7/28/2019 18001034 Anatomy Presentation Ho 5Muscles http://slidepdf.com/reader/full/18001034-anatomy-presentation-ho-5muscles 1/38 Muscles Muscle is one of our 4 tissue types and muscle tissue combined with nerves, blood vessels, and various connective tissues is what makes up those muscle organs that are familiar to us. Muscles are quite complex and as we’ll find out, they are a marvel of both biology and physics. 1
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7/28/2019 18001034 Anatomy Presentation Ho 5Muscles
Movement of body parts and of the environmentMovement of blood through the heart and thecirculatory vessels.Movement of lymph through the lymphaticvesselsMovement of food (and, subsequently, foodwaste) through the GI tractMovement of bile out of the gallbladder and intothe digestive tractMovement of urine through the urinary tractMovement of semen through the malereproductive tract and female reproductive tractMovement of a newborn through the birth canal
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7/28/2019 18001034 Anatomy Presentation Ho 5Muscles
The ability to receive and respond to a stimulusIn skeletal muscle, the stimulus is a neurotransmitter(chemical signal) release by a neuron (nerve cell).In smooth muscle, the stimulus could be aneurotransmitter, a hormone, stretch, pH, Pco2, or Po2.(the symbol means “a change in” )In cardiac muscle, the stimulus could be a
neurotransmitter, a hormone, or stretch.The response is the generation of an electricalimpulse that travels along the plasma membrane of the muscle cell.
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Epimysium surroundsseveral bundles known asfascicles.Each fascicle is a bundle of super-long skeletal musclecells (muscle fibers),surrounded by a layer of dense irregular CT called theperimysium ( peri =around).Each muscle cell extends thelength of the whole muscle
organ and is surrounded bya fine layer of looseconnective tissue, theendomysium.The epi-, peri-, andendomysium are allcontinuous with oneanother.
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In this photomicrograph, you should notice: the epimysium on the left, the multiplefascicles, the translucent perimysium partitioning them , and the multiple muscle fibersmaking up the fascicles.
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7/28/2019 18001034 Anatomy Presentation Ho 5Muscles
Most span joints and are attached to bones.The attachment of the muscle to the immoveable bonein a joint is its origin, while the attachment to themoveable bone is its insertion.
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7/28/2019 18001034 Anatomy Presentation Ho 5Muscles
Indirect attachments aretypical. The muscle CTextends and forms eithera cordlike structure (atendon ) or a sheetlikestructure ( aponeurosis )which attaches to theperiosteum orperichondrium.
Muscle attachments maybe direct or indirect .
Direct attachments are less common. Theepimysium is fused to a periosteum or aperichondrium.
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7/28/2019 18001034 Anatomy Presentation Ho 5Muscles
as a skeletal muscle fiber becausethey are so long.Their diameter can be up to 100um and their lengthcan be as long as 30cm.They’re so large because a single skeletal muscle cellresults from the fusion of hundreds of embryonicprecursor cells called myoblasts.
A cell made from the fusion of many others is known as asyncytium.
Each skeletal muscle fiber will have multiple nuclei.
Why? 14
7/28/2019 18001034 Anatomy Presentation Ho 5Muscles
Muscle fiberPM isknown assarcolemmaMuscle fibercytoplasmis known assarcoplasm
Sarcoplasm has lots of mitochondria ( why ?), lots of glycogen granules(to provide glucose for energy needs) as well as myofibrils andsarcoplasmic reticuli .
Sarcolemma has invaginations that penetrate through the cell calledtransverse tubules or T tubules .
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7/28/2019 18001034 Anatomy Presentation Ho 5Muscles
Muscle cell version of the smoothendoplasmic reticulum.Functions as a calcium
storage depot inmuscle cells.Loose network of thismembrane boundorganelle surrounds allthe myofibrils in amuscle fiber. We willsee why this is soimportant soon.
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MyofibrilsEach muscle fiber contains rodlike structures called
myofibrils that extend the length of the cell. They arebasically long bundles of protein structures calledmyofilaments and their actions give muscle the ability tocontract.The myofilaments are classified as thick filaments andthin filaments.
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Each thin filament is made up of 3 different typesof protein: actin, tropomyosin, and troponin.
Each thin filament consists of a long helical doublestrand. This strand is a polymer that resembles a stringof beads. Each “bead” is the globular protein actin. Oneach actin subunit, there is a myosin binding site.Loosely wrapped around the actin helix and covering themyosin binding site is the filamentous protein,tropomyosin.Bound to both the actin and the tropomyosin is a trio of proteins collectively known as troponin.
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Each myofibril is made up 1000’s of repeatingindividual units known as sarcomeres (pictured below)Each sarcomere is an ordered arrangement of thick and thin filaments. Notice that it has:
regions of thin filaments by themselves (pinkish fibers)a region of thick filaments by themselves (purple fibers)regions of thick filaments and thin filamentsoverlapping.
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SarcomereThe sarcomere is flanked by 2 protein structuresknown as Z discs.The portion of the sarcomere which contains thethick filament is known as the A band. A standsfor anisotropic which is a fancy way of saying thatit appears dark under the microscope.
The A band contains a zone of overlap (btwn thick & thin filaments) and an H zone which contains only thick filaments
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Here is a longitudinal section of skeletal muscle. See themultiple nuclei (N) pressed against the side of the musclefibers. The light I bands and dark A bands are labeled for
you. What do you think the F stands for?
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Smooth MuscleInvoluntary, non-striated muscle tissueOccurs within almost every organ, formingsheets, bundles, or sheaths around other tissues.Cardiovascular system:
Smooth muscle in blood vessels regulates blood flowthrough vital organs. Smooth muscle also helps
regulate blood pressure.Digestive systems:Rings of smooth muscle, called sphincters, regulatemovement along internal passageways.Smooth muscle lining the passageways alternatescontraction and relaxation to propel matter through thealimentary canal.
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Are smaller: 5-10um in diameterand 30-200um in length
Are uninucleate: contain 1centrally placed nucleusLack any visible striationsLack T-tubulesHave a scanty sarcoplasmicreticulum
• Smooth muscle tissue is innervated by the autonomic nervous system unlikeskeletal muscle which is innervated by the somatic nervous system (over whichyou have control)
• Only the endomysium is present. Nor perimysium or epimysium.
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Single Unit Smooth MuscleMore commonCells contract as a unitbecause they are allconnected by gap junctions -protein complexes that spanthe PM’s of 2 cells allowingthe passage of ions betweenthem, i.e., allowing thedepolarization of one to causethe depolarization of another.Some will contractrhythmically due to
pacemaker cells that have aspontaneous rate of depolarization.
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Single Unit Smooth MuscleNot directly innervated.Diffuse release of neurotransmitters atvaricosities (swellings alongan axon).Responsive to variety of stimuli including stretchand concentration changesof various chemicalsFound in the walls of thedigestive tract, urinarybladder, and other organs
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Multi Unit Smooth
7/28/2019 18001034 Anatomy Presentation Ho 5Muscles
Innervated in motor unitscomparable to those of skeletalmusclesNo gap junctions. Each fiber isindependent of all the others.Responsible to neural & hormonal controlsNo pacemaker cellsLess commonFound in large airways to thelungs, large arteries, arrector pili,internal eye muscles (e.g., themuscles that cause dilation of the pupil)Why is good to have the digestive smooth muscle single
unit and the internal eye muscles multi-unit? 37
Cardiac
7/28/2019 18001034 Anatomy Presentation Ho 5Muscles
Striated, involuntarymuscleFound in walls of the heartConsists of branchingchains of stocky musclecells. Uni- or binucleate.Has sarcomeres & T-tubulesCardiac muscle cells are
joined by structures calledintercalated discs – whichconsist of desmosomes andgap junctions.
Why do you suppose these
Notice the branching andthe intercalated disc,indicated by the blue arrow.