The document summarizes the three main types of muscle tissue: skeletal, smooth, and cardiac. Skeletal muscle is striated and voluntary, controlling movement. Smooth muscle is involuntary and found in organs. Cardiac muscle is striated like skeletal but contracts rhythmically like smooth. Each type has distinct characteristics at the microscopic level of fibers, nuclei, and junctions. Regeneration capacity is limited in cardiac, moderate in skeletal from satellite cells, and active in smooth tissue.

1. MUSCLE TISSUE
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2. Muscle types
Muscle tissues in the body can broadly be classified into two
categories:-
a) Those that can function as single contractile units
1. Pericytes:- they are smooth like cells that surround blood
vessels-capillaries.
2. myoepithelal cells:- form important component of certain
secretory glands where they function to expel secretions
from glandular acini.
3. Myofibroblasts:- are cells that have a contractile role in
addition to being able to secrete collagen. They are
dominant in areas where tissues undergo repair.
b) Those that contract as group of cells (multicellular muscles)
1. skeletal muscles - they are the somatic muscles
2. smooth muscles - visceral muscles
3. cardiac muscles - heart muscles

3. Pericytes in the capillary walls

4. Multicellular muscle types

5. The multicellular Muscle Tissue
• Characteristics
– Cells are referred to as fibers
– Contracts or shortens with force when stimulated
– Moves entire body and pumps blood
• Types
– Skeletal:attached to bones
– Cardiac: muscle of the heart.
– Smooth: muscle associated with tubular
structures and with the skin. Nonstriated and
involuntary.

6. Skeletal muscles
- Are responsible for movement of the skeleton
and organs such as the globe of the eye and the
tongue.
- They are often referred to as voluntary muscles
because they are usually under voluntary control.
- The arrangement of the contractile proteins gives
rise to prominent cross- striations in histological
preparations hence the name striated muscles.
-

7. Skeletal muscles (contd.)
• specialized names such as sarcolemma /plamalemma –
plama-membrane, sarcoplasm- cytoplasm, sarcoplasmic
reticulum –endoplasmic reticulum are usually applied.
- they are composed of extremely elongated, multinucleate
contractile cells bound together by collagenous supporting
tissue.
- skeletal muscle contraction is controlled by a large motor
nerve( NB> individual nerve fibres branching within the
muscle to supply a group of muscles fibres is called a motor
unit.) damage to this muscle fibre leads to atrophy

8. Skeletal Muscle Tissue
Figure 4.14a

9. Organization of Skeletal Muscle
• The masses of fibers that make up skeletal muscles are
arranged in regular bundles surrounded by an external
sheath of dense connective tissue that surrounds the
entire muscle the epimysium
• From the epimysium, thin septa of connective tissue
extend inward, surrounding the bundles of fibers
within a muscle and are called the perimysium .
• Each muscle fiber is itself surrounded by a delicate
layer of connective tissue, the endomysium (Gr. endon,
within, + mys), composed mainly of a basal lamina and
reticular fibers.

11. Cross-section slide of a skeletal muscle

12. Clinical notes on Variations in diameter of
skeletal muscles
• The variation in diameter of skeletal muscle fibers depends on factors such
as:- (1). the specific muscle, (2) the age (3) sex, 4. state of nutrition, (4)
physical training of the individual.
• Hypertrophy:- it is the formation of new myofibrils and a pronounced
growth in the diameter of individual muscle fibers. This process,
characterized by augmentation of cell volume due to exercising that
enlarges the musculature and decreases fat depots.
• hyperplasia (hyper + Gr. plasis, molding):- it is the tissue growth by an
increase in the number of cells. it does not occur in either skeletal or
cardiac muscle but does take place in smooth muscle, among the cells
have not lost the capacity to divide by mitosis.
• Hyperplasia is rather frequent in organs such as the uterus, where both
hyperplasia and hypertrophy occur during pregnancy.
• Muscular dystrophy : it is the weakness and wasting of muscles due to
disease caused by a defective protein involved in muscle function.

13. Organization of Skeletal Muscle Fibers
• As observed with the light microscope,
longitudinally sectioned muscle fibers show cross-
striations of alternating light and dark bands.
• The darker bands are called A bands (anisotropic,
and the lighter bands are called I bands (isotropic,
ie, do not alter polarized light).
• In the electron microscope, each I band is bisected
by a dark transverse line, the Z line.
• The smallest repetitive subunit of the contractile
apparatus, is called the the sarcomere and extends
from Z line to Z line and is about 2.5 m long in
resting muscle.

16. Slide of a skeletal muscle : longitudinal
section

17. EM showing sarcomeres and T-Tubules

18. Smooth muscles
– named so because the arrangement of the contractile protein does
not give rise to cross striations
– they form muscular component of visceral structures such as the
blood vessels, GIT, the uterus, urinary bladder giving an alternative
name –visceral muscles
– they are under hormonal and autonomic nervous control hence
described as involuntary muscles
– the muscles are specialized for continuous contractions of low force
and for along period.(rhythmic contractions)
– muscle fibers are spindle shaped with only one nucleus that is
centrally placed
– the fibers are bound together in an irregular branching fasciculi, and
the arrangement varying from one organ to the other
– contraction is through a formation of a calcium-calmoduline
complex that controls actin and myosin fibres

19. Smooth Muscle Tissue
Figure 4.14c

20. Slide of the smooth muscle

21. EM of smooth muscle cells

22. Cardiac muscles
– they have many structural and functional intermediate to skeletal and smooth
muscles.
– They provide for continuous, rhythmic contractility to the heart
– They are “striated” like the skeletal muscles they are readily distinguishable
from the skeletal and therefore should not be called striated muscle
– The contractions of cardiac muscle is strong and utilize a good deal of energy
– Cardiac muscle fibers are essentially long cylindrical cells with one or at most
two nuclei.
– The ends of the fibers are split longitudinally into a small number of branches
– Between the ends of adjacent cardiac muscle cells are specialized intercellular
junctions called intercalated discs.
– These discs permit extreamly rapid spread of contractile stimuli from one cell
to another thus enabling the muscle to contract as a single unit-synsytium

24. Cardiac Muscle Tissue
Figure 4.14b

25. Slide of a cardiac muscle

26. Elecron micrograph of a cardiac muscle

27. Regeneration of Muscle Tissue
The three types of adult muscle have different potentials for regeneration after
injury.
• Cardiac muscle: has almost no regenerative capacity beyond early childhood.
Defects or damage (eg, infarcts) in heart muscle are generally replaced by the
proliferation of connective tissue, forming myocardial scars.
• Skeletal muscle,:-they can undergo limited regeneration. The source of
regenerating cells is the satellite cells. They are a sparse population of
mononucleated spindle-shaped cells that lies within the basal lamina surrounding
each mature muscle fiber.
– The Satellite cells are inactive myoblasts that persist after muscle differentiation.
– After injury or certain other stimuli, the normally quiescent satellite cells become activated,
proliferating and fusing to form new skeletal muscle fibers.
– satellite cells have been implicated in muscle hypertrophy, where they fuse with their parent fibers
to increase muscle mass after extensive exercise.
• The Smooth muscles:- are capable of an active regenerative response. After injury,
viable mononucleated smooth muscle cells and pericytes from blood vessels
undergo mitosis and provide for the replacement of the damaged tissue.