18001034 Anatomy Presentation Ho 5Muscles

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Muscles

Muscle is one of our 4 tissue types andmuscle tissue combined with nerves,blood vessels, and various connectivetissues is what makes up those muscle

organs that are familiar to us.Muscles are quite complex and as we’llfind out, they are a marvel of both

biology and physics. 1



Muscle Functions1. Production of Movement

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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Muscle Functions

2. Maintenance of posture Muscle contraction is constantlyallowing us to remain upright.The muscles of your neck arekeeping your head up right now.

As you stand, your leg muscleskeep you on two feet.

3. ThermogenesisGeneration of heat. Occurs viashivering – an involuntarycontraction of skeletal muscle.

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MuscleFunctions

4. Stabilization of jointsMuscles keep the tendonsthat cross the joint niceand taut. This does awonderful job of

maintaining the integrityof the joint.

All the things muscles do fall under one of these 4 categories.

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3 Types of Muscle Tissue

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Characteristics of Muscle

Tissue1. Excitability

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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Characteristics of Muscle

Tissue2. Contractility

The ability to shorten forcibly when adequately

stimulated.This is the defining property of muscle tissue.

3. ExtensibilityThe ability to be stretched

4. ElasticityThe ability to recoil and resume original length afterbeing stretched.

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Skeletal Muscle – theorgan

Skeletal muscle organsare dominated bymuscle tissue but alsocontain nervous,vascular and assorted

connective tissues.The whole muscle issurrounded by a layerof dense irregularconnective tissue

known as theepimysium.( epi = ?,mysium =muscle).

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Skeletal Muscle –

the organ

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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Skeletal Muscle – Blood & Nerve

SupplyEach skeletal muscle istypically supplied byone nerve, an arteryand one or more veins.

What is the function of each of these 3 items?

They all enter/exit viathe connective tissuecoverings and branchextensively.

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Skeletal Muscle Attachments

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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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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Skeletal MuscleMicroanatomy

Each skeletal muscle cell is known

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



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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SarcoplasmicReticulum

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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Myofilaments

2 types of myofilaments (thick & thin) make upmyofibrils.Thick myofilaments are made the protein myosin

A single myosin protein resembles

2 golf clubs whose shafts havebeen twisted about one another

About 300 of these myosinmolecules are joined together toform a single thick filament

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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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Note the relationship between the thin and thick filaments

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Myofibrils

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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The portion of the sarcomerewhich does not

contain anythick filament isknown as the Iband . The Iband contains

only thinfilament and islight under themicroscope ( it is isotropic ).

One I band isactually partof 2sarcomeres atonce .

In the middle of the H zone is a structure called the Mline which functions to hold the thick filaments to oneanother

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Here we have several different crosssections of a myofibril. Why are theydifferent?

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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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T-Tubules and the SR Each musclefiber hasmany T-

tubulesTypicallyeachmyofibril hasa branch of a T-tubule

encircling itat each A-I junction

At each A-I junction, the

SR willexpand andform adilated sac(terminalcisterna).

Each T-tubule will be flanked by aterminal cisterna. This forms a so-calledtriad consisting of 2 terminal cisternaeand one T-tubule branch.

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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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Smooth Muscle

Integumentary system:Regulates blood flow to the superficial dermis

Allows for piloerectionRespiratory system

Alters the diameter of the airways and changes theresistance to airflow

Urinary systemSphincters regulate the passage of urineSmooth muscle contractions move urine into and outof the urinary bladder

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Smooth Muscle

Reproductive systemMales

Allows for movement of sperm along the male reproductivetract.

Allows for secretion of the non-cellular components of semen Allows for erection and ejaculation

Females Assists in the movement of the egg (and of sperm) throughthe female reproductive tractPlays a large role in childbirth

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Smooth MuscleSmooth muscle cells:

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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Smooth Muscle

Smooth muscle is always maintaining anormal level of activity – creating muscletone.Smooth muscle can respond to stimuli by

altering this tone in either direction.Smooth muscle can be inhibited and relaxSmooth muscle can be excited and contract

Possible stimuli include neurotransmitters,hormones, pH, Pco2, Po2, metabolites(such as lactic acid, ADP), or even stretch.

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Types of Smooth Muscle

Smooth muscle varies widely from organ toorgan in terms of:

Fiber arrangementResponsiveness to certain stimuliHow would the types of integral proteins that a smooth muscle cell contained contribute to this ?

Broad types of smooth muscle:Single unit (a.k.a. visceral)Multi unit

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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



Multi-Unit SmoothMuscle

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



CardiacMuscle

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.

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18001034 Anatomy Presentation Ho 5Muscles

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