MuscleLaboratory

Thomas A. Marino, Ph.D.Albert Lamperti, Ph.D.

Marvin Sodicoff, Ph.D.

Temple University School of Medicine

ObjectivesObjectives

To be able to recognize and understand how skeletal, smooth and cardiac muscle is organized so that it functions properly.

To be able to identify the subcellular organization of the different types of muscle.

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Skeletal muscle - Longi. sections, Low, Med., High mags.Skeletal muscle cells are multinucleated and do not branch but rather have a

relatively straight course. Their nuclei are located at the periphery of the cell (not seen well here). Cross-striations are an obvious characteristic of skeletal muscle cells.

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Skeletal Muscle - Cross Sections, Low, Medium, High magsPolygonally-shaped cross sections of skeletal muscle cells demonstrate their peripherally placed nuclei just under the sarcolemma (cell membrane). Endomysial connective tissue surrounding each muscle cell contains blood vessels with their endothelial cells.

Skeletal muscle - low & high magThe connective tissue that surrounds: 1. the muscle bundle is the epimysium,

a dense irregular connective tissue, 2. a fascicle of muscle fibers is the perimysium, 3. the muscle fiber is the endomysium . The endomysium is made up of reticular fibers.

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Skeletal muscle - high mag.Neuromuscle spindles in cross section have small intrafusal muscle fibers

surrounded by a connective tissue sheath. The larger extrafusal muscle fibers surround the spindle. Compare the muscle spindle to the small nerve bundle below it.

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Skeletal muscle, muscle spindle - high mag.The intrafusal muscle fibers are small striated skeletal muscle fibers which

lie in a fluid-filled space which is surrounded by the connective tissue capsule. Sensory and motor nerves end on these intrafusal muscle fibers.

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At the fine structural level it is easier to see the A and I bands. I bands are divided by Z lines. A sarcomere runs from one Z line to the next. A series of sarcomeres that run the length of the muscle fiber is called a myofibril. The A band is divided by the H band which in turn is divided by the M line. The H band is the region where only myosin exists. The I band is the region where only actin exists.

EMEMSkeletal muscleSkeletal muscle

Longitudinal Longitudinal SectionSection

EM 2EM 2Skeletal muscleSkeletal muscle

In cross sections of myofibrils , you can see cross sections of actin and myosin filaments. Depending where along the sarcomere you make your section, determines whether you will see just actin filaments, actin and myosin filaments or only myosin filaments. Also note the mitochondria in the field.

Slide 99 Image 1/2Slide 99 Image 1/2 Tongue, low mag.Deep to the stratified squamous epithelium that covers the tongue is skeletal

muscle that is composed of small muscle cells that are arranged in a variety of planes.

Tongue, high mag.At higher magnification you can see skeletal muscle cells that are cut in all

different directions. Here note the multiple nuclei in the muscle fibers.

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Pubic symphysis - low magnificationSkeletal muscle inserts into the dense fibrous connective tissue that

surrounds bone and cartilage - the periosteum and the perichondrium, respectively.

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Cardiac Muscle - Longi Sections, Low, Medium, High magsCardiac muscle like skeletal is striated though the striations are usually not as

well defined. In addition, individual cardiac muscle cells are branched and have centrally located nuclei (may be binucleate). The endomysial connective tissue carries the richest blood supply of all three muscle types.

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Cardiac Muscle - cross section, very low - high mags.In cross section the centrally placed nuclei and the variety of sizes of the

sectioned cells are seen. Due to branching cardiac muscle cells cut in cross section do not appear as homogeneous in size and shape as skeletal muscle cells.

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Slide 68 Image 1Slide 68 Image 1 Cardiac muscle -high magThe striations of the branching cardiac muscle cells as well as the

intercalated disks can be seen. Just like skeletal muscle, cardiac muscle has A, I, and H bands as well as M and Z lines.

EM EM Cardiac Cardiac musclemuscle

In cardiac muscle, the cells connect to one another via intercalated disks. These disks consist of junctional complexes that include: gap junctions, desmosomes, and fasciae adherentes.

Cardiac muscle -low magnificationJust under the endocardium is a layer of connective tissue that contains

Purkinje cells, cells of the cardiac conduction system. Deep to the Purkinje cells locate the myocardium composed of cardiac muscle cells.

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Cardiac muscle -higher magnificationThe typical characteristics of ordinary cardiac muscle cells include the

branching as well as centrally placed nuclei. In contrast Purkinje cell cytoplasm stains more lightly due to fewer organelles and large accumulations of glycogen . These are also bigger cells.

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Cardiac muscle -high magnificationThis high power view of Purkinje cells demonstrates the lighter cytoplasmic

staining of these cells due to fewer organelles and marginal myofibrils. It is also possible to find binucleate Purkinje cells. Also note the prominent nucleolus in these Purkinje cells.

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Another characteristic of cardiac muscle tissue is the intercalated disk, a region where two cardiac muscle cells contact each other via junctional complexes. This band is a region where the adjacent cell membranes and their junctions stain darkly.

Cardiac muscle -high magnification

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Smooth Muscle - cross & longi section, very low - high magsIn the wall of the small intestine smooth muscle is cut in cross and

longitudinal sections. Smooth muscle cells are the smallest of the muscle cell types. They are fusiform in shape and have centrally-placed nuclei. They do not have the characteristic cross striations seen in cardiac and skeletal muscle.

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Duodenum

low & medium mag.The epithelial lining of the duodenum is located internal to the smooth

muscle. Smooth muscle is a major component of the wall of the intestines. Smooth muscle cells in the outer longitudinal layer are cut in cross section and those in the inner circular layer are cut longitudinally. In between these layers of smooth muscle (bracket) can be found blood vessels, nerves and connective tissue elements.

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Artery -

Low mag. A muscular artery has a

smooth muscle layer surrounding the vessel lumen. In the two images you can see the smooth muscle cells cut in cross and longitudinal section. Note the appearance of the smooth muscle cells embedded in the connective tissue matrix.

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Anal Canal - med. & high mag.This section, stained with a trichrome stain, distinguishes smooth muscle

from connective tissue. Note the smooth muscle cells surrounding the lumen of the blood vessel. Smooth muscle interweaves with the

connective tissue deep to the underlying the simple columnar epithelium lining the anal canal.

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Uterine Tube - low. & med. mag.This section, routinely stained with H & E, demonstrates that it is possible to

distinguish smooth muscle from connective tissue. Smooth muscle surrounds the lumen of the small arteries. Smooth muscle interweaves with the connective tissue deep to the underlying the simple columnar epithelium lining the uterine tube.

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Slide 61Image 1/1 Esophagus - low

& high magThe muscular wall of the

middle 1/3 of the esophagus, is a mixture of smooth and skeletal muscle. Both stain pink, but smooth muscle has more nuclei per unit area and skeletal muscle cells have peripheralized nuclei and are striated.

DemoDemo Muscle, 3 types - high mag.In this composite slide are cross and

longitudinal sections of all three types of muscle. Based primarily on the location of the nuclei, the presence or absence of striations and the size and shape of the cell, it is possible to distinguish these cell types.