by Talib F. Abbas
 Motility is a widespread biological phenomenon that
reaches its highest manifestation in the specialized
tissue of muscle.
 skeletal muscle is the major executive arm of the
nervous.
 we could have no knowledge if they were not
communicated by muscle which express our mental
activities by speech, song , and cries , by writing, by
gestures and facial expressions, and by morte complex
forms of behavior, both sessile or locomotory,
individual or social.
 Muscle cells, like neurons, can be excited chemically,
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electrically, and mechanically to produce an action
potential that is transmitted along their cell
membranes.
The contract proteins : Myosin & Actins.
Smooth muscle contract involuntary .
Heart muscle have their own autonomic conducting
system.
Skeletal muscle need nervous stimulation.
 Sarcotubular system: T system and a sarcoplasmic
reticulum.
 The sarcoplasmic reticulum, which forms an irregular
curtain around each of the fibrils, has enlarged
terminal cisterns in close contact with the T system
at the junctions between the A and I bands.
 T system with a cistern of the sarcoplasmic reticulum
on either side has led to the use of the term triads.
 The nerve fiber forms a complex of branching nerve
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terminals that invaginate into the surface of the
muscle fiber but lie outside the muscle fiber plasma
membrane. The entire structure is called the motor
end plate.
synaptic gutter or synaptic trough.
synaptic space or synaptic cleft.
synaptic transmitter ( Acetylcholine ).
adenosine triphosphate (ATP).
Acetylcholinesterase.
Curare & botulinum toxin.
 1. An action potential trigger in fibers.
 2. the nerve secretes a neurotransmitter substance.
 3. The acetylcholine acts to open “acetylcholinegated”
 4. Allows large quantities of sodium ions to diffuse .
 5. The action potential travels along nerve fiber.
 6. The action potential depolarizes the muscle.
 7. The calcium ions initiate attractive forces between
the actin and myosin filaments, contractile process.
 removal of calcium ions from the myofibrils causes the
muscle contraction to cease.
 sliding of the thin filaments over the thick filaments.
 The width of the A bands is constant.
 Z lines move closer together.
 This “power stroke” depends on the simultaneous
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hydrolysis of ATP.
Troponin I is bound to actin and tropomyosin and
covers the sites where myosin heads interact with
actin.
Excitation–contraction coupling.
Depolarization of the T tubule by dihydropyridine
receptors (DHPR).
In cardiac muscle, influx of Ca2+ via ryanodine
receptor (RyR).
 A single action potential causes a brief
contraction followed by relaxation. This
response is called a muscle twitch.
 The twitch starts about 2 ms after the start
of depolarization.
 “Fast” muscle fibers 7.5 ms.
 . “Slow” muscle fibers 100 ms.