Muscle PhysiologyPart Two

Lecture OutlineMuscle FunctionMuscle CharacteristicsMuscle Tissue TypesSkeletal MuscleGeneral Functions of Skeletal MuscleFunctional AnatomyPhysiologyEnergetics & FatigueContraction StrengthSkeletal Muscle TypesAdaptive ResponsesCardiac Muscle PhysiologySmooth Muscle Physiology

Skeletal MuscleEnergetics & FatigueATP use is required formaintenance of resting membrane potentialsNa+/K+ ATPaseexocytosis of ACh at the NMJPossibly kinesin ATPasemoving myosin heads back to energized statemyosin ATPasereturn of Ca2+ into sarcoplasmic reticulumCa2+ ATPase

Skeletal MuscleEnergetics & FatigueSources of ATP for muscle actionFree ATPOnly have enough stores for about 5-6 seconds of intense activityPhosphagen SystemTransfer of high energy phosphate from creatine phosphate to ADP to make ATP

enough for approximately another 10-15 seconds of highly intense muscle action

Skeletal MuscleEnergetics & FatigueSources of ATP for muscle action contGlycolysis (Glycogen-Lactic Acid System)Glycogenolysis converts glycogen to glucoseGlucose is split into 2 pyruvate molecules with a net result of 2 ATP, if oxygen is present, pyruvate is converted to acetyl coenzyme A,If oxygen is not present,pyruvate is converted to lactic acidContributes to lactic acid accumulation in the muscle tissueProvides enough ATP for an additional 30-40 seconds of intense activity

Skeletal MuscleEnergetics & FatigueSources of ATP for muscle action contAerobic RespirationCitric Acid Cycle + Electron Transport ChainHighly efficient production of 30 32 molecules of ATP (net)Long term as long as oxygen and fuel are present

There are three sources of ATP for aerobic muscle to use: carbohydrates, fats, and amino acid proteins. Carbohydrates metabolize the most efficiently and are therefore used first. If carbohydrates are not available, your body metabolizes fat and amino acid proteins. All three of these reactions are called Aerobic Glycolysis because they use glucose and oxygen:1. Carbohydrate Metabolism: Glucose + 02 36ATP + C02 + H20 2. Fat Metabolism: Fatty Acid + 02 130 ATP + C02 + H20 3. Amino Acid Protein Metabolism: Amino Acids + 02 15 ATP + C02 + H20

Skeletal MuscleEnergetics & FatigueWhat causes muscle to fatigue?

Skeletal MuscleTypesAll skeletal muscle is skeletal muscle?Yes but there are varietiesOxidative vs. Glycolyticratio is dependent on geneticsGlycolytic muscles3 types (Type IIa, IIb, IIx)Fast contraction actionGenerally paler in color due to lower amounts of myoglobin and vascularityutilize anaerobic pathways for energynot use for long term endurance activitiesOxidativeUse aerobic processesLong term endurance activitiesHighly vascular, more myoglobin

Skeletal MuscleTypes

Skeletal MuscleTypes

Skeletal MuscleTypes

Skeletal MuscleStrength of ContractionThe response of skeletal muscle to an action potential in a motor neuron is the twitch of the muscle.Single twitches may not generate enough force to get the job doneWhat happens when resistance is greater than the force of contraction?Isometric contractionHow then can a stronger contraction be created in muscle tissue?

Skeletal MuscleStrength of ContractionIncrease the frequency of action potentialsCalled summation, as the twitches add together

Skeletal MuscleStrength of ContractionSummation can lead to tetanusunfused and fused depending on frequency of action potentials

Skeletal MuscleStrength of Contractionalter the length of the muscle prior to contractionOptimal overlap of myosin and actin allows for the generation of a stronger contraction

Skeletal MuscleStrength of ContractionIncrease the number of functional motor unitsMotor unit is a motor neuron and the muscle fibers it innervatesRecruitment is adding additional motor units to increase strength

Skeletal MuscleStrength of ContractionMuscle hypertrophythis is an adaptive response to stressing the muscle and causes an increase in the size of muscle cellsmay be the result of myofibril enlargement or increase in sarcoplasmic volumeMuscle hyperplasiaincrease in muscle due to formation of new muscle cellstheories vary as to how

Skeletal MuscleAdaptive ResponseTable taken from: http://www.criticalbench.com/muscle-fiber-type.htm

Cardiac MuscleGeneral FeaturesShares features with both skeletal and smooth muscleLike skeletal Striatedsarcomere structureUnlike skeletal Muscle fibers shortermay be branchedhave single nucleusT-tubules are larger, less frequent and over the z-discsLike smooth Electrically linked to one another; some exhibit pacemaker potentialsunder sympathetic and parasympathetic control as well as hormone control

Cardiac MusclePhysiologyAdaptations for continued contractionsIncreased vascularityIncreased mitochondriaIncreased levels of myoglobinAdaptation to prevent summationInflux of Ca2+ from ECF through L-type Ca2+ channels causing a CICR (Calcium Induced Calcium Release) from the sarcoplasmic reticulum sustains the depolarized state which increases the refractory period...More on this later

Smooth MuscleFunctional CharacteristicsVariations in smooth muscle physiology allow for different autonomic tissues to have different characteristicsVascular smooth muscleRespiratory smooth muscleDigestive wall smooth muscleUrinary smooth muscleReproductive smooth muscleOcular smooth muscle

Smooth MuscleFunctional CharacteristicsSarcolemma contains caveolae which containReceptorsprostacyclin, endothelin, serotonin, muscarinic receptors, adrenergic receptors g proteinsSecondary messenger generatorsAdenylyl cyclasePhospholipase Cion channelsL-type Ca2+ channels & K+ channels, protein kinasessarcolemmasmooth muscle cellcaveolae

Smooth MuscleFunctional CharacteristicsContraction is controlled byAcetylcholineNorepinephrineNitric OxideElectrical properties and action varyMay depolarize without contractionMay hyperpolarizeMay contract without a change in membrane potentialThis results in smooth muscle having many operating parameters and integrates the different responses

Smooth MuscleFunctional Anatomical Characteristicsactin myosin are longer but still create contractile forceSmooth muscle myosin isoform is slower and longerMore actin in smooth muscle (10 to 15:1 actin:myosin ratio vs. 2-4:1 ratio in skeletal)actin anchored in focal adhesions (attachment plaques) on the sarcolemma and dense bodies intracellularlyCaveolaeContain variety (see previous slides) of membrane receptors and proteinsAutonomic nerves terminate with multiple swellings called varicosities

Smooth MuscleDifferences between single and multi-unit smooth muscle

Smooth Muscle

Smooth MuscleContraction

Smooth MuscleRelaxation