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

- [Narratore] Una contrazione
muscolare volontaria

inizia nel cervello,
come sforzo consapevole

del lobo frontale alla
corteccia motoria primaria

prima di attivare un neurone alfa motorio

collocato nella parte anteriore
della colonna dorsale.

Il segnale passa dai nervi
alla fibra muscolare specifica

come il bicipite,

dove il potenziale d'azione termina

sulla placca motrice,

dove il motoneurone stabilisce
un contatto sinaptico

con la fibra muscolare
e attiva il rilascio di

acetilcolina del neurotrasmettitore,

che si diffonde attraverso
una fenditura sinaptica

e si lega ai ricettori.

Di conseguenza, il sarcolemma
diventa più permeabile

agli ioni di sodio, generando
maggior potenziale d'azione

che si diffonde su tutta
la superficie esterna

fino alla parte interna
della fibra muscolare

mediante i passaggi o tubuli T,

che attivano il rilascio di ioni di calcio

dal reticolo sarcoplasmico
alle miofibrille.

Questo rilascio di calcio

innesca l'attività dei
crossbridge sull'actina-miosina

e il movimento di accorciamento

e contrazione del muscolo.

Webb, R. Clinton. "Contrazione e rilassamento della muscolatura liscia". Advances in Physiology Education 27, n. 4 (1 dicembre 2003): 201–6. [<a href="https://doi.org/10.1152/advan.00025.2003" target="__blank">Sorgente</a>]

Kuo, Ivana Y. e Barbara E. Ehrlich. "Segnalazione nella contrazione muscolare". Cold Spring Harbor Perspectives in Biology 7, n. 2 (febbraio 2015). [<a href="https://doi.org/10.1101/cshperspect.a006023" target="__blank">Sorgente</a>]

contrazione muscolare

Nei muscoli scheletrici, l'acetilcolina viene rilasciata dai terminali nervosi alla piastra terminale, il punto di comunicazione sinaptica tra i motoneuroni e le fibre muscolari. Il legame dell'acetilcolina ai suoi recettori sul sarcolemma consente l'ingresso di ioni di sodio nella cellula e innesca un potenziale d'azione nella cellula muscolare. Così, segnali elettrici dal cervello vengono trasmessi al muscolo. Successivamente, l'enzima acetilcolinesterasi degrada l'acetilcolina per prevenire la stimolazione muscolare eccessiva.

 

Gli individui con il disturbo Myasthenia gravis, sviluppano anticorpi contro il recettore dell'acetilcolina. Ciò previene la trasmissione di segnali elettrici tra il neurone motorio e la fibra muscolare e compromette la contrazione muscolare scheletrica. Myasthenia gravis viene trattata con farmaci che inibiscono l'acetilcolinesterasi (consentendo maggiori opportunità per il neurotrasmettitore di stimolare i recettori rimanenti) o sopprimere il sistema immunitario (prevenire la formazione di anticorpi).

<h4>Contrazione muscolare liscia</h4>

A differenza dei muscoli scheletrici, i muscoli lisci presenti nelle pareti degli organi interni sono innervati dal sistema nervoso autonomo e subiscono contrazioni involontarie. La contrazione è mediata dall'interazione tra due proteine del filamento: actina e miosina. L'interazione di actina e miosina è strettamente legata alla concentrazione di calcio intracellulare. In risposta al neurotrasmettitore o ai segnali ormonali o allo stiramento del muscolo, il calcio extracellulare entra nella cellula attraverso i canali di calcio sul sarcolemma o viene rilasciato intracellulare dal reticolo sarcoplasmico. All'interno della cellula, il calcio si lega alla proteina regolatoria calmodulina. Il complesso calcio-calmodulina attiva quindi l'enzima miosina chinasi a catena luminosa , che fosforila i terminali della miosina e gli permette di interagire con l'actina, causando il contrarsi del muscolo.

Contrazione muscolare

 

Nei muscoli scheletrici, l'acetilcolina viene rilasciata dalle terminazioni nervose sulla piastra terminale del motore, il punto di comunicazione sinaptica tra il motore ...

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KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

Muscle Contraction

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

nerve-signals-that-trigger-muscle-contraction

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bone structure

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Types of Joints in the Human Body

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skeletal muscle anatomy

Muscle Fibers, Tendons, and Contraction

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classification of skeletal muscle fibers

Skeletal Muscle Fiber Speed and Energy

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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

Motor units control skeletal muscle movement. A motor unit includes one efferent motor neuron, which carries signals away from the central nervous system, and all of the muscle fibers it innervates. A single motor neuron can connect with multiple muscle fibers, but each muscle fiber is innervated by only one motor neuron. Lower motor neurons are the efferent neurons that control skeletal muscle, the most abundant type of muscle in the body. Their cell bodies are found in the spinal cord or...

the spinal cord

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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.

Nerve Signals That Trigger Muscle Contraction | JoVE K12

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Nerve Signals That Trigger Muscle Contraction

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