Histology of Muscle types histology o.ppt

Husto

1. THE MUSCULAR
TISSUE
Dr Ayesha Fuad

2. Muscle Tissue
Muscle tissue is contractile, meaning it can
shorten itself.
Three characteristics help us tell the types apart:
 The cell shape
 The placement and number of nuclei
 The level of organization of the contractile
fibers, actinand myosin (ie. whether its
striated or not).

4. Copyright © McGraw-Hill CompaniesFigure 10-1

5. MUSCLE TERMINOLOGY
Myofiberor myocyte: a muscle cell
Sarcolemma: the plasma membrane of a muscle cell
Sarcoplasm: the cytoplasm of the muscle cell
Sarcoplasmicreticulum: the endoplasmic reticulum
of a muscle cell
Sarcosome: the mitochondria of a muscle cell
Sarcomere: the contractile or functional unit of
muscle

6. Copyright © McGraw-Hill CompaniesFigure 10-2

7. Muscle Classification
Morphological classification (based on structure)
1. Striated
2. Non striated or smooth.
Functional classification
1. Voluntary
2. Involuntary.

8. Types of muscle
Skeletal muscle: which is striated and
voluntary
Cardiac muscle: which is striated and
involuntary
Smooth muscle: which is non striated and
involuntary

9. SKELETAL MUSCLE
Long, CylindricalCells
Non branching
Multinucleated
Diameter 10-100 µm
Run the length of the muscle.
Striationsare prominant. The
actinand myosin are very
highly organized .
The strands of actinand myosin
are compacted into the center of
the cell which causes the nuclei
to be pushed to the periphery
of the cell, just inside the cell
membrane.

10. Connective Tissue Organization
Endomysium. dense
connective tissue layer
around the cells.
The cells are grouped
together into groups called
fascicles which are
surrounded by dense
connective tissue called the
Perimysium.
Many fascicles are grouped
into a single muscle which
is wrapped with a 3rd
dense CT layer, the
Epimysium.

11. Copyright © McGraw-Hill CompaniesFigure 10-3

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13. Role of C.T
Transmission of mechanical forces
Entry of blood vessels
Myotendinousjunctions

14. Muscle Fibre/ Muscle cell
Sarcoplasm–little RER or free ribosomes.
Myofibrils –long , filamentous bundles running parallel
to the long axis of the fibre.
Diameter 1-2 µm
Myofilaments–Thick and thin

15. Myofibril
A myofibril is a cylindrical
bundle of contractile proteins
found within the muscle cell.
Myofibrils are composed of
individual contractile proteins
called myofilaments.
These myofilamentsare
generally divided into thick
and thin myofilaments.
Thick= Myosin
Thin= Actin

16. Sarcomere
The thin myofilamentsare
composed mainly of a protein
known as Actin.
Actinfilaments are anchored
into the z-line of a sarcomere.
The thick myofilamentsare
composed mainly of the
protein myosin.
It is the orderly overlapping of
the actinand myosin filaments
that give cardiac and skeletal
muscle their striated
appearance (light and dark
bands).

17. The light bands are known
as I bands. The I bands are
composed mainly of actin
filaments.
Each I band is bisected by a
protein disc known as the Z-
line.
Actinfilaments are
anchored into the Z-line.
During muscle contraction
the actinfilaments slide over
the myosin filaments which
results in a shortening of the
I band.

18. Sarcomere–it is the repetitive , functional
subunit of the contractile apparatus.
Extends from Z-line to Z-line
2.5 µm in resting muscle

19. Z = Zwischenscheibe= between discs
M = Mitte= middle
H = Hell = light

21. In the middle of the A band is a somewhat lighter area
known as the H zone. This zone has myosin not
overlapped by actin).
In the middle of the H zone we see a dark band known as
the M line.
The M line is comprised of protein fibers that function to
anchor the myosin filaments

22. During muscle contraction the actin sliding
over the myosin encroaches into this area so
that the H zone shortens.

23. Striations
Actinfilament / thinner →
lighter striations
Myosin filament / thicker →
darker striation
Distance between 2 adjacent Z
lines:Sarcomere
Striation of actinalone → I
band
Striation of myosin alone → H
zone
Length of myosin → A band
Central thickening of each
myosin filament → M line

24. Thin filaments
1.0 µm long and 8.0 nm wide
Composition:
 F-actin
 Tropomyosin
 Troponin

25. The F-actinstrands are formed
by molecules of G-actinwhich are
spherical.
Each thin myofilamentcontains
two such chains that coil around
each other.
Tropomyosinmolecules are long,
thin molecules that wrap around
the chain of actin.
Troponinconsists of a globular
complex of 3 proteins.
TroponinC
TroponinT
TroponinI

26. TnTattaches to
tropomyosin
TnCbinds calcium ions
TnIinhibits actin-myosin
interaction

27. Thick Filaments
1.6 um long and 15 nm wide
Composed of Myosin
510 kilodaltonprotein
Composition:
2 heavy chains (polypeptide)
4 light chains
Globular head with two specific binding sites; one for
ATP & one for actin

28. Aggregate in tail to tail to form bipolar thick
filaments
Bare zone --------H band

29. Copyright © McGraw-Hill CompaniesFigure 10-9

30. Myosin head
The MYOSIN HEADhas several
important characteristics:
It has ATP-binding sites into
which fit molecules of ATP.
It has ACTIN-binding sites into
which fit molecules of ACTIN..
It has a "hinge"atthe point where
it leaves the core of the thick
myofilament. This allows the
head to swivel back and forth, and
the "swivelling" actually causes
muscle contraction.

32. Transverse tubules (or t-tubules for
short).
The SARCOLEMMA has a
unique feature: it has holes in
it.
These "holes" lead into tubes
called Transverse Tubules
These tubules pass down into
the muscle cell and go around
the myofibrils.
The function of T-TUBULES
is to conduct impulses from
the surface of the cell
(SARCOLEMMA) down into
the cell

33. Copyright © McGraw-Hill CompaniesFigure 10-10

34. The SarcoplasmicReticulum
The endoplasmic reticulum
of the muscle cell.
Specialisedfor Ca ion
sequestration
There are sac-like regions
of the sarcoplasmic
reticulum known as
terminal cisternae. The
terminal cisternaeact as
calcium storage sites.
Two terminal cisternaeare
associated with a T tubule
to form a structure known
as a triad.

36. Events Of Muscle Contraction

37. Copyright © McGraw-Hill Companies

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40. No change in length of filaments
Only a small number of myosin heads align
with actin–binding sites
Actin–myosin bridges detach when myosin
binds anew ATP molecule
Rigor mortis
Single muscle contraction= hundreds of bridge
forming and breaking cycles

41. Motor End Plate

42. Copyright © McGraw-Hill CompaniesFigure 10-13

44. Motor Unit
A single nerve fibreand all the muscle fibresit
innervates, is called a motor unit.
1 axon –1-160 muscle fibres
Delicate movements-fine control-small motor
unit
Coarse movements-large motor unit

45. Copyright © McGraw-Hill CompaniesFigure 10-13

46. Muscle Spindle
Sensory receptors in striated muscle and
tendons
Encapsulated proprioceptors
Specialisednonstriatedmuscle fibres
(Intrafusalfibres)
 Nuclear bag fibres
 Nuclear chain fibres

47. Copyright © McGraw-Hill CompaniesFigure 10-14

48. Tendon Organ
Golgi tendon organ
Detect changes in tension within tendons
produced by muscle contraction
Inhibit contraction if tension becomes
excessive

49. Types Of Skeletal Muscles
(according to their speed of contraction &
metabolic activity)
Type I/ Slow oxidative
fibers
Type IIa/ Intermediate
oxidative glycolytic fibers
Type IIb / Fast glycolytic
fibers

50. Type I Fibres
Slow, red oxidativefibres
Many mitochondria
Abundant myoglobin–protein with iron that
binds O2-dark red colour
Slow, continouscontractions over prolonged
periods e.gpostural muscles of back.

51. Type IIaFibres
Oxidative glycolytic
Many mitochondria
Much myoglobin
Considerable glycogen
Intermediaatein colourand energy metabolism
Rapid contractions and short bursts of activity-
athletics

52. Type II b fibres
Fast, white glycolytic
Fewer mitochondria
Less myoglobin
Abundant glycogen
Rapid contractions
Fatigue easily
Small muscles-eye and digits

53. Copyright © McGraw-Hill CompaniesFigure 10-15

54. Differentiation depends upon-innervation
Fibresof single motor unit-same type
If nerves exchanged-fibreschange their
characteristics
Denervation-fibreatrophy and paralysis

55. Cardiac Muscle
Elongated cells
85-100 µm length
15 µm diameter
Often branched
Mononucleatedor
binucleated.
Nuclei central
Cardiac muscle is
striated.
Intercalated discs

56. Copyright © McGraw-Hill CompaniesFigure 10-1

58. Elongated, branching cells with complex junctions
between extended processes
Tightly knit interwoven bundles of cells
Myofibrils

59. L.S. OF CARDIAC MUSCLE
T.S. OF CARDIAC MUSCLE

60. Cardiac muscle Cell
Sarcoplasmmore abundant = striations less
visible
Abundant Glycogen and fat droplets =
Storehouse of energy
Mitochondria-
-50% cytoplasmicvolume
-Large in size near myofibrils
-Continousaerobic metabolism

61. Intercalated Discs
Highly specialisedintercellular junctions
L/M appearance
E/M = Transverse Component
Desmosomes
Fascia adherentes
Lateral component
Gap junctions

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63. SarcoplasmicReticulum
T-tubules are typically wider than in skeletal muscle,
but there is only one T-tubule set for each
sarcomere,
It is located close to the Z-line.
It does not form continuous cisternaebut instead an
irregular tubular network around the sarcomerewith
only small isolated dilations in association with the
T-tubules.

65. Smooth Muscle
Spindle shaped cells,
fusiform(tapering at both
ends).
Single centrally placed
nucleus.
Diameter-6 µm
Lengthvariable-
20 µm in walls of blood
vessels
200 µm in wall of
intestine
500 µm in wall of
pregnant uterus

66. Arranged in the form of
sheets or bands
Tightly packed
arrangement
Narrow portion of one
cell against wider
portion of another

67. Sarcolemma
Ordinary cell
membrane with an
external lamina
(basement
membrane), reticular
fibres
Gap junctions
between adjacent
cells
Single rod shaped
nucleus
Cockscrewshaped in
contracted cell
Scalloped edges of
cell

69. Sarcoplasm
No visible striations
No t-tubules
Rudimentary Sarcoplasmicreticulum
Thick & thin myofilamentspresent but no sarcomeres
Thin filaments in smooth muscle do not contain
troponin.
Calcium does not bind to troponinbut, rather, to a
protein called Calmodulin. The calcium-calmodulin
complex 'activates' myosin which then binds to actin&
contraction begins
Cytoplasmicorganelles are concentrated at each end of
nucleus.

70. Contractile Apparatus of Smooth
Muscle
Lattice like network of actinand myosin.
Crisscross obliquely
Actinfilaments insert into attachment plaqueslocated
on the cytoplasmicsurface of the plasma membrane.
From here, they extend into the cytoplasm and
interact with myosin filaments. The myosin filaments
interact with a second set of actinfilaments which
insert into intracytoplasmaticdense bodies.

71. Invaginations of cell
membrane called
Caveolae.
Act like T-tubules
Beneath membrane are
smooth ER and
cytoplasmicvesicles

73. Gap Junctions

74. Copyright © McGraw-Hill CompaniesFigure 10-21

75. Thickened appearance
of plasma membrane
because of:
Densities along its
internal aspect
Prominent external
lamina over its
outer aspect

76. Regulation of Contraction
Autonomic nerves
Hormones
Degree of stretch
Multiunit
Unitary
Importance of Gap
junctions
Neuromuscular
junctions

77. Regeneration
Skeletal Muscle
Limited regeneration (Satellite cells)
Hypertrophy
Hyperplasia
Cardiac Muscle
No regenerative capacity
Fibroblast activity
Smooth Muscle
Active regeneration (pericytes)