The Muscular System

The Muscular SystemThe word muscle comes from the Latin word for mouse.The essential function of muscle tissue is to contract, or shortenMuscles are responsible for all body movement, they are the machines of the body.

Imburgia Trk 2 Anatomy

Muscle typesThere are three types of muscle:Skeletal (striated)SmoothCardiacMuscles differ in how they are stimulated, body location, and cell structure


Muscle typesHowever: all muscles have some common features 1.) all muscle cells are elongated, which is why muscle cells are known as muscle fibers2.) The contractile ability of muscle depends on two types of myofilaments.


Muscle types3.) Prefixes myo, mys, and sarco refer to muscleMyocardial infarction: heart attackSarcoplasm : muscle cell cytoplasm


Skeletal MusclesAttach to skeletonLong, spindle shaped, multi-nucleatedSome skeletal muscles are 30cm (1 foot) in length)Appear to have stripes, so they are called striated.


Skeletal MusclesSkeletal muscles are voluntarySkeletal muscles can be activated by reflexes as wellSkeletal muscles are made of soft tissue, and yet can exert tremendous force.How are they prevented from being ripped apart?


Skeletal MuscleSkeletal muscles are bundled together by connective tissue which strength and protection providesEach muscle fiber is enclosed in connective tissue called endomysiumSeveral sheathed muscle fibers are then wrapped together by a more coarse connective tissue called perimysium


Connective Tissue Wrappings of Skeletal MuscleEndomysium around single muscle fiberPerimysium around a fascicle (bundle) of fibersFigure 6.1


Connective Tissue Wrappings of Skeletal MuscleEpimysium covers the entire skeletal muscleFascia on the outside of the epimysiumFigure 6.1


Skeletal Muscle AttachmentsEpimysium blends into a connective tissue attachmentTendon cord-like structureAponeuroses sheet-like structureSites of muscle attachmentBonesCartilagesConnective tissue coverings


Skeletal Muscle The fibers enclosed by the perimysium form a bundle of fibers called a fascicleMany fascilcles are bound together by a very tough overcoat of connective tissue called epimysium, which covers the entire muscle


Skeletal muscleEpimysia merge together to form cord-like tendons, or sheet-like aponeurosesAponeuroses attach muscles indirectly to bones, cartilages or connective tissues to one anotherTendons anchor muscles, and serve to conserve space


Skeletal musclesMuscles can be spindle shaped, arranged in a fan, and circular


Smooth MuscleHave no striationsAre involuntaryAre found in the walls of hollow, visceral organsThey change the size and shape of organsAre usually arranged in sheets or layers


Smooth Muscle CharacteristicsHas no striationsSpindle-shaped cellsSingle nucleusInvoluntary no conscious controlFound mainly in the walls of hollow organsFigure 6.2a


Smooth MusclesIn most cases there are 2 layers; one arranged circularly, and the other longitudinallyThis arrangement allows for the movement of material such as food, waste and urineProvide slow, sustained contractions


Cardiac MuscleFound only in the heartStriated, but involuntaryFibers arranged in a spiral or figure 8 formationContain intercalated discs, which allow for adjacent cells to rapidly communicate with each other.


Cardiac Muscle CharacteristicsHas striationsUsually has a single nucleusJoined to another muscle cell at an intercalated discInvoluntaryFound only in the heartFigure 6.2b


Cardiac MuscleThe arrangement of fibers and intercalated discs allow heart activity to be closely coordinatedHeart rate is kept by an internal pacemaker located within the heartThe heart can be stimulated by the nervous system when the need arises


Muscle Functions1.) Produce movementSkeletal muscles are responsible for all locomotionThey respond quickly to changes in the environment


Muscle functions2.) Maintain postureSkeletal muscles work constantly against the pull of gravity, making almost constant adjustments so we can hold position


Muscle functions3.) Stabilize JointsSkeletal muscles exert force on the bones and stabilize jointsTendons are used to reinforce joints that have poorly fitted articular surfaces


Muscle functions4.) Generate heatBody heat is a by product of muscle activity.ATP are used to power muscular contractionSkeltal muscles accounts for at least 40% of body mass, therefore, skeletal muscle is the type most responsible for heat generation


Why I was supposed to pay attention in Chemistry


Microscopic Anatomy of Skeletal MuscleThe plasma membrane surrounding the muscle fibers is called the sarcolemmaThe cytoplasm of the fibers is packed with ribbo-like organelles called myofibrils


Microscopic Anatomy of Skeletal MuscleThe length of each myofibril has alternating light (I) and dark (A) bandsIt is the perfect alignment of the light and dark bands that give the muscles their striped appearanceThe banding pattern provides clues as to how the muscles work


Microscopic Anatomy of Skeletal MuscleMyofibrils are made of tiny contractile units called sarcomeresSmaller units within the satcomeres called myofilaments are responsible for producing muscle movementMyofilaments are thread-like proteinsThere are 2 types of myofilaments


Microscopic Anatomy of Skeletal MuscleThick filaments= myosinThin filaments= actinRemember them by syllable countMuscular contraction is produced by actin fibers sliding over the myosin fibers


Microscopic Anatomy of Skeletal MuscleCells are multinucleateNuclei are just beneath the sarcolemmaFigure 6.3a


Microscopic Anatomy of Skeletal MuscleSarcolemma specialized plasma membraneSarcoplasmic reticulum specialized smooth endoplasmic reticulumFigure 6.3a


Microscopic Anatomy of Skeletal MuscleOrganization of the sarcomereThick filaments = myosin filamentsComposed of the protein myosinHas ATPase enzymesFigure 6.3c


Microscopic Anatomy of Skeletal MuscleOrganization of the sarcomereThin filaments = actin filamentsComposed of the protein actinFigure 6.3c


Microscopic Anatomy of Skeletal MuscleMyosin filaments have heads (extensions, or cross bridges)Myosin and actin overlap somewhatFigure 6.3d


Microscopic Anatomy of Skeletal MuscleAt rest, there is a bare zone that lacks actin filamentsSarcoplasmic reticulum (SR) for storage of calciumFigure 6.3d


Nerve Stimulus to MusclesSkeletal muscles must be stimulated by a nerve to contractMotor unitOne neuronMuscle cells stimulated by that neuronFigure 6.4a


Nerve Stimulus to MusclesNeuromuscular junctions association site of nerve and muscleFigure 6.5b


Nerve Stimulus to MusclesA type of nerve cell called a motor neuron can stimulate one muscle cell, or hundreds of them.Specialized structures of the neuron called axons form junctions with the muscle called neuromuscular junctions


Nerve Stimulus to MusclesA microscopic spaces known as the synaptic cleft separates the axon from the muscle fibersChemicals known as neurotransmitters are released into the synaptic cleft when an impulse reaches the axonal terminal


Nerve Stimulus to MusclesThe neurotransmitters diffuse across the cleft, attach to the muscle fiber, and cause a contraction.Acetylecholine (ACh) is the neurotransmitter responsible for stimulating skeletal muscleACh changes the permeability of the muscle cell membrane


Nerve Stimulus to MusclesNa+ rush into the cell interior, changing the electrical charge, and generating an action potential.


Nerve Stimulus to MusclesSynaptic cleft gap between nerve and muscleNerve and muscle do not make contactArea between nerve and muscle is filled with interstitial fluidFigure 6.5b


The Sliding Filament Theory of Muscle ContractionActivation by nerve causes myosin heads (crossbridges) to attach to binding sites on the thin filamentMyosin heads then bind to the next site of the thin filamentFigure 6.7


The Sliding Filament Theory of Muscle ContractionThis continued action causes a sliding of the myosin along the actinThe result is that the muscle is shortened (contracted)Figure 6.7


The Sliding Filament TheoryFigure 6.8


The Sliding Filament Theory of Muscle ContractionWhen muscle fibers have been activated by the nervous system:Structures on the myosin filaments attach to special binding sites located on the actin filamentsThe myosin heads(now attached to the actin filaments) act like spring loaded hinges, and pull the thin filaments toward the center of the sarcomere


The Sliding Filament Theory of Muscle ContractionThis attachment, pulling, detachment, and reattachement process happens repeatedly and quicklyThese events are driven by ATP, and the presence of CalciumThe attachment of the cross bridges depends on Ca +


The Sliding Filament Theory of Muscle ContractionThis process takes thousandths of a secondAcetylcholine is broken down by the enzyme cholinesteraseThis ends the muscle contraction, and limits the system to one contraction per impulse


Graded responsesMuscle cells respond according to an all or nothing ruleThis states that a muscle cell will contract to its fullest if stimulatedMuscle cells DO NOT partially contract


Graded responsesMuscles are composed of thousands of muscle cells, and can therefore react with a graded responseThis means muscles can shorten to different degreesThis is accomplished in 2 ways


Graded responses1.) Changing the frequency of muscle stimulation2.)Changing the number of cells stimulated


Graded responsesMost muscles do not have a chance to completely relax between nerve impulsesBecause of this, the results these rapid impulses are summed togetherThis results in a fused, or complete tetanusUntil that point is reached, the muscles are in unfused, or incomplete tetanus


Types of Graded ResponsesTwitchSingle, brief contractionNot a normal muscle functionFigure 6.9ab


Types of Graded ResponsesTetanus (summing of contractions)One contraction is immediately followed by anotherThe muscle does not completely return to a resting stateThe effects are addedFigure 6.9ab


Unfused (incomplete) tetanusSome relaxation occurs between contractionsThe results are summed


Types of Graded ResponsesFused (complete) tetanusNo evidence of relaxation before the following contractionsThe result is a sustained muscle contractionFigure 6.9cd


Muscle Response to Strong StimuliMuscle force depends upon the number of fibers stimulatedMore fibers contracting results in greater muscle tensionMuscles can continue to contract unless they run out of energy


Energy for Muscle ContractionInitially, muscles used stored ATP for energyBonds of ATP are broken to release energyOnly 4-6 seconds worth of ATP is stored by musclesAfter this initial time, other pathways must be utilized to produce ATP


Energy for Muscle ContractionDirect phosphorylationMuscle cells contain creatine phosphate (CP)CP is a high-energy moleculeAfter ATP is depleted, ADP is leftCP transfers energy to ADP, to regenerate ATPCP supplies are exhausted in about 20 secondsFigure 6.10a


Energy for Muscle ContractionAerobic RespirationSeries of metabolic pathways that occur in the mitochondriaGlucose is broken down to carbon dioxide and water, releasing energyThis is a slower reaction that requires continuous oxygenFigure 6.10b


Energy for Muscle ContractionAnaerobic glycolysisReaction that breaks down glucose without oxygenGlucose is broken down to pyruvic acid to produce some ATPPyruvic acid is converted to lactic acidFigure 6.10c


Energy for Muscle ContractionAnaerobic glycolysis (continued)This reaction is not as efficient, but is fastHuge amounts of glucose are neededLactic acid produces muscle fatigueFigure 6.10c


Muscle Fatigue and Oxygen DebtWhen a muscle is fatigued, it is unable to contractThe common reason for muscle fatigue is oxygen debtOxygen must be repaid to tissue to remove oxygen debtOxygen is required to get rid of accumulated lactic acidIncreasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less


Types of Muscle ContractionsIsotonic contractionsMyofilaments are able to slide past each other during contractionsThe muscle shortensIsometric contractionsTension in the muscles increasesThe muscle is unable to shorten


Muscle ToneSome fibers are contracted even in a relaxed muscleDifferent fibers contract at different times to provide muscle toneThe process of stimulating various fibers is under involuntary control


Effects of Exercise on MuscleResults of increased muscle useIncrease in muscle sizeIncrease in muscle strengthIncrease in muscle efficiencyMuscle becomes more fatigue resistant


Effects of Exercise on MuscleThe amount of work done by a muscle is reflected in changes to that muscle itself.Inactivity due to loss of nerve supply, immobilization, or anything else, leads to muscle wastingThis loss is known as atrophy


Effects of Exercise on MuscleAerobic exercise is endurance exercise.This results in stronger, more flexible muscles, with greater resistance to fatigue.These changes are related to increased blood supply and increased mitochondrial synthesis, and increased oxygen storage capacity


Effects of Exercise on MuscleAerobic exercise has a profound and beneficial effect on the overall bodyMetabolism is more efficientDigestion and elimination increaseCoordination increasesThe skeleton becomes stronger


Effects of Exercise on MuscleAerobic exercise does NOT cause skeletal muscles to increase in sizeMuscle size increases as a result of resistance ( isotonic ) exerciseIncreased muscle size results from individual muscle cells synthesizing additional contractile fibers


Types of MovementEvery skeletal muscle has at LEAST 2 points of attachment to a bone, or other connective tissueThe Origin of a muscle is defined as that part of the muscle attached to the immovable or less movable boneThe Insertion is defined as that part of the muscle attached to the more movable bone


Types of MovementWhen a muscle contraction occurs, the insertion ( and the structure it is attached to ) move toward the origin This movement is known as the action of the muscle


Muscles and Body MovementsMovement is attained due to a muscle moving an attached boneFigure 6.12


Muscles and Body MovementsMuscles are attached to at least two pointsOrigin attachment to a moveable boneInsertion attachment to an immovable boneFigure 6.12


Important Terms Describing Muscle MovementFlexion: decreases the angle of a joint, bringing two bones closer togetherExtension : opposite of flexion, increases the angle of a joint moving two bones apart. (angles > 180o is hyperextension e.g. pointing your chin to the ceiling)


Important Terms Describing Muscle MovementAbduction: moving a limb away from the mid-lineAdduction: movement of a limb toward the mid-lineRotation: movement of a bone around its longitudinal axis(shaking your head no)Circumduction: combines flexion, extension, abduction and adduction. The proximal end of the limb is stationary and the distal end moves in a circle


Important Terms Describing Muscle MovementPronation: moving the palm of the hand from an anterior facing to a posterior facing position(radius and ulna cross)Supination: the opposite of pronation, (radius and ulna are parallel)Inversion:Turning the sole of the foot so it faces mediallyEversion: Turning the sole of the foot so it faces laterally


Important Terms Describing Muscle MovementDorsiflexion: movement of the ankle that moves the instep dorsally toward the tibiaPlantar flexion: pointing the toes, opposite of dorsiflexion


Types of MusclesBecause muscles can only contract, they must be paired(at least) acting against one another.When several muscles are working together to produce a movement, the muscle that has the major responsibility for the motion is called the prime mover.


Types of MusclesThose muscles that oppose, or reverse this motion are called antagonists.Synergists: help prime movers by producing the same motion, or by reducing undesirable motion.Fixators: Are specialized synergists. These muscles stabilize the origin of a prime mover so that all the tension can be used to move the insertion bone.


Naming of MusclesMuscles are named based on several criteria based on structural or functional characteristics.Direction of muscles fibers: named in reference to an imaginary line, usually the mid-line of the body, or the long axis of a limb bone.Rectus (straight): fibers run parallel to the imaginary lineOblique (slanted): fibers run slanted or obliquely to the imaginary line


Naming of MusclesRelative size: maximus (largest); minimus(smallest); longus(long) e.g gluteus maximus, the largest of the gluteus muscle groupLocation of muscle: muscles named for the bone they are associated with. (e.g. temporalis, frontalis)


Naming of MusclesNumber of origins: biceps, triceps or quadraceps , mean 2,3, or 4 origins respectively.Location of origin and insertion: muscles can be named for their attachment sites. For example, sternocleidomastoid (sterno:sternum;cleido:clavicle;mastoid, mastoid process of temporal bone)


Naming of MusclesShape of muscle: deltoid, triagular muscle that caps the shoulder.Action of muscle: terms such as flexor, extensor, adductor appearing in muscle names describe the action.


Naming of MusclesArrangement of Fascicles:Fascicle arrangements vary, producing muscles with different structures and properties:Circular : fascicles are arranged in concentric rings.Usually found surrounding body openings(sphincters)


Naming of MusclesConvergent: the fascicles converge toward a single insertion tendon(pectoralis major)Parallel: the length of the fascicles run parallel to the long axis of the muscle.These are strap-like muscles.A modification of parallel arrangement is called fusiform.


Naming of MusclesFusiform : spindle shaped muscle with expanded belly.( biceps brachii)Pennate : feather patternShort fascicles attach obliquely to a central tendon.(extensor digitorum longus)If the fascicles insert into only one side of the tendon, the muscle is unipennate


Naming of MusclesIf the fascicles insert into opposite sides of the tendon or from several different sides the muscle is bipennate, or multipennate.A muscles fascicle arragnement determines its range of motion and power.The longer and more parallel the fascicles are to the long axis, the more the muscle can shorten.


Naming of MusclesSuch muscles are not usually powerful.Muscle power depends on the total number of muscle cells in the muscle.Bipennate muscles shorten very little, but are very powerful


Gross Anatomy of Skeletal MusclesThere are 700 + muscles in the human bodyWe will discuss important muscles, and the superficial skeletal musclesThe best approach is to study muscles in logical groupings


Muscles of the head and neckFrontalisOrbicularis OculiOrbicularis OrisBuccinatorZygomaticusMuscles Used for Chewing::MasseterTemporalis


Head and Neck MusclesFigure 6.15


Neck MusclesPlatysmaSternocleidomastoid


Trunk MusclesAnterior::Pectoralis majorIntercostal musclesMuscles of the Abdominal Girdle::Rectus abdominusExternal ObliqueInternal ObliqueTransversus abdominus


Trunk MusclesFigure 6.16


Superficial Muscles: AnteriorFigure 6.21


Superficial Muscles: PosteriorFigure 6.22


Muscles of the Lower LegFigure 6.20


Muscles of the Pelvis, Hip, and ThighFigure 6.19c


Deep Trunk and Arm MusclesFigure 6.17


Head and Neck MusclesFigure 6.15


The Muscular System

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