physiology : muscular system

part of dr . hanaa

2. Muscular System
Locomotion
( movement of the parts or the whole body).

3. Types of muscles
•According to the histological structure
1-Striated muscles, contain striations.
2-Unstriatedmuscles, 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-Unvoluntarymuscles, contract without control of us.

4. Skeletal muscle

9. •according to protein in myosin: two types:
a) Slow unit
* red -dark-respond slowly-long twitch duration (up to
100 ms) -low mitochondrial ATP aseactivity ,
* 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
movement
* Ex. Weighlifters

10. 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
(Triceps)
•Ends with tendons

11. Structure
Each muscle composed of many myofibrils(muscle
fibers).
Cylindrical shape, multinucleated.
Each myofibril composed of many myofibrils .
Each myofibril composed of many repeated sarcomeres.
Myofibrileappear 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 .

18. Molecular structure:
Myosin:
•Thick helical protein filament.
•Consists of heads and tails.
•By proteiolyticenzyme(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 aseactivity , 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.

19. Actin:
•Thin filaments actin with small amount of tropomyosinand
troponin.
•In ionic environment of the cell, actinexist 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;

20. •Troponin and tropomyosin
(Regulatory agent in muscle contraction)
At rest ,tropomyosinblock 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
tropomyosin.

23. 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

24. CARDIAC MUSCLES:
They contract involuntary, and rythimitically.
They obey all or non law.
They are auto stimulated (pace maker).
Striated muscle
Pump blood
Adapted for resistant to fatigue
**A lot mitochondria (aerobic respiration)
**Numerous myoglobins(O2 storing pigment)
**Good blood supply

25. Intercalated discs (support contration) double membrane separating
adjacent cells.
Cell junctions fuse together the plasma membranes of cardiac muscle cells,
allow the cells to contract as a unit.

26. Smooth muscle
Unstriated
Walls of hollow organs
( gastrointestinal tube & respiratory system )
Two types
multi-unit: without interconnection,iris
single-unit :(walls of viscera)

27. Spindle shape –single nucleus
Arranged in sheets
Few mitochondria(depend on anaerobic glycolysis)
Contain myosin & actin (not arranged into
sarcomeres)
Stimulated by
Autonomic nervous system ( involuntary)
Hormons( vasoconstriction & vasodilators)
adrenalin

28. 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
respond,increasing
stimulus no more effect
will resulted.

31. Steps of Contraction:
•Release of transmitter at motor end
plate.
•Generation of action potential.
•Inward spread of depolarization
along T-tubules.
•Release of Ca
++
ions.
•Binding of Ca
++
ions to troponin C.
•Uncovering myosin binding sites on
actin.
•Formation of cross-Linkage between
actin and myosin
•Sliding of actin over myosin,
producing shortening.

33. Steps Of Relaxation:
•Ca
++
ions pumped back
into sarcoplasmic
reticulum.
•Release of Ca
++
ions from
troponin.
•Cessation of interaction
between actin and
myosin.

34. Changes accompanying muscle contraction:
Thermal Change:
Heat of contraction and relaxation.
PH Changes:
Accompanied the chemical changes, acid by
splitting ATP or base by breakdown of CP.
Electrical change:
Direct or indirect depolarization through the
connected nerve.
Chemical change:
(Aerobic or anaerobic) oxidative respiration,
CP is an immediate source of ATP ( phosphrelate
ADP).

35. Mechanical
changes:
Sliding of actin
filament over the
myosin filaments,
( cross bridge).