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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

MUSCLE TYPES

• SKELETAL MUSCLE• SMOOTH MUSCLE• CARDIAC MUSCLE

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

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

CARDIAC MUSCLE

• SPECIALIZED MUSCLE• FOUND ONLY IN HEART• INVOLUNTARY• CONTROLLED BY AUTONOMIC

NERVOUS SYSTEM, INTRINSIC FACTORS, AND HORMONES

• STRIATED

EMBRYONIC DEVELOPMENT OF MUSCLE

SKELETAL MUSCLE

• EXCEPT FOR HEAD AND LIMBS --DEVELOP FROM SOMITES

• SOMITES MASES OF MESODERMAL CELLS ALONG VERTEBRAE

• MYOTOMES DIFFERENTIATE TO MUSCLE CELLS

• HEAD OF EMBRYO DEVELOPS FROM GENERAL MESODERM

• LIMBS DEVELOP FROM MESODERMAL CONDENSATIONS

• SOME PROBABLY MIGRATE TO LIMBS FROM MYOTOMES

SKELETAL MUSCLE

• MUSCLE FIBERS ARISE FROM MYOBLASTS

• INDIVIDUAL MYOBLASTS FUSE TO FORM MULTINUCLEATED

• AS MATURE FORMS EXTENSIVE MEMBRANE SYSTEM AND CONTRACTILE PROTEINS

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

SMOOTH MUSCLE

• DIGESTIVE TUBE AND BODY ORGANS

• MESODERM MIGRATES AND FORMS THIN LAYER

• DEVELOP INTO SMOOTH MUSCLE

CARDIAC MUSCLE

• FORMATION SIMILAR TO SMOOTH• MIGRATION OF MESODERM TO

HEART TUBE• HAS INTRINSIC CONTRACTION

GROSS ANATOMY OF MUSCLE

• CONNECTIVE TISSUE COVERINGS• ATTACHMENTS• MUSCLE SHAPE

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

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

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

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

MUSCLE SHAPE• UNIPENNATE--ALL FASCICUL INSERT ON ONE

SIDE OF TENDON• BIPENNATE--FASCICULI INSERT ON BOTH SIDES

OF TENDON• MULTIPENNATE-- SEVERAL TENDONS CONVERGE• CONVERGENT--FASCICULI CONVERGE FROM

BORAD ORIGIN TO SINGLE NARROW TENDON• SPHINCTER--CIRCULAR MUSCLES

MICROSCOPIC ANATOMY OF SKELETAL MUSCLE

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

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

ANISOTROPIC BANDS

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

TYPES OF MYOFILAMENTS

• THICK FILAMENTS• THIN FILAMENTS

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

THICK FILAMENTS

• OCCUR IN A BAND• OVERLAP WITH THIN FILAMENTS• H ZONE ONLY HAS THICK FILAMENTS• M LINE MADE OF FINE FILAMENTS

THAT CONNECT THICK FILAMENTS• M LINE CONTAINS PROTEIN

MYOMESIN

THIN FILAMENTS

• OCCUPY I BAND AND PART OF A BAND

• ATTACH TO Z LINES• MAKE HEXAGONAL ARRANGEMENT

AROUND THICK FILAMENTS

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

TRANSVERSE TUBULES

• TUBULAR INVAGINATIONS OF SARCOLEMMA

• EXTEND DEEPLY INTO SKELETAL MUSCLE FIBER

• IMPORTANT FOR TRANSMISSION OF ACTION POTENTIAL

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

SKELETAL MUSCLE CONTRACTION

• EXPERIMENTALLY ARE TWO TYPES OF CONTRACTIONS WE CAN SEE

• ISOTONIC• ISOMETRIC• IN REALITY BOTH OCCUR AND ARE

HARD TO SEPARATE

ISOMETRIC

• LENGTH OF MUSCLE STAYS CONSTANT

• DEVELOPS FORCE AND TENSION• OCCUR WHEN LIFT OBJECTS TO

HEAVY OR FIXED IN PLACE

ISOTONIC

• MUSCLE SHORTENS UNDER A CONSTANT LOAD

• EVEN THOUGH NOT PURE --WALKING, RUNNING, LIFTING ARE CALLED ISOTONIC

SKELETAL MUSCLE CONTRACTION

• OCCURS AT CELLULAR LEVEL• MUST HAVE STIMULATION FROM

NERVOUS SYSTEM• INTERACTION BETWEEN ACTIN AND

MYOSIN• DEVELOP TENSION AND SHORTENS

FIBERS

NEUROMUSCULAR JUNCTION

• MOTOR NEURONS SUPPY INNERVATION

• SPECIALIZED JUNCTIONS --DO NOT TOUCH

• MOST SKELETAL MUSCLE FIBERS HAVE ONLY ONE NEUROMUSCULAR JUNCTION

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

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

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

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

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

CONTRACTION MECHANISMS

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

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

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

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

CONTRACTILE REGULATION

WHY DON’T 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

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

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

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

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

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

MUSCLE FATIGUE

• INTENSE MUSCLE ACTIVITY CANNOT CONTINUE FOREVER

• INABILITY OF A MUSCLE TO MAINTAIN A PARTICULAR STRENGTH OF CONTRACTION OR TENSION OVER TIME

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

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

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

SKELETAL MUSCLE RESPONSES

• MOTOR UNITS COMBINE TO CAUSE CONTRACTION OF THE MUSCLE AS A WHOLE

• CONTRACTIONS WILL VARY IN BOTH STRENGTH AND DURATION

MUSCLE TWITCH

GRADED MUSCULAR CONTRACTIONS

MULTIPLE MOTOR UNIT SUMMATION

WAVE SUMMATION

TETANUS

ASYNCHRONOUS MOTOR UNIT SUMMATION

DEVELOPMENT OF MUSCLE TENSION

CONTRACTILE AND SERIES ELASTIC ELEMENTS

MUSCLE TENSION AND SERIES ELASTIC ELEMENTS

TYPES OF TENSION ACHIEVED IN SKELETAL

MUSCLE

LENGTH OF MUSCLE AND MUSCLE TENSION

LOAD AND VELOCITY OF SHORTENING

ACTION OF MUSCLE

LEVERS AND MUSCLES

CLASSES OF

LEVERS

CLASS I LEVERS

CLASS II LEVERS

CLASS III LEVERS

LEVERS AND MOVEMENT

SKELETAL MUSCLE FIBER TYPES

SLOW TWITCH, RED, FATIGUE RESISTANT FIBERS

• TYPE I 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

FAST TWITCH, RED, FATIGUE RESISTANT FIBER

• TYPE II a 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

FAST TWITCH, WHITE, FATIGABLE FIBER

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

UTILIZATION OF FIBERS IN SKELETAL MUSCLE

EXERCISE AND ITS EFFECT ON THE SKELETAL

MUSCLES

MUSCLES AND NERVOUS SYSTEM

SOMATIC MOTOR SYSTEM

PYRAMIDAL VS EXTRAPYRAMIDAL TRACTS

PYRAMIDAL TRACTS

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

OVER SKELETAL MUSCLES

EXTRAPYRAMIDAL TRACTS

• ARISE IN ANY AREA OTHER THAN THE PRECENTRAL GYRUS

• MODIFY OR DIRECT MUSCLE CONTRACTIONS

PROPRIOCEPTION

• KINESTHETIC SENSE• PROPRIOCEPTORS MONITOR

POSITION OF JOINTS, TENSION IN TENDONS AND LIGAMENTS AND STATE OF MUSCLE CONTRACTION

MAJOR PROPRIOCEPTORS

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

CLINICAL CONDITIONS

MUSCLE ATROPHY

CRAMPS

MUSCULAR DYSTROPHY

MYASTHENIA GRAVIS

AGING OF THE MUSCULAR SYSTEM

SMOOTH MUSCLE

SMOOTH MUSCLE ARRANGEMENTS

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

PACEMAKER ACTIVITY

• RESULT OF AUTOMATIC CHANGES IN THE PERMEABILITY OF ION CHANNELS IN THE PLASMA MEMBRANE

• WHEN THRESHOLD IS REACHED AN ACTION POTENTIAL OCCURS

SLOW WAVE POTENTIALS

• RESULT OF CYCLIC CHANGES IN RATE OF SODIUM ION TRANSPORT

• CAUSES CYCLIC CHANGES IN SODIUM MEMBRANE POTENTIAL

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

EXTERNAL FACTORS AND SMOOTH MUSCLE CONTRACTION

• NEURAL ACTIVITY• HORMONES• OTHER CHEMICALS

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

CONTRACTION AND RELAXATION OF SMOOTH MUSCLE DEPENDS ON THE

ACTIVITY OF MYOSIN LIGHT CHAIN KINASE AND

MYOSIN LIGHT CHAIN PHOSPHATASE

SPEED AND COST OF SMOOTH MUSCLE

CONTRACTION• SMOOTH MUSCLE CAN GENERATE

AS MUCH CONTRACTILE TENSION AS SKELETAL

• USES MUCH LESS ATP• CONTRACTS MORE SLOWY

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

CONTRACTION WHEN STRETCHED

• CAN UNDERGO GREATER STRETCHING

• DUE TO ARRANGEMENT OF THIN AND THICK FILAMENTS

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

SMOOTH MUSCLE TONE

• LOW LEVEL OF MUSCLE TENSION• DUE TO PRESENCE OF CALCIUM

IONS• IMPORTANT IN CARDIOVASCULAR

SYSTEM

CARDIAC MUSCLE

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

NUCLEUS/NUCLEI

STRUCTURE OF CARDIAC MUSCLE

SHORT AND BROAD T TUBULES

NO TRIADS

T TUBULES SURROUND THE SARCOMERES AT Z LINES

NO TERMINAL CISTERNAE IN SARCOPLASMIC

RETICULUM

SARCOPLASMIC RETICULUM TUBULES

CONTACT T TUBULES AND CELL MEMBRANE

ACTION POTENTIAL TRIGGERS RELEASE OF CALCIUM IONS

FROM SARCOPLASMIC RETICULUM AND THE ENTRY OF CALCIUM IONS FROM THE

EXTRACELLULAR FLUIDS

INTERCALATED DISCS

• INTERTWINING OF CELL MEMBRANES

• BOUND BY GAP JUNCTIONS AND DESMOSOMES

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

THE COST OF CONTRACTION

• ALMOST TOTALLY DEPENDENT ON AEROBIC RESPIRATION

• LOTS OF MITOCHONDRIA• LOTS OF MYOGLOBIN• GLYCOGEN AND LIPID INCLUSIONS