Muscle

chapter 9. Muscle

근육해부학

     Fascicle > fiber > myofibril > myofilament

근수축의 종류

     1 ) isometric contraction

     2) isotonic contraction

         - concentric contraction       ex; A gymnast lifting one leg up laterally until her foot's above her head

         -  eccentric contraction         ex; A person lowerig the weight back to the chest after doing "bench press"

cross bridges 

     Sliding of the filaments is produced by the action of cross bridges that extend from the thick filaments toward the thin filaments.

cross bridges cycle

     1 ) The myosin head has an actin-binding site for forming cross bridges with the actin in the thin filaments; it also has an ATPase site that hydrolyzes ATP into ADP and Pi, which stay bound to the myosin head.

     2 ) The hydrolysis of ATP activates ("cocks") the myosin head, changing its orientation so that it can undergo a power stroke and prodce sliding of the filaments; however, the myosin heads do not bind to actin when a muscle is at rest.

     3 ) When the myosin head is allowed to bind to actin, the  Pi group is relesed and the power stroke occurs; after that, the myosin head releases he ADP and binds a new ATP.

    4 ) Binding to a new ATP allows the myosin head to release from the actin; then, the ATPase breaks down that ATP to again activate the myosin head so that another power stroke can occur and the muscle can shorten to a greater extent.

Ca^2＋release channels...

     are located in the sarcoplasmic reticulum.

    are opened by voltage-gated Ca^2＋ channels

    are 10 times larger than the voltage-gated  Ca^2＋ channels

    permit diffusion of  Ca^2＋ out from the terminal cisternae.

<muscle fibers 2 종류>

-typeⅠfibers

slow contraction speeds adapted for aerobic respiration

⪧풍부한 모세혈관, 수많은 미토콘드리아, 호기성 호흡효소, 고농도 미오글 로빈(느린 연축섬유에 산소를 운반해 주는 적색 색소)

-typeⅡfibers

fast contraction speeds adapted for anaerobic respiration (fermentation)

⪧모세혈관과 미토콘드리아가 더 적고 미오글로빈 수가 더 적음

⪧고농도의 글리코겐과 해당효소에 의해 혐기성 호흡을 하는데 적응

   fast glycolytic fibers ; 눈 빨리 깜빡 거리는 것 _ rely mainly on glycolysis

   fast oxidative fibers ; 장딴지 근육 _ more capacity for aerobic 호흡

endurance training vs high-resistance (weight) training

-endurance training

It increases aerobic capacity by about 20%.

It increases the proportion of energy obtained from fatty acids.

It allows muscle glycogen to become depleted at a slower rate.

-high-resistance (weight) training

It promotes hypertrophy of typeⅡfibers.