Name: calcium control in muscle contraction
Uploaded: 2025-10-23T11:47:01.000Z
Duration: 1 min 26 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Life Science

SC.912.L.14

SC.912.L.14.17

Cross-bridge Cycle

- [Eğitimci] İnce ve kalın filamentlerin üst üste geldiği bölgenin artarak sarkomer uzunluğunun kısalmasına yol açmasıyla kas kasılması gerçekleşir.
 Moleküler düzeyde ise kasılma, miyozinin globüler baş kısmına bağlı olan ATP'nin ADP'ye hidrolizinin gerçekleşmesiyle olur, bu süreçte miyozin başı, yüksek enerjili bir hale gelir ve aktinle birleşerek çapraz bir bağ oluşturur.
 ADP salınımı, miyozin başının düşük enerjili bir duruma geri dönmesini ve aktinin sarkomer merkezine doğru hareket etmesini sağlar.
Yeni bir ATP molekülünün miyozin başına bağlanması, miyozin başının aktinden ayrılmasına neden olur.
 Aynı miyozin başının aktine bir sonraki bağlanışı, Z hattına daha yakın bir kısımda gerçekleşecektir.
 Bu bağlanma işlemi, tropomiyozin ve troponin adlı iki düzenleyici protein ile sarkoplazmik retikulumda depolanan ve buradan salınan kalsiyum konsantrasyonuyla kontrol edilir.
Tropomiyozin, aktindeki miyozin bağlanma bölgesini kaplarken troponin de mümkün olduğunda kalsiyuma bağlanır ve tropomiyozini aktin üzerindeki miyozin bağlanma bölgesinden uzağa hareket ettirir.
 Bu düzenlenişte çapraz bir köprü oluşur ve kas kasılır.
 Kas lifinde kalsiyum ve ATP var olduğu sürece bu döngü gerçekleşmeye devam eder.

Guellich, Aziz, Elisa Negroni, Valérie Decostre, Alexandre Demole ve Catherine Coirault. "İskelet Kası Distrofilerinde Değişen Çapraz Köprü Özellikleri." Fizyolojide Sınırlar 5 (14 Ekim 2014). [<a href="https://doi.org/10.3389/fphys.2014.00393" target="__blank">Kaynak</a>]

Debold, Edward P. "Çapraz Köprü Düzeyinde Kas Yorgunluğuna İlişkin Son Bilgiler." Fizyolojide Sınırlar 3 (1 Haziran 2012). [<a href="https://doi.org/10.3389/fphys.2012.00151" target="__blank">Kaynak</a>]

Rall, Jack A. "İskelet Kasını Çizgili Yapan Nedir? Endosarkomedik ve Ekzosarkomerik Hücre İskeletindeki Keşifler." Fizyoloji Eğitimindeki Gelişmeler 42, no. 4 (15 Kasım 2018): 672–84. [<a href="https://doi.org/10.1152/advan.00152.2018" target="__blank">Kaynak</a>]

Çapraz-köprü döngüsü

Kas kasıldıkça, ince ve kalın filamentler arasındaki örtüşme artar ve ATP şeklinde enerji kullanılarak sarkomerin (kasın kasılma birimi) uzunluğunu azalır. Moleküler düzeyde, bu, ATP'nin bağlanmasını ve hidrolizini ve aktinin miyozin ile hareketini içeren döngüsel, çok aşamalı bir süreçtir.

Miyozin kafasına bağlı olan ATP, ADP'ye hidrolize edildiğinde, miyozin aktine bağlı yüksek enerjili bir duruma geçer ve bir çapraz köprü oluşturur. ADP serbest bırakıldığında, miyozin kafası düşük enerjili bir duruma hareket eder ve aktini sarkomerin merkezine doğru hareket ettirir. Yeni bir ATP molekülünün bağlanması, miyozini aktinden ayırır. Bu ATP hidrolize edildiğinde, miyozin başı aktine bağlanır, bu sefer aktinin bir kısmı sarkomerin ucuna daha yakındır. Düzenleyici proteinler troponin ve tropomiyosin, kalsiyum ile birlikte miyozin-aktin etkileşimini kontrol etmek için birlikte çalışır. Troponin kalsiyuma bağlandığında, tropomiyosin aktin üzerindeki miyozin bağlanma bölgesinden uzaklaşır, miyozin ve aktinin etkileşime girmesine ve kas kasılmasının gerçekleşmesine izin verir.

<h4>Kalsiyum</h4>

Kas kasılmasının bir düzenleyicisi olarak, kas liflerinde kalsiyum konsantrasyonu çok yakından kontrol edilir. Kas lifleri motor nöronlarla yakın temas halindedir. Motor nöronlardaki aksiyon potansiyelleri, kas liflerinin yakınında nörotransmitter asetilkolinin salınmasına neden olur. Bu, plazma membranı boyunca ve transvers veya T-tübüller olarak adlandırılan plazma membranının invajinasyonları yoluyla taşınan kas hücresinde bir aksiyon potansiyeli (depolarizasyon) oluşturur.

T-tübül kas içinde derine yerleşmiştir ve sapkoplazmik rtikulum (SR) olarak adlandırılan özelleşmiş endoplazmik retikulum organlarına komşu yerleşim gösterir. SR içinde hapsedilmiş kalsiyum (local yükler ile açılıp kapanan iyon kanalları) depolarizasyona yanıt olarak voltaj kapılı kalsiyum kanalları açıldığında sitoplazmaya akar ve kasların kasılmasına sebep olur.

Motor nöronlardan gelen sinyal durduğunda, kalsiyumun SR'ye geri pompalanmasıyla kas gevşemesi başlar, sitoplazmik kalsiyum seviyelerini azalır ve bir sonraki kasılmaya hazırlanırken SR kalsiyum depolarını yeniler.

<h4>Kas Dejenerasyonu</h4>

Sağlıklı kaslar kasılabilir, ancak hastalıklı kaslar genellikle bu yeteneği kaybeder. Myastenia gravis gibi hastalıklar, kasın motor nöron stimülasyonunu önleyerek kas atrofisine ve kas kütlesinde azalmaya neden olur. Amyotrofik lateral skleroz (ALS veya Lou Gehrig hastalığı) motor nöronların dejenere olmasına neden olur, bu da benzer şekilde kas dejenerasyonuna ve atrofiye yol açar.

Çapraz-köprü Döngüsü

Kas kasıldıkça, ince ve kalın filamentler arasındaki örtüşme artar ve sarkomerin uzunluğunu azaltır - kasılma birimi ...

Education

JoVE Core

Biology

Biyoloji

Human Biology

İnsan Biyolojisi

Musculoskeletal System

Kas İskelet Sistemi

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

calcium control in muscle contraction

Calcium control in muscle contraction depends on ATP, motor neurons, and the sliding action of actin and myosin. As a muscle contracts, the thin and thick filaments overlap more, and the sarcomere, which is the contractile unit of the muscle, becomes shorter. This process uses energy from ATP and happens in a repeating cycle at the molecular level.

Myosin drives the movement of actin through a cross-bridge cycle. When ATP attached to the myosin head is hydrolyzed to ADP, myosin shifts into a high-energy state and binds actin. This forms a cross-bridge. When ADP is released, the myosin head moves to a lower-energy state and pulls actin toward the center of the sarcomere. A new ATP molecule then binds to myosin and causes it to detach from actin. After that ATP is hydrolyzed, myosin can bind again, this time to a new site on actin closer to the end of the sarcomere.

Troponin, tropomyosin, and calcium regulate this interaction. When troponin binds calcium, tropomyosin moves away from the myosin-binding site on actin. That shift lets myosin and actin interact, and muscle contraction can occur. Calcium concentration in muscle fibers is tightly controlled so this switch can happen at the right time.

Motor neurons start the process by signaling nearby muscle fibers. Their action potentials trigger release of the neurotransmitter acetylcholine near the muscle cell. This produces an action potential, or depolarization, in the muscle cell membrane. The signal travels along the plasma membrane and through T-tubules, which are inward folds of the membrane that carry the signal deep into the muscle. T-tubules sit next to the sarcoplasmic reticulum, or SR, a specialized endoplasmic reticulum that stores calcium.

When depolarization reaches the SR, voltage-gated ion channels open and release calcium into the cytoplasm. The rise in calcium allows the muscle to contract. When signaling from the motor neuron stops, relaxation begins. Calcium is pumped back into the SR, which lowers calcium in the cytoplasm and restores the SR calcium supply for the next contraction.

Healthy muscle can contract, but diseased muscle may lose that ability. Myasthenia gravis can prevent motor neuron stimulation of muscle, which can lead to muscle atrophy and a decrease in muscle mass. Amyotrophic lateral sclerosis, or ALS, also called Lou Gehrig's disease, causes motor neurons to degenerate. That loss of motor neurons can likewise lead to muscle degeneration and atrophy.

Calcium Control in Muscle Contraction

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cross-bridge cycle

Calcium control in muscle contraction depends on ATP, motor neurons, and the sliding action of actin and myosin. As a muscle contracts, the thin and thick filaments overlap more, and the sarcomere, which is the contractile unit of the muscle, becomes shorter. This process uses energy from ATP and happens in a repeating cycle at the molecular level. Myosin drives the movement of actin through a cross-bridge cycle. When ATP attached to the myosin head is hydrolyzed to ADP, myosin shifts into a...

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key terms and concepts

Learn how calcium, troponin, tropomyosin, and ATP control muscle contraction, from motor neuron signaling to relaxation and muscle degeneration.

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Calcium Control in Muscle Contraction

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