEPTORS MONITOR POSITION OF JOINTS,
  TENSION IN TENDONS AND LIGAMENTS AND STATE OF
  MUSCLE CONTRACTION

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MAJOR PROPRIOCEPTORS

• MUSCLE SPINDLES
• GOLGI TENDON ORGANS
• JOINT CAPSULE RECEPTORS
• BELOW CONCIOUSNESS

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CLINICAL CONDITIONS
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MUSCLE ATROPHY
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CRAMPS
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MUSCULAR DYSTROPHY
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MYASTHENIA GRAVIS
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AGING OF THE MUSCULAR SYSTEM
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SMOOTH MUSCLE

• UNINUCLEATE
• SPINDLE SHAPED
• SMALLER THAN SKELETAL MUSCLE
• NO T TUBULES
• POORLY DEVELOPED SARCOPLASMIC RETICULUM
• HAVE ACTIN BUT NOT TROPONIN

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SMOOTH MUSCLE ARRANGEMENTS

• SINGLE AND MULTIUNIT
• SOME MUSCLES HAVE TYPICAL ARRANGEMENT OF ONE OR
  THE OTHER
• OTHER MUSCLES HAVE ARRANGEMENTS THAT FALL BETWEEN
  THE TWO

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SINGLE-UNIT SMOOTH MUSCLE

• VISCERAL SMOOTH MUSCLE
• MOST COMMON ARRANGEMENT
• FOUND IN SMALL ARTERIES, VEINS, INTESTINES,
  UTERUS AND OTHER STRUCTURES
• CONNECTED BY GAP JUNCTIONS
• MANY CELLS RESPOND AS A UNIT

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MULTIUNIT SMOOTH MUSCLE

• LESS COMMON
• PRESENT IN LARGE ARTERIES, LARGE AIRWAYS TO
  LUNGS, AND OTHER STRUCTURES
• FEW GAP JUNCTIONS
• EACH CELL OR SMALL GROUP OF CELLS RESPONDS
  INDEPENDENTLY
• GENERALLY NOT SELF EXCITABLE

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EXTERNAL FACTORS AND SMOOTH MUSCLE CONTRACTION

• NEURAL ACTIVITY
• HORMONES
• OTHER CHEMICALS

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MECHANICS OF SMOOTH MUSCLE CONTRACTION

• CROSS BRIDGES BETWEEN MYOSIN AND ACTIN CREATE
  FORCES
• CALCIUM COMES FROM EXTRACELLULAR AND
  INTRACELLULAR SOURCES
• CALCIUM BINDS TO CALMODULIN
• ACTIVATES MYOSIN LIGHT CHAIN KINASE
• LIGHT MYOSIN CHAINS PHOSPHORYLATED

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CONTRACTION AND RELAXATION OF SMOOTH MUSCLE
DEPENDS ON THE ACTIVITY OF MYOSIN LIGHT CHAIN
KINASE AND MYOSIN LIGHT CHAIN PHOSPHATASE
96
SPEED AND COST OF SMOOTH MUSCLE CONTRACTION

• SMOOTH MUSCLE CAN GENERATE AS MUCH CONTRACTILE
  TENSION AS SKELETAL
• USES MUCH LESS ATP
• CONTRACTS MORE SLOWY

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STRESS RELAXATION RESPONSE

• SMOOTH MUSCLE CAN BE STRETCHED MORE BEFORE SEEING
  INCREASE IN TENSION
• ALLOWS HOLLOW ORGANS TO EXPAND WITH OUT
  APPRECIABLE CHANGES IN PRESSURE ON CONTENTS

98
CONTRACTION WHEN STRETCHED

• CAN UNDERGO GREATER STRETCHING
• DUE TO ARRANGEMENT OF THIN AND THICK FILAMENTS

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AMOUNT OF SHORTENING DURING CONTRACTION

• CAN SHORTEN MORE
• CAN CONTRACT FROM TWICE ITS NORMAL LENGTH TO 1/2
  ITS NORMAL LENGTH
• ALLOWS YOU TO VARY DIAMETER OF LUMENS

100
SMOOTH MUSCLE TONE

• LOW LEVEL OF MUSCLE TENSION
• DUE TO PRESENCE OF CALCIUM IONS
• IMPORTANT IN CARDIOVASCULAR SYSTEM

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CARDIAC MUSCLE

• CARDIOCYTES
• CARDIAC MYOCYTES
• 10-20 MICRONS IN DIAMETER
• 50-100 MICRONS IN LENGTH
• ONE TO TWO CENTRAL NUCLEUS/NUCLEI

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STRUCTURE OF CARDIAC MUSCLE
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SHORT AND BROAD T TUBULES
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NO TRIADS
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T TUBULES SURROUND THE SARCOMERES AT Z LINES
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NO TERMINAL CISTERNAE IN SARCOPLASMIC RETICULUM
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SARCOPLASMIC RETICULUM TUBULES CONTACT T TUBULES
AND CELL MEMBRANE
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ACTION POTENTIAL TRIGGERS RELEASE OF CALCIUM IONS
FROM SARCOPLASMIC RETICULUM AND THE ENTRY OF
CALCIUM IONS FROM THE EXTRACELLULAR FLUIDS
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INTERCALATED DISCS

• INTERTWINING OF CELL MEMBRANES
• BOUND BY GAP JUNCTIONS AND DESMOSOMES

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MAJOR FUNCTIONAL CHARACTERISTICS OF CARDIAC MUSCLE

• AUTORYTHMICITY
• PACEMAKER CELLS
• AUTONOMIC NERVOUS SYSTEM AFFECTS RATE OF
  CONTRACTION
• CONTRACTIONS LAST LONGER
• NO WAVE SUMMATION
• NO TETANIC CONTRACTIONS

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THE COST OF CONTRACTION

• ALMOST TOTALLY DEPENDENT ON AEROBIC RESPIRATION
• LOTS OF MITOCHONDRIA
• LOTS OF MYOGLOBIN
• GLYCOGEN AND LIPID INCLUSIONS