( movement of the parts or the whole body).
Types of muscles
• According to the histological structure
1- Striated muscles, contain striations.
2- Unstriated muscles, no striations (smooth).
• According to the position :
1- Skeletal muscles, present around the skeleton.
2- Cardiac muscles, present in the heart.
3- Visceral muscles, present in the viscera and urinary bladder.
• According to the ability of controlling the contraction:
1- Voluntary muscles, contract under our control.
2- Unvoluntary muscles, contract without control of us.
• according to protein in myosin: two types:
a) Slow unit
* red - dark- respond slowly- long twitch duration (up to
100 ms) - low mitochondrial ATP ase activity ,
* Produce ATP slowly
* In large limp muscle
* Ex. marathon runners (more red fibers)
b) Fast unit
* Pale(white) - short twitch duration ( 7 ms) - * produce
ATP quickly – more powerful contractions – fine ,skilled
* Ex. Weighlifters
Skeletal (voluntary; striated) muscle
• Attach to skeleton
• Function in movement (bone)
• Contract voluntary
C.N.S. neuromuscular junction
• Connect to the bone through the beginning
(origin) other end (insertion)
• If the origin formed of 2 parts(Biceps) or 3
• Ends with tendons
Each muscle composed of many myofibrils(muscle
Cylindrical shape, multinucleated.
Each myofibril composed of many myofibrils .
Each myofibril composed of many repeated sarcomeres.
Myofibrile appear as alternated dark and light bands.
Light band is called Isotropic band (I),
Dark band is called Anisotropic band (A).
Each sarcomere composed of many myofilaments.
( thin ) actin , troponin , tropomysin
( thick ) myosin .
• Thick helical protein filament.
• Consists of heads and tails.
• By proteiolytic enzyme(trypsin) broken into:
** light meromyosin (LMM) : H-zone
No ATPase activity and can’t combine with actin.
No heads at the H-zone.
** Heavy meromyosin (HMM) contain ATP ase activity , can
combine with actin.
• Release the heads from the tails if treated with pepsin enzyme.
• The head of the myosin molecule forms cross bridge with the
adjacent actin filament.
•Thin filaments actin with small amount of tropomyosin and
•In ionic environment of the cell, actin exist in the fibrous
form (F-actin) containing 2 chains of actin monomer coiled
around each other.
•In the absence of salts, actin becomes globular (G-actin).
•The change from F- actin to G- actin is reversible and is
called ( G F ) transformation;
• Troponin and tropomyosin
(Regulatory agent in muscle contraction)
At rest ,tropomyosin block the binding of actin to myosin.
• Troponin is formed of 3 subunits:
Troponin (I) inhibit the interaction of myosin to actin.
Troponin (C) which contain the binding sites of Ca++ that
initiate the contraction of the myofilaments.
Troponin (T) binds the other troponin component to
Classification according to the movement
• 1- a) Flexor; bends one part upon another.
• b) Extensor; straightens or extends part.
• 2- a) Adductor; draws a part towards the axis
• b) Abductor; draws a part away of the axis
• 3- a) Depressor; lowers a part.
• b) Elevator; elevate or raise a part.
• 4- a) Constrictor; constricts or close an organ.
• b) Dilator; cause dilation of the same organ.
• 5- Rotator Muscle; rotates on part on another
They contract involuntary, and rythimitically.
They obey all or non law.
They are auto stimulated (pace maker).
Adapted for resistant to fatigue
**A lot mitochondria (aerobic respiration)
**Numerous myoglobins (O2 storing pigment)
**Good blood supply
Intercalated discs (support contration) double membrane separating
Cell junctions fuse together the plasma membranes of cardiac muscle cells,
allow the cells to contract as a unit.
Walls of hollow organs
( gastrointestinal tube & respiratory system )
multi-unit: without interconnection,iris
single-unit :(walls of viscera)
Spindle shape –single nucleus
Arranged in sheets
Few mitochondria(depend on anaerobic glycolysis)
Contain myosin & actin (not arranged into
Autonomic nervous system ( involuntary)
Hormons ( vasoconstriction & vasodilators)
EFFECT OF STIMULUS:
a- In skeletal Muscle:
• Threshold Stimulus:
no responds occur.
• Minimal Stimulus:
responds by minimal observed line.
• Submaximal Stimulus:
increasing the stimulus, the number of
responding fibers increase
• Maximum Stimulus:
all muscle fibers contract.
• Supra-maximum Stimulus:
increasing the stimulus, no more effect.
B- In cardiac Muscle:
• Sub-minimal stimulus;
no responds occur.
• Threshold value;
all muscle fibers
stimulus no more effect
Steps of Contraction:
• Release of transmitter at motor end
• Generation of action potential.
• Inward spread of depolarization
• Release of Ca++ ions.
• Binding of Ca++ ions to troponin C.
• Uncovering myosin binding sites on
• Formation of cross-Linkage between
actin and myosin
• Sliding of actin over myosin,
Steps Of Relaxation:
•Ca++ ions pumped back
•Release of Ca++ ions from
•Cessation of interaction
between actin and
Changes accompanying muscle contraction:
Heat of contraction and relaxation.
Accompanied the chemical changes, acid by
splitting ATP or base by breakdown of CP.
Direct or indirect depolarization through the
(Aerobic or anaerobic) oxidative respiration,
CP is an immediate source of ATP ( phosphrelate
Sliding of actin
filament over the
( cross bridge).