Muscular tissue is composed of muscle fibers that contract in response to electrical signals. There are three types of muscle tissue - skeletal, cardiac, and smooth muscle. Skeletal muscle is striated, voluntary, and attached to bones. It contracts through a sliding filament mechanism where actin and myosin interact powered by ATP hydrolysis. At the neuromuscular junction, a nerve impulse triggers the release of acetylcholine which binds receptors and generates a muscle action potential, causing contraction.

1. Muscular Tissue
Muscle: an organ composed of one of
three types of muscle tissue (skeletal,
cardiac or smooth) , specialized for
contraction to produce voluntary or
involuntary movement

2. Muscular Tissue

3. Muscular Tissue
A group of cells (fibers) specialized to
produce motion in response to muscle
action potentials by its qualities of
contractility, extensibility, elasticity and
excitability

4. Properties of Muscular Tissue
1. Excitability: an ability of muscle to
generate impulse
aaahhh…
ooohhhh…
aaauuchh…

5. 2. Contractility: it is either shortening or
development of tension or both
A. Isotonic Contraction-contraction in which
tension remains same whereas changes
occurs in the length of muscle fiber. E.g.
flexion of arm
B. Isometric Contraction-contraction in
which length of muscle fibers remain
same and tension is increased. E.g.
holding book by hand, pulling any heavy
object

6. 3. Muscle Tone- the muscle fibers always
maintain a state of slight contraction with
certain degree of vigor and tension. This
is a state of partial contraction of
muscles. It is achieved by the contraction
of a few muscle fibres at a time.
4. Extensibility- an ability of muscle fibers
to stretch without being damaged
5. Elasticity- an ability of muscle fibers to
return to its original length and shape
after contraction or extension

7. Functions of Muscular tissue
Through sustained contraction or alternating
contraction & relaxation, muscular tissue
has four functions:
1. Producing Body Movements-
movements of the whole body such as
walking and running, and localized
movements such as holding pen,
nodding head, rely on integrated
functioning of bones, joints and skeletal
muscles

8. 2. Stabilizing Body Positions- Skeletal
muscle contractions stabilize joints and
help maintain body positions such as
sitting & standing
3. Storing and moving substances
within body- sustained contractions of
sphincters temporarily stores food in
stomach and urine in urinary bladder.
Cardiac muscle contractions pump blood
through blood vessels of the body.
-cont.

9. Smooth muscles contractions move food
and substances such as bile, enzymes
through g.i.t., push gametes through
passageway of reproductive system,
propel urine through urinary system.
Skeletal muscle contractions promote the
flow of lymph and helps the return of blood
to heart.
4.Generating heat- As muscular tissue
contracts, it produces heat, by
thermogenesis. Heat generated by muscle
is used to maintain normal body temp.

10. Types of Muscular Tissue
Muscle Striations Control Nerve
Supply
Skeletal Present Voluntary Somatic
Cardiac Present Involuntary Autonomic
Smooth Absent Involuntary Autonomic

11. Skeletal Muscle tissue
• Skeletal muscle cells are found to be roughly
cylindrical in shape, diameter ranges from 10-
100ųm and maybe as long as 35 cm.
• Each cell, commonly called a fiber, has several
nuclei situated just under the sarcolemma or cell
membrane of each muscle fiber.
• The muscle fibres lie parallel to one another and,
when viewed under the microscope, they show
well-marked transverse dark and light bands,
hence the name striated or striped muscle.

13. Sarcoplasm: the cytoplasm of muscle fibres,
contains:
• bundles of myofibrils, which consist of filaments
of contractile proteins including actin and
myosin
• many mitochondria, which generate chemical
energy (ATP) from glucose and oxygen by
aerobic respiration
• glycogen, a carbohydrate store which is broken
down into glucose when required
• myoglobin, a unique oxygen-binding protein
molecule, similar to hemoglobin in red blood
cells, which stores oxygen within muscle cells.

14. A myofibril has a
repeating series of dark
and light bands,
consisting of units
called sarcomeres.
A sarcomere represents
the smallest functional
unit of a skeletal muscle
fibre and consists of:
• thin filaments of actin
• thick filaments of
myosin.

15. • Each thick filament composed of about
300 molecules of Myosin. Each myosin
molecule has two heads and a twisted
tail. Tail form shaft of filament. The
head project outwards from the shaft in
a spiraling fashion

16. • Thin filament composed of actin as
major and troponin & tropomyosin as
minor components.
• Individual actin molecule join to form actin
filament, that is twisted into helix.
• On each actin molecule, is myosin-binding
site, where myosin head can attach.
• In a relaxed muscle myosin is blocked
from binding to actin because strands of
tropomyosin cover myosin binding-sites.

17. Physiology of Contraction
Sliding-Filament mechanism:
In this process, thin filaments slide inward
over thick filament and may overlap.
As a result sarcomere shortens.
Shortening of sarcomeres causes
shortening of whole muscle fiber, which
causes shortening of entire muscle i.e.
contraction

18. Physiology of Contraction
• Propagation of Muscle Action Potential(MAP)
initiates the process of contraction. It causes
opening of Ca 2+
channel in sarcolemma.
Ca 2+
flows into sarcoplasm around the thick
and thin filaments.
• Ca 2+
combines with troponin and changes its
shape. This change moves troponin-
tropomyosin complex away from myosin
binding site on actin. Then contraction cycle
begins.

19. Contraction Cycle
Four Steps:
1.ATP Hydrolysis -The myosin head
includes ATP-binding site and ATPase.
Myosin heads hydrolyze ATP and become
reoriented and energized.
ADP
p

20. Contraction Cycle
2.Formation of Crossbridges- The
energised myosin head attaches to
myosin binding site on actin and releases
phosphate group. This attachment is
referred as Crossbridge.
ADP
p

21. Contraction Cycle
3.Powerstorke-release of ADP from myosin
head and with force crossbridges moves
toward the centre of sarcomere i.e. sliding
of thin filament over thick filament.This is
termed as Powerstroke.

22. Contraction Cycle
4.Detachment of myosin from actin- At
the end of powerstroke, the crossbridges
remains firmly attached to actin until
another molecule of ATP binds to myosin.
Then myosin head detaches from actin.
The contraction cycle continues as long as
ATP is available and Ca2+
level near the
filament is sufficiently high.

23. Neuromuscular Junction
• Anatomy

24. Neuromuscular Junction
• MNJ is the synapse between a somatic
neuron and a skeletal muscle fiber.
• Synaptic end bulbs- at MNJ the end of
motor neuron, called axon terminal divides
into a cluster of synaptic end bulbs.
• Each bulb contains hundreds of
membrane enclosed sacs called synaptic
vesicles.
• Inside each synaptic vesicle are
thousands of molecules of
neurotransmitters- Acetylcholine (Ach)

26. Neuromuscular Junction
• Motor end plate- It is region of
sarcolemma opposite the synaptic end
bulbs. Each motor end plate has 30 -40
million Ach receptors.
• Physiology
• A nerve impulse (Nerve Action
Potential) elicits Muscle Action
Potential in the following way:-

27. Neuromuscular Junction
1. Release of Ach- Arrival of nerve
impulse at the synaptic end bulbs
causes many synaptic vesicles o
undergo exocytosis.
2. During exocytosis, the synaptic
vesicles fuse with neuron’s plasma
membrane.
3. The Ach the diffuses across the
synaptic cleft between neuron and
motor end plate.

28. Neuromuscular Junction
4. Activation of Ach receptors: Binding of
two molecules of Ach to the receptor on
motor end plate open an ion channel.
Cations most importantly Na+
flow across
the membrane (sarcolemma)
5. Production of Muscle Action potential:
The influx of Na+ makes muscle fiber
more positively charged.This change
triggers muscle action potential

29. Neuromuscular Junction
6. Termination of Ach activity- The effect of
Ach binding is for moment, because Ach
is rapidly broken down by enzyme acetyl
cholinesterase. This cannot activate Ach
receptors.
7. This ends production of Muscle Action
Potential and muscle gains its original
form.

30. Neuromuscular Junction