The Muscular System

Mrs. AshleyThe Muscular SystemFunctions of the Muscular SystemMovement-responsible for all types of body movement both voluntary and involuntaryAdd in digestionPump bloodSupporting soft tissues in body cavitiesMaintaining body temperatureGuarding entrances and exits to body

Three Types of MusclesSkeletal MusclesCardiac MusclesSmooth MusclesComparison of Skeletal, Cardiac, and Smooth Muscles

Comparison of Skeletal, Cardiac, and Smooth Muscles

Characteristics of MusclesSkeletal and smooth muscle cells are elongated (muscle cell = muscle fiber)Contraction of muscles is due to the movement of microfilamentsAll muscles share some terminologyPrefixes myo and mys refer to musclePrefix sarco refers to flesh

Skeletal MusclesProduce movementMaintain postureStabilize jointsGenerate heatSkeletal muscle tissue Associated with & attached to the skeleton Under our conscious (voluntary) control Microscopically the tissue appears striated Cells are long, cylindrical & multinucleate

Sites of Muscle AttachmentsSites of muscle attachmentBonesCartilagesConnective tissue coverings

Microanatomy of a Muscle Fiber (cell)

Microanatomy of a Muscle Fiber (cell)

Cardiac MuscleCardiac muscle tissue Makes up myocardium of heart Unconsciously (involuntarily) controlled Microscopically appears striated Cells are short, branching & have a single nucleus Cells connect to each other at intercalated discs

Smooth MuscleSmooth (visceral) muscle tissue Makes up walls of organs & blood vessels Tissue is non-striated & involuntary Cells are short, spindle-shaped & have a single nucleus Tissue is extremely extensible, while still retaining ability to contract

Physiology of skeletal muscle contraction

Skeletal muscles require stimulation from the nervous system in order to contract Motor neurons are the cells that cause muscle fibers to contractStimulation and Contraction of Single Skeletal Muscle CellsExcitability (also called responsiveness or irritability)ability to receive and respond to a stimulusContractilityability to shorten when an adequate stimulus is receivedExtensibilityability of muscle cells to be stretchedElasticityability to recoil and resume resting length after stretching

The Nerve Stimulus and Action PotentialSkeletal muscles must be stimulated by a motor neuron (nerve cell) to contractMotor unitone motor neuron and all the skeletal muscle cells stimulated by that neuronControl of Muscles Skeletal muscles are made up of thousands of muscle fibers A single motor neuron may directly control a few fibers within a muscle, or hundreds to thousands of muscle fibers All of the muscle fibers controlled by a single motor neuron constitute a motor unit

The Nerve Stimulus and Action Potential

The size of the motor unit determines how fine the control of movement can be small motor units precise control (e.g. eye muscleslarge motor units gross control (e.g. leg muscles)

Recruitment is the ability to activate more motor units as more force (tension) needs to be generatedHypertrophy stressing a muscle (i.e. exercise) causes more myofilaments/myofibrils to be produced within muscle fibers; allows for more cross bridges resulting in more force (strength) as well as larger sizeThere are always some motor units active, even when at rest. This creates a resting tension known as muscle tone, which helps stabilize bones & joints, & prevents atrophyHow Muscles WorkFor muscles to create a movement, they can only pull, not push Muscles in the body rarely work alone, & are usually arranged in groups surrounding a joint A muscle that contracts to create the desired action is known as an agonist or prime mover A muscle that helps the agonist is a synergist A muscle that opposes the action of the agonist, therefore undoing the desired action is an antagonist

Anatomy of the Muscular System

OriginMuscle attachment that remains fixedInsertionMuscle attachment that movesActionWhat joint movement a muscle producesi.e. flexion, extension, abduction, etc.

Muscles and Body MovementsMovement is attained due to a muscle moving an attached boneMuscles are attached to at least two pointsOriginAttachment to a moveable boneInsertionAttachment to an immovable bone

Skeletal muscle movements

Flexion/extensionAbduction/adductionRotation left/right; internal(medial)/external(lateral)pronation/supinationElevation/depressionProtraction/retractionDorsiflexion/plantarflexionInversion/eversion

Types of Body MovementsFlexionDecreases the angle of the jointBrings two bones closer togetherTypical of bending hinge joints like knee and elbow or ball-and-socket joints like the hipExtensionOpposite of flexionIncreases angle between two bonesTypical of straightening the elbow or kneeExtension beyond 180 is hypertension

Types of Body MovementsRotationMovement of a bone around its longitudinal axisCommon in ball-and-socket jointsExample is when you move atlas around the dens of axis (shake your head no)

Types of Body MovementsAbductionMovement of a limb away from the midlineAdductionOpposite of abductionMovement of a limb toward the midline

Types of Body MovementsCircumductionCombination of flexion, extension, abduction, and adductionCommon in ball-and-socket joints

Types of Body MovementsDorsiflexionLifting the foot so that the superior surface approaches the shin (toward the dorsum)Plantar flexionDepressing the foot (pointing the toes)Planting the foot toward the sole

Special MovementsInversionTurn sole of foot mediallyEversionTurn sole of foot laterally

Special MovementsSupinationForearm rotates laterally so palm faces anteriorlyRadius and ulna are parallelPronationForearm rotates medially so palm faces posteriorly Radius and ulna cross each other like an X

Special MovementsOppositionMove thumb to touch the tips of other fingers on the same hand

Naming of Skeletal MusclesBy direction of muscle fibersExample: Rectus (straight)By relative size of the muscleExample: Maximus (largest)By location of the muscleExample: Temporalis (temporal bone)By number of originsExample: Triceps (three heads)By location of the muscles origin and insertionExample: Sterno (on the sternum)By shape of the muscleExample: Deltoid (triangular)By action of the muscleExample: Flexor and extensor (flexes or extends a bone)

a) Convergent(d) Circular

Muscles of the shoulder

Muscles of the shoulderMuscles that move the arm

Muscles that move the arm

Muscles that move the forearm and wrist

Muscles that move the thigh

Muscles that move the thigh

Muscles that move the leg

Muscles that move the foot and toes

Muscles that move the foot and toes

Muscles that move the foot and toes

Muscles that move the foot and toes

List of Muscles to KnowTrapeziusLatissimus dorsiGluteus mediusGluteus maximusCalcaneusFrontalisOrbicularis oculiZygomaticusOrbicularis orisTemporalisOccipitalisBuccinatorMasseterExternal obliqueLinea albaExternal intercostalInternal obliqueLevator scapulaeDeltoidPectoralis majorPectoralis minorTricheps brachiiMore List of Muscles to KnowFlexor Carpi ulnarisFlexor carpi raialisExtensor carpi ulnarisFlexor digitorum longusFibularis musclesGastrocnemiusTibialis anteriorThe Nerve Stimulus and Action Potential

The Nerve Stimulus and Action Potential

The Nerve Stimulus and Action PotentialSynaptic cleft Gap between nerve and muscleNerve and muscle do not make contactArea between nerve and muscle is filled with interstitial fluidAction potential reaches the axon terminal of the motor neuronCalcium channels open and calcium ions enter the axon terminal

The Nerve Stimulus and Action Potential

Transmission of Nerve Impulse to MuscleSodium rushes into the cell generating an action potentialOnce started, muscle contraction cannot be stoppedMuscle fiber contraction is all or noneWithin a skeletal muscle, not all fibers may be stimulated during the same intervalDifferent combinations of muscle fiber contractions may give differing responsesGraded responsesdifferent degrees of skeletal muscle shortening

Contraction of Skeletal MusclesGraded responses can be produced by changing:The frequency of muscle stimulationThe number of muscle cells being stimulated at one time

Types of Graded ResponsesTwitchSingle, brief contractionNot a normal muscle functionSumming of contractionsOne contraction is immediately followed by anotherThe muscle does not completely return to a resting state due to more frequent stimulationsThe effects are addedUnfused (incomplete) tetanusSome relaxation occurs between contractions but nerve stimuli arrive at an even faster rate than during summing of contractionsUnless the muscle contraction is smooth and sustained, it is said to be in unfused tetanus

Types of Graded ResponsesFused (complete) tetanusNo evidence of relaxation before the following contractionsFrequency of stimulations does not allow for relaxation between contractionsThe result is a smooth and sustained muscle contraction

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 ContractionAerobic respirationGlucose is broken down to carbon dioxide and water, releasing energy (about 32 ATP)A series of metabolic pathways occur in the mitochondriaThis is a slower reaction that requires continuous oxygenCarbon dioxide and water are produced

Energy for Muscle ContractionAnaerobic glycolysis and lactic acid formationThis reaction is not as efficient, but is fastHuge amounts of glucose are neededLactic acid produces muscle fatigue

Muscle Fatigue and Oxygen DeficitWhen a muscle is fatigued, it is unable to contract even with a stimulusCommon cause for muscle fatigue is oxygen debtOxygen must be repaid to tissue to remove oxygen deficitOxygen 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 shortens and movement occursExample: bending the knee; rotating the armIsometric contractionsTension in the muscles increasesThe muscle is unable to shorten or produce movementExample: push against a wall with bent elbows

Muscle ToneSome fibers are contracted even in a relaxed muscleDifferent fibers contract at different times to provide muscle tone and to be constantly ready

Effect of Exercise on MusclesExercise increases muscle size, strength, and enduranceAerobic (endurance) exercise (biking, jogging) results in stronger, more flexible muscles with greater resistance to fatigueMakes body metabolism more efficientImproves digestion, coordinationResistance (isometric) exercise (weight lifting) increases muscle size and strength

Transmission of Nerve Impulse to Muscle