Muscle Muscle Physiology Physiology

Dr Taha Sadig AhmedDr Taha Sadig Ahmed

04/18/2304/18/23 11

2204/18/2304/18/23

The Muscle Action PotentialThe Muscle Action Potential

RMP = RMP = -90 mV-90 mV ( same as in ( same as in nerves ) nerves )

Duration of AP = Duration of AP = 1-5 ms1-5 ms ( longer duration than nerve ( longer duration than nerve AP , which is usually about 1 ms AP , which is usually about 1 ms ) . ) .

Conduction velocity (CV) in a Conduction velocity (CV) in a muscle fiber ( cell) = muscle fiber ( cell) = 3-5 m/s3-5 m/s ( slower than big nerves ) . ( slower than big nerves ) .

RMP= - 90 mV

Amplitude

إرتفاعه

3304/18/2304/18/23

Muscle Contraction Muscle Contraction There are 4 important muscle proteins :There are 4 important muscle proteins :A/ two contractile proteinsA/ two contractile proteins that slide upon each that slide upon each

other during contraction :other during contraction :(1)(1) ActinActin(2)(2) MyosinMyosin

B/ And two regulatory proteins :B/ And two regulatory proteins : Troponin Troponin excitatory to contraction excitatory to contraction Tropomyosin Tropomyosin inhibitory to contraction inhibitory to contraction

4404/18/2304/18/23

The The EPPEPP at the motor end- at the motor end-plate triggers a plate triggers a muscle APmuscle AP

The muscle AP spreads The muscle AP spreads down inside the muscle down inside the muscle through the through the Transverse Transverse Tubules Tubules

( T-tubules )( T-tubules ) to reach the to reach the Sarcoplasmic Sarcoplasmic

Reticulum (SR) . Reticulum (SR) . In the SR the muscle AP In the SR the muscle AP

opens calcium channelsopens calcium channels ( in the walls of the SR) ( in the walls of the SR)

calciumcalcium passively flows out passively flows out ( by concentration gradient ) ( by concentration gradient )

of the SR into muscle of the SR into muscle cytoplasmcytoplasm Ca++Ca++ combines with combines with TroponinTroponin Tropomyosin gets moved Tropomyosin gets moved Myosin heads combines Myosin heads combines with Actinwith Actin

Skeletal muscle is made up of many cylinderical ,multinucleated muscle Skeletal muscle is made up of many cylinderical ,multinucleated muscle cells ( fibers) cells ( fibers)

The fibers ( cell ) can be 10 to 100 ten micron in diameter , and can be The fibers ( cell ) can be 10 to 100 ten micron in diameter , and can be hundreds of centimeters long.hundreds of centimeters long.

& is covered by a cell-membrane called & is covered by a cell-membrane called SarcolemmaSarcolemma..

04/18/2304/18/23 55

One muscle cell ( fiber )

Sarcolemma

04/18/2304/18/23 66

Each cell contains between few hundreds to a few thousands Each cell contains between few hundreds to a few thousands MyofibrilsMyofibrils

The myofibril is striated The myofibril is striated

ccand hasand has

dark bands dark bands called A-bands) and called A-bands) and

light bands light bands called I-bands (I-bands). called I-bands (I-bands).

Each MyofibrilEach Myofibril

Is made of Is made of 3000 Actin3000 Actin filaments filaments

And And 1500 Myosin1500 Myosin filaments . filaments .

Each myofibrilEach myofibril is striatedis striated

It is made of It is made of SarcomeresSarcomeres

And each sarcomere is limited by two Z-lines (Z disk) And each sarcomere is limited by two Z-lines (Z disk) The sarcomere contains both the The sarcomere contains both the

(i) A band (i) A band and and (ii) I band light(ii) I band light

04/18/2304/18/23 77

Z-lines

8804/18/2304/18/23

9904/18/2304/18/23

A-bands consist mainly of thick filament Myosin The ends of Actin are Z-Discs(Z-lines ).

I-bands consist of thin filament Actin. The part of the Myofibril lying between two Z-discs is called Sarcomere .

101004/18/2304/18/23

Sliding Filament MechanismSliding Filament MechanismWhen contraction takes place Actin & Myosin slide upon each other , & the distance between two z-discs decreases This is called Sliding Filament Mechanism .

Z-line come closer together I-band gets smaller , and eventuallymay disappearA-band does not become smaller or bigger

111104/18/2304/18/23

121204/18/2304/18/23

Actin is made of globular protein callled G-actin G-actins are attached together to form F-actin strand ( chain ) Each two strands wind together to form double helix called Actin Filament Tropomyosin lies in the groove between the F-actin strands to cover the active sites on actin that bind the head of myosinTroponin is attached to tropomyosin and to actin

Two Actin filaments

Groove between the 2 F-actin strands Tropomyosin

covering active sites on Actin

131304/18/2304/18/23

Attachment of Ca++ to Attachment of Ca++ to TroponinTroponin initiates tcontraction initiates tcontraction and when is activated by Ca++ it will move the and when is activated by Ca++ it will move the Tropomyosin away from the Tropomyosin away from the active sites active sites on actinn & on actinn & expose them expose them for Myosin .for Myosin .> then > then myosin head myosin head will immediately attach to these will immediately attach to these actin active sites actin active sites > when the myosin head attaches to actin it forms a > when the myosin head attaches to actin it forms a “ “ cross-bridge”cross-bridge”

Each 200 myosin molecules aggregate to form a Each 200 myosin molecules aggregate to form a myosin filament , from the sides of which project myosin filament , from the sides of which project myosin heads in all directions .myosin heads in all directions .

Myosin Myosin

Myosin Myosin

Each Myosin molecule has Each Myosin molecule has

(1) Head (1) Head

( 2 ) Tail ( 2 ) Tail

(3) Hinge (joint ) (3) Hinge (joint )

Furthermore , eFurthermore , each myosin head contains ach myosin head contains (1) ATP-binding site , &(1) ATP-binding site , &

(2) ATP-ase enzyme .(2) ATP-ase enzyme .

1616 04/18/2304/18/23

1717 04/18/2304/18/23

Sliding FilamentsSliding Filaments

Attachment of Myosin to Actin activates the enzyme Attachment of Myosin to Actin activates the enzyme ATPaseATPase in the Myosin Head in the Myosin Head

ATPase ATPase breaks down ATP releasing energybreaks down ATP releasing energy This energy is used in the This energy is used in the ““Power Stroke Power Stroke ”” to move the to move the

myosin head myosin head leading to pulling & dragging of actin leading to pulling & dragging of actin sliding of actin on myosin sliding of actin on myosin The “ power stroke ” means tilting of the Myosin cross-bridge and The “ power stroke ” means tilting of the Myosin cross-bridge and

dragging dragging ( pulling ) of actin filament( pulling ) of actin filament

181804/18/2304/18/23

191904/18/2304/18/23

A new ATP binding to Myosin head is essential for detachment of Myosin from Actin

Then , on Then , on order to order to release the release the head of head of Myosin from Myosin from Actin , a new Actin , a new ATP is needed ATP is needed to come and to come and combine with combine with the head of the head of Myosin .Myosin .

The Cross-Bridge CycleThe Cross-Bridge Cycle

202004/18/2304/18/23

Q: What is Rigor Mortis ?Q: What is Rigor Mortis ? Q: ATP is neede for 3 things : what Q: ATP is neede for 3 things : what

are they ?are they ?Q: Is muscle relaxation a passive or Q: Is muscle relaxation a passive or

active process ? Why ?active process ? Why ?Q: Q: What happens to A-band and I-What happens to A-band and I-

band during contraction ?band during contraction ? Q: Ca++ is needed in nerve & Q: Ca++ is needed in nerve &

muscle : when and where muscle : when and where ??

222204/18/2304/18/23

Why do we need the ATP in Why do we need the ATP in contraction ?contraction ?

ATP is needed for 3 things :ATP is needed for 3 things :(1) Power stroke.(1) Power stroke.(2) Detachment of myosin from actin (2) Detachment of myosin from actin

active sites . active sites . (3) Pumping C++ (3) Pumping C++ back into the back into the

Sarcoplasmic reticulumSarcoplasmic reticulum