Neuromuscular transmission Flashcards
(15 cards)
What is the neuromuscular junction?
A chemical synapse between a motor neuron and a muscle fiber, enabling signal transmission for muscle contraction.
How does the motor neuron connect to the muscle fiber?
The motor neuron’s axon divides and forms short branches, creating an elliptical end plate with the muscle fiber.
What is the synaptic cleft?
A 30-nanometer space between the presynaptic motor axon and the sarcolemma, through which neurotransmitters are released.
What are the key events at the neuromuscular junction?
Motor neuron action potential (AP) reaches the terminal. Ca²⁺ influx occurs. Neurotransmitter (NT) vesicles migrate & fuse to the membrane. NT is released via exocytosis. NT diffuses across the cleft. Binds to ACh receptors in muscle. Depolarization leads to muscle contraction.
What is the role of Ca²⁺ in muscle contraction?
Ca²⁺ binds to Troponin C, causing a structural change in tropomyosin. Myosin binding sites on actin are exposed. Actin-myosin interaction leads to muscle contraction.
How do botulinum and tetanus toxins affect the neuromuscular junction?
Botulinum toxin inhibits ACh release, causing paralysis. Tetanus toxin affects inhibitory neurons, causing muscle spasms.
How do nerve gases and snake venoms affect the neuromuscular junction?
Nerve gases disrupt neurotransmission. Snake venom can block or overactivate neuromuscular signals, leading to paralysis or spasms.
What is myasthenia gravis?
An autoimmune disorder where antibodies attack ACh receptors, leading to muscle weakness.
How does neuromyotonia differ from myasthenia gravis?
Instead of muscle weakness, neuromyotonia causes hyper-excitation of motor nerves, leading to excessive muscle activity.
What are the three types of muscles?
Skeletal – Striated, voluntary, multiple nuclei, attached to bones.
Smooth – Non-striated, involuntary, single nucleus, found in organs.
Cardiac – Striated, involuntary, single nucleus, found in the heart.
What are the key proteins in muscle contraction?
Myosin (thick filament, ATPase site)
Actin (thin filament, binds to myosin) Tropomyosin (covers myosin binding sites)
Troponin (regulates contraction)
What happens during the sliding filament mechanism?
Myosin heads pull actin filaments inward, shortening the sarcomere. The muscle fiber shortens without changing the length of thick/thin filaments.
What is the role of ATP in muscle contraction?
Myosin heads bind to ATP and hydrolyze it to ADP + Pi. This provides energy for the power stroke, pulling actin filaments. ATP is needed to detach myosin and reset for another cycle.
How does calcium trigger muscle contraction?
Ca²⁺ is released from the sarcoplasmic reticulum. Binds to troponin, exposing myosin binding sites on actin.Myosin binds to actin, triggering the power stroke.
What is the walk-along mechanism of muscle contraction?
Myosin heads attach to actin, pull, release, and repeat. This “ratchet” motion shortens the muscle fiber with each cycle.
