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Skeletal Muscle Tissue

Date post: 13-Jan-2016
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Skeletal Muscle Tissue. Skeletal Muscle Tissue Arrangement. Myofibrils – contractile elements of muscle tissue. Skeletal Muscle Cont. Muscle fiber – Muscle cell; composed of several myofibrils. Skeletal Muscle Cont. - PowerPoint PPT Presentation
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Skeletal Muscle Skeletal Muscle Tissue Tissue
  • Skeletal Muscle Tissue

  • Skeletal Muscle Tissue ArrangementMyofibrils contractile elements of muscle tissue

  • Skeletal Muscle Cont.Muscle fiber Muscle cell; composed of several myofibrils

  • Skeletal Muscle Cont.Each muscle fiber is surrounded by a thin sheath of areolar connective tissue called endomysium

  • Muscle Tissue Cont.Fascicles A bundle of muscle fibers. There are usually between 10 to 100 muscle fibers in a fascicle.

  • Muscle Tissue Cont.Each fascicle is surrounded by a layer of dense irregular connective tissue called perimysium

  • Muscle Tissue Cont.Whole muscle made up of several fascicles

  • Muscle Tissue Cont.The whole muscle is surrounded by a dense irregular connective tissue called epimysium

  • Muscle TissueAll three connective tissues (endomysium, perimysium, epimysium) extend beyond the muscle fiber to form a tendon.

  • Muscle TissueTendon Composed of dense regular connective tissue that attaches muscle to the periosteum of the bone

  • General Features of Skeletal MuscleStriated

  • General Features of Skeletal MuscleVoluntary

  • General Features of Skeletal MuscleMultinucleated

  • General Features of Skeletal MuscleControlled by the somatic (voluntary) division of the nervous system

  • Microscopic Anatomy of Muscle FibersMuscle Fiber = Muscle Cell

  • Microscopic Anatomy cont.Sarcolema plasma membrane of muscle cells or muscle fibers

  • Microscopic Anatomy cont.The multiple nuclei of each muscle fiber is located beneath the sarcolema

  • Microscopic Anatomy cont.T (tranverse tubules) Invagination of the sarcolema that tunnel in from the surface to the center of each muscle fiber

  • Microscopic Anatomy cont.Sarcoplasm cytoplasm of a muscle fiber

  • Microscopic Anatomy cont.Sarcoplasmic reticulum fluid filled system of membranous sacs. Calcium is stored here.

  • Microscopic Anatomy cont.Dilated ends of SR are called terminal cisterns

  • Microscopic Anatomy cont.Myofibrils are composed of functional units called sarcomeres responsible for the striations

  • Microscopic Anatomy cont.Each sarcomere is separated from the next by z discs

  • Microscopic Anatomy cont.Sarcomeres are composed of thick (myosin) and thin (actin) filaments

  • Microscopic anatomy cont.A band is the part of the sarcomere composed of thick (myosin) and thin (actin) filaments

  • Microscopic anatomy cont.The A band is the dark striation seen under the microscope

  • Microscopic Anatomy cont.I Band is the part of the sarcomere that contains only thin (actin) filaments

  • Microscopic Anatomy cont.I Band is the light striation seen underneath the microscope

  • Microscopic AnatomyThe H zone is the part of the A band that contains only thick filaments (myosin)

  • Microscopic AnatomyM line is the middle of the sarcomere and is composed of supporting proteins that hold the thick filaments together

  • How does a nerve initiate contraction?Neuromuscular junction the region of contact between a motor neuron and a skeletal muscle fiber

  • Initiation of ContractionSynaptic cleft the region between the neuron and muscle fiber

  • Initiation of ContractionThe tips of axon terminals are called synaptic end bulbs

  • Initiation of ContractionSynaptic vessicles membrane enclosed sacs that contain the neurotransmitter acetylcholine (Ach) located in the synaptic end bulb

  • Initiation of ContractionMotor end plate the region of the sarcolema opposite of the synaptic end bulb

  • Initiation of ContractionEach motor end plate contains between 30 to 40 million Ach receptors

  • Initiation of Contraction / 4 Steps1. Once the nerve impulse arrives at the synaptic end bulb, the synaptic vesicles release Ach via exocytosis.

  • Initiation of Contraction / 4 Steps2. When two ACh molecules bind to the ACh receptors at the motor end plate it opens the cation channel and Na+ can flow across the membrane.

  • Initiation of Contraction / 4 Steps3. Once the inside of the muscle fiber is more positively charged, a muscle action potential is triggered, which propogates along the sarcolema and into the T tubule system.

  • Initiation of Contraction / 4 Steps4. ACh is broken down by acetylcholinesterase in the extracellular matrix of the synaptic cleft.

  • Calciums RoleOnce the action potential propagates along the sarcolema and into the T tubules Ca2+ release channels in the SR membrane open causing Ca2+ to flow out of the SR into the cytosol.

  • Calciums RoleCalcium binds to troponin on the actin filaments causing the troponin-tropomyosin complexes to move away from the myosin binding sites on actin.

  • Contraction / 4 Steps1. ATP hydrolysis ATP is hydrolyzed into ADP and a phospate by ATPase on a myosin head

  • Contraction / 4 Steps2. Attachment of myosin to actin to form crossbridges myosin binds to actin on the myosin binding site and the phosphate is released.

  • Contraction / 4 Steps3. Power stroke The myosin pushes the thin filament past the thick filament toward the M line releasing ADP.

  • Contraction / 4 Steps4. Detachment of myosin from actin When ATP binds to the myosin head, the myosin head detaches from actin.

  • ContractionAs the muscle contracts the I band and H zone decreases

  • RelaxtionOnce nerve impulses stop;Acetylcholinesterase breaks down the remaining acetylcholineMuscle action potentials stopCalcium levels in cytosol decreasesContraction stops

  • How do calcium levels decrease?Ca2+ release channels closeCa2+ active transport pumps move Ca2+ back into the SRIn the SR calsequestrin binds to Ca2+ enabling more Ca2+ to be sequestered within the SR

  • Rigor MortisCalcium leaks out of the SR therefore allowing myosin heads to bind to actin.ATP production ceases so myosin cannot detach form actin.Muscles therefore become rigid (cannot contract or stretch)

  • AtrophyMuscle fibers decrease in size due to loss of myofibrils

  • HypertrophyMuscle fibers increase in diameter due to the production of more myofibrils.

  • ATP and MuscleMuscle fibers need ATP for powering the contraction cycle and to pump Ca2+ into the SR.

  • ATP and Muscle ATP is made by;Creatine phosphateAnaerobic cellular respirationAerobic cellular respiration

  • Creatine PhosphateWhen the muscle is relaxed creatine kinase (CK) transfers a phosphate from ATP to creatine forming creatine phosphate and ADP.

  • Creatine PhosphateATP + Creatine ADP + Creatine PhosphateThis reaction is catalyzed by creatine kinase

  • Creatine PhosphateWhen a muscle contracts CK tranfers a phosphate from creatine phosphate to ADP forming ATP and creatine.

  • Creatine PhosphateCreatine Phosphate + ADP Creatine and ATPThis reaction is catalyzed by CK

  • Anaerobic Cellular RespirationDoes not require oxygenATP is formed by a process called glycolysisA glucose is converted into two pyruvic acid molecules

  • Anaerobic RespirationGlycolysis uses two ATP but forms 4 ATP for a net gain of twoPyruvic acid is converted into lactic acid

  • Anerobic RespirationMuscle fibers attain their glucose via diffusion from the blood and glycogen stored within muscle fibers

  • Aerobic RespirationRequires oxygenTakes place in mitochondriaThe two molecules of pyruvic acid produced in glycolysis enter the kreb cycle.Aerobic respiration results in a net gain of 36 ATP.

  • Aerobic RespirationIn aerobic respiration oxygen is attained via the diffusion of oxygen from blood and oxygen released by myoglobin

  • Aerobic RespirationMyoglobin is a protein found in muscle cells that binds oxygen

  • Motor UnitsThere is only one neuromuscular junction per fiber.

  • Motor UnitsA somatic motor neuron branches out and forms neuromuscular junctions with many muscle fibers.

  • Motor UnitsA motor unit consists of a somatic motor neuron plus all the skeletal muscle fibers it stimulates

  • Motor UnitsAll muscle fibers in a motor unit contract in unison

  • Motor UnitMuscles that produce precise movements are made up of small motor units.

  • Red Muscle FibersHave a high myoglobin content

  • White Muscle FibersHave a low myoglobin content

  • 3 Main Types of Skeletal Muscle FibersSlow Oxidative FibersFast Oxidative-Glycolytic FibersFast Glycolytic Fibers

  • Slow Oxidative FibersSmallest in diameterContain large amounts of myoglobinGenerate ATP by aerobic cellular respirationLarge amounts of mitochondrial and blood capillariesATPase in the myosin head hydrolyzes ATP slowly

  • Fast Oxidative-Glycolytic FibersIntermediate in diameterHigh myoglobin contentGenerates ATP by aerobic and anaerobic respirationHigh content of mitochondria and blood capillariesATPase hydrolyzes ATP quickly

  • Fast Glycolytic FibersLargest in diameterLow myoglobin contentFew blood capillaries and mitochondriaGenerate ATP by anaerobic respirationATPase hydrolyzes ATP quickly

  • Motor UnitMuscle fibers of a single motor unit are of the same type

  • Origin and InsertionMost muscles cross at least one joint and are attached to the articulating bones that form the joint.

  • Origin and InsertionWhen a muscle contracts, it draws one articulating bone toward the other.

  • Origin and InsertionThe attachment of the stationary bone is the origin.

  • Origin and InsertionThe attachment of the movable bone is the insertion

  • Twitch contractionThe contraction of all the muscle fibers in a motor unit in response to a single action potential

  • MyogramA record of a muscle contraction

  • Myogram of a Twitch ContractionLatent periodContraction periodRelaxation period

  • Myogram of a Twitch ContractionLatent period Lasts two millisecondsCalcium ions are released from SR

  • Myogram of a Twitch ContractionContraction period 10 100 msec

  • Myogram of a Twitch ContractionRelaxation Period 10 100 msecActive transport of calcium into SR

  • Frequency of StimulationWave summation When a second stimulus occurs before the muscle has relaxed, the second contraction is stronger than the first.

  • Frequency of StimulationUnfused tetanus When a skeletal muscle is stimulated at a rate of 20 to 30 times per second, it can only partially relax between stimuli resulting in a sustained but wavering contraction.

  • Frequency of StimulationFused tetanus When a skeletal muscle is stimulated at a rate of 80 to 100 stimuli per second, a sustained contraction results in which individual twitches cannot be discerned.

  • Motor Unit RecruitmentNot all motor units in a muscle are not stimulated at once to prevent fatigue.

  • Concenteric Isotonic ContractionA muscle shortens and pulls on a tendon, which produces movement and reduces the angle at a joint.

  • Eccenteric Isotonic ContractionThe length of a muscle increases during contraction.

  • Isometeric ContractionsThe muscle doesnt shorten because the force of the load equals muscle tension.