2The Muscular SystemMuscles are responsible for all types of body movementThree basic muscle types are found in the bodySkeletal muscleCardiac muscleSmooth muscle
3Characteristics of Muscles Muscle cells are elongated (muscle cell = muscle fiber)Contraction of muscles is due to the movement of microfilamentsAll muscles share some terminologyPrefix myo refers to musclePrefix mys refers to musclePrefix sarco refers to flesh
4Smooth Muscle Characteristics Has no striationsSpindle-shaped cellsSingle nucleusInvoluntary – no conscious controlFound mainly in the walls of hollow organs
5Cardiac Muscle Characteristics Has striationsUsually has a single nucleusJoined to another muscle cell at an intercalated discInvoluntaryFound only in the heart
6Classification of muscle VoluntaryInvoluntarySkeletalCardiacSmoothLimbsHeartVisceraStriatedNon-striatedNote: Control, Location and Structure
7Muscle Control Type of muscle Nervous control Type of control Example SkeletalControlled by CNSVoluntaryLifting a glassSkeletalCardiacRegulated by ANSInvoluntaryHeart beatingSmoothControlled by ANSInvoluntaryPeristalsis
8Skeletal MuscleThere are about 650 muscles in the human body. They enable us to move, maintain posture and generate heat. In this section we will only study a sample of the major muscles.There are about 650 muscles in the human body. They enable us to move, maintain posture and generate heat. In this unit will only study a sample of the major muscles.
9Function of Skeletal Muscles Produce movementMaintain postureStabilize jointsGenerate heat
10Skeletal Muscle Characteristics Most are attached by tendons to bones
11Skeletal Muscle Characteristics Cells are multinucleateStriated – have visible bandingVoluntary – subject to conscious controlCells are surrounded and bundled by connective tissue
12Connective Tissue Wrappings of Skeletal Muscle Endomysium – around single muscle fiberPerimysium – around a fascicle (bundle) of fibers
13Connective Tissue Wrappings of Skeletal Muscle Epimysium – covers the entire skeletal muscleFascia – on the outside of the epimysium
14Skeletal Muscle Attachments Epimysium blends into a connective tissue attachmentTendon – cord-like structureAponeuroses – sheet-like structureSites of muscle attachmentBonesCartilagesConnective tissue coverings
15Microscopic Anatomy of Skeletal Muscle Cells are multinucleateNuclei are just beneath the sarcolemma
25Properties of Skeletal Muscle Activity Irritability – ability to receive and respond to a stimulusContractility – ability to shorten when an adequate stimulus is received
26Nerve Stimulus to Muscles Skeletal muscles must be stimulated by a nerve to contractMotor unitOne neuronMuscle cells stimulated by that neuron
27Nerve Stimulus to Muscles Neuromuscular junctions – association site of nerve and muscle
28Nerve Stimulus to Muscles Synaptic cleft – gap between nerve and muscleNerve and muscle do not make contactArea between nerve and muscle is filled with interstitial fluid
29Transmission of Nerve Impulse to Muscle Neurotransmitter – chemical released by nerve upon arrival of nerve impulseThe neurotransmitter for skeletal muscle is acetylcholineNeurotransmitter attaches to receptors on the sarcolemmaSarcolemma becomes permeable to sodium (Na+)
30Transmission of Nerve Impulse to Muscle Sodium rushing into the cell generates an action potentialOnce started, muscle contraction cannot be stopped
31The Steps in Muscle Contraction When a muscle is relaxed, myosin and actin filaments are not attached.
32The Steps in Muscle Contraction Myosin attaches to a binding site on an actin filament. Calcium is required to make a binding site available for myosin.
34The Steps in Muscle Contraction The myosin head rotates and causes the actin filament to slide along the myosin filament. The sliding causes the filaments to overlap more, and the sarcomere becomes shorter.
35The Steps in Muscle Contraction During contraction, myosin attaches to binding sites on actin, forming cross-bridges. Using ATP, the cross-bridges pull the actin toward the center of the sarcomere.
36The Steps in Muscle Contraction After the myosin head has rotated as far as it can, it must let go of the actin fiber. ATP is required for myosin to detach from actin. The myosin head snaps back into its original position, using the energy in the ATP. The ATP becomes ADP and releases a phosphate ion.
37The Steps in Muscle Contraction Calcium exposes a new actin binding site and myosin reattaches to actin. Steps 1 through 3 happen again.
38The Steps in Muscle Contraction The cross-bridges break, myosin binds to another site, and the cycle begins again until the muscle fiber is contracted.In this way, the myosin heads walk along actin filaments and step at available binding sites. This grabbing and pulling action repeats, the sarcomere shortens, and the Z lines are pulled closer together.
39To summarize . . .Myosin filaments bind to actin filaments, actin filaments move inward, and sarcomeres shorten to cause muscle contraction.
40Contraction of a Skeletal Muscle Muscle fiber contraction is “all or none”Within a skeletal muscle, not all fibers may be stimulated during the same intervalDifferent combinations of muscle fiber contractions may give differing responsesGraded responses – different degrees of skeletal muscle shortening
41Types of Graded Responses TwitchSingle, brief contractionNot a normal muscle function
42Types of Graded Responses Tetanus (summing of contractions)One contraction is immediately followed by anotherThe muscle does not completely return to a resting stateThe effects are added
43Types of Graded Responses Unfused (incomplete) tetanusSome relaxation occurs between contractionsThe results are summed
44Types of Graded Responses Fused (complete) tetanusNo evidence of relaxation before the following contractionsThe result is a sustained muscle contraction
45Muscle Response to Strong Stimuli Muscle 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
46Energy for Muscle Contraction Initially, 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
47Energy for Muscle Contraction Direct 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 seconds
48Energy for Muscle Contraction Aerobic 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 oxygen
49Energy for Muscle Contraction Anaerobic glycolysisReaction that breaks down glucose without oxygenGlucose is broken down to pyruvic acid to produce some ATPPyruvic acid is converted to lactic acid
50Energy for Muscle Contraction Anaerobic glycolysis (continued)This reaction is not as efficient, but is fastHuge amounts of glucose are neededLactic acid produces muscle fatigue
53Five Golden Rules of Gross Muscle Activity all muscles cross at least one jointbulk of muscles lies proximal to the joint crossedall muscles have at least 2 attachments: origin & insertionmuscles only pull/never pushduring contraction the muscle insertion moves toward the origin
54Muscles and Body Movements Movement is attained due to a muscle moving an attached bone
55Muscles and Body Movements Muscles are attached to at least two pointsOrigin – attachment to an immoveable boneInsertion – attachment to a movable bone
57Types of Muscle Contractions Isotonic contractionsMyofilaments are able to slide past each other during contractionsThe muscle shortensIsometric contractionsTension in the muscles increasesThe muscle is unable to shortenMyofilaments “skidding their wheels”
58Muscle Tone Some fibers are contracted even in a relaxed muscle Different fibers contract at different times to provide muscle toneThe process ofstimulating variousfibers is underinvoluntary control
59Muscle ToneWhen muscles are not worked they atrophy (waste away) and become flaccid.
60Effects of Exercise on Muscle Aerobics result in stronger muscles due to increase blood supplyMuscle fibers increase mitochondria and oxygen storageMuscle becomes more fatigue resistantHeart enlarges to pumpmore blood to bodyDoes not increase skeletalmuscle size
61Effects of Exercise on Muscle Results of increased muscle use from resistance trainingIndividual muscle cells make more contractile filaments & connective tissue increasesIncrease in muscle sizeIncrease in muscle strength
63Muscle Fatigue and Oxygen Debt When 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
78Diseases and Disorders of the Muscular System Myalgia: Muscle pain due to strain, tearing of muscle fibers. It also is a symptom of an immune response along with a fever.Myositis: Inflammation of muscle tissue due to injury or disease.Charley Horse (fibromyositis): Inflammation of muscle tissue and the tendons associated with that muscle due to injury (tear or severe bruising- contusion)Cramps: Painful, involuntary muscle spasms
79Cerebral PalsyThis disorder is characterized by paralysis and or weakened muscles due to loss of muscle tone. It can be caused due to lack of oxygen to the region of the motor region of the cerebrum of the brain which controls conscious control of muscles. This is often attributed to complication during birth.
80PoliomyelitisPoliomyelitis: Polio is due to a viral infection which affects the motor neurons that control skeletal muscles. It often leads to paralysis and can result in death by paralysis of the diaphragm. Due to vaccine developed by Jonas Salk, the virus has been virtually eliminated in the US. However, it still poses a threat in developing countries.
81Muscular DystrophyCongenital muscle-destroying disease affect specific muscle groupsMuscle fibers degenerate & atrophy due to an absence of dystrophin, a protein that helps keep muscle cells intactDuchenne’s M.D Most common & serious—Mostly in males (diagnosed between2-6 yrs)Survival is rare beyond early 30’sX-linked recessive
82Myasthenia gravisRare adult disease caused by antibodies to acetylcholine receptors at the neuromuscular junction which prevents the muscle contraction from occurringDrooping upper eyelids, difficulty swallowing & talking, muscle weakness & fatigueDeath occurs when respiratory muscles cease to function
83Aging Connective Tissue increases Amount of Muscle tissue decreases Muscles become stringier(sinewy)Body weight declines due to loss of muscle massBy age 80, muscle strength usually decrease by 50% without weight training exercises
84Types of MusclesPrime mover – muscle with the major responsibility for a certain movementAntagonist – muscle that opposes or reverses a prime moverSynergist – muscle that aids a prime mover in a movement and helps prevent rotationFixator – stabilizes the origin of a prime mover
85Naming of Skeletal Muscles Direction of muscle fibersExample: rectus (straight)Relative size of the muscleExample: maximus (largest)
86Naming of Skeletal Muscles Location of the muscleExample: many muscles are named for bones (e.g., temporalis)Number of originsExample: triceps (three heads)
87Naming of Skeletal Muscles Location of the muscle’s origin and insertionExample: sterno (on the sternum)Shape of the muscleExample: deltoid (triangular)Action of the muscleExample: flexor and extensor (flexes or extends a bone)