Muscular system
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Muscles are primarily designed for movement
Types of
muscles of human body :
- Skeletal muscle ( has bony attachment, related to
skeleton)
- Cardiac muscle ( muscles of heart, myocardium is
formed by cardiac muscle)
- Smooth muscle( muscles of viscera)
Histological classification
of muscle:
- Striated muscle:(cross pattern seen within the muscle
cells) skeletal muscle, and
cardiac muscle
- Non striated muscle: (no cross pattern within the muscle
cells) Smooth muscles
Functional
classification of muscles:
- Voluntary muscles: skeletal muscle
- Involuntary muscles: cardiac and smooth muscle
Skeletal
muscle:
Parts of a
skeletal muscle: each muscle of body has two part
1.
a
fleshy part
2.
a
fibrous part : (ex: tendon or aponeurosis)
Features of
skeletal muscle:
- each skeletal muscle has at least two attachment sites – origin
(proximal attachment )
and insertion (distal
attachment )
- each skeletal muscle has to cross at least one joint
- Skeletal Muscle can move particular part of body
- Every muscle can relax (increase the length of muscle) &
contract (shortening of muscle )
- skeletal muscle situated in front of a joint and also behind the
joint
Q. What do you
mean by Origin and insertion of a skeletal muscle?
Each muscle has two ends which attached with bone, cartilage and other
structure.
During movement one end is fixed and other end is
move.
Fixed end usually consider
as origin of a muscle and
Movable end consider as
insertion of a muscle.
But both end of muscle may move or fixed
Origin:
the
end of muscle which is situated near the trunk is known as origin
Insertion: the end of muscle
which is situated far from the trunk is known as insertion
Classification of skeletal
muscles
i)
According
to the colour skeletal muscles are two types :
|
Red muscle
• Less
cross-striation and large number of mitochondria and myo-haemoglobin
•
Contraction is slow but more sustained
•
Examples: antigravity muscle of the
trunk, brachialis, soleus
|
White muscle
•
More cross-striation and less number of
mitochondria and myo-haemoglobin
•
Contraction is rapid but less sustained
•
Examples: biceps brachii
|
ii)
Morphological
classification of skeletal muscle: (According
to the direction of the muscle fibers present
in fleshy part of muscle)
- Parallel 2.Triagular 3. Pennate 4. Spiral
5. Cruciate
|
1. Parallel :
|
|
|
|
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Quadrilateral
:
(thyrohyoid)
|
Long and
strap like :
sartorius
|
Strap with
tendinous
intersections :
rectus
abdominis
 
|
Fusiform: Gastrocnimius
|
|
2.
Triangular: Fibres are oblique to the
line of pull Temporalis
|
5. Cruciate
:sternocleidomastoid,
messeter
|
4. Spiral:
Sternocostal fibres of pectoralis major and latissimus dorsi
 
|
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3. Pennate
|
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Unipennate : soleus
|
Bipennate rectus femoris
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Multipennate : deltoid
|
Circumpennate : tibialis anterior
|
|
|
|
|
|
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What
is contraction of muscle?
50-55% shortening of fleshy part of a
muscle from its resting length is known as contraction of muscle
Structural
organization of a skeletal muscle
Muscle: is formed by
several muscle bundles and surrounded by a connective tissue layer known epimysium
Muscle bundle: is formed by
several muscle fibers and surrounded by a connective tissue layer known perimysium
Muscle
fiber or muscle cell is surrounded by a connective tissue layer known endomysium.
Each muscle fiber is formed by
myofibrils
Myofibrils: are thread
like structures (situated along the long axis of the entire length of muscle
fibres. ) which are formed by myofilaments( myosin and actin) .
Each
myofibril contain a dark area known as A band and a light
area known as I band
Myofilaments: are longitudinally oriented protein
filaments lies within each myofibrils . They contain two types of protein filaments
thick filament: myosin and
thin
filament –actin, tropomyosin,
troponin
Cross
striation.: Due to particular arrangement of myofilament, some areas of (skeletal
/ cardiac) muscle fibres appear dark and some area white which is known as cross
striation.
|
Dark area
of cross striation
|
Light
area of cross striation .
|
|
Dark area known as A band:
|
Light area known as I band
|
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A band contains whole myosin filament and part
of actin filament.
|
I band contain part of actin filament
|
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A band
contain H band:
this area contain only myosin filament but no
actin filament (less dark area)
H band contain M line :
Myosin filament link together transversely. this
is represented by M line
|
I band contain Z line : each I band contain a
central Z line. Actin filaments are transversely attached with each
other
|
Each
muscle fiber is an individual muscle cell and consists of following parts
Sarcolemma:
cell membrane of muscle fibre
Sarcoplasm
: cytoplasm of muscle fiber
Sarcoplasmic
reticulum : smooth surfaced endoplasmic reticulum which surrounds the
myofibrils
Nuclei:
multiple peripherally placed nuclei.
(In embryo it is situated in the center
but later pushed to periphery otherwise they interrupted the contractile
mechanism of muscle fiber)
Mitochondria:
they are situated in rows between the
myofibrils
Myofilament :
Form by thick filament : myosin
Thin filament : actin, troponin ,
tropomyosin
Neuromuscular junction connects the nervous
system to the muscular system via synapses.
Terminal
end of axon (process of neuron) connect with sarcolemma (cell membrane of muscle
cells) So action potential of nerve transmitted to muscle and a contraction
(shortening of length of muscle) is beginning.
Q: What is sarcomere?
Ans
: Sarcomere: The segment of a myofibril
between two adjacent Z lines, representing the contractile (functional) unit of
striated muscle.
Muscle tone: it means a partial state of
contraction of a muscle to maintain a constant muscle length. A muscle is not
completely relaxed even in resting condition.
Regeneration
of muscles:
Skeletal
muscle: usually do not regenerate if part of muscle fiber is destroyed moderate
regeneration is possible.
Cardiac muscle: regeneration
is not
possible
Smooth muscle: regeneration is possible
Mechanism
of contraction: In short :
Action potential of nerve ending causes
–
releases Ca++ that results release of
Acetylcholine (ACh)
---ACh binds with the sarcolemma
---so, Muscle Fiber Action Potential initiated
through T tubule action potential passage
--- sarcoplasmic reticulum release Ca ++ ions
– Calcium ions bind to the troponin on the thin filament
—roll the tropomyosin deeper aspect and exposed actin
(which allow actin myosin interaction)
– ATP bind with myosin
heads and develop affinity for actin
–myosin bind with actin
–causes Movement of myosin head toward the M line
– overriding of
myosin and actin filament is result- initiates contraction.
Ca++ ion activate ATPase which rapidly hydrolyses ATP and disconnect
myosin head from actin
