1) Skeletal muscle tissue consists of long, cylindrical multinucleated cells called muscle fibers. Muscle fibers contain contractile myofibrils composed of actin and myosin filaments that generate force. 2) Muscle fibers are classified based on their structure and function into three types - skeletal, cardiac, and smooth muscle. Skeletal muscle is striated and voluntary. 3) The basic contractile unit of skeletal muscle is the sarcomere, composed of overlapping actin and myosin filaments. Contraction occurs when the filaments slide past each other towards the center of the sarcomere.

1. JIMMA UNIVERSITY INSTITUTE OF HEALTH
DEPARTMENT OF BIOMEDICAL SCIENCE
PRESENTATION- BASIC HISTOLOGY
TITILE- MUSCLE TISSUE
Date March 2024
Jimma,Ethiopia
Prepared By Bikila Belay
Id No-rm0435/15-0
Submitted To:-Mr. Tilahun Alemayehu(assistant
Professor Of Anatomy)

2. • Prepared By Bikila Belay
Id No-rm0435/15-0
Submitted To:-Mr. Tilahun Alemayehu(assistant
Professor Of Anatomy)

3. Contents
 Introduction to muscle tissue
 Morphological & functional classification of muscle tissue.
 Skeletal muscle tissue:-
 Cardiac muscle tissue
• Cardiac muscle cells
• Microscopic structure of cardiac muscle
Smooth muscle tissue
• Structures of smooth muscle
• Location of Smooth muscle
• Contraction of smooth muscle
• Medical application of smooth muscle tissue

4. INRTODUCTION TO MUSCLE TISSUE
 Muscle tissue is composed of cells specialized for
contraction.
 Muscle is classified into three types according to their
structure and function.
Classification based on:-
 Morphological classification (based on structure).
• There are two types of muscle based on the morphological
classification system.
1. Striated
2. Non striated or smooth.

5.  Functional classification
• There are two types of muscle based on a functional
classification system
1. Voluntary
2. Involuntary
Striated muscle subdivided on the basis of location
 Cardiac muscle is a type of striated muscle found in the
wall of the heart and in the base of the large veins that
empty into the heart.
 Visceral striated muscle is morphologically identical to
skeletal muscle but is restricted to the soft tissues, namely,
the tongue, pharynx, lumbar part of the diaphragm, and
upper part of the esophagus.

6. Skeletal muscle is attached to bone and is responsible for movement of the axial
and appendicular skeleton and for maintenance of body position and posture.

7. SKELETAL MUSCLE
Skeletal (or striated) muscle consists of muscle fibers,
which are long, cylindrical multinucleated cells with
diameters of 10-100 μm.
Their length varies from almost a meter, as in the sartorius
muscle of the lower limb, to as little as a few millimeters, as
in the stapedius muscle of the middle ear.
 Ranges from 0.1cm to more the 30cm in length.

8. STRUCTURE OF SKELETAL MUSCLE
• A.Connective tissue investments convey neural and
vascular elements to muscle cells and provide a vehicle that
harnesses the forces of muscle contraction.
• 1. Epimysium surrounds an entire muscle and forms
aponeuroses, which connect skeletal muscle to muscle, and
tendons,which connect skeletal muscle to bone.
• 2. Perimysium surrounds fascicles (small bundles) of muscle
cells.
• 3. Endomysium surrounds individual muscle cells and is
composed of reticular fibers and an external lamina.

9. Mysium = Flesh
Epi = Over
Peri = Surrounding
Organization of skeletal muscle

10. SKELETAL MUSCLE
(a) A cross section of striated muscle demonstrating all three layers of connective
tissue and cell nuclei. The endomysium (En) surrounds individual muscle, and
perimysium (P) encloses a group of muscle fibers comprising a fascicle. A thick
epimysium (E) surrounds the entire muscle. All three of these tissues
contain collagen types I and III (reticulin). (X200; H&E)

11. Skeletal muscle
(b) An adjacent section immunohistochemically stained for laminin, which specifically
stains the external laminae of the muscle fibers, surrounded by endomysium. (X400;
Immunoperoxidase)

12. Skeletal muscle
(c) Longitudinal section of a myotendinous junction. Tendons develop together with
skeletal muscles and join muscles to the periosteum of bones.
The dense collagen fibers of a tendon (T) are continuous with those in the three
connective tissue layers around muscle fibers (M), forming a strong unit that allows
muscle contraction to move other structures. (X400; H&E)

13. Skeletal muscle
A cross sectional view of skeletal muscle.

14. Skeletal muscle
longitudinal section of skeletal muscle

15. Skeletal Muscle tissue
• Fibres are arranged parallel to each other.
• Formed by fusion of multiple myoblasts during embryonic
life.
• Myofibrils: contractile elements
• Sarcomere: fundamental contractile unit
• Myofilaments: contain thick (myosin, 15 nm in diameter and
1.5 μm long) and thin (actin,7 nm in diameter and 1.0 μm
long) filaments.
• Nerve supply:
Motor fibres
Sensory fibres

16. Myofibrils
 Myofibrils are built from three kinds of proteins:-
1) Contractile proteins eg. Actin & Myosin
• Generate force during contraction
2) Regulatory proteins eg. Tropomyosin, troponin
• Switch the contraction process on and off
3) Structural proteins eg. Dystrophin,Titin,Myomesin,
And Nebulin
• Align the thick and thin filaments properly
• Provide elasticity and extensibility
• Link the myofibrils to the sarcolemma
 The other role of Actin & Myosin are:-
□cytokinesis, □ Exocytosis □ cell migration.

17. Skeletal Muscle tissue Myofibrils
Ultrastructures of myofibrils in skeletal muscle

18. Skeletal Muscle tissue Myofibrils
Ultrastructures of sarcomere.T tubles,and Triads in skeletal muscle

19. Skeletal muscle cross-striations
 Cross-striations are evident in H&E stained preparations of
longitudinal sections of muscle fibers.
Z discs
 Separate one sarcomere from the next
 Thick and thin filaments overlap one another
A band
 Darker middle part of the sarcomere
Thick and thin filaments overlap
I band
 Lighter, contains thin filaments but no thick filaments
 Z discs passes through the center of each I band
H zone
 Center of each A band which contains thick but no thin filaments
M line
 Supporting proteins that hold the thick filaments together in the H zone

20. Sarcoplasmic reticulum
 Is the SER of striated muscle cells and is specialized to sequester
calcium ions.
 In skeletal muscle, this anastomosing complex of membrane-limited
tubules and cisternae ensheathes each myofibril.
 At each A–I band junction, a tubular invagination of the sarcolemma,
termed a transverse tubule (or T tubule).
 On each side of the T tubule lies an expansion of the sarcoplasmic
reticulum termed a terminal cisterna.

21. A sarcomere extends from Z
to Z lines.
a. I bands (light bands) made
up of actin filaments
are anchored line to Z
line.
b. A bands(dark bands) are
made up of overlapping
thick and thin filaments.
c. In the center of A bands is
an H zone, consisting
of myosin filaments
only...
Note: Z lines move closer together; I band and H band
become smaller during contraction.

22. A microscopic photo and a scheme of Sarcomere

23. a maximum contraction of sarcomere is about 30%
Titin is a
large
abundant
protein of
striated
muscle.
 To
stabilize
the thick
filament,
center it
between
the thin
filaments.

24. Sarcomeres in different functional stages:
 In the resting state (middle),
interdigitation of thin (actin) and thick
(myosin) filaments is not complete; the H
and I bands are relatively wide.
 In the contracted state (bottom), the
interdigitation of the thin and thick
filaments is increased according to the
degree of contraction.
 In the stretched state (top), the thin and
thick filaments do not interact; the H and
I bands are very wide.
 The length of the A band always remains
the same and corresponds to the length of
the thick filaments; the lengths of the H
and I bands change, again in proportion
to the degree of sarcomere relaxation or
contraction.

25. Longitudinal & Transverse Section of skeletal(striated) muscle muscle of the tongue:stained
H&E,High magnification

26. Above: Skeletal muscle fibers, teased, longitudinal view. Tissue magnified by 200x.

27. Skeletal muscle cells
 Are long, cylindrical, multinucleated and are enveloped by an
external lamina and reticular fibers.
 Their cytoplasm is called sarcoplasm, and their plasmalemma is
called the sarcolemma and forms deep tubular invaginations,orT
(transverse) tubules, which extend into the cells.
 Skeletal muscle cells possess cylindrical collections of myofibrils, 1 to
2µm in diameter, which extend the entire length of the cell.

28. Metabolic classification of skeletal muscle cells
• 1.Types of skeletal muscle cells (also known as muscle fibers)
include
• red (slow contraction but do not fatigue easily),
• white (fast contraction but fatigue easily), and intermediate.
 All three types may be present in a given muscle.
• 2. These three types differ from each other in their.
 content of myoglobin (a protein that is similar to hemoglobin in
that it binds O2),
 number of mitochondria,
 concentration of various enzymes, and rate of contraction.
 In skeletal muscle, pericytes also directly enhance tissue healing by
differentiating into myofibers.

29. Metabolic classification of skeletal muscle cells
3. A change in innervation can change a fiber’s type.
 If a red fiber is denervated and its innervation replaced with
that of a white fiber, the red fiber will change its
characteristics and will become a white fiber.
 Every skeletal muscle fiber in every skeletal muscle is
innervated by a motor neuron at the NMJ(Neuro muscular
Junction.

30.  Myofibrils are composed of longitudinally arranged, cylindrical
bundles of thick and thin myofilaments observable by transmission
electron microscopy.
Characteristics of Red and White muscle fibers.
Type Myoglobin
content
Number of
mitochondria
Enzyme
content
Contraction Primary method
of adenosine
triphosphate
generation
Red(slow,
type 1)
high many High in
oxidative
enzyme; low
ATPase
Slow but
repetitive;
not easily
fatigued
Oxidative
phosphorylation
Intermediate
type(type 2A)
Intermediat
e
Intermediate Intermediate
in oxidative
enzyme and
ATPase.
Fast but not
easily
fatigued
Oxidative
phosphorylation
and anaerobic
glycolysis
White(fast,
type 2B)
Low few Low in
oxidative
enzyme; high
in ATPase
and
Fast and
easily
fatigued
anaerobic
glycolysis

31. Metabolic skeletal muscle cell distribution
 Proportions vary, depending on the action of the muscle,
the person ’s training regimen, and genetic factors.
Postural muscles of the neck, back, and legs have a high proportion
of SO fibers.
Muscles of the shoulders and arms have a high proportion of FG
fibers.
Leg muscles have large numbers of both SO and FOG fibers.
SO-slow oxidative
FG-fast glycolytic
FOG-fast oxidative glycolytic

32. Skeletal muscle fiber types.
Slow oxidative (SO) or type I fibers have high levels of acidic ATPase activity and
stain the darkest. Fast glycolytic (FG) or type IIb fibers stain the lightest. Fast
oxidative-glycolytic (FOG) or type IIa fibers are intermediate between the other two
types (X40). ATPase histochemistry of unfixed, cryostat section, pH 4.2.

33. Skeletal muscle innervation
Innervation consists of motor nerve endings (myoneural
junctions) and
Two types of sensory nerve endings,
Muscle spindles and
Golgi tendon organs.

34. Myoneural Junction Of Skeletal Muscle
Is a collection of specialized synapses of a motor neuron's terminal
boutons with a skeletal muscle fiber's sarcolemma.
Each myoneural junction has three major components:
1. presynaptic (neural) component,
2. synaptic cleft,
3. postsynaptic (muscular) component.
1.The presynaptic (neural) component is the terminal bouton.
 The bouton contains mitochondria and acetylcholine-filled synaptic
vesicles.
 The part of the bouton's plasma membrane directly facing the muscle
fiber is the presynaptic membrane.

35. Myoneural Junction Of Skeletal Muscle
2.The synaptic cleft
 lies between the presynaptic membrane and the opposing postsynaptic
membrane and contains basal lamina.
 The primary synaptic cleft lies directly beneath the presynaptic
membrane and communicates directly with a series of secondary
synaptic clefts created by infoldings of the postsynaptic membrane.

36. Myoneural Junction Of Skeletal Muscle
3.The postsynaptic (muscular) component includes the sarcolemma
(postsynaptic membrane) and the sarcoplasm directly under the synapse.
 The postsynaptic membrane contains acetylcholine receptors and is
thrown into numerous junctional folds.
 The sarcoplasm under the folds contains nuclei, mitochondria,
ribosomes, and glycogen, but lacks synaptic vesicles.

37. Myoneural Junction Of Skeletal Muscle
a) Silver staining can reveal the nerve bundle (NB), the terminal axonal
twigs, and the motor end plates (MEPs, also called neuromuscular
junctions or NMJ) on striated muscle fibers (S). (X1200)

38. Myoneural Junction Of Skeletal Muscle
• Labeled components include the
Z disk (A),
• transverse tubule (or T tubule)
(B),
• synaptic vesicles (C),
• myelin sheath (D),
• basal lamina (E),
• axon (F),
• terminal bouton (G),
• primary synaptic cleft (H),
• secondary synaptic cleft (I), and
• junctional folds (J).
Schematic diagram of a synapse at a myoneural junction.

39. Sensory nerves
Muscle spindle (neuromuscular spindle)- is an elongated,
fusiform sensory organ within skeletal muscle that functions
primarily as a stretch receptor.
Each spindle contains 10 to 15 specialized muscle fibers
(intrafusal fibers) innervated by sensory and motor nerve
fibers and surrounded by a fluid-filled connective tissue
capsule.
1.5 mm in length and are anchored at each end to connective
tissue attached to ordinary muscle fibers (extrafusal fibers).

40. Two general types of muscle fibers are included in spindles:
nuclear bag fibers (which have a swelling in the middle of
the fiber where most of the nuclei are concentrated) and
nuclear chain fibers (which are smaller in diameter and have
a single row of nuclei).
Human muscle spindle contains 3-5 nuclear bag fibers and 8
to 10 nuclear chain fibers.
Muscle spindle (neuromuscular spindle).

41. Muscle spindle (neuromuscular spindle).
Simplified schematic diagram of the intrafusal muscle fibers of a muscle spindle receptor
 Two types of endings formed by sensory
axons:
 primary (or annulospiral) endings
(green) in which the axon wraps around
the equator of nuclear bag or nuclear
chain fibers and
 secondary (flower-spray) endings
(green), which are more common on
nuclear chain fibers.
 Innervated by Sensory and motor
neurons.

42. Muscle spindle (neuromuscular spindle).
 Several muscle spindles can be seen in
tangential section in the central fascicle.
The flattened fibroblasts making up the
capsule can be seen in the inset, as well
as five or six intrafusal fibers. In
general, muscles that are used in
delicate, highly controlled movements
contain the largest numbers of muscle
spindles. The intrinsic muscles of the
hand, for example, contain a relatively
larger number of spindles than do larger
muscles, such as the quadriceps and
gluteus maximus,which are specialized
for producing large amounts of force.
Skeletal muscle muscle spindle, cross section. H&E, 272;

43. Golgi tendon organ (GTO)
• Is (also called Golgi organ, tendon organ, neurotendinous
organ or neurotendinous spindle) is a proprioceptor–a type
of sensory receptor that senses changes in muscle tension.

44. Golgi tendon organ.
 Are in series with extrafusal
skeletal muscle.
 Innervated by Group Ib
afferent neurons.

45. HISTOGENESIS AND GROWTH OF SKELETAL MUSCLE
 All skeletal muscle arises from mesodermal mesenchyme cells.
 The mesenchymal cells become myoblasts; these fuse to form
multinucleated myotubes.
 Myotubes elongate and increase in diameter by incorporating
additional myoblasts, accumulating myofilaments and nuclei in their
cytoplasm.
 Mature muscle fibers cannot divide.
 Exercise and weight bearing elicit a proliferative response from
quiescent stem cells in the muscle tissue, called satellite cells.
 Myostatin is a signaling molecule that slows myogenesis.

46.  a stem cell that lies adjacent to a skeletal muscle fiber and
plays a role in muscle growth, repair, and regeneration.
 lie within the external lamina (basal lamina) of skeletal muscle
cells. These regenerative cells differentiate, fuse with one
another, and form skeletal muscle cells when the need arises
Functions:-
 muscle regeneration
 capacity to expand,
 differentiate,
 Growth and
 muscle adaptation to exercise.

47. CONTRACTION OF SKELETAL MUSCLE
:
+
Cross-bridge muscle contraction cycle: The cross-bridge muscle contraction cycle, which is triggered by Ca2+
binding to the actin active site, is shown. With each contraction cycle, actin moves relative to myosin.

48. Clinical Application
 Duchenne Muscular Dystrophy (DMD)
 Rigor Mortis
 Myasthenia Gravis
Neurotoxins
 Hypertrophy and Atrophy
Regeneration.

49. CARDIAC MUSCLE
 Cardiac muscle is highly organized and contains many types of
cell,including fibroblasts, smooth muscle cells, and cardiomyocytes.
 Cardiac muscle only exists in the heart.
 It contains cardiac muscle cells, which perform highly coordinated
actions that keep the heart pumping and blood circulating
throughout the body.
 Striated and involuntary
 Present exclusively in heart
 Originates in splanchnopleuric mesoderm
 Supplied by ANS (sympathetic & parasympathetic)

50. Microscopic structure of Cardiac Muscle
• Consists of long and thick branching muscle fibres
• Intercalated discs- specialized cell junctions
• These junctions are gap junctions, Desmosomes & Fasciae
adherentes.
• Acts as a functional syncytium
• Centrally placed single oval nucleus
• Faint transverse lines
• Supplied by ANS (sympathetic & parasympathetic)
• Cardiomyocytes are short and narrow, and fairly rectangular
in shape.
• They are around 0.02 mm wide and 0.1 mm (millimeters)
long.

51. Cardiac Muscle

52. Cardiac Muscle
Diagram of the organization of cardiac muscle fiber.
The T tubules of cardiac muscle are
much larger than the T tubules of
skeletal muscle and carry an
investment of external lamina
material in to the cell. They also
differ in that they are located at the
level of the Z disc. The portion of
the sarcoplasmic reticulum adjacent
to the T tubule is not in the form of
an expanded cisterna but rather is
organized as an anastomosing
network.

53. Cardiac Muscle
Lateral Portion:
forms electrical coupling
Transverse portion:
forms mechanical coupling

54. • Intercalated discs-connect cardiac muscle cells with many gap
junctions, allowing for rapid communication between adjacent
cells.
 Arrows in the enlarged image
indicate several intercalated
disks.
 Each intercalated disk appears
as a darker staining line across
the cell.
 An intercalated disk contains
desmosomes which mechanically
hold the cells to each other and
also contains gap juctions which
allow ions to pass freely between
cells.

55. Intercalated disc
• Transverse component- that crosses the fibers at a right
angle to the myofibrils.
• A lateral component- perpendicular to the transverse
component and lies parallel to the myofibrils.
A.Structure of cardiac muscle fiber B,Three-dimensional drawing of an intercalated disc.

56. Cardiac Muscle Fibers :
Light Microscope Picture.
1.Cylindrical/ Fairly rectangular.
• Intermediate in diameter between
skeletal and smooth muscle fibers.
• Branch and anastomose.
2.Covered by a thin sarcolemma.
3.Mononucleated. ( as a cell or fiber it’s
a Mononucleated, but as a tissue it’s a
multinucleated)
4.The Nuclei are oval and central.
5.Sarcoplasm is acidophilic and shows
non-clear striations (fewer myofibrils).
6.Divided into short segments (cells) by
the intercalated discs.
Electronic Microscope Picture.
1) Few myofibrils.
2) Numerous mitochondria.
3) Less abundant SR.
4) Glycogen (Food source) & myoglobin (
oxygensource).
5) Intercalated discs: are formed of the two cell
membranes of 2 successive cardiac muscle
cells, connected together by junctional
complexes (desmosomes and gap junctions).

57. Cardiac Muscle Fibers :
Cardiac Muscle in longitudinal section (phase-contrast optics).
Cardiac muscle in longitudinal section can be identified by centrally placed round to
oblong nuclei, striations, branching, and intercalated discs (arrow).

58. Cardiac Muscle Fibers:
The Purkinje fibers:
Purkinje fibers

59. SMOOTH MUSCLE
• Spindle elongated cells
• 30 microns in length and 5 μm wide
• 200-500 micron wide in pregnancy
• Non-striated, involuntary
• Supplied by Autonomic Nervous System
• Smooth muscle consists of thick and thin filaments that
are not arranged into sarcomeres giving it a non-striated
pattern.
• SMOOTH MUSCLE LOCATION
viscera and vascular system.
arrector pili muscles of the skin.
intrinsic muscles of the eye.
Walls of airways to the lungs.

60. Structures of smooth muscle cell tissue
 Relaxed and contracted smooth mus-
cle cells: cytoplasmic and peripheral
densities.
 The nucleus of the smooth muscle cell
assumes a corkscrew shape

61. Structures of smooth muscle cell tissue cont.d
 Nucleus
 Cytoplasmic organelles
 Filaments in smooth muscle
 Cytoplasmic densities
 Gap junctions
•Dense bodies are analogous to Z
lines (plaques into which actin
filaments insert).
•Myosin heads oriented in “side
polar” arrangement.
•Contraction pulls dense bodies
together
•Contraction is slow and sustained.

62. Light micrograph of a longitudinal section and cross sections of smooth muscle cells
from the monkey duode-num. LS, longitudinal section of smooth muscle fibers; CS,cross
section of smooth muscle fibers; arrows, nuclei of smooth muscle cells.Plastic section
(×270).

63. Smooth Muscle Contd
Smooth Muscle:wall of small intestine(transverse and longitudinal
section).stain:hematoxylin and eosin.

64. Gap junctions
• Cardiac and some smooth muscle cells
• Facilitate the spread of excitation.
• Its collectively called the nexus.
• Smooth muscle cells utilize gap junctions to
transmit signals and coordinate contraction.

65. Filaments in smooth muscle
a. Contractile filaments (actin and myosin) are not organized into
myofibrils.
They are attached to peripheral and cytoplasmic densities and aligned
obliquely to the longitudinal axis of smooth muscle cells.
 Thick filaments (composed of myosin II) are each surrounded by as
many as 15 thin filaments.
 In contrast to striated muscle, the heads of the myosin molecules all
point in the same direction.
Prior to contraction, the myosin II molecule is inactive and cannot
bind to the actin filament because the tail of the myosin molecule
(light meromyosin) is attached to the heavy meromyosin,
 Thin filaments are composed of actin, caldesmon, tropomyosin, and
calponin.
Caldesmon functions similarly to TnT and TnI in that it masks the
sites where myosin binds to effect muscle contraction.

66. b. Intermediate filaments
• Are attached to cytoplasmic densities and include vimentin
and desmin in vascular smooth muscle cells and desmin
only in nonvascular smooth muscle cells.

67. Smooth muscle contraction
Stimulated
Conformational change.
catalyzes phosphorylated
Thick filament formation
Resulting in contraction
Dephosphorylation

68. 1. Ca2+ ions released from caveloae/SER and complex with calmodulin
2. Ca2+-calmodulin activates myosin light chain kinase
3. MLCK phosphorylates myosin light chain
4. Myosin unfolds & binds actin; ATP-dependent contraction cycle
ensues.
5. Contraction continues as long as myosin is phosphorylated.
6. “Latch” state: myosin head attached to actin dephosphorylated causing
decrease in ATPase activity –myosin head unable to detach from actin
(similar to “rigor mortis” in skeletal muscle).
7. Smooth muscle cells often electrically coupled via gap junctions.
Smooth Muscle Contraction Cntd
also Ca+ dependent, but mechanism is different than striated muscle

69. Smooth Muscle Contraction Cnt.d
Triggered by:
• Voltage-gated Ca+
channels activated
by depolarization
• Mechanical
stimuli
• Neural
stimulation
• Ligand-gated Ca+
channels

70. Initiation of contraction Contd
In vascular smooth muscle,
Triggered by a nerve impulse, with little impulse from cell
to cell.
 In visceral smooth muscle,
Triggered by stretching of the muscle itself (myogenic).
In the uterus during labor, it is triggered by oxytocin.
In smooth muscle elsewhere in the body- epinephrine.
 Innervation of smooth muscle is by sympathetic
(noradrenergic) nerves and cholinergic) nerves of the
autonomic nervous system, which act in an antagonistic
fashion to stimulate or depress activity of the muscle.

71. CONTRACTILE NON MUSCLE CELLS
A. Myoepithelial cells
 Arise from ectoderm and can contract to express secretory material
from glandular epithelium into the ducts and out of the gland.
 Similar in morphology to smooth muscle cells, they have a
basketlike shape and several radiating processes.
 Attached to the underlying basal lamina via hemidesmosomes.
 They contain actin, myosin, and intermediate filaments, as well as
cytoplasmic and peripheral densities to which these filaments attach.
 Contraction is similar to that of smooth muscle and occurs via a
calmodulin-mediated process.
 In lactating mammary glands, they contract in response to oxytocin.
 In lacrimal glands, they contract in response to acetylcholine.

72. B. Myofibroblasts
 Arise from mesenchymal cells and possess vimentin as their
characteristic intermediate filaments as well as caldesmon and
cytokeratins
 Higher amounts of actin and myosin and are capable of contraction.
 Contract during wound healing to decrease the size of the defect
(wound contraction).

73. B. Pericytes
Pericytes are spatially isolated cells that surround capillaries.
Together with vascular smooth muscle cells (vSMCs) that
surround large vessels (arteries, arterioles, venules, and
veins), they make up the mural cells that support blood
vessels.
SEM micrograph of pericytes in blood vessels

74. MEDICALAPPLICATION
Benign tumors called leiomyomas commonly
develop from smooth muscle fibers.
They most frequently occur in the wall of the
uterus, and
called fibroids
It become large to produce painful pressure and
unexpected bleeding.

75. Differences between skeletal, cardiac and smooth muscles
Regeneration Limited (satellite cells
and myogenic cells
from bone marrow)
None (in normal
condition)?
Present

76. All muscle tissues have 4 characteristics in common:
•Excitability - is the ability to respond to a stimulus
•Contractility -is the ability of muscle cells to forcefully shorten.
•extensibility - they can be stretched.
•elasticity - they return to normal length after stretching/relaxed.

77. Reference
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