Histology

1. HISTOLOGY OF MUSCLES
Dr. Rabia Inam Gandapore
Assistant Professor
Head of Department Anatomy
(Dentistry-BKCD)
B.D.S (SBDC), M.Phil. Anatomy (KMU),
Dip. Implant (Sharjah, Bangkok, ACHERS) , CHPE
(KMU),CHR (KMU), Dip. Arts (Florence, Italy)

2. Teaching Methodology
 LGF (Long Group Format)
 SGF (Short Group Format)
 LGD (Long Group Discussion, Interactive discussion with the use of models or diagrams)
 SGD (Short Group)
 SDL (Self-Directed Learning)
 DSL (Directed-Self Learning)
 PBL (Problem- Based Learning)
 Online Teaching Method
 Role Play
 Demonstrations
 Laboratory
 Museum
 Library (Computed Assisted Learning or E-Learning)
 Assignments
 Video tutorial method

3. Goal/Aim (main objective)
 To help/facilitate/augment the students about the:
1. Histological features of Skeletal muscles.

4. Specific Learning Objectives (cognitive)
At the end of the lecture the student will able to:
 Recognize the Histological features of the Skeletal muscles.
 Sketch labeled diagram of the different types of Muscles

5. Psychomotor Objective: (Guided response)
 A student to draw labelled diagram of different types of muscles

6. Affective domain
 To be able to display a good code of conduct and moral values in the class.
 To cooperate with the teacher and in groups with the colleagues.
 To demonstrate a responsible behavior in the class and be punctual, regular, attentive and
on time in the class.
 To be able to perform well in the class under the guidance and supervision of the teacher.
 Study the topic before entering the class.
 Discuss among colleagues the topic under discussion in SGDs.
 Participate in group activities and museum classes and follow the rules.
 Volunteer to participate in psychomotor activities.
 Listen to the teacher's instructions carefully and follow the guidelines.
 Ask questions in the class by raising hand and avoid creating a disturbance.
 To be able to submit all assignments on time and get your sketch logbooks checked.

7. Lesson contents
Clinical chair side question: Students will be asked if they know what is the function of
Outline:
 Activity 1 The facilitator will explain the student's histological features of skeletal muscles.
 Activity 2 The facilitator will ask the students to make a labeled diagram of the Skeletal muscles
 Activity 3 The facilitator will ask the students a few Multiple Choice Questions related to it with flashcards.

8. Recommendations
 Students assessment: MCQs, Flashcards, Diagrams labeling.
 Learning resources: Langman’s T.W. Sadler, Laiq Hussain Siddiqui, Snell Clinical Anatomy, Netter’s
Atlas, BD Chaurasia’s Human anatomy, Internet sources links.

9. Histology Of Muscles
 SKELETAL MUSCLE
 CARDIAC MUSCLE
 SMOOTH MUSCLE

10. Muscles
 Motors of body
 Contractile tissue helps in movements
 Trichrome and H&E stains
Functions:
 Excitability
 Contractility
 Extensibility
 Elasticity
 Strength
 Support

11. Muscle Tissue
1. Striated Muscle: regularly arranged contractile units
A. Skeletal Muscle:
 long, cylindrical multinucleated cells
 Peripheral nuclei
 Contraction is quick,vigorous & under voluntary control.
 Used for locomotion, mastication & phonation.
A. Cardiac Muscle:
 Elongated, branched cells
 Single centrally placed nucleus
 Intercalated discs at ends.
 Contraction is involuntary, vigorous & rhythmic.
2. Smooth Muscle: possesses contractile machinery, but its irregularly arranged (non-striated).
 Cells are fusiform with central nucleus.
 Contraction is involuntary, slow & long lasting.

12. Skeletal Muscle
Investments
Epimysium: dense
irregular connective
tissue.
Perimysium: less dense
irregular connective
tissue
Endomysium: basal
lamina & reticular fibers
All Muscle Cells
Have Basal
Laminae!

13. No. Striated /Skeletal Non-Striated/ Smooth Cardiac
1 Long, Cylindrical Spindle Shaped Short, Cylindrical
2 Fibres unbranched Unbranched branched
3 Multi-Nucleated Uni-Nucleated Uni-Nucleated
4 Bounded by Sarcolemma Plasmalemma Plasmalemma
5 Light and dark bands present absent Faint present
6 No inter-calated discs No present
7 Nerve supply CNS ANS ANS
8 Abundant blood supply Scanty Abundant
9 Very rapid contraction Slow Rapid
10 Gets fatiged No fatigue No fatigue
11 Voluntary Involuntary Involuntary
12 Limbs, body wall, tongue,
pharynx, beginning of
oesophagus
Distal part oesophagus, urogenital
tract, urinary bladder, blood vessels,
iris of eye, arrector pilli of hair
Wall of heart

14. Skeletal Muscle

15. Skeletal Muscle
Morphology
 Skeletal Muscle= Striated Muscle
 Long & Cylindrical
 Multi-Nucleated
 Peripheral nuclei (Endomysium)
 Triad: One T- Tubule system & 2 terminal
cisternae of Sarcoplasmic reticulum
 Contracts quickly
 Voluntary control
 Prominent cross striations
 Fiber diameter large
• Multi-nucleated and striated
• A bands - anisotropic (birefringent in polarized light)
• I bands - isotropic (do not alter polarized light)
• Z lines (Zwischenscheiben, Ger. “between the
discs”)
• H zone (hell, Ger. “clear”)
Skeletal Muscle as seen in longitudinal
section in the light microscope

16.  Unbranched
 No intercalated disc
 Myofribrils (Actin, Myosin, I Band, A Band, H zone, M-Line, Z-Line, Krause’s membrane)
 Glycogen
 Collagen fibers, capillaries
Functions
 Locomotion
 Mastication
 Phonation
Location
 All skeletal muscles with bones

17. Skeletal Muscle as seen in transverse section in the light microscope

18. Organization of Skeletal Muscle Fibers the SARCOMERE
Contractile unit of striated muscle
• Structures between Z lines
• 2 halves of I bands
• A band
• H zone
• M line (Mittelscheibe, Ger.“middle of the disc”)
• Myofilaments
• Actin
• Myosin
• Other structural proteins
• Titin (myosin-associated)
• Nebulin (actin-associated)
• Myomesin (at M line)
• actinin (at Z line)
• Desmin (Z line)
• Vimentin (Z line)
• Dystrophin (cell
membrane)

20. Transverse Section of Skeletal Muscle: TEM view
• H zone: thick filaments only
–At M-line: thick filaments and myomesin lattice
• A band: thick & thin filaments
• I Band: thin filaments only
I A

21. T-tubule System:
Propagation of Signal & Release of
Ca2+
T (transverse) Tubules
• run perpendicular (transversely) to myofibrils
• conduct membrane depolarization deep
into fibers
Sarcoplasmic Reticulum
• smooth ER
• site of Ca2+ storage
• Release terminal cisternae abut
T-tubules forming triads when myofibrils are
viewed in longitudinal section
Longitudinal section of muscle showing triads
• 1 T tubule
• 2 terminal cisternae of sarcoplasmic reticulum
• Normally at A/I junctions in mammals (this sample is from an amphibian)

23. Neuromuscular Junction
Synapse:
• Action potential (AP) stimulates release of acetylcholine from axon
terminal into synaptic cleft
• Acetylcholine in synaptic cleft binds Na+ channel receptors –initiates
sarcolemma AP
Signal Propagation:
T (transverse) Tubules
• Run perpendicular (transversely) to myofibrils
• Conduct membrane depolarization deep into fibers
Intracellular Ca2+ release: Sarcoplasmic Reticulum
• Smooth ER, site of Ca2+ storage
• Voltage-gated channels in SR detect membrane depolarization in T-
tubule and release Ca2+

25. Muscle Innervation: Motor End Plate
1. Pre-synaptic terminal
2. Sarcolemma
3. Synaptic vesicles
4. Acetylcholine receptors
5. Mitchondrion

26. Ca2+ Stimulates Myosin-Actin Binding and Initiates Contraction
• Myosin-actin binding inhibited by TnI
• TnC binds Ca2+ (if present) and induces release of TnI from actin
• Myosin binds actin; hydrolysis of ATP induces power stroke
• Actin filaments move relative to myosin

28. Contraction Cycle
1. ATP binds myosin – myosin releases actin
2. ATP hydrolysis induces conformational change – myosin head cocks forward 5nm
(ADP+Pi remain bound to myosin).
3. Myosin binds weakly to actin, causing release of Pi
4. Release of Pi induces strong binding, power stroke, and release of ADP
Myosin remains bound to actin if no more ATP is available (rigor conformation)

30. Cardiac Muscle

31. Cardiac Muscle
 Elongated
 Branched cells (3 dimensional network)
 1 or 2 centrally placed nuclei
 Intercalated disc
 Contraction Involuntary (ANS)
 Vigorous, Self-Excitatory & Electrically coupled
 Rhythmic
 Cardio-myocytes (muscle cells) connected by
intercalated disc
 Diads of 2 lines = T-tubules (2x larger in diameter)
& Sarcoplasmic without terminal cisternae
 Muscle fibers less parallel
 Myofibrils (longitudinal striations)
 Punctate appearance of sarcoplasm
 Extensive capillaries network in
endomysium
 Prominent cross striations
 Fibers diameter medium
 I-Band short when contracted
 Gap junctions
 Adhesive junctions
 Increased mitochondria
 Glycogen & Secretory granules

32. Cardiac Muscle
Functions
 Rhythmic contraction of heart to pump blood
Location
 Heart: Ventricles & auricles of heart

33. Cardiac Muscle (longitudinal section)

34. Cardiac Muscle (longitudinal section) Cardiac Muscle (transverse section)

35. Transverse Section of Cardiac Muscle versus Skeletal Muscle

36. Cardiac Muscle (TEM)
T Tubule/SR Diads

37. Intercalated Discs Couple Heart Muscle Mechanically and Electrically

39. Smooth Muscle

40. Smooth Muscles
 Possesses contractile machinery
 Irregularly arranged (Non-Striated)
 Cells are fusiform, Cell membrane indistinct
 Central nucleus (elongated), Increased nuclei
 Contraction involuntary modulated in a neuroendocrine manner, slow, long lasting,
 Fiber diameter small
 Caveolae: dispersal of caveolin & lipid from caveolar during stress increase
surface area & elasticity of plasma membrane
 Unbranched
 No intercalated disc

41.  No longitudinal striations
 No Myofibrils
 Action, myosin, alpha actinin (similar to
Z-line), intermediate filament of desmin
 Collagen (II, III, IV), elastin, fibroblast,
Connective tissue & Proteoglycans
 Connective tissue = collagen fiber

43. Function
 House keeping functions of body= Contract & Relax
Location
 Small intestine
 Jejunum
 Vagina
 Gastroesophageal Junction
 Blood vessels
 GI tract
 Urogenital walls
 Dermis of skin

44. Smooth Muscle (longitudinal section)

45. Smooth Muscle Viewed in Transverse and Longitudinal Section

46. Ultrastructure of Smooth Muscle:
• actin and myosin filaments
• intermediate filaments of desmin (also vimentin in vascular smooth muscle)
• membrane associated and cytoplasmic dense bodies containing alpha actinin (similar to Z lines)
• relatively active nucleus (smooth muscle cells make collagen, elastin, and proteoglycans)

47. Smooth Muscle Viewed in
Cross Section (TEM)
What is the structure marked by * ?
Also, note collagen – SMC secrete ECM:
collagen (I,III, IV), elastin, and proteoglycans

48. More Ultrastructure of Smooth Muscle Cells:
• Microtubules (curved arrows)
• Actin filament (arrowheads)
• Intermediate filaments
• Dense bodies (desmin/vimentin plaques)
• Caveoli (membrane invaginations & vesicular system contiguous
with SER –functionally analogous to sarcoplasmic reticulum)

49. Smooth Muscle Contraction:
Also Ca+ dependent, but mechanism is different than striated muscle
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).
Triggered by:
• Voltage-gated Ca+ channels activated by depolarization
• Mechanical stimuli
• Neural stimulation
• Ligand-gated Ca+ channels

50. Smooth Muscle (vascular)
Relaxed Contracted
Mechanics of Smooth Muscle
Contraction
• 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
Additional notes:
• Contraction cycle generally about ~10% as fast as skeletal muscle
• Visceral (unitary) smooth muscle cells may be electrically
coupled via gap junctions and exhibit either rhythmic or tonic
contraction –innervation generally MODIFIES smooth muscle
activity rather than initiating it.
• Multiunit smooth muscle cells are innervated individually and can
contract rapidly for more precise control.
• Innervation is always at a distance (no motor end plates)

51. Smooth Muscle
VERSUS
Nerve
VERSUS
Connective
Tissue

54. Skeletal Muscle Cardiac Muscle Smooth Muscle

55. Muscle Regeneration and Growth
Skeletal Muscle
• Increase in size (hypertrophy)
• Increase in number (regeneration/proliferation)
• Satellite cells are proposed source of regenerative cells
Smooth Muscle
• Increase in size (hypertrophy)
• Increase in number (regeneration/proliferation)
• Smooth muscle cells are proliferative (e.g. uterine myometrium and vascular smooth muscle)
• Vascular pericytes can also provide source of smooth muscle
Heart Muscle
• Increase in size (hypertrophy)
• Formerly thought to be non-proliferative
• Post-infarction tissue remodeling by fibroblasts (fibrosis/scarring)
• New evidence suggests mitotic cardiomyocytes and regeneration by blood or vascular-derived stem cells

56. Skeletal Muscle Satellite Cell

57. Activated satellite cell in Skeletal muscle

58. Thank You
ANY QUESTIONS?