Mechanism Of Muscle Contraction Flashcards
What does motor unit mean
Single motor neuron and the muscle fibres it innervates
In the muscles of fine movements what is the Muscle fibers/Neuron ratio
3-6
In the muscles of gross movements what is the Muscle fibers/Neuron ratio
Several hundreds (100-200)
What is meant by motor pool
Group of AHC that supply one skeletal muscle
Multiple motor unites
Each muscle is composed of
A number of muscle fibres arranged parallel to each other
Characters of muscle fibres
Cylindrical
10-100um diameter
Transverse striations
What’s the name of the muscle Fiber cell membrane
Sarcolemma
What’s the name of the muscle fibres cytoplasm
Sarcoplasm
The contractile elements called
Myofibrils
Each muscle fibres contain ………………. of myofibrils
Hundreds to thousands
When the muscle is fully stretched The thin filaments Covers all the sarcomere except
Middle of H-band
Thin filaments formed of
Actin
Regulatory proteinis :
Tropomysin
Troponin
Actin is formed of :
2 chains of a Globular actin molecules (called G-Actin molecules) twisted in a spiral manner
G-actin molecules has
An active site which the crossbridge of myosin binds with
Tropomyosin formation and site
It’s formed from two light chains twisted around each other
Found in the groove between the two actin chains
Function of tropomyosin
Inhibits the active site of G-actin
Mostly by physical covering
Troponin parts and function
TnT : bind with tropomyosin
TnC : bind with calcium ion
TnI : inhibits the interaction between actin and myosin
Thick filaments found in
A-band
Myosin parts called
Head
Arm
Tail
Myosin flexible points (hinges)
Junction between arm and head
Junction between arm and tail
Body of myosin filament is formed of
Tails of myosin molecules
Crossbridge of myosin filament is formed of
Heads and arms of myosin molecules
Head of myosin has :
Actin Binding site
ATPase activity site
Longitudinal tubules are ………… to the ……………
Parallel - myofibrils
Longitudinal tubules form chambers called ………… near …………..
Cisternae - T-tubules
Functions of cisternae
Stores Calcium ions at high concentrations due to calcium pump up to 10,000 folds
T-tubules are formed of
Infolds of the sarcolemma
T-tubules penetrate the ……….. from …………
Muscles fibers - side to side
T-tubules contains
Extracellular fluid
T-tubules are ………. to ……….
Parallel - Z-line
Function of T-tubules
Transmit the action potential to the interior
What does Excitation contraction coupling and mechanism of contraction (ECCMC)
The process by which action potential of the muscles fibers initiates contraction
How many steps ECCMC have
5
1st step of ECCMC
Action potential is transmitted to the interior through T-tubules
2nd step of ECCMC
Release of calcium ions from cisternae to the sarcoplasm through voltage-gated calcium channels
3rd step of ECCMC
Activation of actin by calcium ions
Ca2 bind to troponin-C >
Lateral movement of troponin-tropomyosin copmlex >
Uncovering of active site of actin.
4th step of ECCMC
Interaction between activated actin and cross bridge of myosin to cause contraction through walk along theory
Steps of walk along theory
1- Myosin converts ATP > ADP+Pi
2- Myosin head attaches to actin active site
3- Power stroke
4- New ATP bind to the head of myosin and causes detachment
5- ATP converts again
6- Myosin head attaches to a new active site of actin
The cycle of the walk along theory continue until
Z-line reaches the end of myosin filaments
5th step of ECCMC
Relaxation, by active reuptake of calcium ions into Cisternae by calcium pump
Factors resposible for gradation of muscle activity
Gradation of strength :
1- Number of motor units
2- Frequency of discharge in nerve fibers
3- Gradation of onset (Asynchronous activation)
Types of tubules in the sarcoplasm
Longitudinal tubules Transverse tubules (T)
