Muscle contraction events describing the sliding-filament concept are listed as follows. Show
Without the addition of a new ATP molecule, the cross bridges remain attached to the actin filaments. This is why corpses become stiff with rigor mortis (new ATP molecules are unavailable). Stimulation of muscle contraction Neurons, or nerve cells, are stimulated when the polarity across their plasma membrane changes. The polarity change, called an action potential, travels along the neuron until it reaches the end of the neuron. A gap called a synapse or synaptic cleft separates the neuron from a muscle cell or another neuron. If a neuron stimulates a muscle, then the neuron is a motor neuron, and its specialized synapse is called a neuromuscular junction. Muscle contraction is stimulated through the following steps:
Phases of a muscle contraction A muscle contraction in response to a single nerve action potential is called a twitch contraction. A myogram, a graph of muscle strength (tension) with time, shows several phases, shown in Figure 1:
Figure 1.The phases of a myogram.
Quality of a muscle contraction The following factors contribute to the strength and maximum duration of a muscle contraction:
What are the steps of muscle contraction in order?Muscle Contraction. Depolarisation and calcium ion release.. Actin and myosin cross-bridge formation.. Sliding mechanism of actin and myosin filaments.. Sarcomere shortening (muscle contraction). What is the next step in muscle contraction after calcium ions binds to actin?The muscle contraction cycle is triggered by calcium ions binding to the protein complex troponin, exposing the active-binding sites on the actin. As soon as the actin-binding sites are uncovered, the high-energy myosin head bridges the gap, forming a cross-bridge.
What happens to the actin when a muscle contracts?In muscle contraction, the actin filaments slide along the myosin filaments. This is driven by the heads of the myosin molecules, which bind to actin and, in a sequence of binding and release movements, 'walk' along the actin filament. This repetitive binding and release is powered by the hydrolysis of ATP (Fig.
How does the position of the actin filaments change during muscle contraction?As discussed later, the motor activity of myosin moves its head groups along the actin filament in the direction of the plus end. This movement slides the actin filaments from both sides of the sarcomere toward the M line, shortening the sarcomere and resulting in muscle contraction.
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