1. HISTOLOGY OF MUSCULAR SYSTEM LECTURE for
PCI/MEDICAL SCIENCE STUDENTS.
DEPARTMENT: ANATOMY TEAM UNIT
By: Merga S. (MSC in clinical anatomy)
June, 2023
6/8/2023 1
2. MUSCLE TISSUES AND CONTRACTILE CELLS
Outlines
– Introduction
– General features of muscle tissues
– Types of muscle tissues and contractile cells
– Distinguishing characteristics
– Contractile elements of muscle tissues
– Injuries and regeneration capabilities
3. Muscular tissue introduction
• Muscle tissue makes up nearly half of an individual’s total
body weight.
• Each muscle is an individual organ made up of muscle
tissue, nerves, blood vessels, and connective tissue.
• Human has about 700 muscles (skeletal muscle)
Myocytes : cells of muscle tissue
Myology, the study of muscles
4. Muscle Tissue:
• Associated with the bones of the skeleton,
the heart and in the walls of the hollow
organs of the body.
Functions:
• Movement
• Maintains posture
• Produces heat
• Facial expressions
• Pumps blood
• Peristalsis
5. Highly Contractile Cells:
– enable movement of large tissues or organs and include:
1. Muscle cells/fibers:
– aggregated to form muscle organs which move large structures
such as the skeleton or the viscera.
2. Myoepithelial cells:
– function as single contractile units surrounding the secretory
acini and small ducts of some exocrine glands.
3. Pericytes:
– are perivascular contractile cells
– invest very small blood vessels (capillaries and postcapillary
venules) and regulate the pressure by altering the diameter of
these vessels.
4. Myofibroblasts: contractile cells found in healing wounds; play
an important role in contraction and shrinkage of the resultant
scar tissue.
6. Muscle Tissue:
– is composed of muscle cells, differentiated for optimal
contractility & moderate amount of ECM and CT which
connect muscle cells together and carry nerve fibers &
blood capillaries to them.
– Individual muscle cells are long and narrow (i.e. longer than
wide) so they are called muscle fibers or myofibers.
– Muscle cells are derived from mesenchyme.
7. Distinguishing Features of Muscle Tissues
1. Elongated, cylindrical or spindle-like morphology
2. Moderate cellularity
3. High vascularity
4. Heavy innervation
5. Mesenchymal origin
6. External lamina
7. Regeneration
8. Hypertrophy
9. Hyperplasia
10. Excitability/Irritability
11. High contractility
12. Extensibility
13. Elasticity
8. Types of Muscle Tissues:
– Three types of muscle tissues can be
distinguished on the basis of morphologic &
functional characteristics and the structure of
each type is adapted to its physiologic role.
1. Skeletal and visceral striated muscles
2. Cardiac muscle: also has cross-striations
3. Smooth muscle: consists of collections
of fusiform cells that do not show
striations.
9. 1. SKELETAL AND VISCERAL STRIATED MUSCLES
– composed of bundles of very long non-branching,
cylindrical, multinucleated fibers that show cross-striations
(a regular pattern of alternating light & dark bands along
the entire length of the cell)
– contraction is quick, forceful (vigorous) & under voluntary
control.
10.
11. 2. CARDIAC MUSCLE:
• also has cross-striations & composed of elongated,
branched individual cells that lie parallel to each
other.
– connected end-to-end by intercalated disks,
structures found only in cardiac muscle.
Contraction of cardiac muscle is involuntary,
vigorous, & rhythmic.
14. 3. SMOOTH MUSCLE:
consists of collections of fusiform cells that do not show
striations.
Their contraction process is slow & subject to involuntary
control.
15.
16. Distribution of Smooth muscle tissues
• Found within almost every organ-system, forming
sheets, bundles, or sheaths around other tissues.
In Cardiovascular system:
– Smooth muscle tissue in the wall of the blood
vessels regulates blood flow through vital organs.
– Smooth muscle also helps regulate blood
pressure in arterioles (precapilliary sphincter).
17.
18. – Smooth muscle lining the digestive tract alternates contraction
and relaxation (peristalsis) to propel matter through the
alimentary canal.
– Found in the mucosa (muscularis mucosae) and muscularis
externa of the tubular GIT.
– arranged in inner circular & outer longitudinal layers but in
the stomach consists of three layers (inner oblique, middle
circular, outer longitudinal).
– Rings of smooth muscle, called sphincters, regulate movement
along internal passageways.
In Digestive systems:
19.
20. 20
Plicae ciculares (folds)
of the jejunum.
longitudinal section
mucosa and submucosa
(SM), plicae (P),
villi (V). two layers of the
muscularis (M). serosa (S),
21. Smooth/Visceral Muscle…
Integumentary system:
– Regulates blood flow to the superficial dermis
– Allows for piloerection (Arrector pilli muscles)
Respiratory system
– Alters the diameter of the airways and changes the
resistance to airflow (especially in bronchioles)
Urinary system
– Sphincters regulate the passage of urine
– Smooth muscle contractions move urine into and out of
the ureter and urinary bladder (detrusor muscle in the
urinary bladder).
22. Skeletal muscle Cardiac muscle Smooth muscle
Location: attached to
the skeleton, in
tongue, pharynx,
esophagus
Found in the
myocardium of the
heart
Found in the blood
vessels & viscera
Striated Striated Non-striated
Voluntary Involuntary Involuntary
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Muscle Tissues
23. Muscle structure
A. Connective Tissue Component
• A skeletal muscle is mainly composed of striated
muscle cells and connective tissue.
Each skeletal muscle has two parts:
the connective tissue sheath that extend to form
specialized structures that aid in attaching the muscle
to bone and the fleshy part the belly.
By: Merga S. 23 6/8/2023
24. Muscle tissue….
• Three layers connective tissue protect & strengthened
skeletal muscle.These are:
• Epimysium: the outermost connective tissue sheath that
encircle the entire muscle.
• Perimysium: surrounds group of muscle fibers & separates
them into fascicles.
• Endomysium: a connective tissue that surrounds individual
muscle fiber.
By: Merga S. 24 6/8/2023
25. A skeletal muscle consists of striated muscle fibers held together by
connective tissues.
1. Endomysium
– Delicate layer of loose areolar CT rich in reticular fibers,
and small diameter capillaries and finest neuronal
branches running parallel to the muscle fibers.
– Immediately surrounds individual muscle fibers,
– Derived from perimysium.
– House a rich network of capillaries surrounding each
muscle fiber.
26. 2. Perimysium
– Loose CT surrounding a group of muscle fibers that form
a bundle (fascicle)
– Derived from epimysium
– Thicker than the endomysium and therefore houses
larger blood vessels (arterioles and small veins) and
nerves.
3. Epimysium
– Sheath of a fibro-elastic CT
– Surrounds the collection of fascicles of the entire muscle
– Major vascular and nerve supply of the muscle
penetrates here
27.
28. In this photomicrograph, you should notice: the epimysium on the left,
the multiple fascicles, the translucent perimysium partitioning them, and
the multiple muscle fibers making up each fascicle.
30. • All Three connective tissue layers may extend beyond the
muscle fiber to form a tendon.
• Tendon is a cord of dense regular connective tissue
composed of collagen fibers that attach muscles to bones.
• Connective tissue also extends into the muscle and divides it
into numerous muscle bundles (fascicles).
By: Merga S. 30 6/8/2023
32. Repair, Healing and Renewal of Skeletal muscles
Some nuclei that appear to belong to the skeletal muscle
fiber are nuclei of small satellite cells.
Satellite cells
– remain as stem cells, interposed between the plasma
membrane of the muscle fiber and its basal/external lamina.
– Proliferate after minor injury to give rise to new myoblasts.
– So long as the external lamina remains intact, the myoblasts
fuse within the external lamina to form myotube which
matures into a new muscle fiber.
– Disruption of the basal lamina results in fibroblast repair of
the injured site with scar tissue formation.
33. Injury and Repair in Cardiac muscle tissue
– Mature cardiac muscle cells are able to divide.
– In the past, it was thought that once cardiac muscle cells are
destroyed, they cannot be replaced by new muscle cells.
– Recently emerging evidences are showing mitotic potential of
cardiac muscle cells at least in the hearts removed from
individuals who had received transplants.
– Although the number of dividing nuclei in these hearts is
low (0.1%), it suggests that damaged cells can potentially be
replaced.
