Muscle tissue consists of elongated muscle cells called fibers that have the ability to contract. The main types are skeletal, cardiac, and smooth muscle. Skeletal muscle is striated and voluntary, attaching to bones to enable movement. Cardiac muscle is also striated but involuntary, found only in the heart walls. Smooth muscle is non-striated and involuntary, surrounding hollow organs. All muscle tissues contain contractile filaments that slide past each other during contraction, but the structures differ between tissue types.

1. MUSCULAR
TISSUES

2. MUSCLE TISSUE
• Abundant, dense tissue
– 40-50% of body weight
• High metabolic activity
– high energy use/output;
– O2 consumption;
– CO2 production

3. MUSCLE TISSUE
• Consist of cells & intercellular substance.
• Cells are called fibres b/c they are elongated.
• Contractile property is due to myofibrils.
• Plasma lemma is called sarcolemma.
• Cytoplasm is called sarcoplasm.

4. Characteristics of Muscle Tissue
• Contractility
– Muscle tissue shortens producing force.
• Excitability
– Responds to nerve impulses by contracting.
• Extensibility
– Ability of a muscle to extend to a predetermined endpoint.
• Elasticity
– Recoils after being stretched.

5. Functions of Muscle Tissue
• Produce movement by contracting
– Locomotion & manipulation
– Movement of blood, food, urine, etc. through hollow organs
• Maintenance of posture
• Stabilize joints
– so that other muscles can produce movement or maintain posture
• Heat production
– Maintenance of body temperature.

6. Three Kinds of Muscle Tissue
• Skeletal muscle:
– Striated, voluntary, attached to skeleton
• Cardiac muscle:
– Striated, involuntary, walls of heart
• Smooth muscle:
– Non-striated, involuntary, wrapping of hollow organs
– E.g.: Stomach, intestines, arteries, bladder, vas deferens, uterus, etc.

7. Skeletal Muscle Tissue
Figure 4.14a

8. • Long, cylindrical cells,
• Multinucleate (nuclei peripheral),
• Cytoplasm = sarcoplasm
• ER = sarcoplasmic reticulum
• Covered by plasma membrane (sarcolemma).

9. Muscle sheath
• Epimysium
– Dense connective tissue that surrounds entire muscle
• Perimysium
– Thin connective tissue layer that surrounds fiber bundles (fascicles)
• Endomysium
– Surrounds each muscle fiber (cell)
– Mainly reticular fibers and basal lamina

11. Architecture of a skeletal
muscle fiber
• Muscle fibers are composed of myofibrils
• Myofibrils are composed of repeating units called sarcomeres
• Sarcomeres are the smallest functional unit of skeletal muscle
• Sarcomeres are composed of overlapping thick and thin
filaments
• Thin filaments are composed of actin and associated proteins
• Thick filaments are composed of myosin

13. Myofibrils
• Made of three types of filaments (or
myofilaments):
– Thick (myosin II)
– Thin (actin)
– Elastic (titin)

14. Thick myofilament:
• Three main proteins: the actin monomer, troponin
complex (comprising three protein components:- troponin-
I, troponin-C and troponin-T) and two strands of
tropomyosin molecules.
• Composed of 2 heavy chains & 2 pair of light chains.
• Heavy chain has a shape of golf club, has 2 binding sites
i.e. for ATP & actin.
• Light chain are of 2 types: one pair of essential light chain
& one of regulatory light chain.

15. Thin myofilament:
• Composed mainly of actin but tropomyosin & troponin is also
present.
• Actin exist as long filamentous polymer called F-actin polymer,
w/c composed of two strands of globular sub units of G-actin (has
an active site that can bind to the head of a myosin molecule).
• Tropomyosin, the protein that blocks the active sites of the thin
filaments when the muscle is relaxed.
• Each tropomyosin molecule has a smaller calcium-binding protein
called troponin bound to it.

16. The Sarcolemma
• The cell membrane of a muscle cell
• Surrounds the sarcoplasm (cytoplasm of muscle fiber)
• A change in transmembrane potential begins contractions
• All regions of the cell must contract simultaneously

17. Muscle Striations
• A striped or striated pattern within myofibrils:
– alternating dark, thick filaments (A bands) and light, thin filaments (I
bands)
• M line:
– the center of the A band
– at midline of sarcomere
• Z lines:
– the centers of the I bands
– at 2 ends of sarcomere

18. H Zone
• The area around the M line
• Has thick filaments but no thin filaments
Titin
• Are strands of protein
• Reach from tips of thick filaments to the Z line
• Stabilize the filaments

19. Sarcomeres
-The contractile units of muscle.
-Structural units of myofibrils.
-Form visible patterns within
myofibrils.

20. Sarcomere regions
• I Band, isotropic- similar polarization characteristics
throughout
• A Band, anisotropic- different polarization characteristics
throughout
• H Band- ‘heller’ or bright
• Z line, between
• M line, ‘mittel’ or middle

21. T-tubules
• Invaginations of sarcolemma that surround myofibril at
every sarcomere in the region of the A-I band
• Adjacent to each T-tubule is a sarcoplasmic reticulum,
which stores calcium.
• Action potential travels along sarcolemma, down T-tubule
• This causes calcium to be released from sarcoplasmic
reticulum

22. The triad
• Formed at A-I junction.
• the triad is a diagnostic feature of skeletal muscle
• It is composed of two terminal cisternae on either side of a T-
tubule.
• It is not found in cardiac or smooth muscle.
Cisternae
• Concentrate Ca2+
(via ion pumps)
• Release Ca2+
into sarcomeres to begin muscle contraction

24. Cardiac Muscle Tissue
Figure 4.14b

25. • Bundles form thick myocardium
• Cardiac muscle cells are single cells (not called fibers)
• Cells branch with 1-2 nuclei in center.
• Cells join at intercalated discs (intercellular junction)
• Here “fiber” = long row of joined cardiac muscle cells
• Inherent rhythmicity: each cell! (muscle cells beat separately
without any stimulation)
• Cells are small, have short, wide T tubules but no triads
• have SR with no terminal cisternae
• are aerobic (high in myoglobin, mitochondria)

26. Intercalated Discs
• Are specialized contact points between
cardiocytes
• Join cell membranes of adjacent cardiocytes (gap
junctions, desmosomes & fasciae adherent)
Functions of Intercalated Discs
• Maintain structure
• Enhance molecular and electrical connections
• Conduct action potentials

27. Smooth Muscle Tissue
Figure 4.14c

29. Characteristics of Smooth Muscle Cells
1. Long, slender, and spindle shaped
2. Have a single, central nucleus
3. Have no T tubules, myofibrils, or sarcomeres
4. Have no tendons or aponeuroses.
5. Contractions are slow, sustained and resistant to fatigue
6. Does not always require a nervous signal: can be stimulated by
stretching or hormones

30. 7. Contain contractile apparatus, w/c enables shortening.
8. Have scattered myosin fibers, have more heads per thick filament
9. Have thin filaments attached to dense bodies, w/c transmit
contractions from cell to cell.

31. Dense bodies
• Round, amorphous bodies scattered through the cytoplasm of
smooth muscle fibers.
• Intermediate filament & actin are inserted into dense bodies.
• They contain α-actinin (actin binding protein)
• Actin filaments within the cells are either anchored to the internal
surface of the plasma membrane, or onto irregularly placed dense
bodies (rather than z-lines).
• Contractile units are situated diagonally across the cell (rather than
running parallel as in skeletal muscle)

32. • 6 major locations:
1. Inside the eye
2. Walls of vessels
3. Respiratory tubes
4. Digestive tubes
5. Urinary organs
6. Reproductive organs

33. Thank You