HISTOLOGY OF MUSCLE
TISSUE
Dr ATA ABENG
Learning objectives
1- Distinguish the three types of muscle
2- Describe how they differ in struture and function
PLAN
I- INTRODUCTION
II- CONTRACTILE UNITS
III- TYPES OF MUSCLES
IV-COMPARISON OF SKELETAL, CARDIAC, AND SMOOTH MUSCLE
V- CONCLUSION
I- INTRODUCTION
• Terms used in muscle:
- Muscle fiber refers to muscle cells
- Sarcolemma refers to cell membrane of muscle cells
- Sarcopasm: cytoplasm
II- CONTRACTILE UNITS (1/2)
• Unicellular contractile units
- Myoepithelial cells: flat, star-shaped, with extensions
- pericytes: surround the blood vessels and also act as stem cells for the
vessels
- Myofibroblasts: spindle-shaped cells
II- CONTRACTILE UNITS (2/2)
• Multicellular contractile units:
- Responsable of movements of the skeleton and certain organs
- Voluntary contraction
- Smooth muscle: component of visceral tructures
- Involuntary contraction controlled by the autonomic vervous system and
certains hormons
- Absence of striation
III- TYPES OF MUSCLES (1/3)
• Muscle is classified into three types: skeletal, cardiac and smooth
muscle
• Muscle cells possess contractile filaments containing actin and myosin
• Contraction may be voluntary (skeletal muscles) or involuntary (cardiac
and smooth muscles)
• All muscle tissues consist of elongated cells called fibers
III- TYPES OF MUSCLES (2/3)
• The cytoplasm of muscle is called sarcoplasm and the surroundingcell
memebrane is called sarcolemma
• Skeletal
- Comprised all named voluntary muscles in the body
- Most originate and/insert in bone
III- TYPES OF MUSCLES (3/3)
• Cardiac: Limited to heart (myocardium) and large blood vessels attached
• Smooth: present in walls and parenchyma of most visceral organs, walls
of blood vessels and skin
III-1- SKELETAL MUSCLE
• The envelops:
- Epimysium: CT which envelops muscles
- Perimysium: CT which envelops muscle bundles/fascicles
- Endomysium: surround muscle fibers
a- Types of skeletal muscle
• Red (slow twitch) muscle
- Contract as slower rate but capable of continuous contraction
- Do not fatigue easily
- High content of red pigments (myoglobin)
- Example: long muscles of the back
a- Types of skeletal muscle
• White (fast twitch) muscle
- Contract rapidly but briefly
- Fatigues fast low myoglobin content
- Fewer mitochondria
- Example: extraocular muscles
Fibers type I Fibers type IIa Fibers type IIb
Fiber diameter small intermediate Large
Myoglobin content High (red fibers) High (red fibers) Low (white fibers)
Rate of fatigue Slow Intermediate Fast
Speed of contraction Slow Fast Fast
Typical major locations Postural muscles of back Major muscles of legs Extraocular muscles
III-1- SKELETAL MUSCLE
III-2- CARDIAC MUSCLE
• Composed of an organized network of interconnected cardiomyocytes
( cells connect at regons called intercalated disks that ontain high
concentrations of membrane junctions
• Contain sarcomeres connected in series generating straited appearance
• Dense vascular blood supply to provide for the high metabolic demands of
cardiac muscle
• Less CT than skeletal muscle, and not organized into bundles
III-2- CARDIAC MUSCLE
FEATURES:
• Striated appearance
• One centrally located ovoid shaped nucleus per cell (occasionally
binucleate cells can be observed)
• Contain more mitochondria compared to skeletal muscle
• Do not have satellite stem cells that can regenerate new cells
III-3- SMOOTH MUSCLE
• Non-striated tissue found throughout
• Less dense blood supply and myoglobin content thant skeletal and cardiac
muscle
• Involuntary muscle that have a variety of functions including regulation of
the diameter of epithelial lumens (blood vessels, GI tract), generate
peristaltic contractions,…
III-1- HISTOLOGIC FEATURES
• Spindle shaped cells with pale eosinophilic cytoplasm
• Single elongated shaped nucleus
• Smooth muscle cells do not contain sarcomeres, thus no striations
• Muscle cell regeneration
III-3- SMOOTH MUSCLE
IV-COMPARISON OF SKELETAL,
CARDIAC, AND SMOOTH MUSCLE
IV-COMPARISON OF SKELETAL,
CARDIAC, AND SMOOTH MUSCLE
IV-COMPARISON OF SKELETAL,
CARDIAC, AND SMOOTH MUSCLE
Property Skeletal Muscle Cardiac Muscle Smooth Muscle
Shape and Size of cells Long, cylindrical Blunt-ended Branched Short, spindle-shaped
Number and location of Many, peripheral One or two, central One, central
nucleus
Striations present Yes Yes No
Sarcomere present Yes Yes No
Voluntary contraction Yes No No
Distinctive characteristics Peripheral nuclei Intercalated disks Lack of striation
Conclusion
