2Introduction Muscular tissue enables the body and its parts to move Movement is caused by ability of muscle cells (called fibers) to shorten or contractMuscle cells shorten by converting chemical energy (obtained from food) into mechanical energy, which causes movementThree types of muscle tissue exist in the bodyWhat causes movement of the body? (skeletal muscle contraction)
3Muscle Tissue Types of muscle tissue Skeletal muscle—also called striated or voluntary muscleIs 40% to 50% of body weight; attached to bonesMicroscope reveals crosswise stripes or striationsContractions can be voluntarily controlled(Cont’d…)What are the three types of muscle tissue? (skeletal, cardiac, and smooth)If someone weighs 120 pounds, about 50 pounds of the body weight comes from the skeletal muscles.
4Muscle Tissue Types of muscle tissue (cont’d) Cardiac muscle—composes bulk of heartCardiac muscle cells branch frequentlyCharacterized by unique dark bands called intercalated disksInterconnected nature of cardiac muscle cells allows heart to contract efficiently as a unit(Cont’d…)What is the value of the interconnected nature of the cardiac muscle? (It increases the efficiency of the heart muscle in pumping blood.)
5Muscle Tissue Types of muscle tissue (cont’d) Nonstriated muscle or involuntary muscle—also called smooth or visceral muscleLacks cross stripes or striation when seen under a microscope; appears smoothFound in walls of hollow visceral structures such as digestive tract, blood vessels, and uretersContractions not under voluntary control; movement caused by contractions is involuntaryFunction—all muscle cells specialize in contraction (shortening)
7Structure of Skeletal Muscle Skeletal muscle: an organ composed mainly of skeletal muscle cells and connective tissueExtend from one bone across a joint to another bone(Cont’d…)
8Structure of Skeletal Muscle (…Cont’d)StructureParts of a skeletal muscle:Origin—attachment to the bone that remains relatively fixed when movement at the joint occursInsertion—point of attachment to the bone that moves when a muscle contractsBody—main part of the muscle(Cont’d…)What are the origin and the insertion point, and what are their roles in movement of the body?
9Structure of Skeletal Muscle (…Cont’d)Muscles attach to the bone by tendons—strong cords of fibrous connective tissueSome tendons: enclosed in synovial-lined tubes and lubricated by synovial fluidBursae—small synovial-lined sacs containing a small amount of synovial fluid(Cont’d…)Tendons do not tear or pull away from bone easily, yet emergency room physicians and nurses frequently see torn or severed tendon injuries.Small, fluid-filled sacs called bursae lie between some tendons and the bones beneath them.What is the role of bursae? (Bursae make it easier for a tendon to slide over a bone when the muscle shortens.)
10Structure of Skeletal Muscle (…Cont’d)Attachments of a skeletal muscle
11Structure of Skeletal Muscle (…Cont’d)Microscopic structureMuscle tissue consists of specialized contractile cells called fibersEach fiber contains two kinds of very fine, threadlike structures:Thick myofilaments =MyosinThin myofilaments =Actin(Cont’d…)What are thick and thin myofilaments composed of?thick myofilaments formed from protein myosin; thin myofilaments composed of actin)
12Structure of Skeletal Muscle (…Cont’d)Sarcomere: basic functional (contractile) unitSeparated from each other by dark bands called Z linesSliding filament model explains mechanism of contractionThick and thin myofilaments slide past each other as a muscle contractsAs the osteon (Haversian system) serves as basic building block in compact bone, sarcomere serves that function in muscle.What is required for contraction? (calcium and energy-rich ATP molecules)
13Functions of Skeletal Muscle MovementMuscles produce movementAs muscle contracts, it pulls the insertion bone closer to the origin boneMovement occurs at the joint between the origin and the insertion(Cont’d…)Describe how muscles produce movement.
14Functions of Skeletal Muscle (Cont’d…)MovementGroups of muscles usually contract to produce a single movementPrime mover—contraction is mainly responsible for producing a movementSynergist—contractions help the prime mover produce a movementAntagonist—actions oppose the action of a prime mover in a movementWhen a muscle group produces movement, what are the components of the group called? (prime mover, synergist, antagonist)When antagonist muscles contract, roles are reversed and they produce opposite movement.Voluntary movement is normally smooth and free of jerks because skeletal muscles work in coordinated teams, not separately.
15Functions of Skeletal Muscle (…Cont’d)PostureTonic contraction: specialized muscle contraction that enables us to maintain body positionOnly a few of a muscle’s fibers shorten at one timeTonic contractions produce no movementTonic contractions maintain muscle tone called posture(Cont’d…)Good posture means that body parts are held in positions that favor best function.Bad posture causes fatigue and may lead to deformity.
16Functions of Skeletal Muscle (…Cont’d)Heat productionSurvival depends on the ability to maintain constant body temperatureFever—an elevated body temperature; often a sign of illnessHypothermia—a reduced body temperatureContraction of muscle fibers produces most of the heat required to maintain normal body temperatureHeat is produced by the breakdown of adenosine triphosphate (ATP) during contractions.
17Fatigue Reduced strength of muscle contraction Caused by repeated muscle stimulationRepeated muscular contraction depletes cellular ATP store and outstrips the ability of the blood supply to replenish oxygen and nutrients(Cont’d…)What can cause a decrease in the strength of muscle contraction? (muscle cells being repeatedly stimulated without adequate rest)
18Fatigue(…Cont’d)Contraction in the absence of adequate oxygen produces lactic acid, which contributes to muscle sorenessOxygen debt—the continued metabolic effort required to burn excess lactic acid that may accumulate during prolonged periods of exerciseLabored breathing is required to help the body pay the oxygen debt – an example of homeostasis at work.What is the body attempting to do on the cellular level during labored breathing following exercise? (to return the cells’ energy and oxygen reserves to pre-exercise levels)
19Role of Other Body Systems in Movement Muscle functioning depends on the functioning of many other parts of the bodyRespiratory, circulatory, nervous, muscular, and skeletal systems play essential roles in producing normal movementsNormal function of one body part depends on the normal function of all other parts.What are some examples of pathologic conditions that might affect movement of the body? (skeletal system disorders. multiple sclerosis, brain hemorrhage, and spinal cord injury)
20Motor UnitStimulation of a muscle by a nerve impulse is required to produce movementMotor neuron: specialized nerve that transmits an impulse to a muscle, causing contractionNeuromuscular junction: specialized point of contact between a nerve ending and the muscle fiber it innervatesMotor unit: the combination of a motor neuron with the muscle cell(s) it innervatesSpecialized chemicals are released by the motor neuron in response to a nerve impulse.
21Muscle StimulusA muscle will contract only if an applied stimulus reaches a certain level of intensityThreshold stimulus: minimal level of stimulation required to cause a muscle fiber to contractOnce stimulated by a threshold stimulus, a muscle fiber will contract completely, a response called all or none(Cont’d…)What is a threshold stimulus?
22Muscle Stimulus(…Cont’d)Different muscle fibers in a muscle are controlled by different motor units having different threshold-stimulus levelsAlthough individual muscle fibers always respond all or none to a threshold stimulus, the muscle as a whole does notHow is a graded response of a muscle accomplished? (Different motor units responding to different threshold stimuli permit a muscle as a whole to execute contractions of graded force.)
23Types of Skeletal Muscle Contraction Twitch and tetanic contractionsTwitch contractions—a quick, jerky response to stimulusSingle contraction of muscle fibers caused by a single threshold stimulusTetanic contractions—sustained, steady muscular contractionsCaused by a series of stimuli bombarding a muscle in rapid succession(Cont’d…)About 30 stimuli per second evoke tetanic contractions in certain types of skeletal muscles.Are twitch contractions significant for normal activity? (no)
24Types of Skeletal Muscle Contraction (…Cont’d)Isotonic contractionsContraction of a muscle that produces movement at a jointThe muscle changes length, causing the insertion end of the muscle to move relative to the point of originMost types of body movements such as walking and running are isotonic contractions(Cont’d…)What is an isotonic contraction?
25Types of Skeletal Muscle Contraction (…Cont’d)Isometric contractionsMuscle contractions that do not produce movementThe muscle as a whole does not shortenNo movement occurs during isometric contractions, but tension within the muscle increasesWhat is an isometric contraction?What are the differences between isotonic and isometric contractions?Pushing against a wall is an example of an isometric contraction.
26Types of Skeletal Muscle Contraction (…Cont’d)Types ofMuscleContraction
27Effects of Exercise on Skeletal Muscles Regular, properly practiced exercise improves muscle tone and posture,Results in more efficient heart and lung functioningReduces fatigue(Cont’d…)What are some of the health benefits of regular exercise?
28Effects of Exercise on Skeletal Muscles Prolonged inactivity causes disuse atrophyRegular exercise increases muscle size, called hypertrophy(Cont’d…)What type of changes do muscles undergo relative to the amount of work they normally do? (disuse atrophy, hypertrophy)c
29Effects of Exercise on Skeletal Muscles (…Cont’d)Strength training: exercise involving contractions of muscles against heavy resistanceIncreases number of myofilaments in each muscle fiberTotal mass of the muscle increasesDoes not increase the number of muscle fibers(Cont’d…)What are examples of strength training? (isometric exercises and weight lifting)
30Effects of Exercise on Skeletal Muscles (…Cont’d)Endurance training: exercise that increases a muscle’s ability to sustain moderate exercise over long periodsSometimes called aerobic trainingAllows more efficient delivery of oxygen and nutrients to a muscle via increased blood flowIncreases the number of blood vessels in a muscleDoes not usually result in muscle hypertrophyWhat are the differences between strength training and endurance training?
32Skeletal Muscle Groups Muscles of the head and neckFacial musclesOrbicularis oculi, orbicularis oris, zygomaticusMuscles of masticationMasseter, temporalSternocleidomastoid—flexes headTrapezius—elevates shoulders and extends head(Cont’d…)What are the names of the “kissing muscle” and the “smiling muscle”? (Orbicularis oculi is the kissing muscle, and zygomaticus is the smiling muscle.)Mastication muscles are among the strongest muscles in the body.
33Skeletal Muscle Groups (…Cont’d)Muscles of the head and neck(Cont’d…)
34Skeletal Muscle Groups (…Cont’d)Muscles that move the upper extremitiesPectoralis major—flexes upper armLatissimus dorsi—extends upper armDeltoid—abducts upper armBiceps brachii—flexes forearmTriceps brachii—extends forearm(Cont’d…)The upper extremity is attached to the thorax by the pectoralis major.What is the name of the “boxer’s muscle”? (triceps brachii)
35Skeletal Muscle Groups (…Cont’d)Muscles of the trunkAbdominal musclesRectus abdominisExternal obliqueInternal obliqueTransversus abdominisRespiratory musclesIntercostal musclesDiaphragm(Cont’d…)Rectus abdominis flexes the spinal column.Which muscles change the size of the chest during respiration? (respiratory muscles)
36Skeletal Muscle Groups (…Cont’d)Muscles of the trunk (Cont’d…)
37Skeletal Muscle Groups (…Cont’d)Muscles that move the lower extremitiesIliopsoas—flexes thighGluteus maximus—extends thighAdductor muscles—adduct thighsHamstring muscles—flex lower legSemimembranosusSemitendinosusBiceps femoris(Cont’d…)Iliopsoas normally flexes the thigh, but can flex the trunk if the thigh is fixed/immovable as in sit-ups.
38Skeletal Muscle Groups (…Cont’d)Muscles that move the lower extremitiesQuadriceps femoris group—extend lower legRectus femorisVastus musclesTibialis anterior—dorsiflexes footGastrocnemius—plantar flexes footPeroneus group—flex footGastrocnemius is sometimes called the toe dancer’s muscle.
39Types of Movements Produced by Skeletal Muscle Contractions Flexion—decreases the angle between two bones at their joint: bendingExtension—increases the angle between two bones at their joint: straighteningAbduction—movement of a part away from the midline of the bodyAdduction—movement of a part toward the midline of the bodyRotation—movement around a longitudinal axis(Cont’d…)What are examples of the types of movements listed here? (Flexion: bending elbow or knee, extension: straightening elbow or knee, abduction: lowering arm. Rotation: shaking head “no”)
40Types of Movements Produced by Skeletal Muscle Contractions (…Cont’d)Flexion and extension of the elbow (Cont’d…)
41Types of Movements Produced by Skeletal Muscle Contractions (…Cont’d)Supination and pronation—hand positions from rotation of the forearmSupination: palm turned to the anterior positionPronation: palm faces posteriorlyDorsiflexion and plantar flexion—foot movementsDorsiflexion: elevation of the dorsum or top of the footPlantar flexion: bottom of the foot is directed downward(Cont’d…)What are the origins of the words “supination” and “pronation”? (supine and prone)
42Types of Movements Produced by Skeletal Muscle Contractions (…Cont’d)Examples of body movements