Skeletal Muscles are Stimulated to Contract by Nerves and Act as Effectors Flashcards
What is the structure of skeletal muscle?
Skeletal muscle consists of long, cylindrical cells (muscle fibers) that are multinucleated. These fibers contain myofibrils made of repeating sarcomeres.
What are myofibrils?
Myofibrils are long, thread-like structures in muscle fibers that contain the contractile proteins actin and myosin, arranged in sarcomeres.
What are sarcomeres?
Sarcomeres are the functional units of muscle contraction, defined by Z lines, and contain actin and myosin filaments that slide past each other during contraction.
What is the role of actin in muscle contraction?
Actin is a thin filament that forms part of the sarcomere. During contraction, it interacts with myosin to form cross-bridges and facilitates sliding of filaments.
What is the role of myosin in muscle contraction?
Myosin is a thick filament that forms part of the sarcomere. Its heads bind to actin to form cross-bridges, pulling actin filaments towards the center of the sarcomere.
How are skeletal muscles stimulated to contract?
Skeletal muscles are stimulated to contract by motor neurons that release acetylcholine at the neuromuscular junction, triggering an action potential in muscle fibers.
What is the neuromuscular junction?
The neuromuscular junction is the synapse between a motor neuron and a muscle fiber, where neurotransmitters (acetylcholine) are released to initiate muscle contraction.
What is an action potential in muscle fibers?
An action potential in muscle fibers is an electrical impulse that spreads along the sarcolemma and T-tubules, causing the release of calcium ions from the sarcoplasmic reticulum.
What is the role of calcium ions in muscle contraction?
Calcium ions bind to troponin, causing a conformational change that exposes myosin-binding sites on actin, allowing cross-bridge formation between actin and myosin.
What is the role of troponin and tropomyosin in muscle contraction?
Troponin and tropomyosin regulate the interaction between actin and myosin. Tropomyosin blocks myosin-binding sites on actin, while troponin controls tropomyosin’s position in response to calcium.
What is the sliding filament theory?
The sliding filament theory describes how muscles contract: myosin heads attach to actin, pull it towards the center of the sarcomere, and then release to repeat the cycle.
What is the role of ATP in muscle contraction?
ATP provides the energy required for the myosin heads to detach from actin, reattach, and perform the power stroke that slides the actin filament.
What is the role of the sarcoplasmic reticulum?
The sarcoplasmic reticulum stores and releases calcium ions in response to action potentials, which is essential for muscle contraction.
What is rigor mortis?
Rigor mortis is the stiffening of muscles after death due to the lack of ATP, which prevents myosin from detaching from actin, causing muscles to remain contracted.
What is a motor unit?
A motor unit consists of a single motor neuron and all the muscle fibers it innervates. The activation of motor units causes muscle contraction.
What is summation in muscle contraction?
Summation occurs when multiple action potentials arrive at a muscle fiber in rapid succession, leading to a stronger, more sustained muscle contraction.
What is tetanus in muscle contraction?
Tetanus is a sustained, maximal contraction of muscle fibers that occurs when action potentials are delivered at a high frequency, preventing relaxation.
How does a neuromuscular junction lead to muscle contraction?
The release of acetylcholine at the neuromuscular junction generates an action potential in the muscle fiber, leading to calcium ion release, which triggers muscle contraction.
