Name: nerve signals that trigger muscle contraction
Uploaded: 2025-10-23T11:49:17.000Z
Duration: 1 min 15 s
Channel: JoVE

Процесс произвольного сокращения скелетных мышц начинается в мозге как сознательное усилие, от фронтальной доли до первичной моторной коры, перед активацией альфа-моторного нейрона, расположенного в передней части рога спинного мозга. Сигнал продолжается вдоль нерва к определенному мышечному волокну, такому как бицепс, где потенциал действия заканчивается на торцевой моторной пластине, на которой моторный нейрон устанавливает синаптический контакт с мышечным волокном и инициирует выход нейротрансмиттера ацетилхолина, который рассеивается в синаптической щели и связывается с рецепторами. В результате сарколемма становится более проницаемой для ионов натрия, что приводит к большим потенциалам действия, которые распространяются по его внешней поверхности и внутрь мышечного волокна через поперечные или Т-канальцы, которые вызывает выброс ионов кальция из саркоплазматического ретикулума в миофибриллы.Это высвобождение кальция инициирует актин-миозиновый поперечный мостик, и позволяет наблюдать за мышцей, которая сокращается и контрактирует.

Уэбб, Р. Клинтон. "Сокращение и расслабление гладких мышц." Достижения в образовании в области физиологии 27, No4 (1 декабря 2003 г.): 201–6. [<a href="https://doi.org/10.1152/advan.00025.2003" target="__blank">Источник</a>]

Куо, Ивана Ю., и Барбара Э. Эрлих. «Сигнализация при сокращении мышц». Перспективы Колд-Спринг-Харбор в биологии 7, No 2 (февраль 2015 г.). [<a href="https://doi.org/10.1101/cshperspect.a006023" target="__blank">Источник</a>]

Мышечное сокращение

Muscle Contraction

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 В скелетных мышцах ацетилхолин выделяется нервными окончаниями на моторной концевой пластине - точке синаптической связи между моторными нейронами и мышечными волокнами. Связывание ацетилхолина с его рецепторами на сарколемме позволяет ионам натрия проникать в клетку и запускает потенциал действия в мышечной клетке. Таким образом, электрические сигналы от мозга передаются к мышце. Впоследствии фермент ацетилхолинэстераза расщепляет ацетилхолин, чтобы предотвратить чрезмерную стимуляцию мышц. 

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 У людей с миастенией вырабатываются антитела против рецептора ацетилхолина. Это предотвращает передачу электрических сигналов между двигательным нейроном и мышечным волокном и ухудшает сокращение скелетных мышц. Для лечения миастении используются препараты, которые ингибируют ацетилхолинэстеразу (что дает нейромедиатор больше возможностей стимулировать оставшиеся рецепторы) или подавляют иммунную систему (предотвращают образование антител). 

<h4> Сокращение гладких мышц </h4>

 В отличие от скелетных мышц, гладкие мышцы стенок внутренних органов иннервируются вегетативной нервной системой и подвергаются непроизвольным сокращениям. Сокращение опосредуется взаимодействием между двумя белками филаментов - актином и миозином. Взаимодействие актина и миозина тесно связано с концентрацией внутриклеточного кальция. В ответ на сигналы нейротрансмиттеров или гормонов или на растяжение мышцы внеклеточный кальций проникает в клетку через кальциевые каналы в сарколемме или высвобождается внутриклеточно из саркоплазматического ретикулума. Внутри клетки кальций связывается с регуляторным белком кальмодулином. Затем комплекс кальций-кальмодулин активирует фермент киназу легкой цепи миозина, который фосфорилирует миозин и позволяет ему взаимодействовать с актином, вызывая сокращение мышцы.

 

В скелетных мышцах ацетилхолин выделяется нервными окончаниями на моторной конечной пластине — точке синаптической связи между моторными ...

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nerve signals that trigger muscle contraction

Nerve signals trigger muscle contraction in both skeletal and smooth muscle, but the two muscle types use different control systems. In skeletal muscle, the signal begins at the motor end plate, which is the synapse between a motor neuron and a muscle fiber. In smooth muscle, contraction is controlled by the autonomic nervous system and happens without conscious control.

In skeletal muscle, motor nerve terminals release acetylcholine. This neurotransmitter binds to receptors on the sarcolemma, the muscle cell membrane, and lets sodium ions enter the cell. That change starts an action potential in the muscle cell and carries the electrical signal from the brain to the muscle. The enzyme acetylcholinesterase then breaks down acetylcholine so the muscle is not overstimulated.

Myasthenia gravis shows what happens when this signaling step is disrupted. In this disorder, antibodies form against the acetylcholine receptor. As a result, the signal between the motor neuron and the muscle fiber is blocked, and skeletal muscle contraction is weakened. Treatment may include drugs that inhibit acetylcholinesterase or medicines that suppress the immune system.

Smooth muscle in the walls of internal organs contracts in a different way. Its contraction depends on the interaction between actin and myosin, two filament proteins. This process is closely linked to calcium levels inside the cell, which can rise after neurotransmitter or hormone signals or when the muscle is stretched.

Calcium can enter smooth muscle from outside the cell through calcium channels on the sarcolemma, or it can be released from the sarcoplasmic reticulum inside the cell. Once inside, calcium binds to calmodulin, a regulatory protein. The calcium-calmodulin complex activates myosin light chain kinase, which phosphorylates myosin and lets it interact with actin, causing contraction.

Nerve Signals That Trigger Muscle Contraction

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skeletal muscle anatomy

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classification of skeletal muscle fibers

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muscle contraction

Nerve signals trigger muscle contraction in both skeletal and smooth muscle, but the two muscle types use different control systems. In skeletal muscle, the signal begins at the motor end plate, which is the synapse between a motor neuron and a muscle fiber. In smooth muscle, contraction is controlled by the autonomic nervous system and happens without conscious control. In skeletal muscle, motor nerve terminals release acetylcholine. This neurotransmitter binds to receptors on the sarcolemma,...

cross-bridge cycle

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...

motor units

How Motor Units Control Muscle Movement

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key terms and concepts

Learn how acetylcholine, calcium, and actin-myosin interactions drive skeletal and smooth muscle contraction, plus how myasthenia gravis disrupts signaling.

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Nerve Signals That Trigger Muscle Contraction

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