Smooth MuscleSmooth Muscle CharacteristicsCharacteristics

Not striatedNot striated Dense bodies instead Dense bodies instead

of Z disks as in skeletal of Z disks as in skeletal musclemuscle

Have noncontractile Have noncontractile intermediate filamentsintermediate filaments

CaCa2+2+ required to required to initiate contractionsinitiate contractions

TypesTypes Visceral or unitaryVisceral or unitary

Function as a unitFunction as a unit MultiunitMultiunit

Cells or groups of Cells or groups of cells act as cells act as independent unitsindependent units

Smooth Muscle Smooth Muscle ContractionContraction

Electrical Properties of Electrical Properties of Smooth MuscleSmooth Muscle

Functional Properties Functional Properties of Smooth Muscleof Smooth Muscle

Some visceral muscle exhibits Some visceral muscle exhibits autorhythmic contractionsautorhythmic contractions

Tends to Tends to contract in responsecontract in response to to sudden stretch but no to slow sudden stretch but no to slow increase in lengthincrease in length

Exhibits Exhibits relatively constantrelatively constant tension: tension: Smooth muscle toneSmooth muscle tone

Amplitude of contractionAmplitude of contraction remains remains constant although muscle length constant although muscle length variesvaries

Smooth Muscle Smooth Muscle RegulationRegulation

Innervated Innervated by autonomic nervous by autonomic nervous systemsystem

NeurotransmitterNeurotransmitter are acetylcholine are acetylcholine and norepinephrineand norepinephrine

Hormones important as Hormones important as epinephrine epinephrine and oxytocinand oxytocin

ReceptorsReceptors present on plasma present on plasma membrane which neurotransmitters or membrane which neurotransmitters or hormones hormones bindbind determines determines responseresponse

Cardiac MuscleCardiac Muscle

Found only in Found only in heartheart StriatedStriated Each cell usually has Each cell usually has one nucleusone nucleus Has intercalated disks and gap junctionsHas intercalated disks and gap junctions AutorhythmicAutorhythmic cells cells Action potentials of longer duration and Action potentials of longer duration and

longer refractory periodlonger refractory period CaCa2+2+ regulates contraction regulates contraction

Cardiac MuscleCardiac Muscle

Elongated, branching cells containing 1-2 centrally located nucleiElongated, branching cells containing 1-2 centrally located nuclei Contains actin and myosin myofilaments Contains actin and myosin myofilaments Intercalated disksIntercalated disks: Specialized cell-cell contacts: Specialized cell-cell contacts Desmosomes hold cells together and gap junctions allow action Desmosomes hold cells together and gap junctions allow action

potentialspotentials Electrically, cardiac muscle behaves as single unitElectrically, cardiac muscle behaves as single unit

Cardiac myocyte action Cardiac myocyte action potential:potential:

Refractory PeriodRefractory Period

AbsoluteAbsolute: Cardiac muscle cell : Cardiac muscle cell completely insensitive to further completely insensitive to further stimulationstimulation

RelativeRelative: Cell exhibits reduced : Cell exhibits reduced sensitivity to additional stimulationsensitivity to additional stimulation

Long refractory period prevents Long refractory period prevents tetanic contractionstetanic contractions

AP-contraction AP-contraction relationship:relationship:

AP in skeletal muscle is AP in skeletal muscle is very short-livedvery short-lived AP is basically over before AP is basically over before

an increase in muscle an increase in muscle tension can be measured.tension can be measured.

AP in cardiac muscle is AP in cardiac muscle is very long-livedvery long-lived AP has an extra AP has an extra

component, which extends component, which extends the duration.the duration.

The contraction is almost The contraction is almost over before the action over before the action potential has finished.potential has finished.

Functions of the HeartFunctions of the Heart Generating Generating bloodblood pressure pressure Routing Routing bloodblood

Heart separates pulmonary and Heart separates pulmonary and systemic circulationssystemic circulations

Ensuring one-way Ensuring one-way bloodblood flow flow Heart valves ensure one-way flowHeart valves ensure one-way flow

Regulating Regulating bloodblood supply supply Changes in contraction rate and Changes in contraction rate and

force match blood delivery to force match blood delivery to changing metabolic needschanging metabolic needs

Orientation of cardiac Orientation of cardiac muscle fibres:muscle fibres:

Unlike skeletal Unlike skeletal muscles, cardiac muscles, cardiac muscles have to muscles have to contract in more than contract in more than one direction.one direction.

Cardiac muscle cells Cardiac muscle cells are striated, meaning are striated, meaning they will only contract they will only contract along their long axis.along their long axis.

In order to get In order to get contraction in two contraction in two axis, the fibres wrap axis, the fibres wrap around.around.

Circulation circuits:Circulation circuits:

Heart WallHeart Wall

Three layers of tissueThree layers of tissue EpicardiumEpicardium: This serous membrane : This serous membrane

of smooth outer surface of heartof smooth outer surface of heart MyocardiumMyocardium: Middle layer composed : Middle layer composed

of cardiac muscle cell and of cardiac muscle cell and responsibility for heart contractingresponsibility for heart contracting

EndocardiumEndocardium: Smooth inner surface : Smooth inner surface of heart chambersof heart chambers

Valve function:Valve function:

Coronary circulation:Coronary circulation:

Pacemaker potential:Pacemaker potential:

Cardiac conducting Cardiac conducting system:system:

EKG:EKG:

Heart SoundsHeart Sounds

First heart sound or “lubb”First heart sound or “lubb” Atrioventricular valves and surrounding fluid Atrioventricular valves and surrounding fluid

vibrations as valves close at beginning of vibrations as valves close at beginning of ventricular systoleventricular systole

Second heart sound or “dupp”Second heart sound or “dupp” Results from closure of aortic and pulmonary Results from closure of aortic and pulmonary

semilunar valves at beginning of ventricular semilunar valves at beginning of ventricular diastole, lasts longerdiastole, lasts longer

Third heart sound Third heart sound (occasional)(occasional) Caused by turbulent blood flow into ventricles and Caused by turbulent blood flow into ventricles and

detected near end of first one-third of diastoledetected near end of first one-third of diastole

Heart sounds:Heart sounds:

Cardiac ArrhythmiasCardiac Arrhythmias

TachycardiaTachycardia: Heart rate in excess of : Heart rate in excess of 100bpm100bpm

BradycardiaBradycardia: Heart rate less than 60 : Heart rate less than 60 bpmbpm

Sinus arrhythmiaSinus arrhythmia: Heart rate varies 5% : Heart rate varies 5% during respiratory cycle and up to 30% during respiratory cycle and up to 30% during deep respirationduring deep respiration

Premature atrial contractionsPremature atrial contractions: : Occasional shortened intervals between Occasional shortened intervals between one contraction and succeeding, one contraction and succeeding, frequently occurs in healthy peoplefrequently occurs in healthy people

Mean Arterial Pressure Mean Arterial Pressure (MAP)(MAP)

Average blood pressure in aortaAverage blood pressure in aorta MAP=CO x PRMAP=CO x PR

CO is amount of blood pumped by heart CO is amount of blood pumped by heart per minuteper minute CO=SV x HRCO=SV x HR

SVSV: Stroke volume of blood pumped during each : Stroke volume of blood pumped during each heart beatheart beat

HRHR: Heart rate or number of times heart beats per : Heart rate or number of times heart beats per minuteminute

Cardiac reserve: Difference between CO at Cardiac reserve: Difference between CO at rest and maximum COrest and maximum CO

PR is total resistance against which PR is total resistance against which blood must be pumpedblood must be pumped

Pressure relationships:Pressure relationships:

Cardiac CycleCardiac Cycle

Heart is two pumps that work Heart is two pumps that work together, right and left halftogether, right and left half

Repetitive contraction (Repetitive contraction (systolesystole) and ) and relaxation (relaxation (diastolediastole) of heart chambers) of heart chambers

Blood moves through circulatory Blood moves through circulatory system from areas of higher to lower system from areas of higher to lower pressure.pressure. Contraction of heart produces the Contraction of heart produces the

pressurepressure

Factors Affecting MAPFactors Affecting MAP

Regulation of the HeartRegulation of the Heart Intrinsic regulationIntrinsic regulation: Results from : Results from

normal functional characteristics, not normal functional characteristics, not on neural or hormonal regulationon neural or hormonal regulation Starling’s law of the heartStarling’s law of the heart

Extrinsic regulationExtrinsic regulation: Involves neural : Involves neural and hormonal controland hormonal control Parasympathetic stimulationParasympathetic stimulation

Supplied by vagus nerve, decreases heart rate, Supplied by vagus nerve, decreases heart rate, acetylcholine secretedacetylcholine secreted

Sympathetic stimulationSympathetic stimulation Supplied by cardiac nerves, increases heart rate Supplied by cardiac nerves, increases heart rate

and force of contraction, epinephrine and and force of contraction, epinephrine and norepinephrine releasednorepinephrine released

Heart HomeostasisHeart Homeostasis Effect of blood pressureEffect of blood pressure

Baroreceptors monitor blood pressureBaroreceptors monitor blood pressure Effect of pH, carbon dioxide, oxygenEffect of pH, carbon dioxide, oxygen

Chemoreceptors monitorChemoreceptors monitor Effect of extracellular ion concentrationEffect of extracellular ion concentration

Increase or decrease in extracellular KIncrease or decrease in extracellular K++ decreases heart ratedecreases heart rate

Effect of body temperatureEffect of body temperature Heart rate increases when body temperature Heart rate increases when body temperature

increases, heart rate decreases when body increases, heart rate decreases when body temperature decreasestemperature decreases

Baroreceptor and Baroreceptor and ChemoreceptorChemoreceptor

ReflexesReflexes