Larry Johnson Texas A&M University

• Histologically identify and functionally characterize each of the 3 types of muscle tissues.
• Describe the organization of the sarcomere as seen in light and electron microscopy.
• Identify the endomysium, perimysium, and epimysium CT sleeves in muscle.
• Relate the functional differences of the three muscle cell types.
From: Douglas P. Dohrman and TAMHSC Faculty 2012 Structure and Function of Human Organ Systems, Histology
Laboratory Manual

MUSCLE
FUNCTION:
• GENERATION OF CONTRACTILE FORCE
DISTINGUISHING FEATURES:
• HIGH CONCENTRATION OF CONTRACTILE
PROTEINS ACTIN AND MYOSIN ARRANGED
EITHER DIFFUSELY IN THE CYTOPLASM
( SMOOTH MUSCLE ) OR IN REGULAR
REPEATING UNITS CALLED SARCOMERES
(STRIATED MUSCLES, e.g., CARDIAC AND
SKELETAL MUSCLES )

MUSCLE
• DISTRIBUTION:
SKELETAL – STRIATED MUSCLES
MOSTLY ASSOCIATED WITH THE
SKELETON

MUSCLE
• DISTRIBUTION:
SKELETAL – STRIATED MUSCLES
MOSTLY ASSOCIATED WITH THE
SKELETON
CARDIAC – STRIATED MUSCLES
ASSOCIATEWD WITH THE HEART

MUSCLE
• DISTRIBUTION:
SKELETAL – STRIATED MUSCLES
MOSTLY ASSOCIATED WITH THE
SKELETON
CARDIAC – STRIATED MUSCLES
ASSOCIATEWD WITH THE HEART
SMOOTH – FUSIFORM CELLS
ASSOCIATED WITH THE VISCERA,
RESPIRATORY TRACT, BLOOD
VESSELS, UTERUS, ETC.

MUSCLE
• HISTOLOGICAL INDENTIFICATION:
SKELETAL MUSCLE – VERY LONG CYLINDRICAL
STRIATED MUSCLE CELLS WITH MULTIPLE
PERIPHERAL NUCLEI

MUSCLE
• HISTOLOGICAL INDENTIFICATION:
SKELETAL MUSCLE – VERY LONG CYLINDRICAL
STRIATED MUSCLE CELLS WITH MULTIPLE
PERIPHERAL NUCLEI
CARDIAC MUSCLE – SHORT
BRANCHING STRIATED
MUSCLE CELLS WITH
CENTRALLY LOCATED NUCLEI

MUSCLE
• HISTOLOGICAL INDENTIFICATION:
SKELETAL MUSCLE – VERY LONG CYLINDRICAL
STRIATED MUSCLE CELLS WITH MULTIPLE
PERIPHERAL NUCLEI
CARDIAC MUSCLE – SHORT
BRANCHING STRIATED
MUSCLE CELLS WITH
CENTRALLY LOCATED NUCLEI
SMOOTH MUSCLE – CLOSELY
PACKED SPINDLE-SHAPED
CELLS WITH A SINGLE
CENTRALLY PLACED NUCLEUS
AND CYTOPLASM THAT
APPEARS HOMOGENEOUS
BY LIGHT MICROSCOPY

MUSCLE
• HISTOLOGICAL INDENTIFICATION:
SKELETAL MUSCLE – VERY LONG CYLINDRICAL
STRIATED MUSCLE CELLS WITH MULTIPLE
PERIPHERAL NUCLEI
CARDIAC MUSCLE – SHORT
BRANCHING STRIATED
MUSCLE CELLS WITH
CENTRALLY LOCATED NUCLEI
SMOOTH MUSCLE – CLOSELY
PACKED SPINDLE-SHAPED
CELLS WITH A SINGLE
CENTRALLY PLACED NUCLEUS
AND CYTOPLASM THAT
APPEARS HOMOGENEOUS
BY LIGHT MICROSCOPY
Myoepithelial cells

• Muscle cells specialized for contraction with apparatus of actin and myosin proteins.
• 3 types:
Skeletal Muscle
Longitudinal sections
Peripheral nuclei
Striations
No branching
Cross section
Peripheral nuclei
Massive cytoplasm
Smooth Muscle
Longitudinal sections
Central nuclei (often fusiform)
Meshwork appearance of cells
No striations
Cross section
Central nuclei
Low cytoplasm to nucleus ratio
Cardiac Muscle
Longitudinal sections
Central nuclei (often elongated)
Striations
Branching cells
Intercalated discs
Cross section
Central nuclei
High cytoplasm to nucleus ratio

Slide 11 : Skeletal muscle (longitudinal and cross sections)
Muscle fibers with peripheral nuclei
Capillary Cross sections of muscle fibers with peripheral nuclei

Slide 052 : Skeletal muscle (longitudinal and cross sections)
Muscle fibers with peripheral nuclei Capillary
Cross striations
(A and I bands)

Slide 052 : Skeletal muscle (longitudinal and cross sections)
Muscle fibers with peripheral nuclei Capillary
Cross striations
(A and I bands)
The increase in muscle mass during exercise results from stimulating formation of new myofibrils and enlargement in the diameter of individual muscle fibers (hypertrophy = increase in size).

CONNECTIVE TISSUE LAYERS OF
SKELETAL MUSCLE
• EPIMYSIUM - COARSE CT
EPIMYSIUM

CONNECTIVE TISSUE LAYERS OF
SKELETAL MUSCLE
•
• EPIMYSIUM - COARSE CT
PERIMYSIUM - LESS COARSE
CT
PERIMYSIUM
EPIMYSIUM

CONNECTIVE TISSUE LAYERS OF
SKELETAL MUSCLE
•
•
• EPIMYSIUM - COARSE CT
PERIMYSIUM - LESS COARSE
CT
ENDOMYSIUM - DELICATE CT
PERIMYSIUM
EPIMYSIUM
ENDOMYSIUM

CONNECTIVE TISSUE LAYERS OF
SKELETAL MUSCLE
EPIMYSIUM, PERIMYSIUM, and ENDOMYSIUM

Slide 11 : Skeletal muscle (longitudinal and cross sections)
Epimysium
Perimysium
Endomysium

Slide 052 Skeletal muscle (longitudinal and cross sections)
Perimysium
Endomysium with its capillaries

CONNECTIVE
TISSUE connect
LAYERS OF
SKELETAL
MUSCLE
• ENDOMYSIUM

CONNECTIVE TISSUE LAYERS OF
SKELETAL MUSCLE
PERIMYSIUM

CONNECTIVE TISSUE LAYERS OF
SKELETAL MUSCLE
PERIMYSIUM
052
• ENDOMYSIUM

052
Skeletal muscles have striations, peripheral nuclei, same thickness throughout their length and do not branch.
Specialized for powerful and rapid contraction. Voluntary.
Found attached to the skeleton.

Slide 12 : Skeletal muscle
(phosphotungstic acid/hematoxylin)
Sarcomere :
Z line to Z line
Z line is
In the I band
I band
A band

CARDIA C
A
SKELETAL
“ A” BAND = dark band
ANISOTROPIC = DOES
ALTER POLARIZED LIGHT
(BIREFRINGENT)

A I
CARDIA C
SKELETAL
“ A” BAND = dark band
ANISOTROPIC = DOES
ALTER POLARIZED LIGHT
(BIREFRINGENT)
“I” BAND = light band
ISOTROPIC = DOES NOT
ALTER POLARIZED LIGHT

(SKELETAL)
SARCOMERES ARE
ORGANIZED FOR
RAPID AND HIGHLY
CONTROLLED
CONTRACTION
A I

SKELETAL MUSCLE cell structure

SKELETAL MUSCLE

SKELETAL MUSCLE

INTERMEDIATE FILAMENTS –
FUNCTION in muscle cells
• MYOFIBRIL ORGANIZATION – MUSCLE cells

INTERMEDIATE FILAMENTS –
FUNCTION in muscle cells
• MYOFIBRIL ORGANIZATION – MUSCLE cells
Cell =

.
CONTRACTION OF
THE SARCOMERE
• THIN FILAMENT
ACTIN (F-ACTIN)
TROPOMYOSIN
TROPONIN
T - ATTACHES TO
TROPOMYOSIN
C - BINDS CALCIUM IONS
I - INHIBITS ACTIN-MYOSIN
INTERACTION
The stoppage of the neural impulse and depletion of free calcium ends the actinmyosin crossbridge cycle in skeletal muscle. ATP is required in this process.

CALCIUM
REGULATION
• TRANVERSE (T) TUBULE
(INVAGINATION OF
SARCOLEMMA)
• TRANSMIT DEPOLARIZATION
OF MEMBRANE DEEP
INTO THE CELL
• SARCOPLASMIC RETICULUM
(SER OF CELL)
RELEASE CA ++ FOR
CONTRACTION - THEN
RECOVER CA ++
• AFTER CONTRACTION
• TRIAD = (T TUBULE AND TWO
ENDS OF SER)

EM 29 : Skeletal
muscle
052

STIMULATION OF MUSCLE CELLS

Slide 13: Skeletal Muscle – muscle spindles (trichrome)
Intrafusal muscle fibers
Muscle spindle:
(stretch receptors)
Nerve fibers

INNERVATION OF MUSCLE
MUSCLE SPINDLE

SMOOTH MUSCLE

SMOOTH MUSCLE
Has a PAS + basement membrane

Slide 35
Muscularis externa
(smooth muscle)
Smooth muscle fibers with central nuclei
Smooth muscles are fusiform with tapered ends, single, central nuclei, and no striations. Involuntary. Found in sphincters and sheets of internal visceral organs and glands.

Slide 63
Submucosa Muscularis externa
Smooth muscle layer arrangement in tubular organs
The layering of smooth muscle in the gut is responsible
for contractions which mix and propel luminal contents forward.

Actin
Myosin

SMOOTH MUSCLE

MUSCULAR ARTERY

Skeletal
Muscle
Smooth muscle

CARDIAC MUSCLE IS STRIATED MUSCLE
• INTERCALATED DISC
• FASCIA ADHERENS
• MACULAE ADHERENS
• GAP JUNCTIONS - LATERAL PORTION

CARDIAC MUSCLE
INTERCALATED DISC
The intercalated discs enables coordinated function via gap junctions to facilitate energy and calcium conductance between neighboring myocytes.

pulmonary artery in the
lungs of a rat
INTERCALATED
DISC

pulmonary artery in the
lungs of a rat
INTERCALATED
DISC nucleus mitochondria

Slide 14
Intercalated discs

CARDIAC MUSCLE –
Diad located at Z line
Diad = (T tubule + one end of SER)

REGENERATION OF MUSCLE
Which type of muscle cells can be replaced in adults?
• SMOOTH – LOTS
• SKELETAL – SOME
• CARDIAC – NONE

Image taken from adultstemcellawareness.wordpress.com
Ischemic heart disease is one of the most significant health problems in the
US. Coronary artery thrombosis usually precedes and precipitates a myocardial infarct, resulting in the death of cardiac myocytes. Eventually scar tissue is formed and there is some loss of contractility.
Lacking muscle mesenchymal satellite cells, adult mammalian cardiac muscle has little potential to regenerate after injury.
Damage is replaced by proliferating fibroblasts and connective tissue growth, forming myocardial scars.

Summary of MUSCLE shapes and excitations of types

Many illustrations in these VIBS Histology YouTube videos were modified
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• from the following books and sources: Many thanks to original sources!
Bruce Alberts, et al. 1983. Molecular Biology of the Cell. Garland Publishing, Inc., New York, NY.
Bruce Alberts, et al. 1994. Molecular Biology of the Cell. Garland Publishing, Inc., New York, NY.
William J. Banks, 1981. Applied Veterinary Histology. Williams and Wilkins, Los Angeles, CA.
Hans Elias, et al. 1978. Histology and Human Microanatomy. John Wiley and Sons, New York, NY.
Don W. Fawcett. 1986. Bloom and Fawcett. A textbook of histology. W. B. Saunders Company, Philadelphia, PA.
Don W. Fawcett. 1994. Bloom and Fawcett. A textbook of histology. Chapman and Hall, New York, NY.
Arthur W. Ham and David H. Cormack. 1979. Histology. J. S. Lippincott Company, Philadelphia, PA.
Luis C. Junqueira, et al. 1983. Basic Histology. Lange Medical Publications, Los Altos, CA.
L. Carlos Junqueira, et al. 1995. Basic Histology. Appleton and Lange, Norwalk, CT.
L.L. Langley, et al. 1974. Dynamic Anatomy and Physiology. McGraw-Hill Book Company, New York, NY.
W.W. Tuttle and Byron A. Schottelius. 1969. Textbook of Physiology. The C. V. Mosby Company, St. Louis, MO.
Leon Weiss. 1977. Histology Cell and Tissue Biology. Elsevier Biomedical, New York, NY.
Leon Weiss and Roy O. Greep. 1977. Histology. McGraw-Hill Book Company, New York, NY.
Nature (http://www.nature.com), Vol. 414:88,2001.
A.L. Mescher 2013 Junqueira’s Basis Histology text and atlas, 13 th ed. McGraw
Douglas P. Dohrman and TAMHSC Faculty 2012 Structure and Function of Human Organ Systems, Histology Laboratory
Manual - Slide selections were largely based on this manual for first year medical students at TAMHSC