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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SKELETAL MUSCLE
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GROSS ANATOMY OF SKELETAL 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 ALONG 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 MHYOSIN 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
• GLYCOSOMES STORE 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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WAVE SUMMATION
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MULTIPLE MOTOR UNIT 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
68
CLASS II LEVERS
69
CLASS III LEVERS
70
LEVERS AND MOVEMENT
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SKELETAL MUSCLE FIBER TYPES
72
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
76
EXERCISE AND ITS EFFECT ON THE SKELETAL MUSCLES
77
MUSCLES AND NERVOUS SYSTEM

• SOMATIC MOTOR SYSTEM

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PYRAMIDAL VS EXTRAPYRAMIDAL TRACTS
79
PYRAMIDAL TRACTS

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

80
EXTRAPYRAMIDAL TRACTS

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

81
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
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SMOOTH MUSCLE ARRANGEMENTS

• SINGLE UNIT
• MULTIUNIT
• MIX OF BOTH

91
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

92
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

93
EXTERNAL FACTORS AND SMOOTH MUSCLE CONTRACTION

• NEURAL ACTIVITY
• HORMONES
• OTHER CHEMICALS

94
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

95
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

97
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

99
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

101
CARDIAC MUSCLE

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

102
STRUCTURE OF CARDIAC MUSCLE
103
SHORT AND BROAD T TUBULES
104
NO TRIADS
105
T TUBULES SURROUND THE SARCOMERES AT Z LINES
106
NO TERMINAL CISTERNAE IN SARCOPLASMIC RETICULUM
107
SARCOPLASMIC RETICULUM TUBULES CONTACT T TUBULES
AND CELL MEMBRANE
108
ACTION POTENTIAL TRIGGERS RELEASE OF CALCIUM IONS
FROM SARCOPLASMIC RETICULUM AND THE ENTRY OF
CALCIUM IONS FROM THE EXTRACELLULAR FLUIDS
109
INTERCALATED DISCS

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

110
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

111
THE COST OF CONTRACTION

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