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Muscle TissueLab 9 – Muscle Tissue

IUSM – 2016

I. IntroductionII. Learning ObjectivesIII. KeywordsIV. Slides

A. Types of Muscle1. Striated

a. Skeletalb. Cardiac

2. SmoothB. Muscle Development (Skeletal)

V. Summary

SEM of partly unraveled skeletal muscle cell exposing the densely packed myofibrils within.

Muscle Tissue

1. Muscle is a highly cellular and vascular tissuespecialized for contraction via the interaction ofmyofilaments (between thin and thick filaments);it is responsible for movement of the body and forchanges in the size and shape of internal organs.

2. There are three basic types of muscle tissue(skeletal, smooth, and cardiac) classified accordingto appearance of their contractile cells and location.

3. Striated muscle is formed during development by thefusion of small individual muscle cells calledmyoblasts into larger, multinucleated myotubes.

Lab 9 – Muscle TissueIUSM – 2016





V. Summary

Learning Objectives

1. Understand the structural features of three general types of muscle cellsand how each is organized to form a contractile tissue that performsspecific types of work.

2. Understand the structural and functional attributes of connective tissuesassociated with muscle and the myotendinous junction.

3. Understand that skeletal muscle contains different types of fibers

4. Understand the arrangement of actin and myosin filaments in all threemuscle types.

5. Understand the arrangement and roles of transverse tubules,sarcoplasmic reticulum, mitochondria, and contractile filaments in theprocess of contraction

6. Understand the locations and roles of intercellular junctions in muscle

7. Understand the response of muscle to injury and the regenerativecapacity of the various types of muscle.






V. Summary

Keywords

A-bandCardiac muscleEndomysiumEpimysiumFasciclesI-bandIntercalated discMuscle fiberMyoblastMyocardiumMyocytes

MyofibrilsMyotubePerimysiumSarcoplasmic reticulumSatellite cellSkeletal muscleSmooth muscleStriated muscleStriationsT tubule






V. Summary

Larynx, Trichrome

look here to see skeletal muscle in longitudinal-section

look here to see skeletal muscle in cross-section






V. Summary

https://vmicro.iusm.iu.edu/virtual_h/msci_07_5.html

Larynx, TrichromeLab 9 – Muscle Tissue

IUSM – 2016





V. Summary

in skeletal muscle, endomysium is a delicate layer of reticular CT surrounding individual muscle fibers (cells);perimysium is thicker connective tissue surrounding a group of fibers to form a bundle or fascicle; epimysiumis a sheath of dense connective tissue surrounding a collection of fascicles that constitute an entire musclethe endo-, peri-, epi- prefixes for surrounding layers of connective tissue will be seen again for other structures, suchas the layers of CT surrounding peripheral nerves, so it is important to be familiar with their meaning and usage

epimysium

perimysium

endomysium

fascicle

individual skeletal muscle fibers (i.e., cells) seen in cross-section







V. Summary

skeletal muscle

surface of tongue; what specific type of tissue is this?

Slide 70: Tongue, H&E

skeletal muscle (or visceral striated muscle, as seen in the tongue) is generally responsible for voluntarymovement within the body, mainly of the skeleton but also other structures such as the eyes and upperesophagus for swallowing; it is composed of long multinucleated cells called muscle fibers which generallyextend the entire length of a muscle from tendon to tendon (up to 2ft long in the sartorius muscle in the thigh)







V. Summary


skeletal musclein longitudinal-section

skeletal muscle in cross-section







V. Summary


notice that the nuclei of the skeletal muscle fibers have been displaced to the periphery of the fiber/cell by all the myofibrils filling the cell

perimysium surrounds the entire muscle fascicle(composed of multiple muscle fibers/cells)

endomysium surrounds individual muscle fibers







V. Summary

Slide 8: Tongue, Trichromeskeletal musclein longitudinal-section

skeletal musclein longitudinal-section

skeletal muscle fiberin cross-section

fibroblast of the endomysium CT

nucleus of a muscle fiber displaced to the periphery, directly under the sarcolemma

numerous capillaries can be seen in the endomysium between the muscle fibers

using the know size of an RBC, estimate the diameter of an adjacent muscle fiber

https://vmicro.iusm.iu.edu/virtual_h/8_bl_5.html






V. Summary

Slide 17 (464): Skeletal Muscle, H&E

cross-striations (fine lines) are the alternating dark and light bands formed by the arrangement of themyofilaments of the sarcomere (best seen in electron micrographs); the dark bands are the A-bands(overlapping actin and myosin filaments) and the light bands are the I-bands (actin filaments); the visiblestriations are the reason both skeletal and cardiac muscle are classified as striated muscle

nuclei of skeletal muscle fibers are displaced to the periphery of the cells directly beneath the sarcolemma

a few nuclei of fibroblasts, forming the endomysium or perimysium, may be seen but can be difficult to identify; the nuclei of endothelial cells of capillaries can also be seen

http://medsci.indiana.edu/a464/virtual/464_17_5.html






V. Summary

Slide 139: Heart, H&E

cardiac muscle is striated muscle, like skeletal muscle; however, it is localized to the walls of the heart and isdistinguishable by: (1) the branching of its muscle fibers; (2) a single nucleus per cell, generally round andfound near the center of the cell; and (3) the presence of intercalated discs between cells, so that the fibersare actually many cells linked end-to-end, unlike the fibers of skeletal muscle which are a singlemultinucleated cell







V. Summary

Slide 139: Heart, H&E

intercalated discs are highly specialized cell-to-cell adhesion junctions found in cardiac muscle; theyphysically bind cells together to create long muscle fibers, so the force of contraction is transmitted betweenthe cells; they also promote the spread of action potentials from cell to cell via gap junctions

intercalated disc(thick, dark lines)

“branching” of fibers is characteristic of cardiac muscle

cross-striations(thin, faint lines)

round, centralized nucleus of cardiac muscle is distinct from the multinucleated peripheral, elongated nuclei of skeletal musclewhat is this

“wear and tear” pigment found near the nuclei

in cardiac fibers?

myofibrils(parallel to fiber direction)







V. Summary

Slide 66: Esophagus, H&E

look in the inner layer to see smooth muscle in longitudinal-section

lumen

look in the outer layer to see smooth muscle in cross-section







V. Summary


smooth muscle fibers are long and tapered at both ends, generally ranging in length from 20-200µm; there areno striations (hence, “smooth”) because the actin and myosin filaments do not show the same degree and kindof organization as seen in striated muscle (skeletal and cardiac); like in cardiac muscle, there is a single, centralnucleus for each cell; however, in smooth muscle the nucleus conforms to the cell shape, unlike the typicallyround nucleus of cardiac fibers; it is under involuntary control and is capable of slow, sustained contractions

elongated, centrally-located nucleus of smooth muscle fiber seen longitudinally







V. Summary


skeletal muscle fiber(cross-section)

smooth muscle fiber(cross-section)

the upper 1/3 of the esophagus is under voluntary control so has skeletal muscle (voluntary muscle); thelower 2/3 is under involuntary control so has smooth muscle (visceral muscle); on this slide, from themiddle portion of the esophagus, the transition between the two muscle types can be seen







V. Summary


unlike skeletal muscle, smooth muscle makes its own surrounding CT, so fibroblasts are much more rare;however, scattered throughout the tissue, the nuclei of endothelial cells (simple squamous epithelium)may be seen lining capillaries

cross-section

longitudinal

capillarycapillary







V. Summary

Slide 21: Ileum, Trichrome

smooth musclein cross-section

smooth musclein longitudinal-section

smooth musclein longitudinal-section smooth muscle

in cross-section

Slide 37: Ileum, H&E

the entire GI tract, including the esophagus seen previously and the ileum – part of the small intestine – seenabove, contains a surrounding layer of smooth muscle called the muscularis; the muscularis is principallycomposed of two layers of smooth muscle, with fibers in one layer having perpendicular orientation to theadjacent layer; contraction of these layers allows the GI “tube” to both shorten in length and reduce thediameter of its lumen








V. Summary

Slide 159: Fetal Mouse Head

look in the oral cavity at the tongue to see developing skeletal muscle

vertebrae endochondral ossification

developing brain

cartilaginous nasal septum

newly-forming woven bone of the mandible

Slide Overview







V. Summary

Slide 159: Fetal Mouse Head

during embryonic development, mesenchymal myoblast cells fuse to form multinucleated myotubes,which will later further differentiate to form mature, striated skeletal muscle fibers

myotubes

myoblasts are the skeletal muscle precursor cells found interspersed amongst the myotubes


a (464): Guinea Pig Head

Slide 130: Fetal Skull

Slide 40a (464): Fetal Tongue, H&E

the development of skeletal muscle in thetongue by the fusion of myoblasts intomyotubes can be seen on several other slides






V. Summary

http://medsci.indiana.edu/a464/virtual/464_12a_5.html


http://medsci.indiana.edu/a464/virtual/464_40a_5.html

Common Confusion:Smooth Muscle vs. Dense Regular CT






V. Summary

Smooth muscle

Smooth muscle: muscle found in the walls of vessels andorgans, so also known as visceral muscle; it lacks the striatedappearance of skeletal and cardiac muscle

Look for: (1) long, tapered cells with a central nucleusconforming to the cell’s shape; (2) nuclei are intracellular,and there are rarely fibroblasts; (3) nuclei appear somewhatclustered and aligned, as the thickest part of one cell stacksagainst the thinnest part of adjacent cell; (4) nuclei mayappear ‘wavy’ if cells are contracted; (5) more abundantvasculature or other tissue types may be visible

Dense regular CT: connective tissue proper with thickbundles of collagen arranged in parallel to provide maximaltensile strength along one axis; it is found in tendons,ligaments, capsules, and aponeuroses

Look for: (1) eosinophilic collagen is regular and denselypacked; (2) nuclei are fewer and often highly flattened butcan have more varied appearance; (3) nuclei located betweencollagen bundles (i.e., they don’t appear to be ‘intracellular’);(4) vasculature is usually poor and sparse

Dense regular CT

Common Confusion:Smooth Muscle vs. Cardiac Muscle in Cross-Section






V. Summary

Smooth muscle

Smooth muscle: muscle found in the walls of vessels andorgans, so is also known as visceral muscle; it lacks thestriated appearance of skeletal and cardiac muscle

Look for: (1) fusiform shape of cells gives the appearance ofcells of differing widths; (2) higher density of nuclei due topacking of cells, but nuclei often appear in clusters ratherthan uniformly distributed; (3) tight packing makesdiscernment of individual cells often difficult

Cardiac muscle: striated muscle found in the walls of theheart; in cross-section it is quickly distinguished fromskeletal muscle by the location of the nuclei

Look for: (1) generally abundant endomysium withinterspersed fibroblasts and capillaries; (2) myofibrils fill themuscle fibers; (3) lipofuscin granules may be seen

Cardiac muscle






V. Summary

Summary

1. Striated muscle includes both skeletal muscle and cardiac muscle; it is identified bythe presence of a distinct cross-striation pattern of alternating lighter-staining I-bands and darker-staining A-bands.

a. Skeletal muscle fibers (under voluntary control) are long, cylindricalmultinucleated cells with peripherally-located nuclei; the fibers are formed bythe fusion of numerous mesenchymal myoblast cells during development.

b. Cardiac muscle, found within the heart, differs from skeletal muscle by havingonly one or two centrally-located round nuclei, branching fibers, andintercalated discs (join cells end-to-end).

2. Smooth muscle is muscle found in the walls of vessels and organs, so is also knownas visceral muscle; it is called smooth because it lacks the sarcomere organization andstriated appearance of skeletal and cardiac muscle; it is under involuntary control andis capable of slow, sustained contractions.

3. Entire skeletal muscles are surrounded by dense connective tissue called epimysium;from the epimysium, less-dense and thinner perimysium extends inward and dividesthe muscle into fascicles (bundles of muscle fibers); a thin layer of reticular connectivetissue, called endomysium, surrounds individual muscle fibers. Within all the layersof the connective tissue there are blood vessels, nerves, and lymphatics.

Comparison of Different Muscle TypesLab 9 – Muscle Tissue

IUSM – 2016





V. Summary

Skeletal Muscle Cardiac Muscle Smooth Muscle

Locations

Function

Striated?

Multinucleated?

Location of nuclei

Cell shape

Branching?

Cell junctions

Connective tissue layers

Regeneration mechanism

Sketch of fibers

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