🧠 Muscle Contraction – Simple Chemical + Electrical Breakdown Flashcards
What triggers a motor neuron to initiate muscle contraction?
An action potential (electrical signal) from the brain or spinal cord.
What causes the release of acetylcholine (ACh) in the neuron?
The entry of calcium ions (Ca²⁺) into the axon terminal.
What is the role of acetylcholine (ACh) at the neuromuscular junction?
ACh binds to receptors on the motor end plate, initiating a new action potential in the muscle fiber.
What happens when ACh binds to its receptor on the muscle fiber?
Sodium (Na⁺) channels open, allowing Na⁺ to rush in and create a muscle action potential.
What structures carry the muscle action potential deep into the fiber?
T-tubules.
What organelle releases calcium ions in response to the action potential?
Sarcoplasmic reticulum (SR).
What protein does calcium bind to in the muscle fiber?
Troponin.
What happens when calcium binds to troponin?
Troponin shifts tropomyosin, exposing binding sites on actin.
What is the role of myosin in muscle contraction?
Myosin binds to actin and pulls it during the power stroke.
What is needed for myosin to detach and reset for another contraction cycle?
ATP.
What enzyme breaks down acetylcholine in the synaptic cleft?
Acetylcholinesterase (AChE).
What happens to calcium ions when the muscle relaxes?
Calcium is pumped back into the sarcoplasmic reticulum.
What happens to tropomyosin during muscle relaxation?
Tropomyosin moves back to cover actin’s binding sites.
What protein blocks myosin from binding to actin when the muscle is at rest?
Tropomyosin.
Why is ATP essential for muscle contraction?
It provides energy for the power stroke and detaches myosin from actin.
