PPT includes structure and histology of different types of muscles i.e., smooth, cardiac and skeletal muscles.

1. PRESENTED BY:
NAME: HITESH
COURSE: B.Sc.(Hons.) ZOOLOGY
COLLEGE ROLL.NO.: 5008
UNIVERSITY ROLL.NO: 19081569002
Submitted to : Dr. Smita Shukla
DELHI UNIVERSITY
SWAMI SHARDHANAND COLLEGE

2.  Muscle is a specialized tissue of mesodermal
origin. About 40-50 per cent of the body weight
of a human adult is contributed by muscles.
They have special properties like excitability,
contractility, extensibility and elasticity.
Muscles have been classified using different
criteria, namely location, appearance and
nature of regulation of their activities.
 Muscle have 4 characteristic properties i.e.
Electrical excitability, Contractility , Extensibility
and Elasticity.

3.  1. Mobility
The muscular system’s main function is to allow
movement. When muscles contract, they
contribute to gross and fine movement.
 2. Stability
Muscle tendons stretch over joints and contribute to
joint stability. Muscle tendons in the knee joint and
the shoulder joint are crucial in stabilization.
The core muscles are those in the abdomen, back, and
pelvis, and they also stabilize the body and assist
in tasks, such as lifting weights.

4.  3. Temperature regulation
 Maintaining normal body temperature is an
important function of the muscular system.
Almost 85 percent of the heat a person generates in
their body comes from contracting muscles.
 4. Organ protection
 Muscles in the torso protect the internal organs at
the front, sides, and back of the body. The bones of
the spine and the ribs provide further protection.
 Muscles also protect the bones and organs by
absorbing shock and reducing friction in the joints.

5.  OTHER PHYSIOLOGICAL FUNCTIONS:
 BREATHING
 CIRCULATION
 DIGESTION
 URINATION. etc.

6.  There are 3 different types of muscles present
in human body and they are
 1. The Skeletal Muscles
 2. The Cardiac muscles
 3. The smooth muscles

7.  Skeletal muscles are called so because they are
closely associated with the skeletal system and
involve in body movements and posture
maintenance.
 These muscles are striated i.e. they have
alternate dark and light bends present in them.
 These muscles can be voluntarily controlled.
 e.g. biceps brachii., triceps brachii.

8.  The cardiac muscles are present in the heart.
 The cardiac muscles are also striated in
appearance.
 The movement i.e. rhythm of cardiac muscles
can’t be voluntarily controlled but they can be
altered by several hormones and
neurotransmitters.
 The presence of intercalated disk is
characteristic feature of the cardiac muscles.

9.  The smooth muscles are found in the visceral
organs of the body like organs of GIT, in the
skin etc.
 These muscles appear smooth under
microscope as they don’t have any striatations
present in them.
 The smooth muscles are involuntary in nature
and controlled by ANS and several hormones
and neurotransmitters can interfere in their
functions.

11.  The outermost layer of a muscle is the epimysium
which wraps together numerous fascicles wrapped
with perimysium. Inside each fascicle are the
individual muscle fibers wrapped around
endomysium. Within the muscle fibers is where the
functional unit of the fiber exists: the sarcomere.
 The sarcomere is the site where contraction occurs on
the cellular level.
 In the sarcoplasm small thread like structures can be
seen and they are known as myofibrils. These
myofibrils runs throughout the length of the muscle
fiber.
 These myofibrils contain myofilaments. These
myofilaments are of two types the thin one is known as
actin and the thick one is known as the myosin. Both of
these filaments are protein.

12.  These myofilaments are confined and arranged
in compartments known as sarcomere. This
regular and repeated arrangement of actin and
myosin forms the striations in the muscle.
 The actin and myosin are contractile protein
and are involved in contraction of muscle along
with them some structural protein are also
there which provide strength, stability,
extensibility to the myofibrils. E.g. titin,
myomesin, neblin, dystrophin etc.
 Troponin and tropomyosin are regulatory
proteins which are also present in the muscle
fibres.

13. Cont.

15.  The boundaries of sarcomere are denoted by z-lines or
disk.
 Then I bands are present as we start moving from z –line
towards the centre in this region only thin filaments i.e.
actin is present. The I bands extend towards both side of
z-lines.
 Dark bands are A bands and are located in the middle of
sarcomere.
 A bands are formed by overlapping actin and myosin
filaments.
 • M line in the middle of A bands represent linkage of
myosin filaments and centre of sarcomere.
 • H bands on each side of M bands contain only myosin
filaments.
 • When muscle contracts, I and H bands shorten, while
A bands stay same.

16.  The cardiac and skeletal muscles are very much
similar in appearance and anatomy. The main
difference is of functionality and locations.
 The cardiac muscles doesn’t get fatigued, they
have a much greater no. of mitochondria for
energy production.
 As described earlier cardiac muscles have
presence of intercalated disk in the, these disk
are very crucial for conduction of electrical
impulse throughout the heart wall.
 These disks are irregular transverse thickenings
of sarcolemma.

18.  The smooth muscle cells are thick at the centre
and tapers towards the end.
 The smooth muscles also contain actin and
myosin but they are not arranged in a repeated
fashion that is why these muscles don’t look
striated when observed.
 These muscles lack T-tubules also but instead
they have caveolae, these are pouch like
invaginations of plasma membrane and contain
extracellular Ca ions.

19.  The thin myofilaments i.e. actin attaches to the
dense bodies which are functionally similar to
z-lines of sarcomere of skeletal muscles.
 Intermediate fibres are also present in these
muscles which connect two adjacent dense
bodies.
 The tension produced during in actin and
myosin during contraction is transmitted to
intermediate fibres, and these intermediate
fibres under the influence pulls the two
adjacent dense bodies.
 So the shortening of the muscle occur in a helix
fashion.

20. CONT.

22.  In the above figure a section of skeletal muscle
can be seen, this shows that the muscle fiber is
multinucleated and the nucleus is present just
below the sarcolemma.
 Cross striations with A and I bands can also be
seen other sarcomere components like z-line,
m-line are also observed.
 Endomysium with blood capillaries and
fibroblast cells are also observed.
 Endomysium surrounding each muscle fiber
and containing connective tissue cells called
fibrocytes.

24.  A transverse section of an skeletal muscle shows
individual muscle fibers surrounded by connective
tissue, the endomysium.
 The muscle fibers in turn are grouped into
fascicles and surrounded by interfascicular
connective tissue called perimysium.
 The muscle spindle can also be observed
containing intrafusal fibres.
 Small nerve fibers associated with the muscle
spindles are the myelinated and terminal
unmyelinated nerve fibers (axons) surrounded by
the supportive Schwann cells.
 s. Small blood vessels and an arteriole from the
perimysium are also seen.

25.  The TEM shows all the details of a myofibril it
depicts all the components of a sarcomere i.e.,
the light and dark bands, the z-line, the m-line, h
band etc.

27.  The above high-magnification photomicrograph
illustrates the cardiac muscle fibers.
 This shows that cardiac muscles also show striations
but are less pronounced.
 This also shows the branching in the cardiac muscle
fibers .
 The figure shows a single central nucleus.
 The dark-staining intercalated disks are also present
and connect individual cardiac muscle fibers.
 Small myofibrils can also be seen within each cardiac
muscle fiber.
 Delicate strands of connective tissue fibers surround
the individual cardiac muscle fibers.
 Endomysium with fibroblasts and capillaries are also
seen here.

28.  The transverse section of cardiac muscle
are characterirised by the clear
perinuclear sarcoplasm i.e., the
sarcoplasm around the nucleus is clear
and doesn’t seen to have any myofibrils.

30.  The above picture shows both the longitudinal
and transverse section of smooth muscles.
 The cells are elongated and tapered at the ends
and have a single nuclei.
 The striations aren’t observed here because the
arrangement of A and I bands are not regular.
 The nuclei is elongated or ovoid in shape.
 Smooth muscle also has a rich blood supply,
that’s why numerous capillaries are observed
between individual fibers.
 Connective tissues along with fibroblasts can
also be observed.