2. What are the major function of muscle tissue
There are four characteristics associated with muscle
tissue
1. Excitability
Tissue can receive and respond to stimulation
2. Contractility
Tissue can shorten and thicken
3. Extensibility
Tissue can lengthen
4. Elasticity
Tissue can return to its resting state 2
INTRODUCTION
3. The characteristic of muscle tissue enable it to perform
some important functions, including:
Movement (both voluntaryily and involuntarily)
Maintaining posture
Supporting soft tissues within body cavities
Guarding entrance and exits of the body
Maintaining body temperature
3
4. Types of Muscles Tissue
4
1. Skeletal Muscle
Responsible for skeletal movement
and organs such as eyeballs.
Fibres are cylindrical in shape and
Striated due to arrangment of
contractile proteins.
Multinucleated and eccentrical
nucleus
Under voluntary control.
Account for 40% body weight
5. 2. Cardiac Muscles
Found only in the wall of the heart,
Striated and involuntary contraction
Muscle fibres are cylindrical but
branched
Intercalated disk is present
Single nucleus that is centrally
located
5
6. 3. Smooth Muscle
Found in walls of hollowed
organs
Non striated
Involuntary contraction
Spindled shape cells with
centrally located nucleus
6
7. Their cells are called fibres because they are elongated
Contractions depend on myofilaments
Actin
Myosin
Cytoplasm is called sarcoplasm
Smooth endoplasmic reticulum is called sarcoplasmic
reticulum
Plasmamembrane is called sarcolemma
Sarcos = flesh
Lemma = sheath
7
Similarities between the three types of Muscles
8. Skeletal Muscle
Skeletal muscle is composed of long, cylindrical,
multinucleated cells that undergo voluntary contraction to
facilitate movement of the body or its parts
During embryonic development, several hundred myoblasts,
precursors of skeletal muscle fibers, line up end to end,
fusing with one another to form long multinucleated cells
known as myotubes.
These newly formed myotubes manufacture cytoplasmic
constituents as well as contractile elements, called myofibrils
Myofibrils are composed of specific arrays of myofilaments,
the proteins responsible for the contractile capability of the
cell
8
10. Endomysium; Reticular fibers surrounding each muscle
fibre plus the external (basal) lamina produced by the muscle
fiber
Perimysium; Dense connective tissue surrounding groups
of fibers and dividing the muscle into fascicles
Epimysium; Dense connective tissue surrounding the entire
muscle, blends with the deep fascia and tendons
Connective Tissue Covering Of Skeletal Muscle
10
11. One of the most important roles of connective tissue is to
mechanically transmit the forces generated by contracting
muscle cells, because in most instances, individual
muscle cells do not extend from one end of a muscle to
the other
11
13. Myofilaments; Visible only with the electron microscope;
composed primarily of actin, which forms 5-nm wide thin
filaments, and myosin, which forms 15-nm wide thick
filaments
Myofibrils; Visible with the light microscope, 1–2 microns
wide, oriented parallel to the long axis of the cell; composed
of bundles of overlapping myofilaments that are arranged in
register, producing an alternating light-dark, striated banding
pattern
Hierarchy Of Skeletal Muscle Organization
13
14. Muscle fiber; Specialized term for a muscle cell, 10–100
microns wide; sarcoplasm is filled with hundreds of
myofibrils, which are oriented parallel to each other and to the
long axis of the muscle fiber.
Muscle fascicle; Collection of muscle fibers surrounded by
perimysium;
collections of muscle fascicles are surrounded by the
epimysium and form a muscle.
14
15. Individual muscle cells(muscle fibre) are grouped together
into elongated bundles – fasciculi
Each fibre is separated by a thin layer of connective tissue
called endomysium
A group of fasciculi are surrounded by a connective tissue
sheath called perimysium
The epimysium is no difference from the deep fascia
15
19. A troponin complex is attached at one specific site on
each tropomyosin molecule
In thin filaments, each tropomyosin molecule spans
seven G-actin molecules and has one troponin complex
bound to its surface
19
20. MYOSIN
Myosin, a much larger complex, can be dissociated
into two identical heavy chains and two pairs of light
chains.
Myosin heavy chains are thin, rodlike molecules
made up of two heavy chains twisted together.
Myosin head (flexible; binds to actin filament)
Myosin head has:
Actin binding site
ATP binding site
ATP-ase activity
20
23. Several hundred myosin molecules are arranged
within each thick filament with their rodlike
portions overlapping and their globular heads
directed toward either end
Analysis of thin sections of striated muscle shows
the presence of cross-bridges between thin and
thick filaments.
These bridges, which are known to be formed by
the head of the myosin molecule plus a short part
of its rodlike portion, are involved in the
conversion of chemical energy into mechanical
energy
23
24. Arrangement of myofilaments within a myofibril in register
result in the banding pattern seen at microscopic levels.
• A band appears dark and contains actin and myosin.
• I band appears light and contains actin only.
24
25. • Z-line, composed of alpha-actinin, is located in the center of the
I band.
• H band is located in the center of the A band and represents the
area where actin is not present.
• M band is located in the center of the H band and represents
areas of cross-connections between myosin filaments.
25
28. Contractile unit of striated muscle fibers, seen in both skeletal
and cardiac muscle fibers
It extend from Z-line to Z-line
Contains α-actinin, protein that binds actin filaments to Z-line
Sarcomeres are repeated in series along the length of each
myofibril.
Adjacent myofibrils maintain the alignment of sarcomeres.
28
SARCOMERE
30. No changes in lenght of :
1. A-band
2. actin and myosin filaments.
30
Alterations In Sarcomeres During Contraction
During contraction occurs
shortening of
1. Sarcomeres shorten.
2. Z-line interval narrows.
3. I-band
4. H-band (in maximal
contraction could disapear
31. MECHANISM OF CONTRACTION
Resting sarcomeres consist of partially overlapping thick and thin
filaments.
During contraction, both the thick and thin filaments retain their
original length.
Because contraction is not caused by a shortening of individual
filaments, it must be the result of an increase in the amount of
overlap between the filaments.
The sliding filament hypothesis of muscle contraction has received
the most widespread acceptance
31
32. The following is a brief description of how actin and
myosin interact during a contraction cycle.
At rest, ATP binds to the ATPase site on the myosin
heads, but the rate of hydrolysis is very slow.
Myosin requires actin as a cofactor to break down ATP
rapidly and release energy.
In a resting muscle, myosin cannot associate with actin,
because the binding sites for myosin heads on actin
molecules are covered by the troponin, tropomyosin
complex on the F-actin filament
32
33. When sufficiently high concentrations of calcium ions
are available, however, they bind to the TnC subunit of
troponin.
The spatial configuration of the three troponin subunits
changes and drives the tropomyosin molecule deeper
into the groove of the actin helix
This exposes the myosin-binding site on the globular
actin components, so that actin is free to interact with the
head of the myosin molecule
33
34. The binding of calcium ions to the TnC unit corresponds
to the stage at which myosin ATP is converted into the
active complex.
As a result of bridging between the myosin head and the
G-actin subunit of the thin filament, the ATP is split into
ADP and Pi (phosphate ion), and energy is released.
This activity leads to a deformation, or bending, of the
head and a part of the rodlike portion (hinge region) of the
myosin
Because the actin is bound to the myosin, movement of
the myosin head pulls the actin past the myosin filament.
The result is that the thin filament is drawn farther into
the A band.
34
35. Although a large number of myosin heads extends from the thick
filament, at any one time during the contraction only a small
number of heads aligns with available actin-binding sites.
As the bound myosin heads move the actin, however, they provide
for alignment of new actin myosin bridges.
The old actin myosin bridges detach only after the myosin binds a
new ATP molecule;
This action also resets the myosin head and prepares it for another
contraction cycle. If no ATP is available, the actin myosin complex
becomes stable;
This accounts for the extreme muscular rigidity (rigor mortis) that
occurs after death.
35
36. A single muscle contraction is the result of hundreds of
bridge-forming and bridge-breaking cycles.
The contraction activity that leads to a complete overlap
between thin and thick filaments continues until Ca2+
ions are removed and the troponin “tropomyosin
complex again covers the myosin-binding site
36
37. During contraction, the I band decreases in size as thin
filaments penetrate the A band.
The H band ”the part of the A band with only thick
filaments” diminishes in width as the thin filaments
completely overlap the thick filaments.
A net result is that each sarcomere, and consequently the
whole cell (fiber), is greatly shortened
37
38. Skeletal Muscle Innervation
Skeletal muscle cells and the single motor neuron that
innervates them constitute a motor unit.
Each skeletal muscle receives at least two types of nerve fibers:
motor and sensory.
The motor nerve functions in eliciting contraction, whereas the
sensory fibers pass to muscle spindles
Additionally, autonomic fibers supply the vascular elements of
skeletal muscle.
The specificity of motor innervation is a function of the muscle
innervated
38
39. Muscle fatigue
For a single muscle fiber, fatigue indicates an
inability to develop tension when it is stimulated
Causes： reduction in the rate of intracellular calcium
release and uptake by sacroplasmic reticulum
It dependent on muscle itself, exercise duration, fiber
type composition, and/or pattern of motor unit
activation
39
40. When muscles cause a limb to move through the joint's
range of motion,
They usually act and are further classified into the
following cooperating groups:
AGONIST MUSCLES
In a desired movement, the muscle mostly
involved with that movement is the agonist or
commonly referred to as prime movers.
Agonist or prime movers may contract concentrically to lift
a weight, or eccentrically to lower that weight.
40
41. ANTAGONISTIC MUSCLES
The muscle that lies directly opposite to the agonist or
prime mover and is responsible for the opposing action of
that movement is the antagonistic muscle.
The triceps are the antagonist muscle to the biceps curl for
instance, and the biceps would be the antagonist in a
triceps extension.
They are responsible for returning a limb to its initial
position.
41
42. SYNERGISTS
These muscles perform, or assist in performing, the
same set of joint motion as the agonists.
Synergists are sometimes referred to as neutralizers
because they help cancel out, or neutralize, extra
motion from the agonists to make sure that the
force generated works within the desired plane of
motion.
42
43. 43
Bundles form thick myocardium Cells are
branch
Cells join at intercalated discs 1-2 nuclei in
center
Inherent rhythmicity: each cell! (muscle
cells beat separately without any stimulation)
Myofilament organisation is similar to skeletal
muscles’s hence the striations
CARDIAC MUSCLES
44. Smooth Muscles
Muscles are spindle-shaped cells
One central nucleus
Grouped into sheets: often running perpendicular to each
other
Peristalsis
No striations (no sarcomeres)
Contractions are slow, sustained and resistant to fatigue
Does not always require a nervous signal: can be
stimulated by stretching or hormones
44
45. Major Locations
Inside the eye
Walls of vessels
Respiratory tubes
Digestive tubes
Urinary organs
Reproductive organs
45
46. Actin and myosin myofilaments are present, but they are
not organized into a regular pattern, they are randomly
arranged.
Electron Dense bodies containing alpha actin are present in
the cytoplasm of smooth muscle cells
These dense bodies Serve as insertion points for
myofilaments to transmit the force of filament sliding
Thus, resemble Z-lines of striated muscle
46
Organization of the Contractile Proteins in
Smooth Muscles
